Polylactide resin composition

Abstract

The polylactide resin composition according to the present invention improves a necking phenomenon by controlling the level of optical isomers of polylactic acid and adjusting the amount of a compound having an epoxy group used.

Description

[0001] Cross-reference to related applications

[0002] This application claims priority and benefit to Korean Patent Application No. 10-2023-0175673, filed on December 6, 2023, and Korean Patent Application No. 10-2024-011138, filed on August 20, 2024, the disclosure of which is incorporated herein by reference in its entirety. Technical Field

[0003] This invention relates to polylactide resin compositions. Background Technology

[0004] LDPE is a typical resin commonly used in film applications, and it possesses both long-chain and short-chain branched structures. Due to these properties, LDPE exhibits high melt strength, rapid production rates, and excellent molding stability. Furthermore, LDPE's properties do not change significantly even at high processing temperatures, and it can be used to manufacture films even under high-temperature processing conditions.

[0005] In contrast to LDPE, polylactic acid (PLA) exhibits low melt strength and melt elasticity due to its linear structure, which reduces molding stability during film production. Increasing production speed to improve productivity exacerbates necking, thus limiting film thinning due to processability considerations. Furthermore, edge weave becomes severe during the molding process, leading to significant variations in film width and thickness. Necking, caused by the inward pushing of the extruded film, increases film thickness and introduces substantial deviations, necessitating improvements in production cost and process stability.

[0006] Since polylactic acid (PLA) alone cannot guarantee film properties similar to LDPE, its performance can be improved by forming blends with other resins or by modifying its structure using compatibilizers. When forming blends with other resins, the compatibility (miscibility) between the two resins must also be considered. Structural changes through copolymerization or chain extenders may cause issues such as condition optimization (processing load, etc.) and color.

[0007] Therefore, in order to improve the necking phenomenon of polylactide resin, the present invention aims to provide a polylactide resin composition that can adjust the optical isomerism of polylactic acid and improve the necking phenomenon using only compounds having epoxy groups. Summary of the Invention

[0008] Technical issues

[0009] The present invention provides a polylactide resin composition in which the neck-in phenomenon is improved.

[0010] Technical solution

[0011] To achieve the above objectives, the present invention provides a polylactide resin composition comprising: a polylactide resin, wherein the D content in the polylactide resin is from 3% to 45% by weight, and a compound having an epoxy group.

[0012] As used herein, the term "polylactide resin" is defined as a homopolymer or copolymer collectively comprising the following repeating units.

[0013]

[0014] Polylactide resin can be prepared by a method that includes the step of forming repeating units through ring-opening polymerization of lactide monomers. Sometimes the polymer obtained after the ring-opening polymerization and repeating unit formation steps is called "polylactide resin".

[0015] The term "lactide monomer" can be defined as follows. Generally, "lactide monomers" can be classified into L-lactide composed of L-lactic acid, D-lactide composed of D-lactic acid, and mesolactide composed of one L-form and one D-form. Furthermore, a mixture of L-lactide and D-lactide in a 50:50 ratio is referred to as D,L-lactide or racemic lactide. It is known that when only high-optical-purity L-lactide or D-lactide from these lactides is used for polymerization, highly stereoregular L- or D-polylactide (PLLA or PDLA) can be obtained. Compared to low-optical-purity polylactide, this polylactide crystallizes rapidly and has high crystallinity.

[0016] In particular, according to the present invention, a polylactide resin with a D content of 3% to 45% by weight is used. The polylactide resin is prepared by ring-opening polymerization of lactide monomers, wherein "D content" refers to the D-lactide content relative to the total weight of the lactide monomers constituting the polylactide resin. For example, when the polylactide resin is prepared using only mesolacide, L and D in the polylactide resin exist in a 1:1 ratio, therefore the D content is 50% by weight.

[0017] If the D content is below 3% by weight, there is a problem that even when using compounds with a large number of epoxy groups, the formation of branched structures is insufficient, the melt strength is not significantly improved, and therefore the change in physical properties is not significant even when manufacturing films. In addition, when the D content exceeds 45% by weight, it is difficult to prepare polylactide with a high D content because the form that exists in nature is mostly L-lactic acid.

[0018] Preferably, according to the present invention, the polylactide resin used has the following D content: 4% or more by weight, 5% or more by weight, 6% or more by weight, 7% or more by weight, 8% or more by weight, 9% or more by weight, or 10% or more by weight; and is 40% or less by weight, 35% or less by weight, 30% or less by weight, 25% or less by weight, or 20% or less by weight.

[0019] Meanwhile, when preparing polylactide resin via ring-opening polymerization of lactide, the composition of lactide (L-lactide, D-lactide, and mesolacide) can be adjusted, thereby regulating the D content in the polylactide resin. Furthermore, after hydrolyzing the prepared polylactide resin, it is converted to methyl lactate via esterification. The total proportion of MDL in the methyl lactate (L-methyl lactate (MLL) and D-methyl lactate (MDL)) is confirmed by gas chromatography, and the D content in the polylactide resin is analyzed.

