Highly branched polylactide resin and method for producing same

Abstract

The present invention uses a specific branching agent, a phosphorus-based compound, and an anhydride-based compound for polylactide resin, thereby enabling high branching of polylactide resin that was not previously possible, and is characterized in that it can be applied to processes that were previously difficult to apply to polylactide resin, such as foaming.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0051459, filed on April 26, 2022, and all contents disclosed in the documents of said Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a polylactide resin composition, a highly branched polylactide resin produced therefrom, and a method for producing the same. [Background technology]

[0003] Conventional petroleum-based plastic materials do not decompose naturally, causing serious environmental pollution, and finding alternative materials has become a top research priority in recent years. In particular, plastic foam is widely used as a packaging cushioning material, but the most commonly used type, EPS (Expanded Polystyrene), not only does not decompose, but also causes environmental pollution by emitting toxic gases when burned.

[0004] Polylactide (or polylactic acid; PLA) resin, a promising alternative to petroleum-based plastics, is manufactured from bio-based raw materials and emits little greenhouse gas carbon dioxide during the manufacturing process. It is also an eco-friendly material that decomposes at specific temperatures and in composting facilities. Furthermore, polylactide resin has the advantages of being less expensive than other biodegradable polymers and possessing high tensile strength and modulus properties.

[0005] However, polylactide resin has the disadvantages of low thermal stability and impact resistance, slow crystallization, and particularly low melt strength, making it difficult to use in foam applications.Therefore, various methods are known to improve the melt strength of polylactide resin, one of which is to extend the long chain branches (LCB) of polylactide resin to branch it.

[0006] Although various branching agents applicable to polylactide resins have been known in the past, there were limitations to how highly branched the polylactide resin could be achieved. Therefore, in the present invention, the inventors have confirmed that by using a specific branching agent and an anhydride-based compound with polylactide resin, a high level of branching of polylactide resin that was previously unattainable can be achieved, leading to the completion of the present invention. Summary of the Invention [Problem to be solved by the invention]

[0007] The present invention provides a polylactide resin composition for producing a highly branched polylactide resin.

[0008] The present invention also relates to a highly branched polylactide resin produced from the polylactide resin composition, and a method for producing the same. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides the following polylactide resin composition: 100 parts by weight of polylactide resin, 0.05 to 1.0 parts by weight of a phosphorus-based compound, and 0.05 to 1.0 parts by weight of an organic acid anhydride, and 0.1 to 5.0 parts by weight of a branching agent represented by the following formula 1: Polylactide resin composition: [Chemical formula 1] [ka]

[0010] In the above Chemical Formula 1, R is [ka] is.

[0011] 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]

[0012] The polylactide resin is 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 referred to as the "polylactide resin."

[0013] In this context, "lactide monomer" is defined as follows: Lactide is generally classified into L-lactide, which is made from L-lactic acid; D-lactide, which is made from D-lactic acid; and meso-lactide, which is made from 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. However, in this specification, "lactide monomer" is defined to include all forms of lactide, regardless of the differences in the properties of each form and the properties of the polylactide resins formed therefrom.

[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 term "organic acid anhydride" as used herein refers to a compound in which water molecules have been removed from an organic acid. In particular, in the present invention, the organic acid anhydride reacts with the terminal hydroxyl groups (-OH) of a polylactide resin to give the polylactide resin a terminal carboxyl group (-COOH). This facilitates the reaction between the terminal carboxyl groups of the polylactide resin and the epoxy groups present in the branching agent, thereby inducing a high degree of branching of the polylactide resin.

[0016] From this viewpoint, the organic acid anhydride is not particularly limited as long as it reacts with the terminal hydroxyl group (-OH) of the polylactide resin to give a carboxyl group (-COOH) at the terminal of the polylactide resin. Examples thereof include succinic anhydride, maleic anhydride, phthalic anhydride, and pyromellitic dianhydride.

[0017] Preferably, the organic acid anhydride is contained in an amount of 0.06 parts by weight or more, 0.07 parts by weight or more, 0.08 parts by weight or more, 0.09 parts by weight or more, or 0.10 parts by weight or more, per 100 parts by weight of the polylactide resin; or 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, 0.6 parts by weight or less, 0.5 parts by weight or less, 0.4 parts by weight or less, 0.3 parts by weight or less, or 0.2 parts by weight or less.

[0018] The branching agent of Chemical Formula 1 is a polyhedral oligomeric silsesquioxane (POSS) compound in which each silicon (Si) atom is substituted with a glycidyl group. The epoxy group of the glycidyl reacts with a polylactide resin having a carboxyl (-COOH) group at its terminal, thereby branching the polylactide resin.

