A high heat distortion temperature polylactic acid blend, method of making and use

Abstract

A kind of high heat distortion temperature polylactic acid blend, preparation method and application belong to the field of biodegradable polymers.The mass fraction of each substance in high heat distortion temperature polylactic acid blend is: polylactic acid 100 parts, oligoester toughening agent 5-15 parts, and biobased microfiber 50-80 parts.The oligoester toughening agent is copolymerized from lactic acid monomer, dibasic acid and dihydric alcohol.The present application combines a large number of biobased polyester microfibers (aspect ratio of 3-10, average diameter of 1-5 μm) and polylactic acid specific high-efficiency polyester toughening agent (containing lactic acid unit, low molecular weight and T g very low), which can effectively build a strong high-heat-resistant skeleton and effectively toughen polylactic acid, realize the synergy of high heat distortion temperature of polylactic acid blend (>80 o C) and better toughness (notched impact strength).This is difficult to achieve by combining ordinary fillers (low aspect ratio or low content) and other polyester toughening agents (high molecular weight, no lactic acid unit).

Description

Technical Field

[0001] This invention belongs to the field of biodegradable polymers, specifically relating to a high heat distortion temperature polylactic acid blend, its preparation method, and its application. Background Technology

[0002] Polylactic acid (PLA) is a bio-based and biodegradable material with advantages such as wide availability of raw materials, high strength, and biodegradability, making it one of the most promising bio-based materials. However, its poor toughness and low heat distortion temperature severely limit the practical application of PLA, especially in areas such as disposable tableware that needs to withstand hot water or hot filling, and medical packaging that requires heat sterilization. For example, hot beverage straws require materials with high heat distortion temperature and good toughness, which should not soften or deform after prolonged immersion in and stirring of hot beverages, and should not easily break brittlely when squeezed or bent.

[0003] There is currently a wealth of research on the heat resistance and toughening modifications of polylactic acid (PLA). Methods such as adding large amounts of fillers, promoting PLA crystallization through annealing, and blending with large amounts of rigid polymers can construct a high heat-resistant skeleton in PLA, effectively increasing its heat distortion temperature. However, the final product is usually brittle with particularly low notched impact strength. Introducing plasticizers, blending with flexible polymers, and copolymerizing with flexible monomers can effectively toughen PLA, but these methods result in products with extremely low heat distortion temperatures. Therefore, simultaneously endowing PLA with both high heat distortion temperature and good toughness remains a significant challenge. Furthermore, existing modification methods often involve recalcitrant biodegradable components, which can transform into microplastics, polluting the environment and potentially being ingested by organisms and transported along the food chain, posing a threat to ecosystem security and human health.

[0004] Therefore, developing polylactic acid blends with high heat distortion temperature, good toughness and high biodegradability is of great significance for the practical application of polylactic acid, but it also faces great challenges. Summary of the Invention

[0005] To address the problems in existing technologies, this invention provides a high heat distortion temperature polylactic acid (PLA) blend, its preparation method, and its application. The specific design concept is as follows: 1) Introducing a large number of bio-based microfibers with an aspect ratio of 3-10 and a diameter of 1-30 micrometers into PLA forms a robust, heat-resistant skeleton, significantly increasing the heat distortion temperature of PLA while maintaining its high biodegradability. It should be emphasized that adding a large amount of low aspect ratio filler, adding a small amount of high aspect ratio filler, or adding a large amount of high aspect ratio nanofiller (which will form low aspect ratio aggregates) all fail to form a robust heat-resistant skeleton and significantly increase the heat distortion temperature of PLA. 2) Preparing a low molecular weight PLA blend containing lactic acid units with a high heat distortion temperature (T...) gThis polylactic acid (PLA)-specific polyester toughening agent, with extremely low concentrations, efficiently toughens PLA, optimizes its processing properties, and maintains its biodegradability. It's important to emphasize that traditional high-molecular-weight polyester toughening agents without lactic acid units have poor toughening efficiency and are difficult to use to optimize PLA processing properties. By combining a large amount of bio-based microfibers and a specific copolyester toughening agent, the heat distortion temperature of the PLA blend is >80°C. o C, Notched impact strength Under composting conditions, the biodegradability rate is >95%, which is difficult to achieve with a combination of ordinary rigid fillers and polyester toughening agents. Furthermore, this high heat distortion temperature polylactic acid blend can be melt-blended and molded, making the preparation method simple, with excellent performance, and easy to industrialize.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows:

