Process for preparing crystalline polylactide

Abstract

The present invention relates to a process for improving the crystallization of polylactide and in particular for increasing the crystallization rate of PLA polymers. The present invention relates to a process for preparing crystalline PLA pellets, which in particular comprises the following steps: a) providing a PLA polymer melt wherein the PLA polymer has D-lactide isomers in a content of between 1.0 and 10.0 wt% of the PLA polymer; b) granulating the PLA polymer melt into PLA granules; and c) crystallizing the PLA pellets, thereby obtaining crystalline PLA pellets, in which the process is characterized in that an amide, preferably a fatty acid amide, is added to the PLA polymer melt prior to granulation to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount of between 10 and 2000 ppm of the PLA polymer melt. The invention also relates to crystalline PLA, in particular crystalline PLA pellets, obtainable by or by carrying out the process of the invention.

Description

Technical Field

[0001] The present invention relates to the field of polylactide processing. The present invention particularly relates to a process for preparing crystallized polylactide. The present invention particularly relates to a process for preparing crystallized PLA pellets and the crystallized PLA pellets obtained thereby. The present invention particularly provides a process for increasing the crystallization rate of polylactide, in particular PLA pellets. Background Art

[0002] The demand for biodegradable polymers with excellent material properties is growing rapidly. Biodegradable polymers can be used in a variety of applications, from biomedicine, additive technology, film, fiber, packaging, automobile to agriculture, etc. Polylactide, which is also called polylactic acid and abbreviated as PLA, has received increasing attention in recent years for its excellent performance in reproducibility, mechanical properties, biocompatibility and biodegradability for use in these applications.

[0003] PLA polymers also find their applications in both rigid and flexible disposable / compostable applications, such as cups, plates, shopping bags, tableware, etc., which are often in direct contact with food. Such polymers may contain inorganic fillers and other additives to enhance, for example, material properties (such as rigidity, thermal properties) and to expand the volume of the resin. However, materials or articles in direct contact with food and beverages need to meet specific standards in terms of safety and (chemical) stability. Such materials or articles should not change the nature, substance or quality of food, and must not transfer its components (i.e. migrate) into food in unacceptable amounts. Therefore, providing a biodegradable polymer that simultaneously meets the standards for being allowed to be used as a "food contact material" is a challenging task.

[0004] PLA is an aliphatic polyester that can be made from renewable resources. Such manufacturing may involve starch, sugar or other renewable organic substrates fermented into lactic acid. Polylactide can be produced by direct polycondensation of lactic acid (i.e. lactate monomer). However, this has the disadvantage of not being easy to reach high molecular weight. Therefore, PLA is usually prepared by ring-opening polymerization (ROP) of lactide (cyclic dimer of lactic acid), and lactide is usually made by: lactic acid is polycondensed into PLA oligomers, and then these oligomers are depolymerized by the so-called "backbiting" mechanism in the presence of a suitable catalyst. After purification, the produced lactide can be converted into PLA with controlled molecular weight by ring-opening polymerization (ROP) in the presence of a polymerization catalyst and an initiator. Ring-opening polymerization allows control of the polymerization process and thus the structure of the produced PLA. This method can be used to make high molecular weight PLA. The molecular weight of the polymer produced by ring-opening polymerization can be controlled by residence time, catalyst and initiator concentrations and temperature. The order and ratio of L- and D-lactic units in the final polymer can also be controlled.After polymerization, polylactide pellets are typically obtained by the steps of melt extrusion and pelletization.

[0005] Solid PLA comes in two forms: amorphous and crystalline. The amorphous form is more transparent and becomes soft and sticky above its glass transition temperature, while the crystalline form is more opaque, white, and remains hard and non-sticky until it reaches the melting point. PLA with a certain degree of crystallinity is often used in various applications.

[0006] Directly after granulation, the PLA pellets formed have an amorphous structure and a very sticky surface, and their soft and sticky behavior makes it difficult to further process, dry and / or store these pellets. In the thermal post-treatment step, which is also referred to as crystallization, the amorphous structure can be converted into a state of at least partial crystallization with a larger arrangement between its molecular chains. Crystallization is a particularly important process because it controls the structure formation of the polymer and thereby strongly affects the properties of the final product. Crystallization is typically carried out in special equipment.

[0007] However, crystallizing PLA becomes difficult because the PLA pellets will be sticky at the beginning of the crystallization process. Handling hot, amorphous, sticky pellets during crystallization is cumbersome and can lead to clogging of equipment and processing problems.

[0008] Moreover, PLA is characterized by a slow crystallization rate. This is especially true during the non-isothermal conditions encountered in normal extrusion and injection molding processes, where it is difficult to achieve high PLA crystallinity in a short period of time. Therefore, the problem of how to enhance crystallization behavior and increase crystallinity has been widely studied in the field of PLA processing.

[0009] It is therefore an object of the present invention to provide an improved process for preparing PLA having a desired degree of crystallinity which overcomes at least some of the above-mentioned disadvantages.

[0010] In particular, it is an object of the present invention to provide an improved process for preparing crystallized PLA pellets having a desired composition allowing them to be effectively used in various downstream applications.

[0011] A further object of the present invention is to provide crystallized PLA pellets with optimal properties so that they can be further processed and used in a wide range of applications without being limited by stability, chemical compatibility, food safety and / or migration issues.

[0012] A further object of the present invention is to provide a simplified and more cost-effective process for obtaining crystallized PLA pellets. Summary of the invention

[0013] It has now surprisingly been found that some or all of the above needs and objects can be achieved individually or in any combination by a process for preparing crystalline polylactide (PLA) as defined herein. The present invention provides an improved process for preparing crystalline PLA, which increases the crystallization rate of PLA polymers and provides easier and smoother processing of PLA polymers into crystalline PLA, while eliminating or at least greatly reducing clogging problems in processing equipment.

[0014] In one aspect, the present invention relates to a process for preparing crystalline polylactide (PLA), the process comprising the steps of:

[0015] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer;

[0016] b) processing the PLA polymer melt into PLA pellets, and

[0017] c) crystallizing the PLA pellets to obtain crystallized PLA,

[0018] The process is characterized in that the amide is added to the PLA polymer melt in an amount between 10 and 2000 ppm of the PLA polymer melt.

[0019] In particular, the amide is added to the PLA polymer melt before processing the PLA polymer melt into PLA pellets.Thus, the present invention also relates to a process for preparing crystallized polylactide (PLA) pellets.

[0020] According to the present invention, there is provided a process for preparing crystallized polylactide (PLA) pellets, wherein the process comprises the following steps:

[0021] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer;

[0022] b) pelletizing the PLA polymer melt into PLA pellets, and

[0023] c) crystallizing the PLA pellets to obtain crystallized PLA pellets,

[0024] The process is characterized in that, prior to step b), an amide is added to the PLA polymer melt to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount of between 10 and 2000 ppm of the PLA polymer melt.

[0025] In a preferred embodiment of the process of the invention, the PLA pellets are crystallized by means of latent heat crystallization.Thus, preferably during pelletization, the average PLA pellet temperature is maintained above the glass transition temperature (Tg) of the PLA polymer.

[0026] In a preferred embodiment of the process of the present invention, the amide is added in an amount between 20 and 1500 ppm, preferably between 30 and 1000 ppm, and more preferably between 50 and 900 ppm of the PLA polymer melt. In some preferred embodiments of the process of the present invention, the amide is added to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the PLA polymer melt.

[0027] The present invention relates in particular to PLA polymers having a D-lactide isomer content between 1.0 and 10.0 % by weight. Such PLA polymers are known to have a lower crystallization rate than pure L-PLA or pure D-PLA. PLA polymer production with a D-lactide isomer content of about 10.0 % by weight or more typically cannot be crystallized industrially and will remain amorphous. In some preferred embodiments of the process of the present invention, a PLA polymer melt is provided, wherein the PLA polymer has a D-lactide isomer content between 1.5 and 8.0 % by weight of the PLA polymer, for example between 2.0 and 6.0 % by weight or between 2.0 and 4.5 % by weight.

[0028] The process of the present invention involves adding a low concentration of an amide as defined herein during the melt processing stage of a PLA polymer (i.e., before pelletization). The inventors have shown that, surprisingly, by adding a small amount of such a compound during the melt stage (i.e., before pelletization), the crystallization rate can be increased and the crystallization time can be reduced in the subsequent crystallization step. This also enables the size of the crystallizer equipment required to prepare crystallized PLA pellets to be reduced. In addition, the process of the present invention allows the problem of clogging of the equipment caused by the stickiness of PLA and / or the inefficient crystallization of PLA polymers to be avoided. The present invention enables the production of different types of PLA with a desired degree of crystallinity at a higher production rate with minimal to no process upsets (failures, upsets) or shutdowns.

[0029] Preferably, the amide added in the process of the invention comprises at least one compound of formula (I) and / or at least one compound of formula (II),

[0030]

[0031] Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0032] Where R 3 , R 4 and R 7 are each independently selected from the group consisting of alkyl and alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0033] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0034] In some embodiments of the process of the present invention, the amide is selected from saturated fatty acid bisamide, unsaturated fatty acid bisamide, saturated fatty acid monoamide, unsaturated fatty acid monoamide, N-alkyl substituted fatty acid monoamide, and any mixture thereof.

[0035] In some preferred embodiments of the process of the present invention, the amide is a saturated fatty acid bisamide, and preferably a saturated fatty acid bisamide of formula (I), wherein R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently is C 4-28 An alkyl group which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0036] In some embodiments of the process of the invention, the amide is added to the PLA polymer melt in the form of a composition consisting of amides as defined herein before step b). Thus, in such an embodiment, the amide is added to the PLA polymer melt in the form of an amide compound itself before step b). In such an embodiment, the amide is added to the PLA polymer melt in the form of a compound before the pelletizing step and is not admixed with any non-amide compound.

[0037] In some embodiments of the process of the invention, the amide is added to the PLA polymer melt in the form of a molten composition obtained by melt blending the amide as defined herein with the PLA polymer before step b). The PLA polymer for blending with the amide may be a non-crystalline or crystalline PLA, and may or may not contain the amide itself.

[0038] In some embodiments of the process of the present invention, the amide is added to the PLA polymer melt prior to step b) in the form of a previously crystallized PLA polymer containing the amide. For example, the amide can be added in the form of a composition consisting of previously crystallized PLA polymer amides. In such embodiments, the previously crystallized PLA is characterized in that:

[0039] - prior to addition to the process of the invention, has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, wherein said crystallinity is determined according to the method specified herein;

[0040] - a content of D-lactide isomers equal to or lower than 10.0 wt.-%, for example between 0 and 10 wt.-%, or between 0.1 and 9.0 wt.-%, or between 0.5 and 8.0 wt.-%, or between 1.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%, based on said previously crystallized PLA, and

[0041] - contains an amide, preferably an amide as defined herein, in an amount of between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm, wherein the ppm are based on the weight of said previously crystallized PLA.

[0042] In some preferred embodiments, a process is provided which includes adding the following steps to the PLA polymer melt prior to step b):

[0043] i) an amide, preferably an amide as defined herein, and

[0044] ii) previously crystallized PLA;

[0045] wherein the previously crystallized PLA is characterized in that:

[0046] - prior to addition to the process, has a crystallinity of at least 20.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, wherein the crystallinity is determined according to the method specified herein;

[0047] - a content of D-lactide isomers equal to or lower than 10.0 wt.-%, for example between 0 and 10 wt.-%, or between 0.1 and 9.0 wt.-%, or between 0.5 and 8.0 wt.-%, or between 1.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%, based on said previously crystallized PLA, and

[0048] - optionally contains amides, preferably amides as defined herein, in a total amount of up to 2000 ppm, wherein the ppm is based on said previously crystallized PLA, or up to 1800 ppm, or up to 1500 ppm, or up to 1000 ppm, or up to 850 ppm, or up to 500 ppm, wherein the ppm is based on said previously crystallized PLA.

[0049] The Applicant has shown that, in addition to the amide as defined herein, which itself improves the crystallization rate, further addition of previously crystallized PLA at the melt stage also has advantages.

[0050] Prior to step b) of the process of the present invention, previously crystallized PLA may be added to the PLA polymer melt at a feed rate from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt provided in step a).

[0051] In some embodiments of the process of the present invention, previously crystallized PLA is added to the PLA polymer, i.e., the PLA polymer melt, before step b), wherein the previously crystallized PLA has a crystallinity of at least 20.0%, e.g., at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%.

[0052] In some embodiments of the process of the present invention, previously crystallized PLA is added to the PLA polymer, i.e., the PLA polymer melt, wherein the previously crystallized PLA has a content of D-lactide isomers equal to or lower than 10.0 wt % of the crystallized PLA polymer, and preferably a content of D-lactide isomers between 0 and 10.0 wt %, or between 0.1 and 9.0 wt %, or between 0.5 and 8.0 wt %, or between 1.0 and 6.0 wt %, or between 2.0 and 4.5 wt %.

[0053] In some preferred embodiments of the present invention, such a process is provided, wherein the amide as defined herein and the previously crystallized PLA are added separately to the PLA polymer melt. In some other preferred embodiments, the amide and the previously crystallized PLA (as defined herein) are blended, preferably melt blended to form a composition, preferably a molten composition, and the composition or molten composition is added to the PLA polymer melt, in particular before pelletizing it.

[0054] Preferably, the previously crystallized PLA as used in the process of the present invention is a crystallized form of the PLA polymer melt provided in step a).

[0055] Preferably, the PLA polymer melt is provided in step a) at a temperature comprised between 160°C and 240°C, preferably between 190°C and 230°C.

[0056] In some embodiments of the process of the present invention, the crystallization (step c) is carried out at a temperature between 90 and 130° C., preferably between 100 and 115° C. In some preferred embodiments, the present invention provides a process for preparing crystallized polylactide (PLA), in particular crystallized PLA pellets, wherein the crystallization step (step c) involves two-step crystallization. To this end, in some preferred embodiments of the process of the present invention, the PLA pellets are crystallized by the following steps, preferably under dry air conditions:

[0057] c1) keeping the PLA pellets moving at a temperature between 90 and 130° C. for a suitable period of time, thereby obtaining pre-crystallised PLA, wherein the pre-crystallised PLA preferably has a crystallinity of at least 3.0%, preferably at least 5.0%; and

[0058] c2) conveying the pre-crystallized PLA to a crystallization vessel and maintaining the pre-crystallized PLA in the crystallization vessel at a temperature between 90 and 130° C. for a suitable period of time to obtain crystallized PLA, whereby the crystallized PLA preferably has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, such as from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%.