[0020] Preferably, the polylactide resin is characterized in that its melting point peak is located in the region below 160°C in the DSC (differential scanning calorimetry) curve. Furthermore, the polylactide resin is observed to have a glass transition temperature of 50°C to 60°C in the DSC curve.

[0021] Furthermore, the polylactide resin used in this invention, with a D content of 3% to 45% by weight, is different from the PLA stereopolymer composite formed by mixing poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA), and the polylactide block copolymer formed by covalently bonding L-lactide-based poly-L-lactide segments with D-lactide-based poly-D-lactide segments. In the case of the polylactide resin used in this invention, a melting point peak is observed in the DSC (differential scanning calorimetry) curve in the region below 160°C. However, in the case of the PLA stereopolymer composite and the polylactide block copolymer, a melting point peak is observed in the region at 170°C or higher, and in the case of the PLA stereopolymer composite, an additional melting point peak is observed in the range of 220°C to 230°C.

[0022] Preferably, the polylactide resin used in this invention has a weight-average molecular weight of 70,000 to 400,000. More preferably, the polylactide resin used in this invention has a weight-average molecular weight of 80,000 or more, 90,000 or more, or 100,000 or more; and 300,000 or less, 250,000 or less, or 200,000 or less.

[0023] Preferably, the number average molecular weight of the polylactide resin used in this invention is 50,000 to 100,000. More preferably, the number average molecular weight of the polylactide resin used in this invention is 55,000 or more, or 60,000 or more; and 90,000 or less, 85,000 or less, or 80,000 or less.

[0024] In addition to polylactide resin, the polylactide resin composition of the present invention also contains compounds having epoxy groups. Without being theoretically limited, the epoxy groups can react with the end groups of the polylactide resin, transforming the linear structure of the polylactide resin into a branched structure. Due to this structure, the melt strength is increased (elasticity is increased), which can improve the necking phenomenon during film formation.

[0025] To branch the polylactide resin, the epoxy-containing compound preferably contains two or more epoxy groups in its molecular structure. Furthermore, the molecular weight of the epoxy-containing compound is preferably between 100 and 10,000. For example, an epoxy compatibilizer having the following structure can be used; commercially available examples include Joncryl ADR 4468 (BASF).

[0026]

[0027] Where R is C 1-20 Alkyl group, where x, y, and z are each integers greater than 1 and less than 20.

[0028] Relative to 100 parts by weight of polylactic acid resin, the polylactic acid resin composition of the present invention preferably contains 0.1 to 5.0 parts by weight of an epoxy-containing compound. If the content of the epoxy-containing compound is less than 0.1 parts by weight, the branched structure of the polylactide resin is not sufficiently formed, resulting in a slight improvement in melt strength. Furthermore, if the content of the epoxy-containing compound is greater than 5.0 parts by weight, a polylactide resin with ultra-high molecular weight will be prepared, which causes problems with deteriorated film-forming processability.

[0029] Furthermore, the polylactide resin composition according to the present invention is substantially free of other components besides polylactide resin and epoxy-containing compounds. The term "substantially free of" means containing less than 0.1 parts by weight, preferably less than 0.01 parts by weight, relative to 100 parts by weight of the polylactide resin composition of the present invention.

[0030] Furthermore, the method for preparing the polylactide resin composition of the present invention is not particularly limited as long as it involves mixing the polylactide resin with a compound having an epoxy group. As an example, each of the above components can be prepared by melt blending.

[0031] Beneficial effects

[0032] As described above, the polylactide resin composition according to the present invention has the effect of adjusting the optical isomerism of polylactic acid and adjusting the amount of epoxy-containing compounds used, thereby improving necking. Detailed Implementation

[0033] In the following sections, embodiments of the invention will be described in more detail by way of examples. However, the following examples are for illustrative purposes only and are not intended to limit the scope of the invention.

[0034] Preparation example: Preparation of polylactide resin

[0035] Preparation Example 1

[0036] 9.4 kg L-LT and 0.6 kg Meso-LT were placed in a 1-Gal reactor and vacuum dried at 60 °C for 1 hour, then heated to 150 °C to dissolve lactide. Sn(Oct)₂ and 2-ethylhexanol were then dissolved in toluene (2.5 mL) and introduced into the reactor. At this point, the molar ratio of lactide to Sn(Oct)₂ was 40000:1, and 0.2 mol% of 2-ethylhexanol relative to lactide was added. The temperature was then slowly increased to 180 °C to avoid significant instantaneous heating, and the temperature was maintained at 180 °C for 3 hours. After the reaction was complete, the reaction product was passed through a water bath to obtain polylactide resin (PLA granules) in strands. The prepared granules were vacuum dried at >40 °C to ensure complete moisture removal.

[0037] Preparation Example 2

[0038] Polylactide resin (PLA granules) was prepared in the same manner as in Preparation Example 1, except that 7.5 kg of L-LT and 2.5 kg of Meso-LT were used.

[0039] Preparation Example 3

[0040] Except that 10 kg of L-LT was used, polylactide resin (PLA granules) was prepared in the same manner as in Preparation Example 1.

