Polylactide resin composition

Abstract

The polylactide resin composition according to the present invention improves the neck-in phenomenon by controlling the level of optical isomers in polylactic acid and the usage of compounds having epoxy groups.

Description

polylactide resin composition

[0001] Cross-citation with related application(s)

[0002] This application claims the benefit of priority to Korean Patent Application No. 10-2023-0175673, filed December 6, 2023, and Korean Patent Application No. 10-2024-0111386, filed August 20, 2024, the entire contents of which are incorporated herein by reference.

[0003]

[0004] The present invention relates to a polylactide resin composition.

[0005]

[0006] LDPE is a representative resin widely used in film applications, possessing both long-chain and short-chain branch structures. These characteristics contribute to its high melt strength, rapid productivity, and excellent molding process stability. Furthermore, its physical properties do not change significantly at high processing temperatures, enabling film production even under high-temperature processing conditions.

[0007]

[0008] In contrast to LDPE, polylactic acid (PLA) inherently has low melt strength and melt elasticity due to its linear structural characteristics, which reduces processing stability during film manufacturing. Increasing production speeds to increase productivity increases the neck-in phenomenon, limiting the ability to thin the film for processability. Furthermore, edge weave during the molding process increases, leading to significant deviations in the width and thickness of the resulting film. Neck-in occurs when the film exiting the extrusion process is pushed inward, which can increase film thickness and increase deviation, making it essential to improve both production costs and process stability.

[0009]

[0010] Because polylactic acid alone cannot achieve film properties comparable to LDPE, it is often blended with other resins or structurally modified using compatibilizers. When blending with other resins, compatibility (miscibility) between the two resins must be considered. Structural modifications through copolymerization or chain extenders can also lead to issues such as condition optimization (processing load, etc.) and color.

[0011]

[0012] Accordingly, in the present invention, in order to improve the neck-in phenomenon of polylactide resin, the degree of optical isomerism of polylactic acid is controlled, and a polylactide resin composition capable of improving neck-in only with a compound having an epoxy group is provided.

[0013]

[0014] The present invention provides a polylactide resin composition with improved neck-in phenomenon.

[0015]

[0016] In order to solve the above problem, the present invention provides a polylactide resin composition comprising a polylactide resin having a D content of 3 to 45 wt% in the polylactide resin, and a compound having an epoxy group.

[0017]

[0018] The term "polylactide resin" used in the present invention is defined to encompass a single polymer or copolymer containing the following repeating units.

[0019]

[0020]

[0021] The above polylactide resin can be manufactured by including a step of forming the above repeating unit by ring-opening polymerization of a lactide monomer, and the polymer obtained after the ring-opening polymerization and the above repeating unit formation process are completed can be referred to as the above “polylactide resin.”

[0022]

[0023] Here, the "lactide monomer" can be defined as follows. Typically, lactide can be classified into L-lactide composed of L-lactic acid, D-lactide composed of D-lactic acid, and Meso-lactide composed of one L-form and one D-form. In addition, a 50:50 mixture of L-lactide and D-lactide is called D,L-lactide or rac-lactide. It is known that when polymerization is performed using only L-lactide or D-lactide with high optical purity among these lactides, L- or D-polylactide (PLLA or PDLA) with very high stereoregularity is obtained, and such polylactide is known to have a fast crystallization rate and high crystallization degree compared to polylactide with low optical purity.

[0024]

[0025] In particular, the present invention uses a polylactide resin having a D content of 3 to 45 wt% within the polylactide resin. The polylactide resin is manufactured by ring-opening polymerization of a lactide monomer, and the "D content" refers to the D-lactide content relative to the total weight of the lactide monomer constituting the polylactide resin. For example, when a polylactide resin is manufactured using only meso-lactide, L and D exist in the polylactide resin in a ratio of 1:1, so the D content becomes 50 wt%.

[0026]

[0027] When the above D content is less than 3 wt%, even if a compound having a large amount of epoxy groups is used, the formation of a branched structure is insufficient, so there is a problem that the melt strength is not significantly improved, and thus the physical properties do not change significantly even when producing a film. In addition, when the above D content exceeds 45 wt%, there is a problem that it is difficult to produce polylactide with a high D content, because most of the form existing in nature is L-lactic acid.

