Polylactide resin composition

Abstract

The polylactide resin composition according to the present invention has the effect of improving neck-in by adjusting the degree of optical isomers of polylactic acid and adjusting the amount of the compound having an epoxy group.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0175673, filed December 6, 2023, and Korean Patent Application No. 10-2024-0111386, filed August 20, 2024, and all contents disclosed in the documents of said Korean patent applications are incorporated herein by reference.

[0002] The present invention relates to a polylactide resin composition. [Background technology]

[0003] LDPE is a typical resin widely used in film applications, and has both long-chain and short-chain branched structures. These properties give it high melt strength, rapid productivity, and excellent molding processing stability. Furthermore, its physical properties do not change significantly even at high processing temperatures, making it possible to produce films even under high-temperature processing conditions.

[0004] Unlike LDPE, polylactic acid (PLA) has low melt strength and melt elasticity due to its linear structure, which reduces the molding process stability during film production. Increasing production speed to improve productivity increases the neck-in phenomenon, limiting the ability to reduce film thickness for processability reasons. Another drawback is that edge weave becomes severe during the molding process, resulting in significant deviations in the width and thickness of the produced film. Neck-in occurs when the film emerges from the extrusion process and is pushed inward, which can increase film thickness and increase deviations, making it essential to improve this in terms of production cost and process stability.

[0005] Because polylactic acid alone cannot ensure the same film properties as LDPE, it is sometimes improved by blending it with other resins or by using a compatibilizer to change the structure. When blending it with other resins, the compatibility (mixability) between the two resins must also be taken into consideration, and structural changes due to copolymerization or chain extenders can lead to problems such as optimizing conditions (processing load, etc.) and color.

[0006] Therefore, in order to improve the neck-in phenomenon of polylactide resins, the present invention aims to provide a polylactide resin composition that adjusts the degree of optical isomers of polylactic acid and can improve neck-in by using only a compound having an epoxy group. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a polylactide resin composition with an improved neck-in phenomenon. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides a polylactide resin composition containing a polylactide resin having a D content of 3 to 45% by weight and a compound having an epoxy group.

[0009] The term "polylactide resin" used in the present invention is defined as a comprehensive term for homopolymers or copolymers containing the following repeating units: [ka]

[0010] The polylactide resin can be produced by forming the repeating unit through ring-opening polymerization of lactide monomers, and the polymer obtained after the ring-opening polymerization and the repeating unit formation processes are completed can be called a "polylactide resin."

[0011] In this context, "lactide monomer" can be defined as follows: Lactide is generally classified as L-lactide, which is made up of L-lactic acid; D-lactide, which is made up of D-lactic acid; and meso-lactide, which is made up of one L-form and one D-form. A 50:50 mixture of L-lactide and D-lactide is called D,L-lactide or rac-lactide. It is known that polymerization using only L-lactide or D-lactide with high optical purity among these lactides results in L- or D-polylactide (PLLA or PDLA) with very high stereoregularity. Such polylactides are known to have a faster crystallization rate and higher crystallinity than polylactides with lower optical purity.

[0012] In particular, the present invention uses a polylactide resin having a D content of 3 to 45% by weight. The polylactide resin is produced by ring-opening polymerization of lactide monomers, and the "D content" refers to the content of D-lactide relative to the total weight of the lactide monomers constituting the polylactide resin. For example, if a polylactide resin is produced using only meso-lactide, the L and D in the polylactide resin will be present in a 1:1 ratio, resulting in a D content of 50% by weight.

[0013] If the 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 slight, the melt strength is not significantly improved, and the physical properties do not change significantly during film production. Also, if the D content exceeds 45 wt%, it is difficult to produce polylactide with a high D content because the form present in nature is almost always L-lactic acid.

[0014] Preferably, in the present invention, a polylactide resin is used having a D content of 4% by weight or more, 5% by weight or more, 6% by weight or more, 7% by weight or more, 8% by weight or more, 9% by weight or more, or 10% by weight or more; or 40% by weight or less, 35% by weight or less, 30% by weight or less, 25% by weight or less, or 20% by weight or less.

