Polylactide resin composition with excellent crystallinity and method for producing same

Abstract

The present invention relates to a polylactide resin composition produced by combining a specific nucleating agent and subjecting it to heat treatment, and is characterized by having excellent crystallinity.

Description

[Technical Field]

[0001] Cross-citation with related applications (etc.) This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0035554, dated March 22, 2022, and all contents disclosed in the Korean patent application and other documents are incorporated herein by reference.

[0002] The present invention relates to a polylactide resin composition having an excellent degree of crystallinity and a method for producing the same. [Background technology]

[0003] Polylactide (or polylactic acid; PLA) resin is an environmentally friendly material that is manufactured from bio-based materials, emits little carbon dioxide, a greenhouse gas, during the manufacturing process, and decomposes at a specific temperature in a composting facility. Recently, it has been attracting attention as a possible alternative to existing crude oil-based resins as a response to regulations on the use of waste plastics and carbon emissions.

[0004] Furthermore, polylactide resin has the advantage of being cheaper than other biodegradable polymers and having high tensile strength and modulus properties.

[0005] However, polylactide resins have the problem of having a rigid polymer backbone repeated in short units and a slow crystallization rate due to slow chain transfer, resulting in a long molding cycle and poor productivity. Therefore, to address these issues, much research is being conducted into improving productivity and heat resistance by introducing substances such as nucleating agents.

[0006] Typically, the nucleating agent is primarily inorganic, such as talc, mica, or nanoclay. It has been reported that adding a portion of these nucleating agents during molding of PLA can improve heat resistance and strength. However, adding an excessive amount of these nucleating agents increases the resin's specific gravity and reduces transparency. Meanwhile, organic nucleating agents such as LAK 301 (aromatic sulfonate drivate), sodium benzoate, N-aminophthalimide, phthalhydrazide, and cadmium phenylmalonate have been used to improve crystallinity and transparency. However, these materials are not bio-based and therefore have poor dispersion characteristics with PLA resin.

[0007] Therefore, there is a need to introduce bio-based organic nucleating agents that can be manufactured into environmentally friendly products without impairing transparency. Also, there is a need to introduce nucleating agents that have fewer dispersion problems with polylactide resins to further improve the crystallinity of polylactide resins. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention aims to provide a polylactide resin composition having excellent crystallinity by using a specific combination of nucleating agents.

[0009] The present invention also relates to a method for producing the polylactide resin composition. [Means for solving the problem]

[0010] In order to solve the above problems, the present invention provides the following polylactide resin composition.

[0011] A polylactide resin composition comprising a polylactide resin, a first nucleating agent, and a second nucleating agent, and heat-treated at 25 to 120°C for 1 to 30 minutes, the first nucleating agent is uracil or orotic acid; The second nucleating agent is a compound containing a lactide oligomer structure. Polylactide resin composition.

[0012] 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]

[0013] The polylactide resin may be produced by forming the repeating unit through ring-opening polymerization of a lactide monomer, and the polymer obtained after the ring-opening polymerization and the repeating unit formation processes are completed may be referred to as the "polylactide resin."

[0014] In this application, "lactide monomer" can be defined as follows. Lactide can generally 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. 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 differences in the properties of each form of lactide and the properties of polylactide resins formed therefrom.

[0015] 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.

[0016] The present invention is characterized in that the crystallinity of such a polylactide resin is improved by using the polylactide resin together with the first and second nucleating agents and by heat-treating the composition at a specific temperature for a specific time.

[0017] Preferably, the heat treatment temperature is 30° C. or higher, 40° C. or higher, 50° C. or higher, 60° C. or higher, 70° C. or higher, 80° C. or higher, or 90° C. or higher, and 115° C. or lower, or 110° C. or lower. Most preferably, the heat treatment temperature is 90 to 110° C.

[0018] Preferably, the heat treatment time is 2 minutes or more or 3 minutes or more, and 25 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, or 5 minutes or less, and most preferably, the heat treatment time is 3 to 5 minutes.

[0019] The first nucleating agent is uracil or orotic acid. The first nucleating agent is a bio-based organic material that acts as a nucleation site when added to polylactide resin, and can induce the formation of crystal nuclei at high temperatures, thereby improving the crystallization rate.