[0059] The crystallinity can be determined according to the method as specified in the Examples section.

[0060] In another aspect, the present invention provides crystallized PLA, in particular crystallized PLA pellets, which can be obtained by or by carrying out the process according to the present invention, and preferably wherein the crystallized PLA pellets have:

[0061] - a D-lactide isomer content of between 1.0 and 10.0 wt.-%, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%, based on the crystallized PLA; and

[0062] - a crystallinity of at least 20.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, wherein the crystallinity is determined according to the method specified in the description; and

[0063] - between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the total amount of amides of the crystallized PLA pellets as defined herein.

[0064] In another aspect, the present invention further relates to the use of an amide as defined herein for increasing the crystallization rate of a PLA polymer, in particular for increasing the crystallization rate of a pellet of a PLA polymer, wherein the PLA polymer has a content of D-lactide isomers between 1.0 and 10.0 wt. % of the PLA polymer, wherein the amide is used in the form of a melt of the PLA polymer, i.e., before pelletization, in an amount between 10 and 2000 ppm of the PLA polymer melt. In an embodiment, the present invention relates to the use of an amide as defined herein for increasing the crystallization rate of a pellet of a PLA polymer as defined herein, wherein the amide is used to form a melt of the PLA polymer before pelletization, the PLA polymer comprising the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, e.g., between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm.

[0065] In some preferred embodiments, the amide is used in the form of a composition consisting of the amide as defined herein, ie in the form of an amide compound.

[0066] In other preferred embodiments, the amide is used in the form of a composition consisting of a previously crystallized PLA polymer containing the amide (ie in the form of a previously crystallized PLA polymer containing the amide).

[0067] In other embodiments, the amide is used in the form of a composition obtained by melt blending an amide as defined herein with a PLA polymer, which PLA polymer may be, for example, a non-crystalline or crystalline PLA, and may or may not contain the amide itself. In some preferred embodiments, the PLA polymer for blending with the amide is a crystalline PLA, which preferably contains the amide.

[0068] In other preferred embodiments, the amide is used in combination with a previously crystallized PLA polymer. Thus, in some preferred embodiments, the present invention relates to the use of an amide as defined herein in combination with a previously crystallized PLA, preferably a previously crystallized PLA as defined herein, for increasing the crystallization rate of pellets of a PLA polymer, wherein the amide and the previously crystallized PLA are added to the melt of the PLA polymer, i.e. before pelletization, either alone or as a blend, preferably as a molten composition.

[0069] In a preferred embodiment, the previously crystallized PLA is used at a feed rate of from 0.5 to 15.0%, such as from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0070] The independent and dependent claims set out particular and preferred features of the invention. Features from the dependent claims may be combined with features of the independent claim or other dependent claims as appropriate.

[0071] The present invention will now be further described. In the following paragraphs, different aspects of the present invention are defined in more detail. Each aspect so defined can be combined with any other one or more aspects unless clearly indicated to the contrary. Especially, any feature that is indicated as preferred or advantageous can be combined with any other one or more features that are indicated as preferred or advantageous. BRIEF DESCRIPTION OF THE DRAWINGS

[0072] Figure 1 The results of a crystallization experiment performed according to Example 2 are shown.

[0073] Figure 2 The results of a crystallization experiment performed according to Example 3 are shown.

[0074] Figure 3 The results of a crystallization experiment performed according to Example 4 are shown.

[0075] Figure 4 is a schematic diagram illustrating a process for preparing crystallized polylactide (PLA) pellets according to an exemplary embodiment of the present invention.

[0076] Figure 5 is a schematic diagram illustrating a process for preparing crystallized polylactide (PLA) pellets according to another exemplary embodiment of the present invention.

[0077] Figure 6 The results of a crystallization experiment performed according to Example 5 are shown. DETAILED DESCRIPTION

[0078] When describing the present invention, the terms used should be interpreted in accordance with the following definitions, unless the context dictates otherwise.

[0079] Unless otherwise defined, all terms used in disclosing the present invention, including technical and scientific terms, have the meaning commonly understood by one of ordinary skill in the art to which the present invention belongs. By way of further guidance, term definitions are included to better understand the teachings of the present invention.

[0080] In the following paragraphs, different aspects of the present invention are defined in more detail. Each aspect so defined can be combined with any other one or more aspects, unless clearly indicated to the contrary. In particular, any feature indicated as preferred or advantageous can be combined with any other one or more features indicated as preferred or advantageous.

[0081] References throughout this specification to "one (single) embodiment" or "an embodiment" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment is included in at least one embodiment of the present invention. Therefore, the phrases "in one (single) embodiment" or "in an embodiment" appearing in various places throughout this specification do not necessarily all refer to the same embodiment, but may refer to the same embodiment. In addition, in one or more embodiments, the particular features, structures, or characteristics may be combined in any suitable manner, as will be apparent to those skilled in the art from this disclosure. In addition, although some embodiments described herein include some features but not other features included in other embodiments, the combination of features of different embodiments is intended to be within the scope of the present invention and to form different embodiments, as will be understood by those skilled in the art.

[0082] As used herein, the terms "comprising, comprises, comprised of" are synonymous with "including, includes," or "containing, contains," and are inclusive or open-ended and do not exclude additional, unrecited members, elements, or method steps. It should be understood that the term "comprising," as used herein, includes the term "consisting of, consists, consists of."

[0083] As used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. By way of example, "a step" means one step or more than one step.

[0084] Unless defined otherwise, all technical and scientific terms used herein have the same meanings as commonly understood by one of ordinary skill in the art.

[0085] The recitation of numerical ranges by endpoints includes all integers and, where appropriate, fractions contained within the range (e.g., 1 to 5 may include 1, 2, 3, 4 when referring to, for example, the number of elements, and 1.5, 2, 2.75, and 3.80 when referring to, for example, measurements). The recitation of endpoints also includes the endpoint values ​​themselves (e.g., 1.0 to 5.0 includes both 1.0 and 5.0). Any numerical range recited herein is intended to include all subranges contained therein.

[0086] As used herein, the term "about" when referring to measurable values ​​such as parameters, amounts, durations, etc., is intended to encompass the specified value and variations of + / -10% or less, preferably + / -5% or less, more preferably + / -1% or less from the specified value, provided such variations are suitable for making in the disclosed invention. It should be understood that the value to which the modifier "about" refers is itself also specifically and preferably disclosed.

[0087] The terms "weight %", "volume %" or "mole %" refer to the weight percentage of a component, the volume percentage of a component or the mole percentage of a component, respectively, based on the total weight, total volume or total moles of the materials including the component.

[0088] When describing the present invention, the terms used should be interpreted in accordance with the following definitions, unless the context indicates otherwise.

[0089] Preferred statements (features) and embodiments and uses of the invention are set forth below. Each statement and embodiment of the invention so defined may be combined with any other statement and / or embodiment, unless expressly indicated to the contrary. In particular, any feature indicated as preferred or advantageous may be combined with any other one or more features or statements indicated as preferred or advantageous. Here, the invention is particularly captured by any one or any combination of one or more of the following numbered statements and embodiments with any other aspects and / or embodiments.

[0090] 1. A process for preparing crystalline polylactide (PLA), the process comprising the following steps:

[0091] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer;

[0092] b) processing the PLA polymer melt into PLA pellets, and

[0093] c) crystallizing the PLA pellets to obtain crystallized PLA,

[0094] The process is characterized in that the amide is added to the PLA polymer melt in an amount between 10 and 2000 ppm of the PLA polymer melt.

[0095] 2. A process according to statement 1, wherein the amide is added to the PLA polymer melt before processing the PLA polymer melt into PLA pellets.

[0096] 3. A process for preparing crystallized polylactide (PLA) pellets, the process comprising the following steps:

[0097] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer;

[0098] b) pelletizing the PLA polymer melt into PLA pellets, and

[0099] c) crystallizing the PLA pellets to obtain crystallized PLA pellets,

[0100] The process is characterized in that, prior to step b), an amide is added to the PLA polymer melt to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount of between 10 and 2000 ppm of the PLA polymer melt.

[0101] 4. A process for preparing crystallized polylactide (PLA) pellets, the process comprising the following steps:

[0102] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer, and

[0103] adding an amide to the PLA polymer melt prior to step b) to form a PLA polymer melt comprising amide in a total amount of between 10 and 2000 ppm of the PLA polymer melt,

[0104] b) pelletizing the PLA polymer melt (i.e., the PLA polymer melt containing amide) formed in step a) into PLA pellets, and

[0105] c) crystallizing the PLA pellets obtained in step b) to obtain crystallized PLA pellets.

[0106] 5. The process according to any one of the preceding statements, wherein the PLA pellets are crystallized by means of latent heat crystallization.

[0107] 6. A process according to any one of the preceding statements, wherein during pelletization the average PLA pellet temperature is maintained above the glass transition temperature (Tg) of the PLA polymer.

[0108] 7. A process according to any of the preceding statements, wherein the amide is added in an amount between 20 and 1500 ppm, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, preferably between 100 and 900 ppm of the PLA polymer melt.

[0109] 8. A process according to any of the preceding statements, wherein the amide is added to form a PLA polymer melt comprising amide in a total amount of between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the PLA polymer melt.

[0110] 9. A process according to any of the preceding statements, wherein the amide comprises at least one compound of formula (I) and / or at least one compound of formula (II),

[0111]

[0112] Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0113] Where R 3 , R 4 and R 7 are each independently selected from the group consisting of alkyl and alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0114] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0115] 10. The process according to any one of the preceding statements, wherein the amide comprises at least one compound of formula (I) and / or at least one compound of formula (II),

[0116] Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from the group consisting of C 1-28 Alkyl and C 2-28alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0117] Where R 3 , R 4 and R 7 Each independently selected from the group consisting of C 1-28 Alkyl and C 2-28 alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0118] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0119] 11. A process according to any of the preceding statements, wherein the amide is a fatty acid amide.

[0120] 12. The process according to any of the preceding statements, wherein the amide is selected from fatty acid bisamides, fatty acid monoamides, N-alkyl substituted fatty acid monoamides, and any mixtures thereof.

[0121] 13. A process according to any of the preceding statements, wherein the amide is selected from saturated fatty acid bisamides, unsaturated fatty acid bisamides, saturated fatty acid monoamides, unsaturated fatty acid monoamides, N-alkyl substituted fatty acid monoamides, and any mixtures thereof.

[0122] 14. A process according to any one of the preceding statements, wherein the amide comprises a fatty acid bisamide, and preferably a fatty acid bisamide of formula (I), wherein R 5 and R 6 are each independently hydrogen, or selected from the group consisting of C 4-28 Alkyl and C 4-28 alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0123] Where R 4 and R 7 Each independently selected from the group consisting of C 4-28 Alkyl and C 4-28 alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0124] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0125] 15. A process according to any one of the preceding statements, wherein the amide comprises a fatty acid bisamide of formula (I) wherein R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently selected from the group consisting of C 4-28Alkyl and C 4-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0126] 16. A process according to any one of the preceding statements, wherein the amide comprises a saturated fatty acid bisamide, preferably a saturated fatty acid bisamide of formula (II),

[0127]

[0128] Where R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently is C 4-28 An alkyl group which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0129] 17. A process according to any of the preceding statements, wherein the amide is selected from the group consisting of ethylene bisstearamide, ethylene biscaprylamide, ethylene biscapramide, ethylene bislauramide, ethylene bismyramide, ethylene bispalmitamide, ethylene bisisostearamide, ethylene bisbehenamide, ethylene bis(12-hydroxystearamide), methylene biscaprylamide, methylene biscapramide, methylene bislauramide, methylene bismyramide, methylene bispalmitamide, methylene bisstearamide, methylene bisisostearamide, methylene bisbehenamide, methylene bis(12-hydroxystearamide), butylene bisstearamide, butylene bisbehenamide, hexamethylene bisstearamide, butylene bis(12-hydroxystearamide), hexamethylene bisbehenamide, hexamethylene bis(12-hydroxystearamide), and N,N'-distearyl adipamide.

[0130] 18. A process according to any of the preceding statements, wherein the PLA polymer has a content of D-lactide isomers between 1.5 and 8.0 wt %, such as between 2.0 and 6.0 wt % or between 2.0 and 4.5 wt % of the PLA polymer.

[0131] 19. The process according to any one of the preceding statements, wherein the PLA pellets are crystallized in step c) under dry air conditions.

[0132] 20. The process according to any of the preceding statements, wherein before step b), the amide is added to the PLA polymer melt in the form of a composition consisting of amides, preferably amides as defined in any of the preceding statements.

[0133] 21. Process according to any of the preceding statements, wherein the amide is added to the PLA polymer melt before step b) in the form of a composition obtained by melt blending an amide, preferably an amide as defined in any of the preceding statements, with a PLA polymer.

[0134] 22. A process according to statement 21, wherein the PLA polymer is non-crystalline PLA.

[0135] 23. A process according to statement 21, wherein the PLA polymer is previously crystallized PLA.

[0136] 24. A process according to any one of Statements 21 to 23, wherein the PLA polymer does not contain amide.

[0137] 25. A process according to any one of Statements 21 to 23, wherein the PLA polymer contains amides, preferably in a total amount of at most 2000 ppm, wherein the ppm is based on the PLA polymer, or at most 1800 ppm, or at most 1500 ppm, or at most 1000 ppm, or at most 850 ppm, or at most 500 ppm, wherein the ppm is based on the PLA polymer.

[0138] 26. A process according to any of the preceding statements, wherein previously crystallized PLA is added to the PLA polymer melt.

[0139] 27. A process according to any one of the preceding statements, wherein the previously crystallized PLA is added to the PLA polymer melt before processing (pelletizing) the PLA polymer melt into PLA pellets.

[0140] 28. A process according to any one of the preceding statements, comprising the step of adding (i) an amide and (ii) previously crystallized PLA to the PLA polymer melt prior to step b), wherein the previously crystallized PLA is characterized in that:

[0141] - prior to addition to the process, has a crystallinity of at least 20.0%, wherein said crystallinity is determined according to the method specified in the description;

[0142] - having a content of D-lactide isomers equal to or lower than 10.0% by weight, based on said previously crystallized PLA, and

[0143] - optionally contains amides, preferably amides as defined in any of the preceding statements, in a total amount of at most 2000 ppm, wherein the ppm is based on said previously crystallized PLA, or at most 1800 ppm, or at most 1500 ppm, or at most 1000 ppm, or at most 850 ppm, or at most 500 ppm, wherein the ppm is based on said previously crystallized PLA.