[0015] Meanwhile, when producing polylactide resin by lactide ring-opening polymerization, the D content in the polylactide resin can be controlled by adjusting the lactide composition (L-lactide, D-lactide, and Meso-lactide). Alternatively, the produced polylactide resin can be hydrolyzed and then converted to methyl lactate by esterification. The D content in the polylactide resin can be analyzed by confirming the ratio of MDL in the total methyl lactate (methyl L-lactate (MLL) and methyl D-lactate (MDL)) using gas chromatography.

[0016] Preferably, the polylactide resin is characterized in that a melting point peak in a DSC (differential scanning calorimeter) curve is present at less than 160° C. The polylactide resin is observed to have a glass transition temperature of 50 to 60° C. in a DSC (differential scanning calorimeter) curve.

[0017] The polylactide resin used in the present invention, which has a D content of 3 to 45% by weight, is different from a PLA stereocomplex formed by mixing poly(L-lactide) (PLLA) and poly(D-lactide) (PDLA) and a polylactide block copolymer formed by covalently bonding poly-L-lactide segments mainly composed of L-lactide and poly-D-lactide segments mainly composed of D-lactide. The polylactide resin used in the present invention is distinguished from the PLA stereocomplex in that a melting point peak is observed below 160°C in a DSC (differential scanning calorimeter) curve, whereas the PLA stereocomplex and polylactide block copolymer have melting point peaks observed above 170°C, and the PLA stereocomplex has another melting point peak observed in the range of 220 to 230°C.

[0018] 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; and 300,000 or less, 250,000 or less, or 200,000 or less.

[0019] 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, and 90,000 or less, 85,000 or less, or 80,000 or less.

[0020] Furthermore, the polylactide resin composition according to the present invention further comprises a compound having an epoxy group in addition to the polylactide resin. Without being 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, which improves melt strength (increases elasticity) and reduces neck-in during film production.

[0021] The epoxy group-containing compound preferably contains two or more epoxy groups in its molecular structure to branch the polylactide resin. The molecular weight of the epoxy group-containing compound is preferably 100 to 10,000. For example, an epoxy compatibilizer having the following structure can be used, and a commercially available product such as Joncryl ADR 4468 (BASF) can be used. [ka] In the above, R is C 1-20 alkyl, and x, y, and z are each an integer of 1 to 20.

[0022] 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. If the content of the compound having an epoxy group is less than 0.1 part by weight, the formation of a branched structure in the polylactide resin is slight, resulting in a slight improvement in melt strength. If the content of the compound having an epoxy group exceeds 5.0 parts by weight, an ultra-high molecular weight polylactide resin is produced, resulting in a problem of poor film formability.

[0023] On the other hand, the polylactide resin composition according to the present invention is substantially free of other components except for the polylactide resin and the compound having an epoxy group. The term "substantially free" means that the other components are contained in an amount of 0.1 part by weight or less, preferably 0.01 part by weight or less, per 100 parts by weight of the polylactide resin composition according to the present invention.

[0024] Meanwhile, the method for producing the polylactide resin composition according to the present invention is not particularly limited as long as it is a method for mixing the polylactide resin and the compound having an epoxy group. For example, the components can be produced by melt blending. [Effects of the Invention]

[0025] As described above, the polylactide resin composition according to the present invention has the effect of improving neck-in by adjusting the degree of optical isomers of polylactic acid and adjusting the amount of the compound having an epoxy group. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, the present invention will be described in more detail with reference to the following examples, but the following examples are merely illustrative of the present invention and are not intended to limit the scope of the present invention.

[0027] Manufacturing example: Manufacturing of polylactide resin Manufacturing Example 1 9.4 kg of L-LT and 0.6 kg of Meso-LT were placed in a 1-gal reactor and dried under vacuum at 60°C for 1 hour. The mixture was then heated to 150°C to dissolve the lactide. Sn(Oct)2 and 2-ethylhexanol were then dissolved in toluene (2.5 mL) and added to the reactor. The molar ratio of lactide to Sn(Oct)2 was 40,000:1, and 2-ethylhexanol was added at 0.2 mol% relative to the lactide. The temperature was then slowly raised to 180°C to avoid sudden heat generation. After the temperature reached 180°C, the reaction was allowed to proceed for 3 hours. After the reaction was complete, the mixture was passed through a water bath and stranded to obtain polylactide resin (PLA pellets). The resulting pellets were vacuum dried at >40°C to thoroughly remove moisture.