[0041] Preparation Example 4

[0042] Polylactide resin (PLA granules) was prepared in the same manner as in Preparation Example 1, except that 9.8 kg of L-LT and 0.2 kg of Meso-LT were used.

[0043] Example: Preparation of polylactide resin composition

[0044] use An extruder (BA-19, Bautek) was used to reactive extrude the components listed in Table 1 below. Specifically, 1 kg of polylactide resin was mixed with the components listed in Table 1 (compounds containing epoxy groups), extruded at a screw speed of 200 rpm, and the maximum temperature was adjusted (190°C to 230°C) to obtain PLA granules. The weight-average molecular weight of the obtained PLA granules was determined using GPC (gel permeation chromatography) under the following conditions, and the melting point and glass transition temperature were determined using DSC (differential scanning calorimetry) according to the following method. The results are shown in Table 1 below.

[0045] (1) Determination conditions of weight-average molecular weight (Mw)

[0046] - Column: PL mixed B x 2

[0047] Solvent: THF

[0048] - Flow rate: 1.0 ml / min

[0049] - Sample concentration: 1.5 mg / ml

[0050] -Injection volume: 100μL

[0051] - Column temperature: 40℃

[0052] - Detector: Waters 2414RID

[0053] -Standard product: PS (Polystyrene)

[0054] (2) Methods for determining melting point (Tm) and glass transition temperature (Tg)

[0055] - Apparatus: DSC (Differential Scanning Calorimetry) 250 (TA Instruments)

[0056] - Measurement Method: The sample was heated to 250°C, above the PLA melting temperature, at a heating rate of 10°C / min, and then stabilized for 5 minutes. The sample was then cooled to -20°C at a cooling rate of 10°C / min and stabilized for 5 minutes. It was then reheated to 250°C at a rate of 10°C / min, and the melting point and glass transition temperature peaks were observed. The temperatures of the melting point peak and glass transition temperature peak were confirmed and listed in Table 1 below.

[0057] [Table 1]

[0058]

[0059] In Table 1, the compound with an epoxy group is Joncryl ADR 4468 (BASF).

[0060] Experimental Example: Evaluation of Necking of Polylactic Acid Resin

[0061] Each granule obtained above was vacuum dried at 85°C for at least 4 hours, and then extruded through a T-die (Eurotech benchtop single-layer cast film equipment, screw). PLA film was produced using a T-die with a width of 120 mm. The necking value was actually measured by measuring the width (X) of the film produced under the same conditions of calendering speed of 3.0 M / m and drawing speed of 4.5 M / m, and the results are shown in Table 2 below.

[0062] - Membrane width deviation: Actual measured value of a 1m film produced based on thickness (<100μm, <50μm, <30μm, <20μm).

[0063] -Neck reduction evaluation: ((T-die width) - (film width)) / 2 = (120 - X) / 2

[0064] [Table 2]

[0065]

[0066] The portions marked "not measurable" in Table 2 indicate severe necking and therefore cannot be made into films.

[0067] Referring to the results of the examples in Table 2, the higher the D content of the polylactide resin, the greater the change in molecular weight under the same extrusion process conditions, which means improved melt strength. It was also confirmed that width deviation was significantly reduced in films prepared at different thicknesses, implying improved stability in film formation processing. In particular, in the case of Example 2 with a D content of 10% by weight, necking did not increase even at thin thicknesses, which is beneficial for high-speed production and cost reduction.

[0068] On the other hand, comparative examples with a D content of less than 3% by weight or without the addition of compounds containing epoxy groups have the problem of large initial necking values ​​and increased necking phenomenon as the manufacturing speed increases.

Claims

1. A polylactide resin composition comprising: Polylactide resin, wherein the D content in the polylactide resin is from 3% to 45% by weight, and Compounds containing epoxy groups.

2. The polylactide resin composition according to claim 1, wherein, The polylactide resin has a melting point peak below 160°C in the DSC (differential scanning calorimetry) curve.

3. The polylactide resin composition according to claim 1, wherein, The D content of the polylactide resin is 10% to 20% by weight.

4. The polylactide resin composition according to claim 1, wherein, Based on 100 parts by weight of the polylactide resin, the content of the epoxy-containing compound is from 0.1 parts by weight to 5.0 parts by weight.

5. The polylactide resin composition according to claim 1, wherein, The weight-average molecular weight of the polylactide resin is between 70,000 and 400,000.

6. The polylactide resin composition according to claim 1, wherein, The number average molecular weight of the polylactide resin is between 50,000 and 100,000.

7. The polylactide resin composition according to claim 1, wherein, The compound having epoxy groups contains two or more epoxy groups in its molecular structure.

8. The polylactide resin composition according to claim 1, wherein, The polylactide resin composition is substantially free of any components other than the polylactide resin and the epoxy-containing compound.

9. The polylactide resin composition according to claim 1, wherein, Based on 100 parts by weight of the polylactide resin composition, the polylactide resin composition contains less than 0.1 parts by weight of other components besides the polylactide resin and the epoxy-containing compound.

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