[0144] 29. A process according to statement 28, wherein the amide and the previously crystallized PLA are added separately to the PLA polymer melt before step b).

[0145] 30. A process according to any preceding statement 28, wherein the amide and the previously crystallized PLA are added in combination to the PLA polymer melt.

[0146] 31. A process according to statement 28 or 30, wherein the amide and previously crystallized PLA are blended to form a composition, and preferably melt blended to form a molten composition, and wherein the composition, and preferably the molten composition, is added to the PLA polymer melt before step b).

[0147] 32. A process according to statement 31 above, wherein the composition, preferably the molten composition, is added to the PLA polymer melt at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt provided in step a).

[0148] 33. A process according to any one of statements 1 to 19, wherein the amide is added to the PLA polymer melt in the form of previously crystallized PLA prior to step b), and wherein the previously crystallized PLA is characterized in that:

[0149] - prior to addition to the process, has a crystallinity of at least 20.0%, wherein said crystallinity is determined according to the method specified in the description;

[0150] - having a content of D-lactide isomers equal to or lower than 10.0% by weight, based on said previously crystallized PLA, and

[0151] - contains an amide, preferably an amide as defined in any of the preceding statements, in an amount between 10 and 2000 ppm, for example between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm, wherein the ppm is based on the weight of said previously crystallized PLA.

[0152] 34. A process according to any of the preceding statements, wherein prior to addition to the process, the previously crystallized PLA has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, such as from 20.0 to 60.0%, or from 30.0 to 55.0%, or from 35.0 to 50.0%, or from 38.0 to 48.0%.

[0153] 35. A process according to any of the preceding statements, wherein the previously crystallized PLA has a content of D-lactide isomers equal to or lower than 10.0 wt.-% of the crystallized PLA polymer, and preferably the content of D-lactide isomers is between 0 and 10.0 wt.-%, or between 0.1 and 9.0 wt.-%, or between 0.5 and 8.0 wt.-%, or between 1.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%.

[0154] 36. A process according to any of the preceding statements, wherein previously crystallized PLA is added to the PLA polymer melt at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % is expressed as compared to the feed rate of the PLA polymer melt provided in step a).

[0155] 37. A process according to any one of the preceding statements, wherein the previously crystallized PLA is a crystallized form of the PLA polymer melt provided in step a).

[0156] 38. Process according to any of the preceding statements, wherein the PLA polymer melt is provided in step a) at a temperature comprised between 160 and 240°C, preferably between 190 and 230°C.

[0157] 39. A process according to any one of the preceding statements, wherein the PLA pellets are crystallized, preferably under dry air conditions, by the following steps:

[0158] c1) keeping the PLA pellets moving at a temperature between 90 and 130° C. for a suitable period of time, thereby obtaining pre-crystallized PLA,

[0159] c2) conveying the pre-crystallized PLA to a crystallization vessel via a suitable conveying system, and maintaining the pre-crystallized PLA in the crystallization vessel at a temperature between 90 and 130° C. for a suitable period of time, thereby obtaining crystallized PLA.

[0160] 40. Process according to any of the preceding statements, wherein the PLA pellets are subjected during step c1) to a temperature between 90 and 120°C, preferably between 95 and 115°C, or between 100 and 115°C.

[0161] 41. Process according to any of the preceding statements, wherein the pre-crystallized PLA obtained in step c1) has a crystallinity of at least 3.0% and preferably at least 5.0%.

[0162] 42. Process according to any of the preceding statements, wherein in step c2) the pre-crystallized PLA is kept at a temperature between 90 and 120°C, such as between 95 and 115°C, or between 100 and 115°C.

[0163] 43. Process according to any of the preceding statements, wherein the crystallized PLA obtained in step c2) has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, such as from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%.

[0164] 44. A process according to any of the preceding statements, wherein the time required to obtain a suitable degree of crystallinity, and preferably a degree of crystallinity as defined in statement 43, is reduced by at least 10%, or at least 15%, or at least 20%, or at least 25%, or at least 35%, or at least 50%, compared to a process in which no amide is added to the PLA polymer melt.

[0165] 45. Crystallized PLA, preferably crystallized PLA pellets, obtainable by or by carrying out a process according to any one of the preceding statements.

[0166] 46. ​​The crystallized PLA according to the preceding statement, having

[0167] - a content of between 1.0 and 10.0 wt.-%, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-% of D-lactide isomers, based on the crystallized PLA; and

[0168] - a crystallinity of at least 20.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, and for example from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%; and

[0169] An amide as defined herein in an amount between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of said crystallized PLA.

[0170] 47. Crystallized PLA pellets obtainable by or by carrying out a process according to any one of the preceding statements, wherein the pellets have

[0171] - a content of between 1.0 and 10.0 wt.-%, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-% of D-lactide isomers, based on the crystallized PLA; and

[0172] - a crystallinity of at least 20.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, wherein the crystallinity is determined according to the method specified in the description; and

[0173] - a total amount of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of said crystallized PLA pellets, of amides as defined in any of the preceding statements.

[0174] 48. Use of an amide (as defined in any of the preceding statements) for increasing the crystallization rate of a PLA polymer, preferably a pellet of a PLA polymer, wherein the PLA polymer has a content of D-lactide isomer between 1.0 and 10.0 wt. % of the PLA polymer, wherein prior to pelletization, the amide is used to form a melt of the PLA polymer, the melt of the PLA polymer comprising the amide in a total amount of between 10 and 2000 ppm of the PLA polymer.

[0175] 49. Use of an amide according to the preceding statement 48 for increasing the crystallization rate of a PLA polymer, preferably a pellet of a PLA polymer, wherein the PLA polymer has a content of D-lactide isomers of between 1.5 and 8.0 wt. %, or between 2.0 and 6.0 wt. %, or between 2.0 and 4.5 wt. % of the PLA polymer.

[0176] 50. Use of an amide according to any of the preceding statements for increasing the crystallization rate of a PLA polymer, preferably a pellet of a PLA polymer, wherein the amide is used in the melt of the PLA polymer in an amount of between 20 and 1500 ppm, preferably between 30 and 1000 ppm and more preferably between 50 and 900 ppm, or preferably between 100 and 900 ppm of the PLA polymer.

[0177] 51. Use of an amide according to any of the preceding statements for increasing the crystallization rate of a PLA polymer, preferably pellets of a PLA polymer, wherein the amide is used in combination with previously crystallized PLA, preferably previously crystallized PLA as defined in any of the preceding statements.

[0178] 52. Use of an amide according to the preceding statement 51 for increasing the crystallization rate of a PLA polymer, preferably pellets of a PLA polymer, wherein the amide and the previously crystallized PLA are added separately to a melt of the PLA polymer, and preferably wherein the previously crystallized PLA is used at a feed rate of from 0.5 to 15.0%, such as from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0179] 53. Use of an amide according to the preceding statement 51 for increasing the crystallization rate of a PLA polymer, preferably a pellet of a PLA polymer, wherein the amide and the previously crystallized PLA are added to a melt of the PLA polymer as a blend, preferably as a molten composition, and preferably wherein the molten composition of the amide and the previously crystallized PLA is fed at a rate (e.g., in kg / h) of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0180] In one aspect, the present invention relates to a process for preparing crystallized polylactide (PLA) and in particular a process for preparing crystallized PLA pellets (i.e., crystallized PLA in pellet form). The present invention relates to such a process, wherein the PLA polymer is first pelletized before crystallization.

[0181] In one embodiment, the present invention is directed to a process for preparing crystalline polylactide (PLA), comprising the steps of:

[0182] a) providing a melt of a PLA polymer (i.e., a PLA polymer melt), wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer;

[0183] b) processing the PLA polymer melt into PLA pellets, and

[0184] c) crystallizing the PLA pellets, preferably under dry air conditions, to obtain crystallized PLA,

[0185] The process is characterized in that the amide is added to the PLA polymer melt in an amount between 10 and 2000 ppm of the PLA polymer melt.

[0186] In an embodiment of the present invention, a process for preparing crystallized polylactide (PLA) pellets is provided, comprising the following steps:

[0187] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer, and adding an amide to the PLA polymer melt in an amount between 10 and 2000 ppm of the PLA polymer melt,

[0188] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0189] c) crystallizing the PLA pellets obtained in step b) to obtain crystallized PLA pellets.

[0190] When referring herein to adding amide to the PLA polymer melt, this corresponds to adding amide to the PLA polymer melt before step b), i.e. before pelletizing, and in a suitable amount so as to form a PLA melt comprising the total amount of amide as given herein, for example between 10 and 2000 ppm, wherein the ppm is based on the PLA polymer melt.

[0191] Therefore, the present invention provides a process for preparing crystallized polylactide (PLA) pellets, comprising the following steps:

[0192] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer, and adding an amide to the PLA polymer melt to form a PLA melt comprising the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt,

[0193] b) pelletizing the amide-containing PLA polymer melt formed in step a) into PLA pellets, and

[0194] c) crystallizing the PLA pellets obtained in step b) to obtain crystallized PLA pellets.

[0195] In other words, the present invention provides a process for preparing crystallized polylactide (PLA) pellets, comprising the following steps:

[0196] a) preparing a melt of a PLA polymer having a D-lactide isomer content between 1.0 and 10.0 wt.-% and comprising amides in a total amount between 10 and 2000 ppm of the PLA polymer melt, wherein the PLA melt is prepared by adding amides to the PLA polymer melt,

[0197] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0198] c) crystallizing the PLA pellets obtained in step b) to obtain crystallized PLA pellets.

[0199] According to the process of the present invention, the PLA polymer melt is formed into a pellet form. The viscous and amorphous PLA polymer pellets are subsequently crystallized into crystalline PLA pellets. The present invention is characterized in that a small amount of amide (amide as defined herein) is added at the PLA melting stage to improve the crystallization rate of the PLA pellets, that is, to increase the crystallization speed of the PLA pellets. Therefore, the present invention relates to a process in which the PLA polymer is first pelletized before crystallization.

[0200] The terms "PLA," "polylactide," and "polylactic acid" and "PLA polymer" are used synonymously herein.

[0201] "PLA polymer" as used herein refers to a polymer of lactide (monomer). Lactide can exist in three different geometric structures, which have a diastereomeric relationship. Therefore, the term "lactide" (or "lactide monomer") as used herein can be L-lactide (derived from two L-lactic acid molecules), D-lactide (derived from two D-lactic acid molecules), meso-lactide (derived from L-lactic acid molecules and D-lactic acid molecules), or a mixture of two or more of the above. A 50 / 50 mixture of L-lactide and D-lactide with a melting point of about 126°C is often referred to as D, L-lactide or racemic lactide in the literature (and is also represented as "rac-lactide" ("rac-Lactide" or "racemic lactide" or "rac-lactide") in this article). Thus, the PLA polymer as defined herein may be a polymer of lactide selected from the group comprising L-lactide, D-lactide, meso-lactide, racemic lactide, and any mixture of two or more thereof.

[0202] According to the present invention, the stereochemical purity of the L isomer of the PLA polymer used in the present process (referred to as isomeric purity) is between 90.0 and 99.0% by weight of the PLA. In other words, the PLA polymer as used in the present invention has a content of D-lactide isomers between 1.0 and 10.0% by weight. The terms "D-lactide isomers" and "D-lactide" and "D-lactate isomers" are used as synonyms herein. It will be understood by those skilled in the art that the term "D-lactide isomers" as used herein refers to D-units that can be derived from D-lactide and / or meso-lactide (i.e., present through D-lactide and / or meso-lactide) or produced by racemization. During the analysis, the PLA chains were decomposed into lactate esters and measured as such.

[0203] In some embodiments, the PLA used in the present process has a content of D-lactide isomers between 1.5 and 8.0 wt %, or between 2.0 and 6.0 wt %, or between 2.0 and 4.5 wt % of the PLA polymer. Examples of PLA polymers for use in the process according to the present invention include, for example, PLA having a D-lactide content of 1.5 or 2.0 or 2.5 or 3.0 or 3.5 or 4.0 or 4.5 or 5.0 or 5.5 or 6.0 wt % based on the PLA. Stereochemical purity can be determined using methods known in the art, such as methine decoupling. 1 H-NMR spectroscopy and chiral column chromatography of methyl lactate (after methylation of the original PLA sample).

[0204] Processes for preparing PLA having an isomeric purity as defined above are well known to those skilled in the art. For example, in an embodiment, PLA is obtained by polymerizing lactide monomers in the presence of a suitable catalyst and preferably in the presence of a compound of formula (III) which acts as a co-initiator and transfer agent for the polymerization,

[0205]

[0206] Where R 8 Selected from the group consisting of: C 1-20 Alkyl, C 6-30 Aryl and C 6-30 Aryl C 1-20 Alkyl, optionally substituted by one or more selected from halogen, hydroxyl and C 1-6 Preferably, R 8 Selected from C 3-12 Alkyl, C 6-10 Aryl and C 6-10 Aryl C 3-12Alkyl, optionally substituted with one or more substituents, each of which is independently selected from the group consisting of halogen, hydroxyl and C 1-6 alkyl group; preferably, R 1 Selected from C 3-12 Alkyl, C 6-10 Aryl and C 6-10 Aryl C 3-12 Alkyl, optionally substituted with one or more substituents, each of which is independently selected from the group consisting of halogen, hydroxyl and C 1-4 The alcohol may be a polyol such as a diol, a triol or a polyhydric alcohol of higher functionality. The alcohol may be derived from biomass such as glycerol or propylene glycol or any other sugar-based alcohol, such as erythritol. The alcohol may be used alone or in combination with another alcohol.

[0207] Non-limiting examples of initiators include 1-octanol, isopropanol, propylene glycol, trimethylolpropane, 2-butanol, 3-butene-2-ol, 1,3-butanediol, 1,4-butanediol, 1,6-hexanediol, 1,7-heptanediol, benzyl alcohol, 4-bromophenol, 1,4-benzenedimethanol and (4-trifluoromethyl)benzyl alcohol; preferably, the compound of formula (I) is selected from 1-octanol, isopropanol and 1,4-butanediol.

[0208] The monomers used in the production of the polylactide as defined herein used in the present invention include L-lactic acid, D-lactic acid, L-lactide formed from two L-lactic acids, D-lactide formed from two D-lactic acids, and meso-lactide formed from L-lactic acid and D-lactic acid.

