Polylactide resin composition with excellent melt strength, and method for producing the same

Abstract

The polylactide resin composition according to the present invention contains a polylactide oligomer whose terminal groups are carboxyl groups, and while maintaining the advantage of biodegradability, it is characterized by excellent melt strength due to a high branching effect.

Description

Technical Field

[0001] Cross-reference of related applications This application claims the benefit of priority based on Korean Patent Application No. 10-2023-0031173 filed on March 9, 2023, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference.

[0002] The present invention relates to a polylactide resin composition having excellent melt strength and a method for producing the same.

Background Art

[0003] Polylactide (or polylactic acid; PLA) resin is manufactured based on bio-based raw materials, reduces the emission of carbon dioxide, a greenhouse gas, during the manufacturing process, and has the characteristics of being decomposed by a specific temperature and composting equipment. It is an eco-friendly material. Recently, as a countermeasure to the use of waste plastics and carbon emission regulations, it has been attracting attention as one of the materials that can replace existing crude oil-based resins. In addition, polylactide resin has the advantages of being less expensive than other biodegradable polymers and having high tensile strength and modulus characteristics.

[0004] However, polylactide has low melt strength and melt elasticity, making it difficult to apply to processes related to stretchability, such as blowing, blow molding, spinning, foaming, and paper coating. As a measure to improve melt strength, many attempts have been made to improve chain entanglements by developing PLA with long chain, branched, cross-linked, or star-shaped structures using CE (chain extenders). However, CE such as diisocyanates are toxic, and using CE negates the advantage of biodegradability. Furthermore, it is difficult to adjust the polymer structure and find the appropriate CE concentration.

[0005] On the other hand, methods to improve melt strength by adding epoxy-based branching agents to neat PLA are also being studied. However, since this mainly involves the reaction between the carbonyl groups of the PLA end groups and the epoxy groups to form a branched structure, the reactivity can vary greatly depending on the PLA acid value (influence of end groups due to additives, initiators, etc.).

[0006] Other approaches include introducing other polymers or micro- or nano-sized fillers. However, mixing with other polymers has limitations, potentially restricting reuse and biodegradation, and the introduction of fillers presents problems in terms of achieving uniform mixing and particle dispersion.

[0007] Therefore, the objective of the present invention is to introduce a compatibilizer and a PLA oligomer with COOH terminal groups into polylactide, thereby maintaining the biodegradability advantages of PLA while improving melt strength through a high branching effect, making it applicable to a wide molding process window. [Overview of the project] [Problems that the invention aims to solve]

[0008] The present invention provides a polylactide resin composition with excellent melt strength. Furthermore, by improving melt strength, the present invention provides a polylactide resin composition that can be applied to molding processes such as blowing, blow molding, spinning, foaming, and paper coating.

[0009] Furthermore, the present invention provides a method for producing the polylactide resin composition. [Means for solving the problem]

[0010] To solve the above problems, the present invention provides the following polylactide resin compositions: Polylactide resin and Polylactide oligomers whose terminal group is a carboxyl group, Contains a compatibilizer, Polylactide resin composition.

[0011] As used in this invention, the term "polylactide resin" is defined as encompassing monopolymers or copolymers containing the following repeating units. [ka]

[0012] The polylactide resin can be manufactured by a step of forming the repeating units by ring-opening polymerization of lactide monomers, and the polymer after such ring-opening polymerization and the formation of the repeating units steps can be referred to as the "polylactide resin".

[0013] In this context, "lactide monomer" can be defined as follows. Normally, 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). Furthermore, a mixture of L-lactide and D-lactide in a 50:50 ratio is called D,L-lactide or rac-lactide. It is known that when polymerization proceeds using only L-lactide or D-lactide with high optical purity, L- or D-polylactide (PLLA or PDLA) with very high stereoregularity is obtained. Such polylactides are known to have a faster crystallization rate and higher crystallinity compared to polylactides with lower optical purity. However, in this specification, "lactide monomer" is defined as encompassing all forms of lactide, regardless of the differences in the properties of lactide according to each form and the differences in the properties of the polylactide resin formed from them.

[0014] On the other hand, the polylactide resin according to the present invention has, for example, a weight-average molecular weight of 70,000 to 400,000.

[0015] The present invention is characterized by improving the melt strength of a polylactide resin by using a polylactide oligomer having carboxyl groups as terminal groups together with such a polylactide resin.

[0016] In this invention, the term "polylactide oligomer having a carboxyl group as its terminal group" means that the terminal end of the polylactide oligomer is a carboxyl group. Specifically, while polylactide oligomers have a hydroxyl group at their terminal end, in this invention, it means that such a hydroxyl group has been modified into a carboxyl group. For this purpose, reactions using a variety of substances can be utilized, and in this invention, succinyl chloride is used for the modification. This will be further elaborated in the examples described later.

[0017] The polylactide oligomer having a carboxyl group as its terminal group may be any one selected from the group consisting of the following: [Chemical formula]

[0018] In the above, R is a substituent represented by the following chemical formula 2: [Chemical formula]

[0019] In the chemical formula 2, n means the number of repeating units.