[0007] A high heat distortion temperature polylactic acid blend, wherein the heat distortion temperature of the high heat distortion temperature polylactic acid blend is >80°C. o C, Notched impact strength Under composting conditions, the complete biodegradability rate is >95%; the high heat distortion temperature polylactic acid blend includes polylactic acid, low polyester toughening agent and bio-based microfiber; the mass fractions of each substance in the high heat distortion temperature polylactic acid blend are: 100 parts polylactic acid, 5-15 parts low polyester toughening agent and 50-80 parts bio-based microfiber.

[0008] Furthermore, the polylactic acid has an optical purity of ≥98% and a melt index of ≤10 g / 10min.

[0009] Furthermore, the low-polyester toughening agent has a molecular weight of 1000~20000 g / mol and a glass transition temperature of less than -30°C. o C; The low-polyester toughening agent is copolymerized from lactic acid monomer, diacid and diol. The mass of lactic acid monomer is 10-30% of the mass of the low-polyester toughening agent. The diol is a combination of two or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol and hexanediol, and its mass is 30-40% of the mass of the low-polyester toughening agent. The diacid is a combination of two or more of oxalic acid, succinic acid, adipic acid and sebacic acid, and its mass is 40-50% of the mass of the low-polyester toughening agent.

[0010] Furthermore, the bio-based microfiber is one or more of cellulose fiber and wood fiber, with an average aspect ratio of 3 to 10 and an average diameter of 1 to 30 micrometers.

[0011] A method for preparing a polylactic acid blend with a high heat distortion temperature, comprising the following specific steps:

[0012] (1) The bio-based microfibers were crushed in a universal pulverizer and then sieved;

[0013] (2) After drying polylactic acid, low polyester toughening agent and bio-based microfiber, add them to the blending equipment in sequence to achieve uniform blending.

[0014] Furthermore, in step (1), the crushing time is 1~5 min, the speed of the crusher is not less than 2000 rpm, and the mesh size of the sieve is not less than 250 mesh when sieving.

[0015] Furthermore, in step (2), the drying temperature is 50-70°C. o C, drying time is 10-14h; the blending equipment is any one of internal mixer, extruder or twin-screw extruder, the temperature is 170~190 ℃, the speed is 50~80 rpm, and the blending time is 5~10 min.

[0016] The above-mentioned application of a high heat distortion temperature polylactic acid blend is characterized in that the polylactic acid blend can be used as a hot drink straw, disposable tableware that can withstand hot water or hot filling, medical packaging that requires heat sterilization, etc.

[0017] Those skilled in the art may also add other optional additives as needed to obtain better performance. These additives can be selected from anti-aging agents, preservatives, bactericides, antistatic agents, crosslinking agents, pigments, fillers, fragrances, etc., and can be added simultaneously or individually.

[0018] The beneficial effects of this invention are:

[0019] (1) This invention combines a large number of bio-based polyester microfibers (aspect ratio of 3~10, average diameter of 1~30 μm) and polylactic acid-specific high-efficiency polyester toughening agent (containing lactic acid units, low molecular weight and T g (Extremely low), which can effectively construct a strong, high-heat-resistant skeleton and effectively toughen polylactic acid, achieving a high heat distortion temperature (>80) for polylactic acid blends. o C) and good toughness (notched impact strength) The synergy between these components is something that is difficult to achieve with a combination of ordinary fillers (low aspect ratio or low content) and other polyester toughening agents (high molecular weight, no lactic acid units).

[0020] (2) All materials used in this invention are biodegradable materials, and have the advantages of wide availability of raw materials, most of which are renewable and inexpensive.

[0021] (3) The polylactic acid blend prepared by the present invention has the advantages of high heat distortion temperature, thermoplastic processing, good toughness and high biodegradability. It can replace petroleum-based plastics for use in hot drink straws, disposable tableware that can withstand hot water or hot filling, medical packaging that requires heat sterilization and other fields. Detailed Implementation

[0022] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that the following specific embodiments are only for illustrating the present invention and are not intended to limit the scope of the present invention. If those skilled in the art make some non-essential adjustments and improvements to the present invention based on the above content, they shall still fall within the protection scope of the present invention.