[0028]

[0029] Preferably, in the present invention, a polylactide resin is used having a D content of 4 wt% or more, 5 wt% or more, 6 wt% or more, 7 wt% or more, 8 wt% or more, 9 wt% or more, or 10 wt% or more; or 40 wt% or less, 35 wt% or less, 30 wt% or less, 25 wt% or less, or 20 wt% or less.

[0030]

[0031] Meanwhile, when manufacturing polylactide resin by lactide ring-opening polymerization, the D content in the polylactide resin can be controlled by controlling the composition of lactide (L-lactide, D-lactide, and meso-lactide). In addition, after hydrolyzing the manufactured polylactide resin, the ratio of MDL in the total methyl lactate (Methyl L-Lactate (MLL) and Methyl D-Lactate (MDL)) can be confirmed by gas chromatography, thereby analyzing the D content in the polylactide resin.

[0032]

[0033] Preferably, the polylactide resin has a characteristic in which a melting point peak exists below 160°C in a DSC (differential scanning calorimetry) curve. In addition, the polylactide resin has a glass transition temperature observed at 50 to 60°C in a DSC (differential scanning calorimetry) curve.

[0034]

[0035] In addition, the polylactide resin having a D content of 3 to 45 wt% in the polylactide resin used in the present invention is different from the PLA stereocomplex formed by mixing poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), and the polylactide block copolymer in which a poly-L-lactide segment having L-lactide as a main component and a poly-D-lactide segment having D-lactide as a main component are covalently bonded, and the polylactide resin used in the present invention is distinguished in that the melting point peak is observed below 160°C in the DSC (differential scanning calorimetry) curve, but the melting point peak is observed above 170°C in the PLA stereocomplex and the polylactide block copolymer, and in the case of the PLA stereocomplex, one more melting point peak is observed in the range of 220 to 230°C.

[0036]

[0037] Preferably, the polylactide resin used in the present invention has a weight average molecular weight of 70,000 to 400,000. More preferably, the polylactide resin used in the present invention has a weight average molecular weight of 80,000 or more, 90,000 or more, or 100,000 or more; or 300,000 or less, 250,000 or less, or 200,000 or less.

[0038]

[0039] Preferably, the polylactide resin used in the present invention has a number average molecular weight of 50,000 to 100,000. More preferably, the polylactide resin used in the present invention has a number average molecular weight of 55,000 or more, or 60,000 or more; or 90,000 or less, 85,000 or less, or 80,000 or less.

[0040]

[0041] In addition, the polylactide resin composition according to the present invention further comprises a compound having an epoxy group in addition to the polylactide resin. Although not limited by theory, the epoxy group can react with the terminal group of the polylactide resin to change the linear structure of the polylactide resin into a branched structure, and due to this structure, the melt strength can be improved (elasticity increased), thereby improving the neck-in phenomenon during film production.

[0042]

[0043] It is preferable that the compound having the above epoxy group include two or more epoxy groups in its molecular structure for branching of the polylactide resin. In addition, the molecular weight of the compound having the epoxy group is preferably 100 to 10,000. For example, an epoxy-based compatibilizer having the following structure can be used, and a commercialized product such as Joncryl ADR 4468 (BASF) can be used.

[0044]

[0045] In the above, R is C 1-20 alkyl, and x, y, and z are each integers greater than or equal to 1 and less than or equal to 20.

[0046]

[0047] Preferably, the polylactide resin composition of the present invention contains 0.1 to 5.0 parts by weight of the compound having an epoxy group relative to 100 parts by weight of the polylactic acid resin. When the content of the compound having an epoxy group is less than 0.1 parts by weight, the formation of a branched structure of the polylactide resin is insufficient, so the effect of improving the melt strength is minimal. When the content of the compound having an epoxy group exceeds 5.0 parts by weight, an ultra-high molecular weight polylactide resin is produced, which causes a problem of poor film forming processability.

[0048]

[0049] Meanwhile, the polylactide resin composition according to the present invention substantially does not contain any other components other than the polylactide resin and the compound having an epoxy group. The term "substantially does not contain" means that it contains 0.1 parts by weight or less, preferably 0.01 parts by weight or less, based on 100 parts by weight of the polylactide resin composition according to the present invention.

[0050]

[0051] Meanwhile, the method for producing the polylactide resin composition according to the present invention described above is not particularly limited as long as it involves mixing the polylactide resin described above and a compound having an epoxy group. For example, each of the above components can be produced by a melt blending method.