[0020] The polylactide oligomer having a carboxy group as the terminal group has repeating units derived from a lactide monomer in the same manner as the polylactide resin. Therefore, not only can the biodegradable properties of the polylactide resin composition of the present invention be maintained, but it also has the characteristic of being excellent in compatibility with the polylactide resin. Further, if a compatibilizer is mixed with the polylactide resin and the polylactide oligomer having a carboxy group as the terminal group, the melt strength can be improved by a high branching effect. Further, it is possible to induce a decrease in viscosity due to an increase in the angular frequency, and not only the melt strength but also the molding processability can be improved.

[0021] The polylactide oligomer having a carboxy group as the terminal group can be adjusted according to the number of repeating units of each lactide. Preferably, the polylactide oligomer having a carboxy group as the terminal group is 1,000 to 70,000.

[0022] Preferably, 1 to 20 parts by weight of the polylactide oligomer having a carboxy group as the terminal group is included with respect to 100 parts by weight of the polylactide resin. When the content is less than 1 part by weight, the effect of using the polylactide oligomer having a carboxy group as the terminal group is slight, and when the content exceeds 20 parts by weight, there is a risk of inhibiting the inherent physical properties of the polylactide resin.

[0023] Furthermore, the polylactide resin composition according to the present invention contains a compatibilizer together with the polylactide resin and the polylactide oligomer whose terminal group is a carboxyl group.

[0024] Preferably, the composition contains 0.1 to 10 parts by weight of the compatibilizer per 100 parts by weight of the polylactide resin. If the content is less than 0.1 parts by weight, the effect of the compatibilizer is minimal, and if the content exceeds 10 parts by weight, it may impair the physical properties of the polylactide resin composition.

[0025] Preferably, the compatibilizer is represented by the following formula: [ka]

[0026] In the above, x, y, and z represent the mole fraction of each repeating unit. R is a heteroatom, or C may be unsubstituted or substituted with one or more functional moieties. 1-10 It is hydrocarbil, n represents the repeating unit.

[0027] As an example, the aforementioned compatibilizer can be a commercially available product, and typically, the epoxy compatibilizer Joncryl ADR 4468 can be used.

[0028] On the other hand, 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, the polylactide oligomer having carboxyl groups as terminal groups, and a compatibilizer. For example, each of the above components can be melt-mixed. [Effects of the Invention]

[0029] The polylactide resin composition according to the present invention, as described above, contains a polylactide oligomer whose terminal groups are carboxyl groups, and while maintaining the advantage of biodegradability, it is characterized by excellent melt strength due to a high branching effect. Furthermore, due to the improved melt strength, the polylactide resin composition can be applied to molding processes such as blowing, blow molding, spinning, foaming, and paper coating. [Brief explanation of the drawing]

[0030] [Figure 1] This shows the results of an experimental example of the present invention. [Figure 2] This shows the results of an experimental example of the present invention. [Figure 3] This shows the results of an experimental example of the present invention. "4032D" refers to the NW 4032D product with a weight-average molecular weight at the 200,000 level. [Figure 4] This shows the results of an experimental example of the present invention. [Modes for carrying out the invention]

[0031] The embodiments of the present invention will be described in more detail below with reference to 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 to the following examples.

[0032] [Manufacturing Example] Manufacturing of PLA oligomer Manufacturing Example 1: Manufacturing of PT-SA PLA oligomers were prepared using pentaerythritol (PT) as an initiator. Specifically, lactide and PT were added to a 500 mL reactor in a molar ratio of 100:1, totaling 75 g each. After adding Sn(Oct)2 catalyst (0.075 g), the reaction was carried out at 180°C for 5 hours to produce the oligomers. To replace the hydroxyl terminal groups of the produced oligomers with carboxyl groups (COOH), the number of moles was calculated using the amount of lactide added (g) and the number-average molecular weight (g / mol) of the produced oligomers. The total number of hydroxyl terminal groups of the produced oligomers was calculated considering the number of terminal groups (4) of the initiator (PT). Next, succinic anhydride (SA) in an amount equivalent to 2 equivalents of the total hydroxyl terminal groups of the oligomers was added to one pot, and the reaction proceeded for an additional 3 hours. After the reaction was complete, the PLA oligomer prepared in the CHCl3 / MeOH solvent system was precipitated and separated to remove unreacted SA and any remaining impurities. The final product was obtained by vacuum drying at 45°C for 12 hours and was named "PT-SA".

[0033] Manufacturing Example 2: Manufacturing of GL-SA PLA oligomers were manufactured using the same method as in Manufacturing Example 1, except that glycerol (GL) was used instead of pentaerythritol (PT), and these were named "GL-SA".

[0034] Manufacturing Example 3: Manufacturing of SB-SA The PLA oligomer was manufactured using the same method as in Manufacturing Example 1, except that D-Sorbitol (SB) was used instead of Pentaerythritol (PT), and this was named "SB-SA".