[0023] The polylactic acid used in the following examples and comparative examples had an optical purity of 98% and a melt index of 2.9 g / 10 min.

[0024] Comparative Example 1:

[0025] The preparation method of pure PLA includes the following steps:

[0026] (1) Place 50 g of polylactic acid at 60 °C o Dry at 180°C for 12 hours, then add to a small internal mixer and heat at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0027] Comparative Example 2:

[0028] The preparation method of polylactic acid / cellulose fiber blend includes the following steps:

[0029] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0030] (2) Polylactic acid and cellulose fibers are heated at 60°C. o Dry at 180°C for 12 hours, then add 33.5 g of polylactic acid and 16.5 g of cellulose fiber sequentially into a small internal mixer and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0031] Comparative Example 3:

[0032] The preparation method of polylactic acid / low polyester toughening agent blend includes the following steps:

[0033] (1) Polylactic acid and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 43.5 g of polylactic acid and 6.5 g of low-polyester toughening agent sequentially into a small internal mixer, and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0034] Comparative Example 4:

[0035] A method for preparing polylactic acid / cellulose fiber / low polyester toughening agent blends with low heat distortion temperature, comprising the following steps:

[0036] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0037] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 32 g of polylactic acid, 13 g of cellulose fiber and 5 g of low-polyester toughening agent sequentially to a small internal mixer and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0038] Example 1:

[0039] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0040] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0041] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 30.5 g of polylactic acid, 15 g of cellulose fiber, and 4.5 g of low-polyester toughening agent sequentially into a small internal mixer and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0042] Example 2:

[0043] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0044] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0045] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 31.5 g of polylactic acid, 15.5 g of cellulose fiber, and 3 g of low-polyester toughening agent sequentially into a small internal mixer, and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0046] Example 3:

[0047] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0048] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0049] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 32.5 g of polylactic acid, 16 g of cellulose fiber, and 1.5 g of low-polyester toughening agent sequentially into a small internal mixer and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0050] Example 4:

[0051] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0052] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0053] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 28.5 g of polylactic acid, 17 g of cellulose fiber, and 4.5 g of low-polyester toughening agent sequentially into a small internal mixer, and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0054] Example 5:

[0055] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0056] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0057] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 27 g of polylactic acid, 19 g of cellulose fiber, and 4 g of low-polyester toughening agent sequentially to a small internal mixer and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0058] Example 6:

[0059] A method for preparing polylactic acid / cellulose fiber / low-polyester toughening agent blends with high heat distortion temperature, comprising the following steps:

[0060] (1) Crush the cellulose fiber in a universal pulverizer with a speed of 2000 rpm for 3 min, and then sieve it twice through a 250 mesh sieve;

[0061] (2) Polylactic acid, cellulose fiber and low polyester toughening agent are mixed at 60°C. o Dry at 180°C for 12 hours, then add 25.5 g of polylactic acid, 20.5 g of cellulose fiber, and 4 g of low-polyester toughening agent sequentially into a small internal mixer, and mix at 180°C. o Mix at 60 rpm for 8 minutes under temperature C.

[0062] Table 1. Specific formulations and typical properties of Comparative Examples 1-4 and Examples 1-6

[0063]

[0064] Note: 1) In this example, the low-polyester toughening agent is copolymerized from propylene glycol, butanediol, succinic acid, sebacic acid, and lactic acid monomers. The specific monomer feed amounts are: propylene glycol 54.1 g, butanediol 45.7 g, succinic acid 47.2 g, sebacic acid 80.9 g, and lactic acid 40 g. The specific preparation process is as follows: The above monomers are added to a 250 mL four-necked round-bottom flask, and then 0.5% of tetrabutyl titanate as a catalyst is added. After nitrogen protection for 25 min, the temperature is raised to 180 °C and esterification is carried out at 240 rpm for 2 h. Then, the pressure is slowly reduced to below 2 kPa within 0.5~1 h and the reaction is carried out for 1 h. Finally, the temperature is raised to 220 °C and high vacuum is drawn to below 50 Pa. After reacting for 1 h, the product is taken out and vacuum dried for 24 h to obtain the low-polyester toughening agent. The number average molecular weight of the obtained low-polyester toughening agent is 16522. g / mol, glass transition temperature is -50.1 g / mol. o C. 2) The specimens for heat distortion temperature test and notched impact strength test are prepared by molding the blend at 180 degrees.

