Polylactide resin composition and method for producing same

Abstract

The present invention relates to a polylactide resin composition using a combination of specific nucleating agents, which relatively increases the mobility of the high molecular weight components of the polylactide resin to improve the crystallinity, and at the same time, the amorphous regions of the polylactide resin have a low glass transition temperature, thereby lowering the glass transition temperature of the polylactide resin composition while simultaneously improving the crystallinity.

Description

[Technical Field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of priority based on Korean Patent Application No. 10-2022-0035551, filed on 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 a low glass transition temperature and excellent crystallinity, 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 materials and emits little carbon dioxide, a greenhouse gas, during the manufacturing process. It also decomposes at a specific temperature and in composting equipment. Recently, it has been attracting attention as a potential alternative to existing crude oil-based resins as a way to address the use of waste plastics and carbon emission regulations.

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

[0005] However, polylactide resin has a problem in that rigid polymer backbone chains are repeated in short units, resulting in slow crystallization speed and long molding cycles due to slow chain mobility, which reduces productivity. Therefore, in order to solve this problem, much research is being conducted to improve productivity and heat resistance by introducing substances such as nucleating agents. In addition, polylactide resin has a brittle property, and to improve this, the T of polylactide resin is g (glass transition temperature) must be low.

[0006] Therefore, a method is needed to increase the crystallinity of polylactide resin while simultaneously lowering the glass transition temperature. However, conventional nucleating agents increase the overall chain mobility of polylactide resin, limiting their ability to simultaneously improve both properties.

[0007] Therefore, in order to simultaneously improve the above properties, the present invention has identified a method for improving the crystallinity by relatively increasing only the mobility of the high molecular weight portion of the polylactide resin, as described below, while at the same time allowing the amorphous region of the polylactide resin to have a low glass transition temperature, thereby completing the present invention. Summary of the Invention [Problem to be solved by the invention]

[0008] The present invention provides a polylactide resin composition having a low glass transition temperature and an excellent degree of crystallinity, 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: A polylactide resin composition comprising: a polylactide resin; a first nucleating agent; and a second nucleating agent, The polylactide resin composition has a glass transition temperature (T g、T ) and crystallinity are 60°C or less and 55% or more, respectively; ΔT in the following equation 1 g is 5 or more, Polylactide resin composition:

number

[0010] 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]

[0011] 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."

[0012] 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.

[0013] 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.

[0014] The present invention is characterized in that the glass transition temperature of the polylactide resin is lowered and the crystallinity is increased by using both the first and second nucleating agents in the polylactide resin.

[0015] The first nucleating agent is uracil or orotic acid. The first nucleating agent is a bio-based organic material that is added to the polylactide resin and acts as a nucleation site, inducing the generation of crystal nuclei at high temperatures and improving the crystallinity.

[0016] 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 content is less than 0.1 wt %, the effect of using the first nucleating agent is minimal, 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 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; or 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.

[0017] The second nucleating agent contains a lactide monomer oligomer structure. Due to this lactide monomer oligomer structure, it has high compatibility with polylactide resins and functions similar to a plasticizer when added to polylactide resins. This creates free volume within the polylactide resin, improving chain mobility and increasing the degree of crystallinity. Furthermore, the second nucleating agent relatively increases the mobility of the high molecular weight components of the polylactide resin, thereby increasing the degree of crystallinity of the polylactide resin. At the same time, the amorphous region of the polylactide resin has a lower glass transition temperature, thereby lowering the glass transition temperature.

[0018] Preferably, the second nucleating agent is a compound represented by the following formula 1: [ka] In the above chemical formula 1, L is any one selected from the group consisting of: [ka] In the above, n1 is an integer from 1 to 30, R is a substituent represented by the following chemical formula 2: [ka] n represents the number of repeating units, R' is hydrogen or acetyl.

[0019] The weight-average molecular weight of the second nucleating agent can be adjusted depending on 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; or 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.

[0020] 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 minimal, 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 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.

[0021] In particular, the polylactide resin composition has a glass transition temperature (T g、T ) and crystallinity of 60°C or less and 55% or more, respectively.

[0022] The term "crystallization temperature" used in the present invention refers to the temperature at which a polylactide resin composition is melted at a predetermined temperature and then cooled to measure the glass transition temperature. Specifically, when a polylactide resin composition is melted at 200°C and then cooled to 120°C at a cooling rate of 40°C / min, the temperature of 120°C is referred to as the "crystallization temperature." Next, after maintaining an isothermal temperature at the crystallization temperature for 60 minutes, the composition is cooled to -50°C at a cooling rate of 40°C / min, and then heated to 200°C at an isothermal rate of 10°C / min to measure a second heating thermogram. The half-height type of the second heating thermogram is used as the glass transition temperature (T g、T Specifically, FIG. 1 is a second heating thermogram of Example 5 described later, and as shown in FIG. 1, the heat capacity C of polylactide during the glass transition process is p Due to the change in heat capacity, a baseline shift is observed. The temperature at half-height of the two baselines is defined as the glass transition temperature. The crystallinity (%) is also calculated from the area of ​​the endothermic peak in the second heating thermogram. Specific methods for measuring the glass transition temperature and crystallinity can be found in the following examples.

[0023] Preferably, the polylactide resin composition has a glass transition temperature (T) measured at a specific temperature (T) of 120 to 130°C. g、T In other words, the polylactide resin composition of the present invention is affected by the crystallization temperature, and when the crystallization temperature is set to 120 to 130°C, the glass transition temperature (T g、T More preferably, the polylactide resin composition has a glass transition temperature (T) measured at a specific temperature (T) of 120 to 130°C. g、T On the other hand, the glass transition temperature (T g、T ) is, for example, 40°C or higher, 41°C or higher, 42°C or higher, 43°C or higher, 44°C or higher, or 45°C or higher.