[0035] Manufacturing Example 4: Manufacturing of MI-SA The PLA oligomer was manufactured using the same method as in Manufacturing Example 1, except that Myo-inositol (MI) was used instead of Pentaerythritol (PT), and this was named "MI-SA".

[0036] Manufacturing Example 5: Manufacturing of GL-O A PLA oligomer was produced in the same manner as in Production Example 1, except that glycerol (GL) was used instead of pentaerythritol (PT) and reacted with succinic anhydride (SA). This oligomer was named "GL-O".

[0037] The weight-average molecular weight was determined for the PLA oligomers produced in the above production examples 1 to 5. Specifically, the weight-average molecular weight (Mw) was measured using a GPC (Gel Permeation Chromatography) instrument, and the specific measurement conditions are as follows. - Column: PLgel Mixed Ex2 - Solvent: THF -Flow rate: 0.7mL / min -Sample concentration: 3.0 mg / mL -Injection volume: 100μl - Column temperature: 40°C -Detector:Waters 2414 RID -Standard: PS (Polystyrene)

[0038] The results are shown in Table 1 below.

[0039] [Example] Production of polylactide resin composition

[0040] Example 1 Melt blending was carried out using a Brabender Mixer. Specifically, 50g of PLA pellets (Anhui BBCA Biochemical & Futerro PLA Corp, FY201, Mw=113,000), 2.5g of GL-SA (pre-produced as a PLA oligomer), and 0.5g of epoxy compatibilizer (Joncryl ADR 4468) were mixed and simultaneously fed into the Brabender Mixer. The mixture was mixed at 200°C for 10 minutes to produce a polylactide resin composition.

[0041] Examples 2-12 As shown in Table 1 below, a polylactide resin composition was prepared in the same manner as in Example 1, except that the types and contents of the remaining components other than PLA pellets were changed.

[0042] Comparative Examples 1-7 As shown in Table 1 below, polylactide resin compositions were prepared in the same manner as in Example 1, except that the types and amounts of the remaining components other than PLA pellets were changed. In Table 1, a content of 0 for each component means that the composition was omitted from the preparation. [Table 1]

[0043] Experimental example: Rheological property evaluation The rheological properties were measured using TA Instruments' ARES-G2 Rheometer (Strain-Controlled Type / Geometry: 25mm diameter parallel plate, 1mm gap). - Measurement conditions: 180°C Temperature, 0.1 rad / s ~ 500 rad / s Angular Frequency, 5 ~ 10% Strain - Amplitude Sweep allows for appropriate strain setting according to the sample (between 5% and 10% for the measured PLA). - Comparison between Phase Angle and Complex Modulus (vGP Plot): Phase Angle is a criterion for determining whether the behavior of a sample is closer to that of a solid or a fluid. Generally, the closer it is to a solid, the higher the Complex Modulus (unlike linear polymers, if LCB is present, the relationship is not linear and inflection occurs).

[0044] The results are shown in Figures 1-4. As shown in Figures 1-4, increasing the content of the compatibilizer or PLA-SA-Oligomer alone did not yield a significant branching effect in polylactide resins with low acid values ​​(Comparative Examples 1-4 and 6). Furthermore, when using GL-O without terminal group substitution, a molecular weight reduction phenomenon occurred (decomposition of the polylactide resin due to transesterification of the OH group) (Comparative Example 5). In addition, there was no branching effect when using a combination of polylactide resin, SA, and compatibilizer instead of PLA-SA-oligomer (Comparative Example 7). However, when the compatibilizer and PLA-SA-Oligomer were applied simultaneously as in the present invention, it was confirmed that the melt strength was improved by increasing the complex viscosity (Examples 1-12).

Claims

1. Polylactide resin and Polylactide oligomers whose terminal group is a carboxyl group, Contains a compatibilizer, Polylactide resin composition.

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

3. The polylactide resin is mixed with 1 to 20 parts by weight of a polylactide oligomer whose terminal group is a carboxyl group. The polylactide resin composition according to claim 1.

4. The polylactide oligomer having a carboxyl group as its terminal group is one selected from the group consisting of the following: Polylactide resin composition according to claim 1: 【Chemistry 1】 In the above, R is a substituent represented by the following chemical formula 2: 【Chemistry 2】 。

5. The polylactide oligomer whose terminal group is a carboxyl group is 1,000 to 70,000. The polylactide resin composition according to claim 1.

6. The mixture contains 0.1 to 10 parts by weight of the compatibilizer per 100 parts by weight of the polylactide resin. The polylactide resin composition according to claim 1.

7. The aforementioned compatibilizer is represented as follows: Polylactide resin composition according to claim 1: 【Transformation 3】 In the above, x, y, and z represent the mole fraction of each repeating unit. R is a heteroatom, or C which is unsubstituted or may be substituted with one or more functional moieties. １－１０ It is hydrocarbil, n represents the repeating unit.

8. The weight-average molecular weight of the aforementioned compatibilizer is 1,000 to 70,000. The polylactide resin composition according to claim 1.

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