[0209] Examples of suitable catalysts for use in the above-mentioned polymerization may include, but are not limited to, oxides, halides or carboxylates of metals from Groups IV, V, VIII of the periodic table, such as antimony trioxide (Sb2O3), tris(phenolates) of zirconium or titanium, stannous oxide (SnO), stannous dichloride (SnCl2) and stannous bis(2-ethylhexylcarboxylate) (Sn(Oct)2). The dosage of the catalyst is determined based on the conditions of the polymerization reaction and is well known to those skilled in the art.

[0210] The PLA polymer obtained after the polymerization stage has an amorphous structure and a very sticky surface. This amorphous structure can be converted into a more crystalline state with a larger alignment between its molecular chains in a thermal post-treatment step, which is also called crystallization. The process of the present invention relates to a process for preparing crystallized PLA. Preferably, the process of the present invention relates to a process for preparing crystallized PLA pellets.

[0211] As used herein, the term "crystallised PLA or crystallized PLA" is intended to mean a PLA or PLA product having a crystallinity of at least 20.0%, such as at least 25.0%. In some preferred embodiments, the crystallized PLA prepared as herein may have a crystallinity of at least 30.0%, or at least 35.0%, or at least 40.0%.

[0212] Crystallinity can be defined as the percentage of the crystalline portion relative to the overall internal structure of the polymer (ie, crystalline and amorphous).Crystallinity can be determined using techniques well known in the art and as illustrated in the Examples section below.

[0213] In some preferred embodiments, the preferred crystallinity of the crystallized PLA prepared according to the process of the present invention is from 20.0 to 60.0%, such as from 30.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%. In an example, the crystallinity of the crystallized PLA prepared according to the process of the present invention can be from 38.0 to 48.0%, or from 40.0 to 45.0%. The process of the present invention is characterized in that a fast crystallization rate and a high crystallinity are provided.

[0214] Thus, the first step of the process of the present invention involves providing a PLA polymer melt.

[0215] "PLA polymer melt" or "PLA melt" as used herein refers to a PLA polymer in a molten state as defined herein. The process of the present invention involves the steps of providing a PLA polymer melt of the aforementioned PLA polymer, and adding an amide to the PLA polymer melt before subjecting the PLA polymer melt to a pelletizing step. The melt of the PLA polymer may be provided by any suitable means, such as by supplying the polylactide formed by the polymerization of the aforementioned lactide monomer to a suitable mixing device or container, such as a static mixer, etc. Preferably, the PLA polymer melt is provided at a temperature of about 160 to 240°C in the process of the present invention. In some preferred embodiments, the PLA polymer melt is provided at a temperature comprised between 190 and 230°C.

[0216] In a preferred embodiment of the process of the present invention, the PLA polymer melt provided in step a) is obtained by a process involving the following steps:

[0217] i. subjecting lactide monomers to a polymerization reaction in the presence of a suitable catalyst, preferably a catalyst as mentioned herein, and optionally a co-initiator, preferably a co-initiator as mentioned herein, to form a reaction mixture comprising polylactide,

[0218] ii. stabilizing such reaction mixture comprising polylactide by adding a catalyst deactivator,

[0219] iii. degassing the reaction mixture to obtain a PLA polymer melt (ie, polylactide as a molten residue), and

[0220] iv. Recovering the PLA polymer melt.

[0221] Catalyst deactivators are known in the art. In particular, the process of the present invention is characterized in that a small amount of an amide as defined herein is added to the PLA polymer melt, i.e. before processing (pelletizing) the PLA polymer melt into PLA pellets. Despite the low amounts used for such compounds, the addition of such compounds has been shown to improve / increase the crystallization rate of PLA (as defined herein).

[0222] In a preferred embodiment of the process of the invention, the amide comprises at least one compound of formula (I) and / or at least one compound of formula (II),

[0223]

[0224] Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0225] Where R 3 , R 4 and R 7 are each independently selected from the group consisting of alkyl and alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0226] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0227] In a preferred embodiment of the process of the invention, the amide comprises at least one compound of formula (I) and / or at least one compound of formula (II),

[0228] Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from the group consisting of C 1-28 Alkyl and C 2-28 alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0229] Where R 3 , R4 and R 7 Each independently selected from the group consisting of C 1-28 Alkyl and C 2-28 alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and

[0230] wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0231] In some embodiments of the process of the present invention, the amide comprises a compound of formula (II), wherein R 1 , R 2 and R 3 Each independently selected from the group consisting of C 1-28 Alkyl and C 2-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups.

[0232] In some embodiments of the process of the present invention, the amide comprises a compound of formula (II), wherein R 1 is hydrogen, and R 2 and R 3 Each independently selected from the group consisting of C 1-28 Alkyl and C 2-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups.

[0233] In some embodiments of the process of the present invention, the amide comprises a compound of formula (II), wherein R 1 and R 2 is hydrogen, and wherein R 3 Selected from the group containing C 1-28 Alkyl and C 2-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups.

[0234] In an example, the amide comprises a compound of formula (II) wherein R 1 and R 2 is hydrogen, and wherein R 3 C 1-28 Alkyl groups such as C 1-22 Alkyl, or C 1-18 Alkyl, or C 1-12 In another example, the amide comprises a compound of formula (I), wherein R 1 and R 2 is hydrogen, and wherein R 3 C 2-28 Alkenyl such as C 2-22 Alkenyl, or C 2-18 Alkenyl, or C 2-12 Alkenyl.

[0235] In some embodiments of the process of the present invention, the amide comprises a fatty acid amide. As used herein, the term "fatty acid amide" means an amide comprising in its structure at least one aliphatic hydrocarbon chain having at least 4 carbon atoms, e.g., from 4 to 28 carbon atoms, which may be saturated or unsaturated.

[0236] In some embodiments of the process of the present invention, the amide comprises fatty acid bisamide. As used herein, the term "fatty acid bisamide" refers to a compound having two amide bonds in one molecule, such as a saturated fatty acid bisamide or an unsaturated fatty acid bisamide.

[0237] In some preferred embodiments of the process of the present invention, the amide comprises a fatty acid bisamide of formula (I),

[0238]

[0239] Where R 5 and R 6 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and wherein R 4 and R 7 Each is independently selected from a group comprising alkyl and alkenyl, wherein each group may be unsubstituted or substituted with one or more hydroxyl groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0240] In some embodiments of the process of the present invention, the amide comprises or consists of a fatty acid bisamide of formula (I), wherein R 5 and R 6 are each independently hydrogen, or selected from the group consisting of C 4-28 Alkyl and C 4-28 alkenyl radical, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and wherein R 4 and R 7 Each independently selected from the group consisting of C 4-28 Alkyl and C 4-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0241] In some embodiments of the process of the present invention, the amide comprises or consists of a fatty acid bisamide of formula (I), wherein R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently selected from the group consisting of C4-28 Alkyl and C 4-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

[0242] In some embodiments of the process of the present invention, the amide comprises or consists of a saturated fatty acid bisamide. In some preferred embodiments of the process of the present invention, the amide comprises a saturated fatty acid bisamide of formula (I), wherein R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently is C 4-28 An alkyl group which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7. Preferred examples of such saturated fatty acid bisamides include, but are not limited to, ethylene bisstearamide, ethylene biscaprylic acid ...

[0243] In some embodiments of the process of the present invention, the amide comprises or consists of an unsaturated fatty acid bisamide. In some preferred embodiments, the amide comprises an unsaturated fatty acid bisamide of formula (I), wherein R 4 and R 7 Each independently selected from C 4-28 alkenyl, optionally substituted with one or more hydroxyl groups, wherein R 5 and R 6 is hydrogen, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7. Preferred examples of such unsaturated fatty acid bisamides include, but are not limited to, for example, ethylenebisoleamide, ethylenebiserucamide, methylenebisoleamide, methylenebiserucamide, butylenebisoleamide, butylenebiserucamide, hexamethylenebisoleamide, hexamethylenebiserucamide, and N,N'-dioleyl-adipamide.

[0244] In some embodiments of the process of the present invention, the amide comprises or consists of fatty acid monoamide. The term "fatty acid monoamide" as used herein refers to an amide compound containing in its structure an aliphatic hydrocarbon having at least 4 carbon atoms and preferably from 4 to 28 carbon atoms, which may be saturated (i.e. "saturated fatty acid monoamide") or unsaturated (i.e. "unsaturated fatty acid monoamide").

[0245] In some preferred embodiments of the process of the present invention, the amide comprises a fatty acid monoamide of formula (II),

[0246]

[0247] Where R 1 and R 2 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and wherein R 3 is selected from the group comprising alkyl and alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxy groups.

[0248] In some embodiments of the process of the present invention, the amide comprises or consists of a fatty acid monoamide of formula (II), wherein R 1 and R 2 are each independently hydrogen, or selected from the group consisting of C 4-28 Alkyl and C 4-28 alkenyl radical, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and wherein R 3 Selected from the group containing C 4-28 Alkyl and C 4-28 An alkenyl group, each of which may be unsubstituted or substituted with one or more hydroxy groups.

[0249] In some embodiments of the process of the present invention, the amide comprises or consists of a saturated fatty acid monoamide. In some preferred embodiments of the process of the present invention, the amide comprises a saturated fatty acid monoamide of formula (II), wherein R 1 and R 2 is hydrogen, and wherein R 3 Selected from C 4-28 Alkyl groups which may be unsubstituted or substituted with one or more hydroxyl groups. Preferred examples of such saturated fatty acid monoamides include, but are not limited to, laurylamide, palmitamide, stearylamide and 12-hydroxystearylamide.

[0250] In some embodiments of the process of the present invention, the amide comprises or consists of an unsaturated fatty acid monoamide. In some preferred embodiments of the process of the present invention, the amide comprises an unsaturated fatty acid monoamide of formula (II), R 1 and R 2 is hydrogen, and wherein R 3 Selected from C 4-28 Alkenyl, which may be unsubstituted or substituted with one or more hydroxyl groups. Preferred examples of such unsaturated fatty acid monoamides include, but are not limited to, oleamide and erucamide.

[0251] In some embodiments of the process of the present invention, the amide comprises or is composed of N-alkyl-substituted fatty acid monoamides. As used herein, the term "N-alkyl-substituted fatty acid monoamides" refers to fatty acid monoamides (e.g., saturated fatty acid monoamides or unsaturated fatty acid monoamides) as defined herein, wherein one amide hydrogen of the fatty acid monoamide is replaced by an alkyl group. Therefore, as used herein, N-alkyl-substituted fatty acid monoamides include "N-alkyl-substituted saturated fatty acid monoamides" and "N-alkyl-substituted unsaturated fatty acid monoamides".

[0252] In some preferred embodiments, the amide comprises or consists of an N-alkyl-substituted fatty acid monoamide of formula (II),

[0253]

[0254] Where R 1 is hydrogen, where R 2 C 1-28 alkyl, optionally substituted with one or more hydroxyl groups, and wherein R 3 Selected from the group containing C 4-28 Alkyl and C 4-28 The group of alkenyl, wherein each group can be unsubstituted or substituted by one or more hydroxyl groups. Preferred examples of such N-alkyl-substituted fatty acid monoamides include but are not limited to N-lauryl lauramide, N-palmityl palmitamide, N-stearyl stearamide, N-behenyl behenamide, N-oleyl oleamide, N-stearyl oleamide, N-oleyl stearamide, N-stearyl erucic acid amide and N-oleyl palmitamide, hydroxymethyl stearamide, N-stearyl-12-hydroxystearamide, N-oleyl-12-hydroxystearyl stearamide (N-oleyl-12-hydroxystearic stearamide) etc.

[0255] In some preferred embodiments of the process of the present invention, the amide is selected from the group consisting of fatty acid bisamide, fatty acid monoamide, N-alkyl substituted fatty acid monoamide, and any mixture thereof.

[0256] In some preferred embodiments of the process of the present invention, the amide is selected from saturated fatty acid bisamide, unsaturated fatty acid bisamide, saturated fatty acid monoamide, unsaturated fatty acid monoamide, N-alkyl substituted fatty acid monoamide, and any mixture thereof.

[0257] Thus, the total amount of amide added to the PLA polymer melt (and therefore present in the PLA polymer melt before pelletizing) is between 10 and 2000 ppm (i.e. 0.001 to 0.2 wt. %), and preferably between 20 and 1500 ppm (0.002 to 0.15 wt. %), preferably between 30 and 1000 ppm (0.003 to 0.1 wt. %), and more preferably between 50 and 900 ppm (0.005 to 0.09 wt. %), and more preferably between 100 and 900 ppm (0.01 and 0.09 wt. %), wherein the ppm is based on the weight of the PLA polymer melt.

[0258] Thus, the present invention relates to the preparation of a melt of a PLA polymer as defined herein and comprising amide in a total amount of between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm, wherein the ppm is based on the weight of the PLA polymer melt.

[0259] In a preferred embodiment of the present invention, a process for preparing crystallized polylactide (PLA) pellets is provided, wherein the process involves adding amide to a PLA melt prior to step b) to form a PLA polymer melt having a total amount of amide of at most 2000 ppm, such as at most 1800 ppm, or at most 1500 ppm, or at most 1000 ppm, or at most 950 ppm, or at most 900 ppm, or at most 900 ppm, wherein the ppm is based on the PLA polymer melt. In a preferred embodiment of the present invention, a process for preparing crystallized polylactide (PLA) pellets is provided, wherein the process involves adding amide to a PLA melt prior to step b) to form a PLA polymer melt having at least 15 ppm, or at least 25 ppm, or at least 50 ppm, or at least 100 ppm, or at least 150 ppm, or at least 300 ppm, or at least 400 ppm, wherein the ppm is based on the PLA polymer melt. In an example, the (total) amount of amide in the PLA polymer melt is 100ppm, or 200ppm, or 300ppm, or 400ppm, or 500ppm, or 600ppm, or 700ppm, or 800ppm, or 900ppm, wherein ppm is based on the weight of the PLA polymer melt. The amide may be a single component or a mixture of multiple components. In the case of a mixture, the aforementioned amount is intended to refer to the total amount of amide added to the PLA polymer melt in the process of the present invention.