[0020] Preferably, the first nucleating agent is included in an amount of 0.1 to 5 wt % based on the total weight of the polylactide resin composition. If the amount is less than 0.1 wt %, the effect of using the first nucleating agent is negligible, while if the amount is more than 5 wt %, the inherent physical properties of the polylactide resin may be impaired. More preferably, the first nucleating agent is included in an amount of 0.2 wt % or more, 0.3 wt % or more, 0.4 wt % or more, or 0.5 wt % or more, and 4.5 wt % or less, 4.0 wt % or less, or 3.5 wt % or less based on the total weight of the polylactide resin composition. The second nucleating agent is a nucleating agent containing a lactide monomer oligomer structure, and due to this lactide monomer oligomer structure, it has high compatibility with polylactide resin and is added to the polylactide resin to function similarly to a plasticizer, thereby forming free volume within the polylactide resin, improving chain transfer and increasing the degree of crystallinity of the polylactide resin.

[0021] Preferably, the second nucleating agent is a compound represented by the following Chemical Formula 1: [Chemical formula 1] [ka]

[0022] In the above formula 1, L is any one selected from the group consisting of: [ka]

[0023] In the above, n1 is an integer from 1 to 4, n2 is an integer from 1 to 30, R is a substituent represented by the following chemical formula 2: [Chemical formula 2] [ka]

[0024] n represents the number of repeating units, R' is hydrogen or acetyl.

[0025] The weight-average molecular weight of the second nucleating agent can be adjusted by adjusting the number of each lactide repeating unit. Preferably, the weight-average molecular weight of the second nucleating agent is 1,000 to 50,000. More preferably, the weight-average molecular weight of the second nucleating agent is 1,100 or more, 1,200 or more, 1,300 or more, 1,400 or more, or 1,500 or more, and 40,000 or less, 30,000 or less, 20,000 or less, 10,000 or less, 9,000 or less, or 8,000 or less.

[0026] Preferably, the second nucleating agent is included in an amount of 3 to 25 wt % based on the total weight of the polylactide resin composition. If the amount is less than 3 wt %, the effect of using the second nucleating agent is negligible, while if the amount is more than 25 wt %, the inherent physical properties of the polylactide resin may be impaired. More preferably, the second nucleating agent is included in an amount of 3.5 wt % or more, 4.0 wt % or more, or 4.5 wt % or more, and 24 wt % or less, 23 wt % or less, 22 wt % or less, or 21 wt % or less based on the total weight of the polylactide resin composition.

[0027] Meanwhile, the method for producing the polylactide resin composition according to the present invention includes the steps of producing the polylactide resin composition (Step 1) and heat-treating the polylactide resin composition produced in Step 1 at 25 to 120°C for 1 to 30 minutes (Step 2). The heat-treatment temperature and time in Step 2 are as described above. [Effects of the Invention]

[0028] The polylactide resin composition according to the present invention described above has excellent crystallinity and processability, and can maintain the properties inherent to polylactide resin. DETAILED DESCRIPTION OF THE INVENTION

[0029] 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]

[0030] Preparation Example 1: Preparation of second nucleating agent (P10-A-oligomer) An oligomer was prepared using PEG-1000 (P10) as an initiator. Specifically, a total of 4.5 g of lactide:P10 was poured into a 20 mL vial at a molar ratio of 16:1. Sn(Oct)2 catalyst was added at 0.1-0.2 wt% and the reaction was carried out at 130°C for 4 hours. The temperature was then adjusted to 120°C, and acetic anhydride (4 equivalents per terminal OH group) was added, and the reaction was continued for an additional 12 hours. After the reaction was completed, the by-product acetic acid and residual acetic anhydride were removed by vacuum drying to prepare a second nucleating agent with a structure in which the terminal groups were substituted with acetyl groups. This was designated P10-A002, and its weight-average molecular weight is shown in Tables 1 to 3 below.

[0031] Preparation Example 2: Secondary Nucleating Agent (Preparation of SB-Oligomer) Oligomers were prepared using sorbitol (SB) as an initiator. Specifically, a total of 4.5 g of lactide:SB was poured into a 20 mL vial at a molar ratio of 24:1, and Sn(Oct)2 catalyst was added at 0.1 to 0.2 wt%. The mixture was then reacted at 130°C for 4 hours. After vacuum drying, the mixture was cooled to room temperature to prepare a secondary nucleating agent, designated SB-O-002. The weight-average molecular weight is shown in Tables 1 to 3 below.