[0024] In addition, the polylactide resin composition has a ΔT g is 5 or more. The above formula 1 means the degree to which the glass transition temperature of the polylactide resin composition according to the present invention measured at a crystallization temperature of the specific temperature (T) is lower than the glass transition temperature measured at a crystallization temperature of 90°C, and the higher this value, the lower the glass transition temperature. Preferably, ΔT in formula 1 g is 5.5 or more, 6.0 or more, or 6.5 or more. g is 15 or less, 14 or less, 13 or less, 12 or less, or 11 or less.

[0025] 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 of mixing the polylactide resin, the first nucleating agent, and the second nucleating agent. For example, the components may be produced by a melt blending method. [Effects of the Invention]

[0026] The polylactide resin composition according to the present invention described above has a low glass transition temperature and an excellent crystallinity, and the processability of the polylactide resin composition can be improved. [Brief explanation of the drawings]

[0027] [Figure 1] FIG. 1 is a diagram showing a method for measuring the glass transition temperature in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] 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.

[0029] Production example: 2nd nucleating agent (P10-A-002 production) An oligomer was prepared using PEG-1000 (P10) as an initiator. Specifically, a total of 4.5 g of lactide:P10 was added to a 20 mL vial at an 8:1 molar ratio. 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 relative to the terminal OH groups) 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 a structure in which the terminal groups were substituted with acetyl groups. This was designated P10-A-002, and its weight-average molecular weight is shown in Table 1 below.

[0030] Examples and Comparative Examples 65 g of PLA pellets (NatureWorks 4032D; weight average molecular weight approximately 200,000) and the first nucleating agent were mixed in the amounts listed in Table 1 below. The mixture was placed in a Haake mixer and mixed at 180°C for 5 minutes at 60 rpm. The second nucleating agents listed in Table 1 below were added in the amounts listed and mixed at 180°C for 5 minutes at 60 rpm. The amounts of the first and second nucleating agents in Table 1 below represent the weight percent (wt%) of the total amount of PLA resin, first nucleating agent, and second nucleating agent.

[0031] Experimental example The physical properties of the polylactide resin composition prepared above were measured by the following methods. 1) Weight average molecular weight The number average molecular weight (Mn) and weight average molecular weight (Mw) of the second nucleating agent prepared above were calculated using a GPC (gel permeation chromatography) device, and the molecular weight distribution (Mw / Mn) of the oligomer was measured. 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℃ -Detector: Waters 2414 RID -Standard: PS (Polystyrene)

[0032] 2) DSC (differential scanning calorimeter) To erase the thermal history of each of the polylactide resin compositions prepared in the Examples and Comparative Examples, the compositions were completely melted at 200°C for 20 minutes. Then, they were cooled to the crystallization temperature shown in Table 1 below at a cooling rate of 40°C / min. After maintaining the temperature at the crystallization temperature for 60 minutes, they were cooled to -50°C at a cooling rate of 40°C / min. The temperature was then raised again to 200°C at a heating rate of 10°C / min, and a second heating thermogram was observed. At this time, T g、T is defined as a half-height type, and the crystallinity (%) was calculated using the following formula (100% crystalline PLA ΔHm=93 J / g). w is the content of the nucleating agent (for example, in the case of 5 wt%, w is 0.05).

[0033] -Crystallization degree: ((area of ​​endothermic peak in the 2nd thermogram, ΔHm-exothermic peak area of ​​cold crystallization, ΔHcc) / (1-w)*(100% crystalline PLA ΔHm))*100 The same process as above was carried out, and the crystallization temperature was set to 90°C. g、90 After measuring, ΔT g was calculated.

number

[0034] The results are shown in Table 1 below. [Table 1]

[0035] As shown in Tables 1 and 2, in the examples in which the first nucleating agent and the second nucleating agent were used simultaneously according to the present invention, it was confirmed that the glass transition temperature was lower and the crystallinity was improved compared to the comparative examples.

Claims

1. A polylactide resin composition comprising: a polylactide resin; a first nucleating agent which is uracil or orotic acid; and a second nucleating agent which is a compound containing a lactide oligomer structure, The polylactide resin composition has a glass transition temperature (T) measured at a specific temperature (T) between 100 and 130°C. ｇ、Ｔ ) and a crystallinity of 60°C or less and 55% or more, respectively; ΔT in the following equation 1 ｇ is 5 or more, Polylactide resin composition: [Equation 1] In the above formula 1, T ｇ、Ｔ is the glass transition temperature (°C) of the polylactide resin composition measured by setting the crystallization temperature to the specific temperature (T), T ｇ、９０ is the glass transition temperature (°C) of the polylactide resin composition measured at a crystallization temperature of 90°C.

2. The first nucleating agent is contained in an amount of 0.1 to 5% by weight based on the total weight of the polylactide resin composition. The polylactide resin composition according to claim 1.

3. The second nucleating agent is contained in an amount of 3 to 25% by weight based on the total weight of the polylactide resin composition. The polylactide resin composition according to claim 1.

4. The polylactide resin composition has a glass transition temperature (T ｇ、Ｔ ) is 56°C or less; The polylactide resin composition according to claim 1.

5. The polylactide resin composition has a glass transition temperature (T ｇ、Ｔ ) is 50°C or less, The polylactide resin composition according to claim 1.

6. ΔT in Equation 1 ｇ is 6.5 or more, The polylactide resin composition according to claim 5.

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

Images