Polylactide resin composition with excellent crystallization half-life and method for producing same

Abstract

The present invention relates to a polylactide resin composition using a specific nucleating agent in combination, which has excellent crystallization half-life and crystallinity, and therefore has excellent processability while maintaining the properties inherent to the polylactide resin of the present invention.

Description

[Technical Field]

[0001] Cross-reference to related application(s) This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0035553, filed March 22, 2022, and all contents disclosed in the documents of this Korean patent application are incorporated herein by reference.

[0002] The present invention relates to a polylactide resin composition having an excellent crystallization half-life and a method for producing the same. [Background technology]

[0003] Polylactide (or polylactic acid; PLA) resin is an eco-friendly material that is manufactured from bio-based raw 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 potential alternative to existing crude oil-based resins as a solution to the use of waste plastics and carbon emission regulations.

[0004] Furthermore, polylactide resins are advantageous in that they are less expensive than other biodegradable polymers and have high tensile strength and modulus properties.

[0005] However, polylactide resins have the drawback of having a long molding cycle due to the slow crystallization rate caused by the short repeating rigid polymer backbone and slow chain mobility, which reduces productivity. To address this issue, much research is being conducted into improving productivity and heat resistance by introducing substances such as nucleating agents.

[0006] Typically, nucleating agents are primarily inorganic, such as talc, mica, and nanoclay. Adding some of these nucleating agents during molding of PLA can improve heat resistance and strength. However, excessive use of these nucleating agents can increase the resin's specific gravity and reduce transparency. Organic nucleating agents, such as LAK301 (aromatic sulfonate drivate), sodium benzoate, N-aminophthalimide, phthalhydrazide, and cadmium phenylmalonate, are used to improve crystallinity and transparency. However, these materials are not biobased and can have dispersion issues with PLA resin.

[0007] Therefore, it is necessary to introduce a bio-based organic nucleating agent that can be manufactured as an eco-product and does not impair transparency. It is also necessary to introduce a nucleating agent that has minimal dispersion problems with polylactide resin to further improve the crystallization half-life and crystallinity of polylactide resin. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a polylactide resin composition having an excellent crystallization half-life by using a combination of specific 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, The polylactide resin composition has a crystallization half-life of 2 minutes or less at a crystallization temperature of 100 to 130°C. 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 context, "lactide monomer" can be defined as follows. Lactides are 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.

[0015] On the other hand, the polylactide resin according to the present invention has a weight average molecular weight of, for example, 70,000 to 400,000.

[0016] The present invention is characterized in that the crystallization half-life of such a polylactide resin is improved by using both the first and second nucleating agents in the polylactide resin.

[0017] In particular, the polylactide resin composition is characterized by having a crystallization half-life of 5 minutes or less at a crystallization temperature of 100 to 130°C. Preferably, the crystallization half-life is 1.9 minutes or less, 1.8 minutes or less, 1.7 minutes or less, 1.6 minutes or less, 1.5 minutes or less, 1.4 minutes or less, 1.3 minutes or less, 1.2 minutes or less, 1.1 minutes or less, or 1.0 minute or less. Also, the crystallization half-life is 0.1 minutes or more, 0.2 minutes or more, 0.3 minutes or more, 0.4 minutes or more, or 0.5 minutes or more.

[0018] The term "crystallization half-time (t)" used in the present invention 1 / 2 )) refers to the time (minutes) required for 50% crystallization to occur and is a useful index for evaluating the relative crystallization rate. To determine the crystallization half-life, the relative crystallinity is first determined. Relative crystallinity refers to the ratio of the area of ​​the exothermic peak at time t to the total area during the isothermal crystallization process. After converting it to relative crystallinity as a function of time, the time at which the relative crystallinity reaches 0.5 can be determined as the crystallization half-life. This process is shown diagrammatically in Figure 1, and more detailed measurement methods can be found in the Examples below.

[0019] The term "crystallization temperature" used in the present invention refers to the temperature at which a polylactide resin is cooled after being melted to a predetermined temperature in order to measure the crystallization half-life. For example, when a polylactide resin is melted at 200°C and then cooled to 120°C at a cooling rate of 40°C / min to 100°C / min, 120°C is referred to as the "crystallization temperature." In the present invention, the crystallization temperature is 100 to 130°C, for example, 100°C, 110°C, 120°C, or 130°C. Specific methods for measuring the crystallization half-life based on the crystallization temperature can be embodied in the following examples.

[0020] Preferably, the polylactide resin composition according to the present invention has a crystallinity of 35% or more at a crystallization temperature of 100 to 130°C. As described above, the polylactide resin composition according to the present invention is characterized by an excellent crystallinity as well as a long crystallization half-life. Preferably, the crystallinity is 40% or more, 45% or more, or 50% or more. The method for measuring the crystallinity can be embodied in the following examples.

[0021] Meanwhile, the first nucleating agent is uracil, a bio-based organic material that is added to the polylactide resin and acts as a nucleation site to induce crystal nucleation at high temperatures, thereby improving the crystallization half-life and degree of crystallization.