[0052]

[0053] As described above, the polylactide resin composition according to the present invention has the effect of improving neck-in by controlling the degree of optical isomerism of polylactic acid and also controlling the amount of compound having an epoxy group used.

[0054]

[0055] Hereinafter, embodiments of the present invention will be described in more detail in the following examples. However, the following examples are merely illustrative of embodiments of the present invention, and the content of the present invention is not limited by the following examples.

[0056]

[0057] Manufacturing example: Manufacturing of polylactide resin

[0058] Manufacturing Example 1

[0059] L-LT 9.4 kg + Meso-LT 0.6 kg were placed in a 1 Gal reactor, vacuum dried at 60°C for 1 hour, and then heated to 150°C to dissolve lactide. Subsequently, Sn(Oct)2 and 2-ethylhexanol were dissolved in toluene (2.5 mL) and introduced into the reactor. At this time, the molar ratio of lactide and Sn(Oct)2 was 40,000:1, and 2-ethylhexanol was added in an amount of 0.2 mol% based on lactide. Subsequently, the temperature was slowly increased to 180°C to avoid excessive instantaneous exotherm, and the reaction was carried out for 3 hours after the temperature was adjusted to 180°C. After completion of the reaction, polylactide resin (PLA pellet) was obtained by stranding through a water bath. The manufactured pellet was vacuum dried at >40°C to sufficiently dry the moisture.

[0060]

[0061] Manufacturing Example 2

[0062] Polylactide resin (PLA Pellet) was manufactured using the same method as Manufacturing Example 1, except that 7.5 kg of L-LT + 2.5 kg of Meso-LT were used.

[0063]

[0064] Manufacturing Example 3

[0065] Polylactide resin (PLA Pellet) was manufactured in the same manner as in Manufacturing Example 1, except that 10 kg of L-LT was used.

[0066]

[0067] Manufacturing Example 4

[0068] Polylactide resin (PLA Pellet) was manufactured using the same method as Manufacturing Example 1, except that 9.8 kg of L-LT + 0.2 kg of Meso-LT were used.

[0069]

[0070] Example: Preparation of polylactide resin composition

[0071] Reactive extrusion was performed using a 19ø extruder (BA-19, Bautek) with the components listed in Table 1 below. Specifically, for 1 kg of polylactide resin, the components listed in Table 1 below (compounds having an epoxy group) were mixed, and extruded at a screw speed of 200 rpm while controlling the maximum temperature value (190 to 230°C) to obtain PLA pellets. The weight average molecular weight of the obtained PLA pellets was measured using GPC (Gel Permeation Chromatography) under the following conditions, and the melting point and glass transition temperature were measured using DSC (Differential Scanning Calorimetry) using the following method. The results are shown in Table 1.

[0072] (1) Measurement conditions for weight average molecular weight (Mw)

[0073] - Column: PL mixed B x 2

[0074] - Solvent: THF

[0075] - Flow rate: 1.0 ml / min

[0076] - Sample concentration: 1.5 mg / ml

[0077] - Injection volume: 100 μl

[0078] - Column temperature: 40 ℃

[0079] - Detector: Waters 2414 RID

[0080] - Standard: PS (polystyrene)

[0081]

[0082] (2) Method for measuring melting point (Tm) and glass transition temperature (Tg)

[0083] - Device: DSC (Differential Scanning Calorimetry) 250 (TA Instruments)

[0084] - Measurement method: 250°C, which is higher than the melting temperature of PLA, at a heating rate of 10°C / min After heating to ℃, it was stabilized for 5 minutes. After that, -20 Up to 10℃ After cooling at a cooling rate of ℃ / min and stabilizing for 5 minutes, the temperature was 250°C to observe the melting point and glass transition temperature peaks. Up to 10℃ It was reheated at a rate of ℃ / min. The temperatures of the melting point peak and glass transition temperature peak were confirmed and are listed in Table 1 below.