[0260] The amide content (in ppm) in the sample can be measured by methods known to those skilled in the art. One method is, for example, that it can be calculated by the nitrogen content of the sample by multiplying the nitrogen content in ppm by the ratio of the molar mass of amide to the molar mass of nitrogen (14 g / mol). The nitrogen content of the sample of the product can be measured according to ASTM D4629. The sample is evaporated and carried to the high temperature zone, oxygen is introduced in the high temperature zone and organically bound nitrogen is converted into nitric oxide (NO). NO contacts ozone and is converted into excited nitrogen dioxide (NO2). The light emitted when the excited NO2 decays is detected by a photomultiplier tube, and the resulting signal is a measure of the nitrogen contained in the sample. Other methods such as gas chromatography for measuring the amide content of the sample can be applied.

[0261] The applicant has found that when the total concentration of amides in the PLA melt and therefore in the obtained PLA pellets is higher than 2000 ppm, problems can be observed when the pellets are processed downstream into various applications. For example, when crystallized PLA pellets with amides at a concentration above 2000 ppm are used in downstream applications such as blown film, sheet casting or thermoforming, undesirable or premature crystallization can occur. This affects the processing efficiency and the quality of the resulting product (film, sheet, etc.). The present invention provides a valuable solution to such problems.

[0262] In the process of the present invention, the amide can be added to the PLA melt provided in step a) in different forms.

[0263] In some embodiments of the present invention, the process involves adding the amide in the form of a composition consisting of amides, i.e., in the form of an amide compound, to the PLA polymer melt prior to step b). Thus, in some embodiments, the process of the present invention involves adding the amide compound (i.e., as a separate compound) to the PLA polymer melt without adding other compounds or compositions. For example, the amide compound can be added to the PLA melt in a liquid state, e.g., in the form of a melt, prior to step b) of the process.

[0264] In some embodiments of the present invention, the process of the present invention involves adding amide in the form of a masterbatch or a masterbatch composition. The term "masterbatch" or "masterbatch composition" as used herein is intended to refer to a composition consisting of a blend of amide and PLA polymer. For example, the masterbatch composition can be a melt composition obtained by melt blending amide and PLA polymer. The PLA polymer used to blend with amide to form a masterbatch composition can in principle be any type of PLA. However, it is preferred that PLA contains D-lactide isomers equal to or less than 10.0% by weight, preferably equal to or less than 8.0% by weight, or equal to or less than 6.0% by weight, or equal to or less than 4.5% by weight. In some embodiments, the PLA polymer used to prepare the masterbatch can be the same PLA polymer provided in step a) of the process of the present invention.

[0265] In a preferred embodiment, the PLA polymer used to prepare the masterbatch composition with amide is added to the PLA polymer melt at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt provided in step a).

[0266] In some embodiments, the PLA polymer used to prepare the masterbatch composition with amide may be a non-crystalline PLA. The term "non-crystalline" is intended to refer to a PLA polymer that has not undergone a crystallization process. The terms "non-crystalline" and "amorphous" are used as synonyms in this specification.

[0267] In some embodiments, the PLA polymer used to prepare the masterbatch composition with amide may be a crystallized PLA, and preferably a previously crystallized PLA as defined herein.

[0268] In some embodiments, the PLA polymer used to prepare the masterbatch composition with amide does not contain amide. In some other embodiments, the PLA polymer used to prepare the masterbatch composition with amide itself also contains amide. If amide is present in the PLA polymer, it is preferably present in a total amount of up to 2000ppm, wherein ppm is based on the PLA polymer, or up to 1800ppm, or up to 1500ppm, or up to 1000ppm, or up to 850ppm, or up to 500ppm, wherein ppm is based on the PLA polymer.

[0269] In a preferred embodiment, the PLA polymer used to prepare the masterbatch composition with amide is a non-crystalline PLA without amide. In an example, the present invention provides such a process, which comprises the following steps:

[0270] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer,

[0271] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0272] c) crystallizing the PLA pellets obtained in step b), optionally under dry air conditions, thereby obtaining crystallized PLA pellets,

[0273] The process further comprises the following steps:

[0274] - preparing a melt composition by melt blending an amide with a PLA polymer, such as a non-crystalline PLA that does not contain an amide, and

[0275] - adding said molten composition to said PLA melt prior to step b) to form a PLA polymer melt having a total amount of amides between 10 and 2000 ppm.

[0276] In another preferred embodiment, the PLA polymer used to prepare the masterbatch composition with amide is a previously crystallized PLA containing amide. In an example, the present invention provides a process comprising the following steps:

[0277] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer,

[0278] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0279] c) crystallizing the PLA pellets obtained in step b), optionally under dry air conditions, thereby obtaining crystallized PLA pellets,

[0280] Wherein the process further comprises the following steps:

[0281] - preparing a melt composition by melt blending the amide with a PLA polymer, such as a previously crystallized PLA containing the amide as provided herein, and

[0282] - adding said molten composition to said PLA melt prior to step b) to form a PLA polymer melt having a total amount of amides between 10 and 2000 ppm.

[0283] The process of the invention can also be described as comprising a step a) of preparing a melt of a PLA polymer having a content of D-lactide isomers between 1.0 and 10.0 wt.-% and comprising amides in a total amount of between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, between 100 and 900 ppm of the PLA polymer melt, wherein the PLA melt is prepared by adding to the PLA polymer melt a masterbatch composition consisting of an amide as defined herein blended with a PLA polymer as defined herein.

[0284] In some embodiments, the process of the present invention may involve adding (i) amide and (ii) previously crystallized PLA polymer to the PLA polymer melt prior to step b). In such an embodiment, the crystallized PLA obtained from the previous crystallization process may be fed to the PLA polymer in combination with the amide at the PLA melting stage (i.e., before pelletization) to further improve the crystallization and crystallization rate of the PLA polymer pellets. More specifically, the present invention provides such a process, wherein both the amide compound and the previously crystallized PLA polymer are added to the PLA polymer melt individually or in combination as a mixture or blend prior to pelletization of the PLA polymer melt, so as to form a PLA polymer melt containing the amide in a total amount as defined herein.

[0285] The term "previously crystallized PLA" as used in the context of the present invention is intended to refer to a PLA polymer that has been previously crystallized, for example, at some time in the past using the process of the present invention or using another method, and which is now mixed / added to the PLA polymer melt (i.e., before processing the PLA polymer melt into PLA pellets). In other words, in some embodiments, crystallized PLA (e.g., pellets) obtained from a first PLA polymer melt can be fed to a second PLA polymer melt in combination with an amide compound.

[0286] It should be understood that in some embodiments of the present invention, the terms "previously crystallized PLA" and "crystallized PLA" can be used as synonyms. In addition, it should be understood that when added to a PLA polymer melt, the previously crystallized PLA undergoes remelting during the mixing step with the PLA polymer melt.

[0287] Preferably, before step b) of the process of the present invention, previously crystallized PLA as defined herein is added to said PLA polymer melt at a feed rate of from 0.5 to 15.0%, e.g. from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % is expressed compared to the feed rate of said PLA polymer melt provided in step a).

[0288] The PLA previously crystallized for addition to the PLA melt is characterized in that it has at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, such as between 20.0 and 60.0%, or between 35.0 and 55.0%, or between 35.0 and 50.0%. It will be clear to those skilled in the art that when referring to the crystallinity of the previously crystallized PLA, it is meant to refer to the crystallinity established (determined) for the previously crystallized PLA before the previously crystallized PLA is added to the PLA polymer melt, and therefore before adding to the process. By blending the previously crystallized PLA with the PLA polymer melt before it is pelletized, it should be understood that the previously crystallized material will experience at least some melting, which will result in a reduction (at least partially) of its crystalline structure. The crystallinity can be measured by the method as given in the Examples section.

[0289] In some preferred embodiments, the previously crystallized PLA for addition to the PLA melt is further characterized in that it has a content of D-lactide isomers equal to or less than 10.0% by weight of the crystallized PLA polymer. The previously crystallized PLA has a content of D-lactide isomers between 0 and 10.0% by weight, or between 0.5 and 8.0% by weight, or between 1.0 and 6.0% by weight, or between 2.0 and 4.5% by weight.

[0290] In an example, the previously crystallized PLA can be PLLA, i.e., PLA made from 100% L-lactide and with 0 wt% D-lactide, having a crystallinity as defined herein between 20.0 and 60.0%, or between 35.0 and 55.0%, or between 35.0 and 50.0%.

[0291] In another example, the previously crystallized PLA for addition to the PLA melt may include PLA having an amount of D-lactide isomer, such as 0.5, or 1.0, 1.5, or 2.0, or 2.5, or 3.0, or 3.5, or 4.0, or 4.5, or 5.0, or 5.5, or 6.0 wt % of D-lactide isomer, based on the PLA (polymer), and a crystallinity as defined herein between 20.0 and 60.0%. In another example, the previously crystallized PLA for addition to the PLA melt may include PLA having an amount of D-lactide isomer, such as 0.5, or 1.0, 1.5, or 2.0, or 2.5, or 3.0, or 3.5, or 4.0, or 4.5, or 5.0, or 5.5, or 6.0 wt % of D-lactide isomer, based on the PLA (polymer), and a crystallinity as defined herein of between 35.0 and 55.0%. In another example, the previously crystallized PLA for addition to the PLA melt may include PLA having an amount of D-lactide isomer, such as 0.5, or 1.0, 1.5, or 2.0, or 2.5, or 3.0, or 3.5, or 4.0, or 4.5, or 5.0, or 5.5, or 6.0 wt % of D-lactide isomer, based on the PLA (polymer), and a crystallinity as defined herein of between 35.0 and 50.0%.

[0292] In some embodiments, the previously crystallized PLA added to the PLA polymer melt has a different composition than the PLA polymer of the PLA polymer melt. In some embodiments, the previously crystallized PLA added to the PLA polymer melt has a different D-lactide content than the PLA polymer of the PLA polymer melt.

[0293] In some preferred embodiments, the previously crystallized PLA added to the PLA polymer melt has the same composition as the PLA polymer of the PLA polymer melt. Thus, in one example, if the PLA polymer melt provided in step a) of the process of the present invention is a PLA having a D-lactide content of 4 wt%, then it is preferred that the previously crystallized PLA polymer added to the PLA melt is a previously crystallized form of the same PLA.

[0294] The previously crystallized PLA may or may not contain amide, preferably contains amide. For example, such previously crystallized PLA may have been prepared using the process of the present invention.

[0295] In some preferred embodiments, the previously crystallized PLA contains amides (as defined herein) in an amount of at most 2000 ppm, preferably at most 1800 ppm, preferably at most 1500 ppm, preferably at most 1000 ppm, more preferably at most 900 ppm, even more preferably at most 850 ppm, or at most 500 ppm, wherein ppm is expressed based on the previously crystallized PLA. For example, the previously crystallized PLA contains amides in an amount of 400 ppm, or 500 ppm, or 600 ppm.

[0296] In one embodiment, the process of the present invention comprises the following steps:

[0297] a) preparing a melt of a PLA polymer having a content of D-lactide isomers between 1.0 and 10.0 wt.-%, for example between 2.0 and 6.0 wt.-%, and comprising amides in a total amount of between 50 and 900 ppm of the PLA polymer melt, wherein the PLA melt is prepared by adding an amide as defined herein and a previously crystallized PLA containing amide as defined herein to the PLA polymer melt,

[0298] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0299] c) crystallizing the PLA pellets obtained in step b), optionally under dry air conditions, thereby obtaining crystallized PLA pellets.

[0300] In another embodiment, the process of the present invention comprises the following steps:

[0301] a) preparing a melt of a PLA polymer having a content of D-lactide isomers between 2.0 and 4.5 wt.-% and comprising amides in a total amount between 100 and 900 ppm of the PLA polymer melt, wherein the PLA melt is prepared by adding an amide as defined herein and a previously crystallized PLA containing amides as defined herein to the PLA polymer melt,

[0302] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0303] c) crystallizing the PLA pellets obtained in step b), optionally under dry air conditions, thereby obtaining crystallized PLA pellets.

[0304] In some other embodiments of the process of the invention, it is preferred that the amide is added to the PLA melt in the form of a previously crystallized PLA polymer already containing the amide before step b). As used in the following embodiments, "previously crystallized PLA containing the amide" refers to a previously crystallized PLA as defined above, which contains the amide, preferably the amide as defined herein, in an amount between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm, wherein the ppm is based on the weight of the previously crystallized PLA.

[0305] For example, the process of the present invention may provide a process comprising the following steps:

[0306] a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content of between 1.0 and 10.0 wt % of the PLA polymer, and adding previously crystallized PLA containing amides to the PLA melt to form a PLA polymer melt having a total amount of amides of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or preferably between 30 and 1000 ppm, or preferably between 50 and 900 ppm, or preferably between 100 and 900 ppm.

[0307] b) granulating the PLA polymer melt obtained in step a) into PLA pellets, and

[0308] c) crystallizing the PLA pellets obtained in step b), optionally under dry air conditions, thereby obtaining crystallized PLA pellets.

[0309] In an example, step a) of the process of the present invention may involve the steps of providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 2.0 and 6.0 wt % of the PLA polymer, and adding previously crystallized PLA containing amides to the PLA melt to form a PLA polymer melt having a total amount of amides between 50 and 900 ppm.

[0310] In another example, step a) of the process of the present invention may involve the steps of providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 2.0 and 4.5 wt % of the PLA polymer, and adding previously crystallized PLA containing amides to the PLA melt to form a PLA polymer melt having a total amount of amides between 100 and 900 ppm.

[0311] In such an embodiment, the amide provided in the PLA melt thus originates from previously crystallized PLA which already contained amide, and no further additional amide is added separately or exogenously to the PLA polymer melt in the process.

[0312] Adding low amounts of amides as defined herein, in particular for the preparation of a PLA polymer melt having a low amide content prior to pelletization, has been shown to significantly increase the crystallization speed (crystallization rate) of PLA polymers, including PLA polymer pellets, and thus significantly reduce the time required for crystallization and obtaining crystallized PLA and crystallized PLA pellets having a suitable degree of crystallinity. More specifically, the addition of amides as shown herein allows the time required to obtain crystallized PLA (as defined herein) to be reduced by at least 20%, such as at least 25%, or at least 35%, or at least 50%, compared to a process in which no amide is added to the PLA polymer melt.

[0313] This discovery is unexpected. Although the amide is added to the PLA polymer melt in low amounts (i.e., to form a PLA polymer melt containing a low amount of amide), it is still very effective in improving the crystallization rate of the PLA polymer and, in particular, the PLA polymer pellets. Therefore, the process of the present invention allows the delivery of crystallized PLA pellets of good quality, which exhibit desirable properties and easier handling. The crystallized PLA pellets obtained by the process of the present invention can also be easily stored, transported or packaged. Another unexpected advantage of the present invention is that a small amount of amide as disclosed herein does not affect the biodegradability and suitability for food contact applications of the PLA product and the articles made from the crystallized PLA pellets of the present invention.