[0019] Preferably, the branching agent of Chemical Formula 1 is included in an amount of 0.2 parts by weight or more, 0.3 parts by weight or more, 0.4 parts by weight or more, 0.5 parts by weight or more, 0.6 parts by weight or more, 0.7 parts by weight or more, 0.8 parts by weight or more, 0.9 parts by weight or more, 1.0 part by weight or more, 4.0 parts by weight or less, 3.0 parts by weight or less, or 2.0 parts by weight or less, based on 100 parts by weight of the polylactide resin.

[0020] The phosphorus-based compound acts as a nucleophile to induce ring opening of the epoxy group of the branching agent of Formula 1, resulting in chain extension. If the phosphorus-based compound is not added, the reaction between the polylactide resin and the branching agent of Formula 1 does not occur under typical mixing conditions.

[0021] Preferably, the phosphorus-based compound is a compound represented by the following Chemical Formula 2: [Chemical formula 2] [ka]

[0022] In the above Chemical Formula 2, R1, R2 and R3 are each independently C 1-20 Alkyl; C 3-20 Cycloalkyl; unsubstituted or containing one or more C 1-20 Alkyl, or C 1-20 phenyl substituted with alkoxy; or benzyl.

[0023] Preferably, the phosphorus-based compound is triphenylphosphine, tri-m-tolylphosphine, diphenyl(para-tolyl)phosphine, tris(2,6-dimethoxyphenyl)phosphine, tris(4-methoxyphenylphosphine, trimesitylphosphine, tris-3,5-xylylphosphine, tricyclohexylphosphine, tribenzylphosphine, benzyldiphenylphosphine, or diphenyl-normal-propylphosphine, and more preferably triphenylphosphine.

[0024] Preferably, the phosphorus-based compound is included in an amount of 0.06 parts by weight or more, 0.07 parts by weight or more, 0.08 parts by weight or more, 0.09 parts by weight or more, or 0.10 parts by weight or more, based on 100 parts by weight of the polylactide resin; or 0.9 parts by weight or less, 0.8 parts by weight or less, 0.7 parts by weight or less, 0.6 parts by weight or less, 0.5 parts by weight or less, 0.4 parts by weight or less, 0.3 parts by weight or less, or 0.2 parts by weight or less.

[0025] The present invention also provides a branched polylactide resin produced by heat treating the above-mentioned polylactide resin composition.

[0026] As described above, the branching agent contained in the polylactide resin composition reacts with the polylactide resin having a carboxyl (-COOH) group at its terminal to branch the polylactide resin, and a specific heat treatment is carried out for this reaction. A specific method for producing the branched polylactide resin will be described later.

[0027] As the branching of the polylactide resin progresses, the branched polylactide resin has a higher molecular weight than the polylactide resin contained in the polylactide resin composition. Preferably, the branched polylactide resin has a weight-average molecular weight of 200,000 to 800,000. Also, preferably, the weight-average molecular weight of the branched polylactide resin is increased by 1.5 to 5.0 times compared to the polylactide resin contained in the polylactide resin composition.

[0028] More preferably, the weight average molecular weight of the branched polylactide resin is 250,000 or more, 300,000 or more, or 350,000 or more, and 750,000 or less, 700,000 or less, 650,000 or less, 600,000 or less, or 550,000 or less.

[0029] Furthermore, as the branching proceeds, the molecular weight distribution (Mw / Mn) of the branched polylactide resin preferably becomes 1.5 to 3.0, and more preferably, the molecular weight distribution (Mw / Mn) of the branched polylactide resin is 1.8 or more, or 1.9 or more, and 2.9 or less, 2.8 or less, 2.7 or less, 2.6 or less, or 2.5 or less.

[0030] Preferably, the Z-average molecular weight of the branched polylactide resin is 1,000,000 to 2,000,000.

[0031] The present invention also provides a method for producing the branched polylactide resin described above, comprising the steps of: 1) mixing polylactide resin and organic acid anhydride at 170°C to 200°C (Step 1); and 2) Mixing the branching agent of Formula 1 and the phosphorus-based compound with the product of Step 1 (Step 2).

[0032] Step 1 is a step of reacting the terminal hydroxyl group (-OH) of the polylactide resin with an organic acid anhydride to give a carboxyl group (-COOH) at the terminal of the polylactide resin, which is performed before the polylactide resin reacts with the branching agent.

[0033] Step 2 is a step of preparing a branched polylactide resin according to the present invention by reacting the polylactide resin having a terminal carboxy group (—COOH) obtained in Step 1 with the epoxy group of the branching agent of Chemical Formula 1 and adding the phosphorus-based compound to open the ring of the epoxy group.