[0085]

[0086] PLA optical purityPLA compound having epoxy groupTmTgMwExtruded PelletDContent (weight %)TypeTypephr℃℃g / molΔ Mw(GPC)Example 13~5Manufacturing example 1(Joncryl)1.0<160.058.8226,65220Example 210-20Manufacturing example 2(Joncryl)1.0<160.057.0190,79345Comparative example 1<1Manufacturing example 3(Joncryl)1.0172.059.8128,90513Comparative example 21~3Manufacturing example 4(Joncryl)1.0163.859.0132,08617Comparative example 3<1Manufacturing example 3-Unused 173.559.8150,524-Comparative example 41~3 Manufacturing example 4-Unused 166.659.0203,600-Comparative example 53~5 Manufacturing example 1-Unused <160.058.8189,518-

[0087]

[0088] The compound having an epoxy group in Table 1 above is Joncryl ADR 4468 (BASF).

[0089]

[0090] Experimental Example: Neck-in Evaluation of Polylactide Resin

[0091] Each pellet obtained above was vacuum-dried at 85℃ for more than 4 hours, and PLA film was manufactured through T-die extrusion molding (Eurotech benchtop monolayer cast film equipment, Screw ø17.5 mm, T-die width 120 mm). The neck-in value was measured by the film width (X) manufactured under the same conditions of a calendar speed of 3.0 M / m and a haul-off speed of 4.5 M / m, and the results are shown in Table 2 below.

[0092] - Film width deviation: Actual value measured with 1 m of film manufactured according to thickness (<100 μm, <50 μm, <30 μm, <20 μm)

[0093] - Neck-in evaluation: ((T-die width) - (Film width)) / 2 = (120 - X) / 2

[0094]

[0095] Film manufacturing (<100μm)Film manufacturing (<50μm)Film manufacturing (<30μm)Film manufacturing (<20μm)Width deviation (mm)Neck-in (mm)Width deviation (mm)Neck-in (mm)Width deviation (mm)Neck-in (mm)Width deviation (mm)Neck-in (mm)Example 1113.5116.0117.5118.0Example 2114.0113.0113.0113.5Comparative example 1528.51737.5Not measurableNot measurableNot measurableNot measurableComparative example 21435.01542.5Not measurableNot measurableNot measurableComparative example 3428.51238.0Not measurableNot measurableNot measurableComparative example 4529.5633.5332.0 ImmeasurableImmeasurableComparable Example 5728.5431.5835.01338.0

[0096] The part marked as “unmeasurable” in Table 2 above means that the neck-in phenomenon was so severe that it could not be manufactured into a film.

[0097]

[0098] As shown in the results of the examples in Table 2 above, as the D content of the polylactide resin increased, the molecular weight change increased under the same extrusion process conditions, which meant improved melt strength. In addition, it was confirmed that the width deviation was significantly reduced in films manufactured according to thickness, which meant that the film forming processing stability was improved. In particular, in the case of Example 2 with a D content of 10 wt%, the neck-in phenomenon did not increase even at a thin thickness, which means high-speed productivity and also means that it is advantageous for cost reduction.

[0099]

[0100] On the other hand, the comparative examples in which the D content was less than 3 wt% or no compound having an epoxy group was added had a problem in that the initial Neck-in value was large and the Neck-in phenomenon increased as the production speed increased.

Claims

1. A polylactide resin having a D content of 3 to 45 wt% in the polylactide resin, and Comprising a compound having an epoxy group, Polylactide resin composition.

2. In paragraph 1, The above polylactide resin has a melting point peak below 160°C in the DSC (differential scanning calorimetry) curve. Polylactide resin composition.

3. In paragraph 1, The above polylactide resin has a D content of 10 to 20 wt%. Polylactide resin composition.

4. In paragraph 1, Containing 0.1 to 5.0 parts by weight of the compound having the epoxy group relative to 100 parts by weight of the polylactide resin, Polylactide resin composition.

5. In paragraph 1, The weight average molecular weight of the above polylactide resin is 70,000 to 400,000. Polylactide resin composition.

6. In paragraph 1, The number average molecular weight of the above polylactide resin is 50,000 to 100,000. Polylactide resin composition.

7. In paragraph 1, The compound having the above epoxy group contains two or more epoxy groups in its molecular structure. Polylactide resin composition.

8. In paragraph 1, The above polylactide resin composition substantially does not contain any other components other than the polylactide resin and a compound having an epoxy group. Polylactide resin composition.

9. In paragraph 1, The above polylactide resin composition comprises, in addition to the polylactide resin and the compound having an epoxy group, another component in an amount of 0.1 part by weight or less, relative to 100 parts by weight of the polylactide resin composition. Polylactide resin composition.

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