[0314] In addition, surprisingly, the applicant has also found that in the process of the present invention, the addition of previously crystallized PLA as defined herein to the PLA polymer melt in addition to (on top of) the amide also supplied in the process of the present invention (e.g. as a separate feed) further improves the crystallization rate. In fact, it has been shown that the addition of such previously crystallized PLA acts in combination with the amide as defined herein (added as a separate external compound) to further increase the crystallization rate of the PLA polymer pellets, exceeding the crystallization rate obtained when the amide is added without previously crystallized PLA. According to the present invention, the addition of the combination of previously crystallized PLA and amide further promotes the formation and growth of nuclei (i.e. crystallites) in the PLA material (i.e. PLA pellets).

[0315] Advantageously, it has also been found that, in addition to the increase obtained by adding a composition consisting of an amide (i.e., an amide compound), the addition of previously crystallized PLA (pellets) can further increase the crystallization rate of the PLA pellets and thus significantly reduce the time required to perform crystallization of the pellets. The present invention is particularly useful because it can reduce the size of the crystallization equipment and / or can require less (expensive) crystallization equipment.

[0316] The amide and / or previously crystallized PLA (both as defined herein) may be fed to a vessel or other apparatus containing a PLA polymer melt by any suitable means, such as by means of a side feeder or the like.

[0317] The components (amide and / or previously crystallized PLA) can be added to the PLA polymer melt in the solid state (eg in the form of powder or pellets) or can be added to the PLA polymer melt in the molten state.

[0318] In some embodiments of the process of the present invention, both the amide and the previously crystallized PLA are added and added separately to the PLA polymer melt. Such embodiments are for example Figure 4 In the example, the amide as defined herein can be provided to the PLA polymer melt in a molten state by combining it with amorphous (non-crystalline) PLA, such as in a dedicated side extruder (side-extruder) device, to form a melt (i.e., the amide can be dosed with the non-crystalline PLA), and then fed to the PLA polymer melt in a molten state. The previously crystallized PLA as defined herein can also be provided to the PLA polymer melt in a molten state. For example, the previously crystallized PLA can be provided in the form of pellets and fed to a dedicated side extruder device to form a melt, and then fed to the PLA polymer melt in a molten state.

[0319] Amide and previously crystallized PLA can be separately added to the PLA polymer melt at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, for example, from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % represents the feed rate compared with the PLA polymer melt. In an example, if the PLA polymer melt is provided at a feed rate of about 10.000 kg / h in the process of the present invention, the previously crystallized PLA as defined herein can be fed to the PLA melt at a rate of about 200 to 500 kg / h (i.e., 2.0 to 5.0%). In another example, if the PLA polymer melt is provided at a feed rate of about 8.000 kg / h, the previously crystallized PLA as defined herein can be fed to the PLA melt obtained in the process at a rate of about 200 to 600 kg / h (i.e., 2.5 to 7.5%).

[0320] In some other embodiments of the process of the present invention, a combination of amide and previously crystallized PLA (both as defined herein) is added to the PLA polymer melt. Such embodiments are for example Figure 5 As shown in. To this end, the amide as defined herein can be melt blended with previously crystallized PLA (e.g., in a dedicated side extruder device) to form a molten composition, and the molten composition is then fed to the PLA polymer melt. In some preferred embodiments, the process of the present invention involves adding such a molten composition of the amide and the previously crystallized PLA to the PLA polymer melt at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, such as from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % represents a feed rate compared to the PLA polymer melt provided in step a).

[0321] According to the process of the present invention, a PLA polymer melt is formed before pelletizing, which has a total amount of amides between 10 and 2000 ppm, such as between 20 and 1500 ppm, or preferably between 30 and 1000 ppm, or more preferably between 50 and 900 ppm, or more preferably between 100 and 900 ppm. The following example (Example) illustrates how to determine the total amount of amides in a PLA polymer melt subjected to pelletization according to an embodiment of the process of the present invention.

[0322] In an example, a PLA polymer melt is provided at a feed rate of about 10.000 kg / h. Amide is injected directly into the PLA polymer stream at a rate of 5 kg / hr (i.e., 500 ppm), and a previously crystallized PLA containing 500 ppm of amide is injected directly into the PLA polymer melt at a feed rate of 15% of the feed rate of the PLA melt (i.e., at a rate of 1500 kg / h). Therefore, 5.75 kg / hr of amide is fed into the resulting PLA polymer melt feed (i.e., 11500 kg / h), corresponding to a total amount of amide of 500 ppm in the PLA melt.

[0323] In another example, a PLA polymer melt is provided at a feed rate of about 10.000 kg / h. Amide is injected directly into the PLA polymer stream at a rate of 16.5 kg / hr (i.e., 1650 ppm), and a previously crystallized PLA containing 500 ppm of amide is injected separately into the PLA polymer melt at a feed rate of 15% of the feed rate of the PLA melt (i.e., at a rate of 1500 kg / h). Therefore, 17.25 kg / hr of amide is fed into the resulting PLA polymer melt feed (i.e., 11500 kg / h), corresponding to a total amount of amide of 1500 ppm in the PLA melt.

[0324] In another example, a PLA polymer melt is provided at a feed rate of about 10.000 kg / h. The amide is directly injected into the PLA polymer stream at a rate of 5.5 kg / hr (i.e., 550 ppm), and a previously crystallized PLA without ppm of amide is separately injected into the PLA polymer melt at a feed rate of 10% of the feed rate of the PLA melt (i.e., at a rate of 1000 kg / h). Therefore, 5.5 kg / hr of amide is fed into the resulting PLA polymer melt feed (i.e., 11000 kg / h), corresponding to a total amount of amide of 500 ppm in the PLA melt.

[0325] In the next step (step b) of the process of the present invention, the PLA polymer melt is subjected to a pelletizing process to form PLA pellets.

[0326] Granulation can be carried out according to techniques known in the art. For example, the PLA polymer melt can enter a die-face cutting pelletizer. Such a pelletizer generally includes a cooling medium, a plurality of extrusion holes, and a rotating face cutter. Strand cutting pelletizers are also suitable for use in the process of the present invention. The PLA pellets obtained can then be transported to a dehydrating device or dryer to remove moisture. Examples of suitable dehydrating devices or dryers include, for example, centrifugal dryers, vibrating screens, filter cloths, etc.

[0327] As disclosed herein before, the PLA polymer melt is provided in the process of the present invention at a temperature of about 160 to 240° C. Preferably, the pelletizing step is performed within a suitable temperature window so that the average PLA pellet temperature is maintained above the glass transition temperature (Tg) of the PLA polymer. The average PLA pellet temperature can be determined by techniques known to those skilled in the art.

[0328] The obtained PLA pellets are subsequently subjected to crystallization. It is understood that, according to the process of the invention, the crystallization step c) involves the crystallization of said PLA pellets themselves, i.e. the crystallization is applied to the pellets themselves and to the pellets obtained directly from the granulation step. In this respect, the term "directly obtained" is intended to mean that the PLA pellets (obtained in step b) are not subjected to any further processing steps, including for example melting, molding, extrusion, etc., before being subjected to crystallization in step c). According to the invention, the crystallization step c) of the method of the invention is directly applied to the PLA pellets obtained in step b) of the process of the invention.

[0329] According to the process of the present invention, the PLA pellets applied in step c) are not melted before or during crystallization. According to the process of the present invention, the PLA pellets applied in step c) are not molded into articles (such as sheets, films, etc.) before or during crystallization. In other words, the process of the present invention does not involve crystallization of molded articles prepared from PLA pellets or from their molten form.

[0330] The crystallization of PLA pellets can be carried out under dry air conditions in the process of the present invention. "Dry air conditions" as used herein means that dry air is added during the crystallization step to reduce the moisture of the PLA pellets and / or prevent the PLA pellets from absorbing additional moisture from the environment. As used herein, the term "dry air" or "dry air conditions" is intended to refer to air having a dew point of about 5°C or less at atmospheric pressure. Preferably, the dry air as applied in the present invention has a dew point of 0°C or less, and preferably a dew point of -10°C or less. In some embodiments, the dry air as applied in the present invention may have a dew point of less than -20°C to as low as -40°C.

[0331] In a preferred embodiment of the present invention, a process is provided in which PLA pellets are crystallized by means of latent heat crystallization. The term "latent heat crystallization" is generally known in the art and refers to a process in which crystallization occurs by using the inherent (residual) heat in the polymer particles (granulate). Therefore, in the context of the present invention, latent heat crystallization means that PLA pellets are directly crystallized from the melt, i.e., after granulation, crystallization occurs by the heat retained in the PLA polymer (in the pellets). According to the process of the present invention, the average pellet temperature is preferably not lower than the glass transition temperature. Advantageously, no heating step is required to start the crystallization of PLA pellets.

[0332] The glass transition temperature (also referred to as Tg) is the critical temperature in the behavior of an amorphous polymer. The "glass transition temperature" of a polymer is well known in the art and can be defined as the temperature at which the material undergoes a reversible phase change from a rigid, glassy state to a more flexible, rubbery or viscous state. This transition is typically accompanied by significant changes in polymer chain mobility, molecular arrangement, and mechanical properties. The glass transition temperature (Tg) can be determined using techniques well known in the art, such as differential scanning calorimetry (DSC). The typical glass transition temperature of PLA polymers is between 50°C and 60°C, depending primarily on the scanning speed during the DSC thermogram.

[0333] A particular advantage of the process of the present invention is that no additional energy supply (e.g. heating) is required during pelletization and crystallization. For example, it has been found that PLA pellets can be transferred from a pelletizer to a crystallizer without further heat input. Under good process control, it was unexpectedly found that the "heat of crystallization", "heat of fusion" or "latent heat of crystallization" inherently present when transforming from an amorphous molten state to a (partially) crystalline solid state is sufficient to maintain the crystallization temperature for a suitable period of time. In other words, by keeping the PLA pellets in a (narrow) temperature range above the glass transition temperature (Tg) of the PLA polymer, no additional heating is required to promote the recombination of the PLA polymer chains into a crystalline structure. PLA pellets can be kept at a crystallization temperature between 90 and 130°C, preferably between 90 and 120°C, more preferably between 90 and 115°C, and most preferably between 100 and 115°C, without the need for additional (external) heating.

[0334] According to the process of the present invention, preferably a two-step crystallization is applied.

[0335] The first step involves keeping the PLA pellets in motion for a suitable period of time while exposing the pellets to a crystallization temperature between 90 and 130° C., preferably between 90 and 120° C., more preferably between 90 and 115° C., and most preferably between 105 and 110° C. The pellets are kept in motion so that they do not begin to stick together. During this step, the PLA pellets will undergo crystallization to a certain extent, thereby producing pre-crystallized PLA. Such pre-crystallized PLA preferably has a crystallinity of at least 3.0%, such as at least 3.5%, 4.0%, 5.0%, 5.5%, 6.0%, 6.5%, or 7.0%, as defined herein. This first step is suitable for providing pre-crystallization of PLA pellets to reduce their stickiness so that they can be subsequently transported and stored in suitable equipment.

[0336] Suitable systems that allow PLA pellets to remain in motion while being subjected to crystallization temperatures are known in the art. Examples include, but are not limited to, vibrating conveyor devices, continuous fluidized beds, rotary drums, paddle dryers, etc. Such devices may be heated, for example, using hot air, infrared, or other heating devices, as desired.

[0337] According to the invention, the residence time during this (first) pre-crystallization stage can be limited to about 15-60 minutes, for example about 20-40 minutes. Even when such a short residence time is applied, pre-crystallized PLA with a crystallinity of about 3% or more can already be obtained. At such a crystallinity, the stickiness of the PLA pellets is greatly reduced or even non-existent, which further facilitates the processing of the PLA pellets in the next crystallization step.

[0338] In the next step, the obtained pre-crystallized PLA is conveyed to a crystallization vessel and maintained in the crystallization vessel at a temperature between 90 and 130° C., for example between 90 and 120° C., or between 95 and 115° C., or between 100 and 115° C. for a suitable period of time. In this step, a crystallized PLA is obtained having a crystallinity of at least 20.0%, for example at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%. In an example, the crystallized PLA obtained in the process of the present invention has a crystallinity of from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%.

[0339] Suitable examples of crystallization vessels for use in the present invention may include, for example, a silo; placed in an upright position. The pre-crystallized pellets may enter the silo from above, and the effect of gravity causes the pellets to gradually move from the upper part of the silo toward the lower part. A valve may be provided at the outlet of the silo to control the movement rate and discharge rate of the pellets. According to the present invention, the residence time during this (second) crystallization stage may be limited to less than 3 hours, for example less than 2 hours.

[0340] In some preferred embodiments, the first crystallization step, the transport to the crystallization vessel of the second crystallization step, and the second crystallization step are performed at approximately constant temperature.

[0341] In some preferred embodiments, the granulation step and the crystallization step of the process of the present invention are performed within the same temperature range.

[0342] The resulting crystallized PLA can then be cooled for storage and packaging.

[0343] By reference Figure 4 and 5 To further illustrate the process of the present invention. Figure 4 A simplified diagram of an embodiment of the process of the invention is shown, wherein the amide and optionally previously crystallized PLA are fed separately to the PLA polymer melt. Figure 5 A simplified diagram of another embodiment of the process of the present invention is shown, wherein the amide and previously crystallized PLA are first blended into a molten composition and then fed into the PLA polymer melt.