[0065] The above results indicate that pure polylactic acid (PLA) (Comparative Example 1) has poor heat distortion temperature and notched impact strength. Introducing only cellulose fibers (Comparative Example 2) significantly increases the heat distortion temperature of PLA, but reduces its notched impact strength. Introducing only low-polyester toughening agent (Comparative Example 3) significantly increases the notched impact strength of PLA, but reduces its heat distortion temperature. Introducing insufficient cellulose fibers and low-polyester toughening agent (Comparative Example 4) simultaneously increases both the heat distortion temperature and notched impact strength of PLA, but the heat distortion temperature remains below 80°C. o C. Compared with the comparative examples, the present invention, which simultaneously introduces sufficient amounts of bio-based microfibers and low-polyester toughening agents (Examples 1-6), can impart excellent heat distortion temperature (≥80°C) to polylactic acid. oC) and relatively good notched impact strength ( Furthermore, the polylactic acid blends obtained by this method have the characteristics of high biodegradability, high bio-based content, and easy processing and molding. Moreover, the performance of polylactic acid blends can be controlled within a certain range by adjusting the processing conditions and component content.

[0066] Those skilled in the art should understand that the above description is merely a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A high heat distortion temperature polylactic acid blend, characterized in that, The high heat distortion temperature polylactic acid blend has a heat distortion temperature >80°C. o C, Notched impact strength Under composting conditions, the complete biodegradability rate is >95%; the high heat distortion temperature polylactic acid blend includes polylactic acid, low polyester toughening agent and bio-based microfiber; the mass fractions of each substance in the high heat distortion temperature polylactic acid blend are: 100 parts polylactic acid, 5-15 parts low polyester toughening agent and 50-80 parts bio-based microfiber.

2. The high heat distortion temperature polylactic acid blend according to claim 1, characterized in that, The optical purity of the polylactic acid is ≥98%, and the melt index is ≤10 g / 10min.

3. The high heat distortion temperature polylactic acid blend according to claim 1, characterized in that, The low-polyester toughening agent has a molecular weight of 1000~20000 g / mol and a glass transition temperature of less than -30°C. o C; The low-polyester toughening agent is copolymerized from lactic acid monomer, diacid and diol. The mass of lactic acid monomer is 10-30% of the mass of the low-polyester toughening agent. The diol is a combination of two or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol and hexanediol, and its mass is 30-40% of the mass of the low-polyester toughening agent. The diacid is a combination of two or more of oxalic acid, succinic acid, adipic acid and sebacic acid, and its mass is 40-50% of the mass of the low-polyester toughening agent.

4. The high heat distortion temperature polylactic acid blend according to claim 1, characterized in that, The bio-based microfiber is one or more of cellulose fiber and wood fiber, with an average aspect ratio of 3 to 10 and an average diameter of 1 to 30 micrometers.

5. A method for preparing a high heat distortion temperature polylactic acid blend according to any one of claims 1-4, characterized in that, The specific steps are as follows: (1) The bio-based microfibers were crushed in a universal pulverizer and then sieved; (2) After drying polylactic acid, low polyester toughening agent and bio-based microfiber, add them to the blending equipment in sequence to achieve uniform blending.

6. The method for preparing a high heat distortion temperature polylactic acid blend according to claim 5, characterized in that, In step (1), the crushing time is 1~5 min, the speed of the crusher is not less than 2000 rpm, and the mesh size of the sieve is not less than 250 mesh when sieving.

7. The method for preparing a high heat distortion temperature polylactic acid blend according to claim 5, characterized in that, In step (2), the drying temperature is 50-70°C. o C, drying time is 10-14h; the blending equipment is any one of internal mixer, extruder or twin-screw extruder, the temperature is 170~190 ℃, the speed is 50~80 rpm, and the blending time is 5~10 min.

8. The application of a high heat distortion temperature polylactic acid blend according to any one of claims 1-4, or a high heat distortion temperature polylactic acid blend prepared by any one of claims 5-7, characterized in that, The high heat distortion temperature polylactic acid blends are used as hot beverage straws, disposable tableware that can withstand hot water or hot filling, and in the field of medical packaging that requires heat sterilization.

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