[0022] Preferably, 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. If the content is less than 0.1 wt %, the effect of using the first nucleating agent is negligible, while if the content is more than 5 wt %, the inherent physical properties of the polylactide resin may be impaired. More preferably, the first nucleating agent is contained 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 based on the total weight of the polylactide resin composition; or 4.5 wt % or less, 4.0 wt % or less, or 3.5 wt % or less.

[0023] The second nucleating agent is a nucleating agent containing a lactide monomer oligomer structure, and due to its high compatibility with polylactide resins due to this lactide monomer oligomer structure, it is added to polylactide resins to function similar to a plasticizer, thereby forming free volume within the polylactide resin and improving chain mobility of the polylactide resin, thereby improving the crystallization half-life and degree of crystallization.

[0024] Preferably, the second nucleating agent is a compound represented by the following Chemical Formula 1: [Chemical formula 1] [ka] In the above Chemical Formula 1, L is: [ka] In the above, n1 is an integer from 1 to 30, R is a substituent represented by the following chemical formula 2: [Chemical formula 2] [ka] 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 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 content is less than 3 wt %, the effect of using the second nucleating agent is negligible, while if the content 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 based on the total weight of the polylactide resin composition; or 24 wt % or less, 23 wt % or less, 22 wt % or less, or 21 wt % or less.

[0027] 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, the first nucleating agent, and the second nucleating agent. For example, the components can be produced by melt blending. [Effects of the Invention]

[0028] The polylactide resin composition according to the present invention has an excellent crystallization half-life and crystallinity, and therefore has excellent processability while maintaining the inherent properties of the polylactide resin according to the present invention. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic representation of what is meant by crystallization half-life according to the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0030] 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.

[0031] Manufacturing Example: Second Nucleating Agent (Manufacturing of P10-A-002) An oligomer was prepared using PEG-1000 (P10) as an initiator. Specifically, a total of 4.5 g of lactide:P10 was placed in a 20 mL vial at an 8:1 molar ratio. Sn(Oct)2 catalyst was added at 0.1-0.2 wt% and the mixture was reacted 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 secondary nucleating agent with an acetyl-substituted terminal structure. This was designated P10-A-002, and its weight-average molecular weight is shown in Table 1. [Example]

[0032] Examples and Comparative Examples Melt blending was performed using a Haake mixer. Specifically, 65 g of PLA pellets (NatureWorks 4032D; weight-average molecular weight approximately 200,000) were added, followed by the first and second nucleating agents listed in Table 1 below, according to their respective amounts. The powder-type nucleating agent was mixed with the PLA pellets before addition, while the nucleating agent with a melting point lower than the process operating temperature (180°C) was added to the hopper after 5 minutes of blending (when the PLA was completely dissolved). The operation conditions were 180°C, 60 rpm, and 10 minutes. The resulting PLA resin was subjected to isothermal DSC analysis (described below) to confirm its crystallization behavior at each crystallization temperature.

[0033] 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.

[0034] 1) Weight average molecular weight Using GPC (Gel Permeation Chromatography) equipment, 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: -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)

[0035] 2)DSC(differential scanning calorimetry) Each of the PLA resins produced in the examples and comparative examples was subjected to the first heating (1 st The PLA was then completely melted at 200°C for 20 minutes through heating to remove the thermal history. It was then cooled as rapidly as possible at 100°C / min to each crystallization temperature (100-130°C), and the heat flow was observed while maintaining the temperature at each crystallization temperature to measure the crystallization half-life. The crystallinity, Xc, was calculated using the following equation (100% crystalline PLA ΔHm=93 J / g).

[0036] Crystallinity: (exothermic peak area during cooling, ΔHc) / (100% crystalline PLA ΔHm) The results are shown in Table 1 below. [Table 1]

[0037] As shown in Table 1, in the examples in which the first and second nucleating agents were used simultaneously according to the present invention, the crystallinity was at the same or similar level as compared to the comparative examples, but the crystallization half-life was significantly shorter.

Claims

1. A polylactide resin composition comprising: a polylactide resin; a first nucleating agent; and a second nucleating agent, the first nucleating agent is uracil, and is included in an amount of 0.1 to 5 wt % based on the total weight of the polylactide resin composition; the second nucleating agent is a compound containing a lactide oligomer structure having a weight average molecular weight of 1,000 to 10,000, and is included in an amount of 3 to 25 wt % based on the total weight of the polylactide resin composition; The polylactide resin composition has a crystallization half-life of 2 minutes or less at a crystallization temperature of 100 to 130°C. Polylactide resin composition.

2. The polylactide resin composition has a crystallization half-life of 1.3 minutes or less at a crystallization temperature of 100 to 130°C. The polylactide resin composition according to claim 1.

3. The polylactide resin composition has a crystallinity of 35% or more at a crystallization temperature of 100 to 130°C. The polylactide resin composition according to claim 1.

4. The second nucleating agent is a compound represented by the following Chemical Formula 1: The polylactide resin composition of claim 1: [Chemical formula 1] 【Chemical 1】 In the above Chemical Formula 1, L is as follows: 【Chemistry 2】 In the above, n1 is an integer from 1 to 30, R is a substituent represented by the following chemical formula 2: [Chemical formula 2] 【Chemistry 3】 n represents the number of repeating units, R' is hydrogen or acetyl.

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

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