[0344] refer to Figure 4 and 5 The process of the present invention involves supplying in a first step a PLA polymer melt (1), which may be obtained, for example, from a PLA polymerization plant, wherein PLA is prepared by ring-opening polymerization of the corresponding lactide monomer, preferably in the presence of a suitable catalyst. The PLA polymer obtained after polymerization is completely molten. The PLA polymer obtained by such a polymerization process may have a content of D-lactide isomers between 1.0 and 10.0% by weight, for example a content of D-lactide isomers of 4 or 5% by weight. Preferably, the PLA polymer melt is provided at a temperature of about 160 to 240° C. The PLA polymer melt is then conveyed, for example via one or more conveying lines, and, after stabilization, to a pelletizing section (2) to produce PLA pellets. Prior to pelletization, the amide and optionally previously crystallized PLA (both as defined herein) may be fed to a container or other equipment (not shown) containing the PLA polymer melt by any suitable means, for example by means of a side feeder or the like. The container or other equipment containing the PLA polymer melt can be any suitable mixing device or container that allows the PLA polymer melt to be blended with the amide and previously crystallized PLA (if applicable). Suitable mixing devices include, but are not limited to, melt kneaders such as closed kneaders, single-screw or twin-screw extruders. In preferred embodiments, the mixing device can be a static mixer. In some embodiments of the process of the present invention, for example Figure 4As shown in the above, an amide compound (such as an amide compound of Formula I and / or II as defined herein) (5) and previously crystallized PLA as defined herein (6) are added to a PLA polymer melt separately by any suitable means. The amide and previously crystallized PLA can be added to the PLA polymer melt as pure compounds, or mixed and blended with another compound as a masterbatch. For example, the amide can be melt-blended with amorphous (non-crystalline) PLA in a suitable side extruder device, and the resulting blend can be fed to the PLA polymer melt in a molten state.

[0345] In some other embodiments of the process of the present invention, such as Figure 5 As shown in the process, an amide (such as an amide of Formula I and / or II as defined herein) (5) and previously crystallized PLA as defined herein (6) are first blended and then subsequently added together to a PLA polymer melt. For example, the amide may be melt blended with previously crystallized PLA in a suitable device (7) such as a side feeder, and the resulting blend may be fed to the PLA polymer melt in a molten state. The side feeder may be an extruder equipped with a downstream melt pump.

[0346] The resulting PLA polymer melt, thus containing the amide and ultimately the previously crystallized PLA, is then fed into a pelletizing section (2) to form the PLA polymer into PLA pellets. Suitable pelletizers include, for example, die-face cutting pelletizers or strand cutting pelletizers. Optionally, the obtained PLA pellets may be conveyed to a dewatering device or dryer to remove excess moisture.

[0347] The PLA pellets coming out of the pelletizing section are amorphous, which means that they will be soft and sticky above the glass transition temperature, making them difficult to transport, store, process and dry. Therefore, it is preferred to limit the cooling of the pellets and start the crystallization process in the shortest possible time. The PLA pellets are crystallized in the crystallization section (3), which may include any suitable crystallization equipment such as the crystallization equipment described above. Preferred crystallization temperatures include temperatures between 90°C and 130°C, preferably between 90 and 120°C, more preferably between 90 and 115°C, and most preferably between 105 and 110°C.

[0348] The resulting crystallized PLA pellets can be collected and sent to storage and packaging section (4).

[0349] In another aspect, the present invention also relates to crystallized PLA and in particular crystallized PLA pellets obtainable by or by carrying out the process according to the invention.

[0350] In some embodiments, the crystallized PLA obtainable according to or in accordance with the present invention is characterized by

[0351] - it has a content of D-lactide isomers of between 1.0 and 10.0 wt.-%, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%, based on the crystallized PLA; and

[0352] - it has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, and such as from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%; and

[0353] - it contains the amide as defined herein in an amount of between 10 and 2000 ppm of the crystallized PLA, for example between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm.

[0354] In some embodiments, crystallized PLA pellets obtainable or obtainable according to the invention are characterized in that the pellets have:

[0355] - a content of between 1.0 and 10.0 wt.-% of D-lactide isomers, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-%, based on the crystallized PLA pellets; and

[0356] - a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, and such as from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%; wherein said crystallinity is determined according to the method specified in this specification, and

[0357] - a total amount of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of amide as defined herein, based on said crystallized PLA pellets.

[0358] The present invention provides a more energy efficient and cost effective process for preparing a crystallized PLA product, since the use of an additional heat source to achieve crystallization can be avoided. In addition, since crystallization occurs faster, the process of the present invention allows for a reduction in the size of the crystallization equipment. In addition, the crystallized PLA pellets prepared and obtained according to the present invention are particularly advantageous in terms of stability, chemical compatibility, and food safety, allowing them to be applied to many different downstream applications. In addition, the crystallized PLA pellets of the present invention can be easily handled, transported, stored, and / or packaged.

[0359] The crystallized PLA pellets prepared and obtained according to the present invention can be further processed into PLA-based products. Such products may include, but are not limited to, films, sheets, laminates, and packaging materials. The technology for preparing PLA-based products is well known, and includes, but is not limited to, thermoforming, injection molding, blow molding, and extrusion. In contrast to amorphous and sticky PLA pellets or particles, crystallized PLA pellets can advantageously be more easily handled, transported, and fed into downstream manufacturing equipment. In addition, by using crystallized PLA pellets as disclosed herein in downstream processing, it is allowed to reduce the problem of scaling, flow blockage, and the energy demand and consumption of downstream processing equipment can be reduced.

[0360] The presence of an amide as defined herein in crystallized PLA or in crystallized PLA pellets can be determined by techniques known in the art such as, but not limited to, nuclear magnetic resonance (NMR) spectroscopy, nitrogen content analysis, or Fourier transform infrared spectroscopy (FTIR).

[0361] In another aspect, the present invention also relates to the use of an amide as defined herein for increasing the crystallization rate of a PLA polymer, preferably a PLA polymer pellet, wherein the PLA polymer has a content of D-lactide isomers between 1.0 and 10.0 wt. % of the PLA polymer, such as between 1.5 and 8.0 wt. %, or between 2.0 and 6.0 wt. %, or between 2.0 and 4.5 wt. % of the PLA polymer, and wherein the amide is used in a melt of the PLA polymer (i.e. before pelletization) to form or prepare a PLA melt, the PLA melt comprising the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, and preferably between 20 and 1500 ppm of the PLA polymer melt, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, or between 100 and 900 ppm of the PLA polymer melt.

[0362] In some embodiments, the present invention relates to the use of a composition consisting of an amide for increasing the crystallization rate of a PLA polymer pellet (i.e., the use of an amide compound). More specifically, the present invention relates to the use of a composition consisting of an amide for increasing the crystallization rate of a PLA polymer pellet (i.e., the use of an amide compound), wherein the PLA polymer has a content of D-lactide isomers between 1.0 and 10.0% by weight of the PLA polymer, such as between 1.5 and 8.0% by weight of the PLA polymer, or between 2.0 and 6.0% by weight, or between 2.0 and 4.5% by weight of the PLA polymer, and wherein the composition (compound) is used in a melt of the PLA polymer (i.e., before pelletization) to form a PLA polymer melt, the PLA polymer melt containing the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, and preferably between 20 and 1500 ppm of the PLA polymer melt, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, or between 100 and 900 ppm.

[0363] In some embodiments, the present invention relates to the use of a (masterbatch) composition consisting of an amide and a PLA polymer for increasing the crystallization rate of a PLA polymer pellet. More specifically, the present invention relates to the use of a (masterbatch) composition consisting of an amide and a PLA polymer for increasing the crystallization rate of a PLA polymer pellet, wherein the (masterbatch) composition is used in the melt of the PLA polymer (i.e., before pelletization) to form a PLA polymer melt, the PLA polymer melt containing the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, and preferably between 20 and 1500 ppm of the PLA polymer melt, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, or between 100 and 900 ppm. The PLA polymer used in combination with the amide may be a non-crystalline or previously crystallized PLA, and may or may not contain the amide.

[0364] In some embodiments, the present invention relates to the use of previously crystallized PLA containing amide as defined herein for increasing the crystallization rate of PLA polymer pellets. More specifically, the present invention relates to the use of previously crystallized PLA containing amide for increasing the crystallization rate of PLA polymer pellets, wherein the previously crystallized PLA containing amide is used in the melt of the PLA polymer (i.e., before pelletization) to form a PLA polymer melt, the PLA polymer melt containing amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, and preferably between 20 and 1500 ppm of the PLA polymer melt, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, or between 100 and 900 ppm. The previously crystallized PLA is preferably used at a feed rate of from 0.5 to 15.0%, for example, from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0365] In some other preferred embodiments, the present invention also relates to the use of an amide as defined herein for increasing the crystallization rate of a PLA polymer, in particular a PLA polymer pellet, wherein the amide is used in combination with a previously crystallized PLA, preferably a previously crystallized PLA as defined herein. In some preferred embodiments, the present invention relates to the use of a (blended) composition consisting of (i) an amide as defined herein and (ii) a previously crystallized PLA as defined herein for increasing the crystallization rate of a PLA polymer pellet. The blended composition is used in the melt of the PLA polymer (i.e. before pelletization) to form a PLA polymer melt, the PLA polymer melt containing the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt, and preferably between 20 and 1500 ppm of the PLA polymer melt, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, preferably between 100 and 900 ppm.

[0366] Preferably, the present invention relates to such a use, in which both the amide and the previously crystallized PLA are used (added) to the melt of the PLA polymer, either alone or in combination (i.e. as a blend, preferably as a molten composition). In the embodiment in which the amide and the previously crystallized PLA are used alone for adding to the melt of the PLA polymer, it is preferred that the previously crystallized PLA is used at a feed rate of from 0.5 to 15.0%, such as from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0367] In embodiments where an amide and previously crystallized PLA are used in combination to be added to the melt of the PLA polymer, it is preferred that the melt composition of the amide and the previously crystallized PLA is used at a feed rate (e.g., in kg / h) of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 5.0 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt.

[0368] The present invention further provides a process for increasing the crystallization rate of pellets of a PLA polymer having a certain content of D-lactide isomers as provided herein, the process comprising the following steps: adding an amide to a melt of the PLA polymer to form a PLA melt before pelletizing, the PLA melt comprising the amide in a total amount of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the PLA polymer melt. Such an amide may be added as is or in combination with a PLA polymer as described herein.

[0369] The present invention also provides a process for increasing the crystallization rate of pellets of a PLA polymer having a certain D-lactide isomer content as provided herein, the process comprising the following steps: before pelletizing, an amide (e.g., in the form of a compound or masterbatch) and a previously crystallized PLA as defined herein are added to a melt of the PLA polymer to form a PLA melt, the PLA melt comprising the amide in a total amount of between 10 and 2000 ppm of the PLA polymer melt, for example, between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm. The amide and the previously crystallized PLA may be added separately or as a blend, preferably as a molten composition. It is further preferred that the molten composition of amide and previously crystallized PLA is added to the PLA melt at a feed rate of from 0.5 to 15.0%, e.g., from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % means compared to the feed rate of the PLA polymer melt in the process.

[0370] The following examples are only used to illustrate the present invention and should not be construed as limiting its scope in any way. Although the present invention has been shown in some of its forms only, it will be apparent to those skilled in the art that the present invention is not limited thereto, but is susceptible to various changes and modifications without departing from the scope of the present invention.

[0371] Example

[0372] Example 1 - Crystallinity

[0373] The crystallinity of PLA samples (e.g., PLA pellets, pre-crystallized PLA, or crystallized PLA, or previously crystallized PLA) was determined via differential scanning calorimetry (DSC). Differential scanning calorimetry (DSC) can be performed using a Netzsch DSC 3500 Sirius. DSC measurements were performed from 20 to 200°C at a heating rate of 10°C / min, and held at 200°C for 1 minute, then cooled to 0°C at a cooling rate of 10°C / min, held at 0°C for 1 minute, and reheated from 0°C to 200°C at a heating rate of 10°C / min for a second heating run.

[0374] The crystallinity (Xc) of the sample was determined according to the following equation:

[0375]

[0376] in and are the enthalpies of melting and crystallization, respectively;

[0377] in and are the weight fraction of PLA and the melting enthalpy of 100% crystalline PLA, respectively.

[0378] The enthalpy of melting of completely crystalline polymers can be found in the literature. For example, for poly-L-lactide (homo-crystal), =93.7 J / g; for the melting enthalpy, stereocomplex PLA has a different value.

[0379] Example 2

[0380] Example 2 illustrates that when a small amount of amide is added to a PLA polymer melt according to the process of the present invention, the crystallization rate of the PLA polymer increases.

[0381] To illustrate this beneficial effect, the following test protocol was applied.

[0382] Test plan

[0383] After granulation, for example, after passing through a centrifugal dryer to remove excess water, a sample of amorphous PLA pellets is collected directly and placed in an oven at 105°C. Samples of PLA pellets are taken out from the oven at regular intervals and their crystallinity is measured using DSC as described above. Therefore, the crystallinity is measured at different time points during crystallization, and the collected data points are fitted into an S-curve (S-shaped curve). The crystallization curve is typically an S-curve: crystallization usually starts slowly (crystal formation), then increases rapidly (crystal growth), and then the process slows down and reaches a maximum crystallinity (crystals stop growing).

[0384] The PLA polymer used in this example consists of a PLA polymer having about 3.4% by weight of D-lactide isomers. The PLA polymer melt is provided by the PLA polymer. Before pelletizing, N,N'-ethylenebis(stearamide) (EBS; CAS No. 110-30-5) was added to the PLA polymer melt at concentrations of 300 and 500 ppm, respectively, to obtain Examples IE1 and IE2 of the present invention. This is actually achieved by dosing amorphous PLA pellets into the EBS in a side extruder device to prepare the EBS in a molten state. The molten EBS is then fed to the PLA polymer melt of Examples IE1 and IE2 of the present invention at a feed rate of about 2% of the feed rate of the PLA polymer melt. The same amorphous PLA is used for both Examples IE1 and IE2. In the comparative example (CE1), no amide is added to the PLA polymer melt before pelletizing.

[0385] Figure 1 The results of crystallinity measurements performed on the above samples (CE1, IE1, IE2) at different time points are shown. The results show that adding a small amount of EBS to the PLA polymer melt improves crystallization and crystallization rate. The results also show faster crystallization at higher amounts of EBS.

[0386] Example 3

[0387] Example 3 also shows that when a small amount of amide is added to a PLA polymer melt according to the process of the present invention, the crystallization rate of the PLA polymer increases. In this example, the amide is combined (blended) with previously crystallized PLA and fed to the PLA polymer melt. The same test scheme as described for Example 2 is applied to evaluate crystallization and crystallization rate.