[0034] Preferably, the mixing time in step 1 is 30 seconds to 3 minutes. Preferably, the mixing time in step 2 is 3 minutes to 15 minutes. [Effects of the Invention]

[0035] The branched polylactide resin according to the present invention is characterized in that it is highly branched and can be applied to processes that have been difficult to apply to conventional polylactide resins, such as foaming. DETAILED DESCRIPTION OF THE INVENTION

[0036] 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. [Example]

[0037] Example 1 50 g of PLA (NatureWorks 4032D; weight average molecular weight approximately 210,000) and 0.2 wt% of succinic anhydride as an anhydride-based substance based on the PLA weight were added to a Brabender mixer and mixed for 2 minutes at 180°C. After pausing for a while, an additional branching agent (hybrid's Glycidyl POSS cage mixture; product number EP0409; hereafter referred to as "POSS") was added at 1 wt% based on the PLA weight and 0.2 wt% of TPP, and mixed for 10 minutes to produce branched polylactide resins.

[0038] Examples 2 to 10 As shown in Table 1 below, branched polylactide resins were prepared in the same manner as in Example 1, except that the type and content of the anhydride-based substance, the content of the branching agent, and / or the content of TPP were changed.

[0039] Comparative Examples 1 to 6 Polylactide resins were prepared in the same manner as in Example 1, except that the types or amounts of anhydride compounds, TPP (triphenylphosphine), and branching agents were varied as shown in Table 1 below.

[0040] Experimental example The branching degree of the resins prepared in the examples and comparative examples was measured using MALS-GPC. The Mw, Mz, PDI, and Mark-Houwink slope were measured under the following specific measurement conditions:

[0041] Column: PLgel mixed-Bx2 Solvent: Tetrahydrofuran (Stabilized with BHT) Flow rate: 1.0ml / min Sample concentration: 3.0 mg PLA / 1.0 mL THF Injection volume: 100μl Column temperature: 40℃ Detector: Viscotek TDA 305 Data processing: OmniSEC The higher the Mw, Mz and PDI values, and the lower the Mark-Houwink slope, the better the branching. The results are shown in Table 1 below. [Table 1]

[0042] As shown in Table 1, the Examples according to the present invention had higher molecular weight distributions and lower Mark-Houwink slopes than the Comparative Examples, demonstrating good branching. In particular, it was confirmed that no branching of POSS occurred when TPP was not used, and there was almost no difference between the cases where TPP was used at 0.1 wt% and 0.2 wt%. Furthermore, it was confirmed that when an anhydride-based compound was used to replace the terminal -OH groups of the polylactide resin with -COOH groups, it reacted more readily with the epoxy groups of POSS, resulting in better branching than when POSS was used alone. In the case of maleic anhydride, the highest molecular weight was obtained, but the formation of a large amount of gel was also visible to the naked eye.

Claims

1. 100 parts by weight of polylactide resin, 0.05 to 1.0 parts by weight of organic acid anhydride, 0.05 to 1.0 parts by weight of a phosphorus-based compound represented by the following Chemical Formula 2, and 0.1 to 5.0 parts by weight of a branching agent of the following formula 1: Polylactide resin composition: [Chemical formula 1] 【Chemical 1】 In the above Chemical Formula 1, R is 【Chemistry 2】 and [Chemical formula 2] 【Chemistry 3】 In the above Chemical Formula 2, R1, R2, and R3 are each independently C1-20 alkyl; C3-20 cycloalkyl; phenyl that is unsubstituted or substituted with one or more C1-20 alkyl or C1-20 alkoxy; or benzyl.

2. The organic acid anhydride is succinic anhydride, maleic anhydride, phthalic anhydride, or pyromellitic dianhydride; The polylactide resin composition according to claim 1.

3. The organic acid anhydride is contained in an amount of 0.1 to 0.2 parts by weight. The polylactide resin composition according to claim 1.

4. The phosphorus-based compound is triphenylphosphine. The polylactide resin composition according to claim 1.

5. The branching agent of formula 1 is contained in an amount of 0.5 to 2.0 parts by weight. The polylactide resin composition according to claim 1.

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

7. A branched polylactide resin produced by heat treating the polylactide resin composition according to any one of claims 1 to 6.

8. The branched polylactide resin has a weight average molecular weight of 200,000 to 800,000. The branched polylactide resin of claim 7.

9. The branched polylactide resin has a weight average molecular weight of 350,000 to 550,000. The branched polylactide resin of claim 7.

10. The branched polylactide resin has a Z-average molecular weight of 1,000,000 to 2,000,000. The branched polylactide resin of claim 7.

11. The molecular weight distribution (Mw / Mn) of the branched polylactide resin is 2.0 to 3.

0. The branched polylactide resin of claim 7.

12. 1) mixing a polylactide resin and an organic acid anhydride at 170°C to 200°C (Step 1); and 2) mixing the product of step 1 with the branching agent of formula 1 and the phosphorus-based compound (step 2); A method for producing the branched polylactide resin according to claim 7.

13. The mixing time in step 1 is 30 seconds to 3 minutes. A method for producing the branched polylactide resin of claim 12.

14. The mixing time in step 2 is 3 to 15 minutes. A method for producing the branched polylactide resin of claim 12.

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