[0028] Manufacturing Example 2 A polylactide resin (PLA pellets) was produced in the same manner as in Production Example 1, except that 7.5 kg of L-LT and 2.5 kg of Meso-LT were used.

[0029] Manufacturing Example 3 A polylactide resin (PLA pellets) was produced in the same manner as in Production Example 1, except that 10 kg of L-LT was used.

[0030] Manufacturing Example 4 A polylactide resin (PLA pellets) was produced in the same manner as in Production Example 1, except that 9.8 kg of L-LT and 0.2 kg of Meso-LT were used.

[0031] Example: Preparation of polylactide resin composition Reactive extrusion was carried out using a 19mm diameter extruder (BA-19, Bautek) with the ingredients listed in Table 1 below. Specifically, 1 kg of polylactide resin was mixed with the ingredients (compounds having epoxy groups) listed in Table 1 below, and extruded at a screw speed of 200 rpm while adjusting the maximum temperature (190-230°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) as follows. The results are shown in Table 1. (1) Measurement conditions for weight average molecular weight (Mw) -Column: PL mixed Bx2 Solvent: THF -Flow rate: 1.0ml / min -Sample concentration: 1.5mg / ml -Injection volume: 100μl -Column temperature: 40℃ -Detector: Waters 2414 RID -Standard: PS (Polystyrene) (2) Measurement method of melting point (Tm) and glass transition temperature (Tg) - Apparatus: DSC (Differential Scanning Calorimetry) 250 (TA Instruments) - Measurement method: The sample was heated to 250°C, which is above the melting point of PLA, at a heating rate of 10°C / min and then stabilized for 5 minutes. It was then cooled to -20°C at a cooling rate of 10°C / min and stabilized for 5 minutes, after which it was reheated to 250°C at a rate of 10°C / min to observe the melting point and glass transition temperature peaks. The melting point peak and glass transition temperature peak temperatures were measured and are listed in Table 1 below. [Table 1] In Table 1, the compound having an epoxy group is Joncryl ADR 4468 (BASF).

[0032] Experimental example: Neck-in evaluation of polylactide resin Each of the obtained pellets was vacuum dried at 85°C for at least 4 hours and then T-die extrusion molding was performed to produce PLA films (Eurotech benchtop monolayer cast film equipment, screw diameter 17.5 mm, T-die width 120 mm). Neck-in values ​​were measured for the width (X) of films produced under the same conditions of a calendar speed of 3.0 mm / m and a haul-off speed of 4.5 mm / m, and the results are shown in Table 2 below. - Film width deviation: Value measured on 1m of film manufactured according to thickness (<100μm, <50μm, <30μm, <20μm) -Neck-in rating: ((T die width)-(film width)) / 2=(120-X) / 2 [Table 2] In Table 2, the portion marked "impossible to measure" means that the neck-in phenomenon was so severe that it was not possible to manufacture the film.

[0033] As shown in 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. Furthermore, it was confirmed that the width deviation was significantly reduced in films manufactured at different thicknesses, which means improved film forming process stability. In particular, in the case of Example 2, where the D content was 10 wt%, the neck-in phenomenon did not increase even at thin thicknesses, which means high-speed productivity and is advantageous for cost reduction.

[0034] In contrast, in the comparative examples in which the D content was less than 3 wt % or no epoxy group-containing compound was added, the initial neck-in value was large, and the neck-in phenomenon increased as the production rate increased.

Claims

1. a polylactide resin having a D content of 3 to 45% by weight; and a compound having an epoxy group, Polylactide resin composition.

2. The polylactide resin has a melting point peak at less than 160°C in a DSC (differential scanning calorimeter) curve. The polylactide resin composition according to claim 1.

3. The polylactide resin has a D content of 10 to 20% by weight. The polylactide resin composition according to claim 1.

4. The compound having an epoxy group is contained in an amount of 0.1 to 5.0 parts by weight based on 100 parts by weight of the polylactide resin. The polylactide resin composition according to claim 1.

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

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

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

8. the polylactide resin composition is substantially free of any other components other than the polylactide resin and the compound having an epoxy group; The polylactide resin composition according to claim 1.

9. the polylactide resin composition contains, 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; The polylactide resin composition according to claim 1.

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