[0388] The PLA polymer used in this example consists of a PLA polymer having about 3.4% by weight of D-lactide isomers. A PLA polymer melt is provided by the PLA polymer. Prior to pelletization, N,N'-ethylenebis(stearamide) (EBS; CAS No. 110-30-5) is added to the PLA polymer melt at a concentration of 300, 500, 700 or 900 ppm, respectively, to obtain Examples IE3 to IE6 of the present invention. This is actually accomplished by blending (dosing) EBS with previously crystallized PLA pellets into a side extruder device to prepare a composition comprising EBS in a molten state. The molten EBS is then fed to the PLA polymer melt of Examples IE3 to IE6, at a feed rate of about 2% of the PLA polymer melt for IE3, and at a feed rate of about 5% of the PLA polymer melt for IE4 to IE6 (the feed rate is expressed as a % compared to the feed rate of the PLA polymer melt fed to the process). For comparison, a comparative example (CE2) was prepared by adding previously crystallized PLA to a PLA polymer melt before pelletizing. In comparative example CE2, no amide was added. The previously crystallized PLA consisted of a PLA polymer having about 3.4% by weight of D-lactide isomers (the same PLA polymer as applied to form a PLA melt) and about 40% crystallinity. The same previously crystallized PLA was used in all examples CE2 and IE3 to IE6. An overview of the examples of this experiment is given in Table 1. Figure 2 Shown are the results of crystallinity measurements performed at different points in time for different examples.

[0389] Table 1

[0390]

[0391] The results of this experiment show that adding a small amount of amide to a PLA polymer (here blended with previously crystallized PLA) significantly improves crystallization and crystallization rate. The results also show faster crystallization at higher amounts of EBS.

[0392] Example 4

[0393] Example 4 illustrates the beneficial effect on crystallization and crystallization rate of PLA polymer when an amide is fed to a PLA polymer melt thereof in combination with previously crystallized PLA according to the process of the present invention. The same testing protocol as illustrated in Example 2 was applied.

[0394] PLA pellets are prepared by providing a PLA polymer melt and by adding N,N'-ethylenebis(stearamide) (EBS; CAS No. 110-30-5) to the melt. In all Examples IE7, IE8 and IE9, EBS is added at a concentration of 500 ppm. In Examples IE8 and IE9, EBS is applied to the PLA polymer melt in combination with previously crystallized PLA. This is actually accomplished by blending EBS with previously crystallized PLA pellets into a side extruder device to prepare a molten composition comprising EBS and previously crystallized PLA in a molten state. The molten composition is then fed to the PLA polymer melt at a feed rate of 5% (IE8) or 10% (IE9) (the feed rate is expressed as % compared to the feed rate of the PLA polymer melt fed to the process). In Example IE7, EBS is supplied to the PLA melt in the absence of previously crystallized PLA.

[0395] The PLA polymer used in all samples of this example consisted of a PLA polymer according to the present invention having about 3.4 wt% D-lactide isomers. The previously crystallized PLA also consisted of a PLA polymer having about 3.4 wt% D-lactide isomers (the same PLA polymer as applied to form the PLA melt) and about 40% crystallinity. The same previously crystallized PLA was used in IE8 and IE9.

[0396] Figure 3 The results of crystallinity measurements performed at different time points for different examples are shown. The results of this experiment show that adding a small amount of amide in combination (blending) with previously crystallized PLA has a significant beneficial effect on crystallization and crystallization rate. The crystallization rate improves with increasing amounts of previously crystallized PLA.

[0397] Example 5

[0398] Example 5 is another example that illustrates that when a small amount of amide is added to a PLA polymer melt to form a PLA melt having a low amide content according to the process of the present invention, the crystallization rate of the PLA polymer pellets increases. This example further shows the beneficial effect (synergistic improvement) on the crystallization rate when the PLA polymer melt is treated with a combination of an amide compound (e.g., EBS) and a previously crystallized PLA containing amide.

[0399] To illustrate this beneficial effect, the same test protocol as in Examples 2 to 4 was applied.

[0400] In all the examples presented herein, a sample of non-crystallized PLA pellets was collected (at time point T0) directly after pelletization, for example after passing through a centrifugal dryer to remove excess water. At this time point (T0), the sample was placed in a thermos bottle to prevent the sample from cooling. The time was recorded and the sample was immediately taken to the laboratory. At 1 , the sample was taken out of the thermos and placed in an oven at 105° C. At different time intervals (starting from T0 ), the pellets were taken out and the crystallinity was measured by the DSC method as described above (Example 1).

[0401] It was observed that by using this protocol, cooling of the PLA pellets after pelletization was prevented.Thus, the experimental protocol adopted in the Examples section above reproduced latent heat crystallization conditions.

[0402] The PLA polymer used in this Example 5 consists of a PLA polymer having about 3.4% by weight of D-lactide isomers. PLA pellets are prepared by subjecting a melt of the PLA polymer to granulation. Prior to granulation, the PLA polymer melt is treated (injected) with N,N'-ethylenebis(stearamide) (EBS; CAS No. 110-30-5) in Examples IE10 and IE11, and the PLA polymer melt is treated (injected) with previously crystallized PLA in Example IE11. In a comparative example (CE3), no amide and no previously crystallized PLA are added to the PLA polymer melt. The previously crystallized PLA consists of a PLA polymer having about 3.4% by weight of D-lactide isomers (the same as the PLA polymer applied to form the PLA melt), has a crystallinity of about 40%, and an EBS content of about 500 ppm.

[0403] Example IE10 was prepared by dosing EBS with amorphous PLA pellets in a side extruder apparatus to prepare EBS in a molten state. Amorphous PLA pellets were fed to the side extruder at a feed rate of about 5% of the feed rate of the main PLA polymer melt. The mixture of amorphous PLA and EBS was then fed and mixed with the PLA polymer melt in a static mixer before pelletization.

[0404] Example IE11 was prepared by blending (dosing) EBS with previously crystallized PLA pellets into a side extruder device to prepare a composition comprising EBS in a molten state. Previously crystallized PLA was fed into the side extruder at a rate of about 5% compared to the main PLA polymer melt (the feed rate is expressed as % compared to the feed rate of the main PLA polymer melt). The mixture of previously crystallized PLA and molten EBS was then fed and mixed with the PLA polymer melt in a static mixer before pelletizing.

[0405] A summary of the examples of this experiment is given in Table 2, also reporting the total amide concentration in the resulting PLA melt before its pelletization. Figure 6 Shown are the results of crystallinity measurements performed at different points in time for different examples.

[0406] Table 2

[0407]

Claims

1. A process for preparing crystallized polylactide (PLA) pellets, the process comprising the following steps: a) providing a PLA polymer melt, wherein the PLA polymer has a D-lactide isomer content between 1.0 and 10.0 wt % of the PLA polymer; b) pelletizing the PLA polymer melt into PLA pellets, and c) crystallizing the PLA pellets to obtain crystallized PLA pellets, The process is characterized in that, prior to step b), an amide is added to the PLA polymer melt to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount between 10 and 2000 ppm of the PLA polymer melt.

2. The process according to claim 1, wherein the PLA pellets are crystallized by means of latent heat crystallization.

3. The process according to any one of claims 1 to 2, wherein during pelletization, the average PLA pellet temperature is maintained above the glass transition temperature (Tg) of the PLA polymer.

4. The process according to any one of claims 1 to 3, wherein the crystallization is carried out at a temperature between 90°C and 130°C, preferably between 100°C and 115°C.

5. The process according to any one of claims 1 to 4, wherein the amide is added to form a PLA polymer melt, the PLA polymer melt comprising the amide in a total amount of between 20 and 1500 ppm, preferably between 30 and 1000 ppm, preferably between 50 and 900 ppm, preferably between 100 and 900 ppm of the PLA polymer melt.

6. The process according to any one of claims 1 to 5, wherein the amide comprises at least one compound of formula (I) and / or at least one compound of formula (II), Where R 1 , R 2 , R 5 and R 6 are each independently hydrogen, or selected from a group comprising alkyl and alkenyl, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and Where R 3 , R 4 and R 7 are each independently selected from the group consisting of alkyl and alkenyl groups, each of which may be unsubstituted or substituted with one or more hydroxyl groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

7. The process according to any one of claims 1 to 6, wherein the amide is selected from saturated fatty acid bisamides, unsaturated fatty acid bisamides, saturated fatty acid monoamides, unsaturated fatty acid monoamides, N-alkyl substituted fatty acid monoamides, and any mixtures thereof.

8. A process according to any one of claims 1 to 7, wherein the amide is a saturated fatty acid bisamide, and preferably a saturated fatty acid bisamide of formula (I), wherein R 5 and R 6 is hydrogen, where R 4 and R 7 Each independently is C 4-28 An alkyl group which may be unsubstituted or substituted with one or more hydroxy groups, and wherein n is an integer selected from 1, 2, 3, 4, 5, 6, or 7.

9. The process according to any one of claims 1 to 8, wherein the amide is selected from ethylene bisstearamide, ethylene biscaprylamide, ethylene biscapramide, ethylene bislauramide, ethylene bismyramide, ethylene bispalmitamide, ethylene bisisostearamide, ethylene bisbehenamide, ethylene bis(12-hydroxystearamide), methylene biscaprylamide, methylene biscapramide, methylene bislauramide, methylene bismyramide, methylene bispalmitamide, methylene bisstearamide, methylene bisisostearamide, methylene bisbehenamide, methylene bis(12-hydroxystearamide), butylene bisstearamide, butylene bisbehenamide, hexamethylene bisstearamide, butylene bis(12-hydroxystearamide), hexamethylene bisbehenamide, hexamethylene bis(12-hydroxystearamide), and N,N'-distearyl adipamide.

10. The process according to any one of claims 1 to 9, wherein the PLA polymer has a content of D-lactide isomers between 1.5 and 8.0 wt. %, such as between 2.0 and 6.0 wt. % or between 2.0 and 4.5 wt. % of the PLA polymer.

11. Process according to any one of claims 1 to 10, wherein an amide is added to the PLA polymer melt before step b) in the form of a composition consisting of amides, preferably amides as defined in any one of the preceding claims.

12. Process according to any one of claims 1 to 10, wherein the amide is added to the PLA polymer melt before step b) in the form of a composition obtained by melt blending an amide, preferably an amide as defined in any one of the preceding claims, with a PLA polymer.

13. The process according to any one of claims 1 to 11, comprising the step of adding to the PLA polymer melt prior to step b) i) an amide, preferably an amide as defined in any one of the preceding claims, and ii) previously crystallized PLA; wherein the previously crystallized PLA is characterized in that: - prior to addition to the process, has a crystallinity of at least 20.0%, wherein said crystallinity is determined according to the method specified in the description; - having a content of D-lactide isomers equal to or lower than 10.0% by weight, based on said previously crystallized PLA, and - optionally containing amides, preferably amides as defined in any one of the preceding claims, in a total amount of at most 2000 ppm, wherein the ppm is based on said previously crystallized PLA, or at most 1800 ppm, or at most 1500 ppm, or at most 1000 ppm, or at most 850 ppm, or at most 500 ppm, wherein the ppm is based on said previously crystallized PLA.

14. The process according to claim 13, wherein the previously crystallized PLA is added at a feed rate of from 0.5 to 15.0%, e.g. from 1.0 to 12.0%, or from 2.0 to 10.0%, or from 2.5 to 7.5%, wherein % is expressed compared to the feed rate of the PLA polymer melt provided in step a).

15. The process according to any one of claims 13 to 14, wherein the amide and the previously crystallized PLA are added separately to the PLA polymer melt prior to step b).

16. The process according to any one of claims 13 to 14, wherein the amide and the previously crystallized PLA are blended, preferably melt blended, to form a composition, preferably a molten composition, and wherein the composition, preferably the molten composition, is added to the PLA polymer melt before step b).

17. The process of any one of claims 13 to 16, wherein the previously crystallized PLA has a crystallinity of at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%.

18. The process according to any one of claims 13 to 17, wherein the previously crystallized PLA contains amides, preferably amides as defined in any one of the preceding claims, in a total amount of between 10 and 2000 ppm, or between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm, based on the previously crystallized PLA.

19. The process of any one of claims 13 to 18, wherein the previously crystallized PLA has a content of D-lactide isomers between 0.1 and 9.0 wt%, or between 0.5 and 8.0 wt%, or between 1.0 and 6.0 wt%, or between 2.0 and 4.5 wt%.

20. The process according to any one of claims 13 to 19, wherein the previously crystallized PLA is a crystallized form of the PLA polymer melt provided in step a).

21. The process according to any one of claims 1 to 20, wherein the PLA pellets obtained in step b) are crystallized in step c), preferably under dry air conditions, by: c1) keeping the PLA pellets moving at a temperature between 90 and 130° C. for a suitable period of time, thereby obtaining pre-crystallized PLA, wherein the pre-crystallized PLA preferably has a crystallinity of at least 3.0%, preferably at least 5.0%; and c2) conveying the pre-crystallized PLA to a crystallization vessel and maintaining the pre-crystallized PLA in the crystallization vessel at a temperature between 90 and 130° C. for a suitable period of time, thereby obtaining crystallized PLA, wherein the crystallized PLA preferably has a crystallinity of at least 20.0%, such as at least 25.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, such as from 20.0 to 60.0%, or from 35.0 to 55.0%, or from 35.0 to 50.0%, and The crystallinity of the pre-crystallized PLA and the crystallized PLA is measured according to the method specified in the specification.

22. Crystallized PLA pellets obtainable by or by carrying out a process according to any one of claims 1 to 21, wherein the pellets have - a content of between 1.0 and 10.0 wt.-%, for example between 1.5 and 8.0 wt.-%, or between 2.0 and 6.0 wt.-%, or between 2.0 and 4.5 wt.-% of D-lactide isomers, based on the crystallized PLA; and - a crystallinity of at least 20.0%, or at least 30.0%, or at least 35.0%, or at least 40.0%, wherein the crystallinity is determined according to the method specified in the description, and - a total amount of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the crystallized PLA pellets, of amides as defined in any one of the preceding claims.

23. Amide Use of an amide as defined in any one of the preceding claims for increasing the crystallization rate of pellets of a PLA polymer, wherein the PLA polymer has a content of D-lactide isomer between 1.0 and 10.0 wt. % of the PLA polymer, wherein the amide is used to form a melt of the PLA polymer prior to pelletization and is contained in a total amount of between 10 and 2000 ppm, such as between 20 and 1500 ppm, or between 30 and 1000 ppm, or between 50 and 900 ppm, or between 100 and 900 ppm of the PLA polymer.

24. Use of an amide according to claim 23 for increasing the crystallization rate of pellets of a PLA polymer, wherein the amide is used in combination with previously crystallized PLA, preferably wherein the previously crystallized PLA is as defined in any one of claims 13 and 17 to 20, wherein the amide and the previously crystallized PLA are added to the melt of the PLA polymer before pelletization, either alone or as a blend, preferably as a molten composition.

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