[0032] Examples and Comparative Examples 65 g of PLA pellets (NatureWorks 4032D; weight average molecular weight approximately 200,000) were mixed with the primary nucleating agent listed in Tables 1 to 3 below according to the respective content. The mixture was placed in a Haake mixer and mixed at 180°C for 5 minutes at 60 rpm. The secondary nucleating agent listed in Table 1 below was then added according to the respective content and mixed at 180°C for 5 minutes at 60 rpm. In Tables 1 to 3 below, the content of the primary nucleating agent and the secondary nucleating agent is expressed as wt% of the total content of the PLA resin, the primary nucleating agent, and the secondary nucleating agent.

[0033] The mixture was placed in a vacuum oven and dried at 85°C for 4 hours, and then placed in a convection oven and heat-treated at the temperatures and times shown in Tables 1 to 3 below to prepare polylactide resin compositions.

[0034] Experimental Example The physical properties of the first nucleating agent, the second nucleating agent, and the polylactide resin composition prepared above were measured by the following methods.

[0035] 1) Weight average molecular weight Using a GPC (Gel Permeation Chromatography) device, the number average molecular weight (Mn) and weight average molecular weight (Mw) were calculated, and the oligomer molecular weight distribution (Mw / Mn) was measured. The specific measurement conditions are as follows:

[0036] -Column: PLgel Mixed E x 2 Solvent: THF -Flow rate: 0.7mL / min -Sample concentration: 3.0 mg / mL -Injection volume: 100μl -Column temperature: 40℃ -Detector: Waters 2414 RID -Standard: PS (Polystyrene)

[0037] 2)DSC(differential scanning calorimetry) To confirm the effect of the annealing thermal history of the blended PLA samples, Crystallinity analysis was performed during the first heating phase. DSC measurements were performed by heating the sample to 250°C, above the melting point of PLA, at a heating rate of 10°C / min. ΔHm, the melting peak during heating, was measured, and the crystallinity Xc was calculated using the following formula (100% crystalline PLA ΔHm=93 J / g). -1 st Run crystallinity: 1 st Area of ​​the endothermic peak in the thermogram, ΔHm) / 100% crystalline PLA ΔHm) × 100

[0038] [Table 1] [Table 2] [Table 3]

[0039] As shown in Tables 1 to 3, in the examples in which both the first and second nucleating agents were used according to the present invention, it was confirmed that the crystallization temperature and degree of crystallinity were improved even at low contents.

Claims

1. 1) mixing a polylactide resin, a first nucleating agent, and a second nucleating agent to produce a mixture; 2) drying the mixture in a vacuum oven at 85°C for 4 hours to produce a polylactide resin composition; 3) heat-treating the polylactide resin composition prepared in the step above at 25 to 120°C for 1 to 30 minutes; A method for producing a polylactide resin composition, comprising: the first nucleating agent is uracil or orotic acid; The method for producing a polylactide resin composition, wherein the second nucleating agent is a compound containing a lactide oligomer structure.

2. The temperature of the heat treatment is 90 to 110°C. A method for producing the polylactide resin composition according to claim 1.

3. The heat treatment time is 3 to 5 minutes. A method for producing the polylactide resin composition according to claim 1.

4. The polylactide resin composition has a crystallinity of 30% or more. A method for producing the polylactide resin composition according to claim 1.

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

6. The first nucleating agent is contained in an amount of 0.1 to 5 wt % based on the total weight of the polylactide resin composition. A method for producing the polylactide resin composition according to claim 1.

7. The first nucleating agent is contained in an amount of 0.5 to 3.5 wt % based on the total weight of the polylactide resin composition. A method for producing the polylactide resin composition according to claim 1.

8. The second nucleating agent is a compound represented by the following Chemical Formula 1: A method for producing the polylactide resin composition according to claim 1. [Chemical formula 1] 【Chemistry 1】 In the above Chemical Formula 1, L is any one selected from the group consisting of: 【Chemistry 2】 In the above, n1 is an integer from 1 to 4, n2 is an integer from 1 to 30; R is a substituent represented by the following chemical formula 2: [Chemical formula 2] 【Transformation 3】 n represents the number of repeating units; R' is hydrogen or acetyl.

9. The weight average molecular weight of the second nucleating agent is 1,000 to 50,000. A method for producing the polylactide resin composition according to claim 1.

10. The second nucleating agent is contained in an amount of 3 to 25 wt % based on the total weight of the polylactide resin composition. A method for producing the polylactide resin composition according to claim 1.

11. The second nucleating agent is contained in an amount of 4.5 to 21 wt % based on the total weight of the polylactide resin composition. A method for producing the polylactide resin composition according to claim 1.

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