CN106916424A - A kind of high-tenacity heat-resistant type full-biodegradable polylactic acid material and preparation method thereof - Google Patents

Abstract

The invention discloses a high-toughness heat-resistant fully biodegradable polylactic acid material and a preparation method thereof, belonging to the field of processing and modification of polymer materials. The following steps are carried out: industrial grade polylactic acid, dextrorotary polylactic acid, poly(butylene terephthalate-co-butylene adipate) ester, and a small amount of chain extender are melt blended through special twin-screw extrusion , extrusion granulation, the extrusion temperature is 160-195°C. The main purpose of improving the extruder is to strengthen the mixing strength of the screw in the melting section and reduce the shear of the rear section of the screw. This method can greatly increase the crystallization rate of polylactic acid, increase its crystallinity, refine the grain size of polylactic acid, shorten the molding cycle of polylactic acid, improve its dimensional stability and heat resistance, and improve the quality of polylactic acid products. mechanical properties. The high toughness fully biodegradable polylactic acid material prepared by the method has high strength, high toughness and high heat resistance, and the method is simple.

Description

A high-toughness heat-resistant fully biodegradable polylactic acid material and its preparation method

technical field

The invention relates to a high-toughness fully biodegradable polylactic acid material and a preparation method thereof, belonging to the field of processing and modification of polymer materials.

Background technique

Polylactic acid (PLA) is an important lactic acid derivative. It is a kind of polymer material obtained by chemical synthesis or biosynthesis with lactic acid as a monomer. It is non-toxic, non-irritating, and has excellent biocompatibility. Biodegradable and absorbable, strong plasticity, easy to process and shape. It is easily decomposed and metabolized by various microorganisms in nature or enzymes in animals and plants, and finally forms water and carbon dioxide without polluting the environment, so it is considered to be one of the most promising biodegradable polymer materials. Its biggest advantage is its renewability and degradability. Renewability makes its production not dependent on petroleum and will not fluctuate excessively with petroleum prices, making the polylactic acid industry have a good sustainable development capability; and degradability ensures that polylactic acid is an environmentally friendly material, It can alleviate the white pollution problem caused by the current plastic products, so the research on polylactic acid materials has attracted extensive attention from the industry.

Although polylactic acid materials have good molding and processing properties, polylactic acid molecular chains are less flexible and have weaker movement capabilities. Therefore, the orientation of molecular chains is not easy to be removed under the action of shear during processing. Therefore, although polylactic acid products have high strength, but The toughness is poor, the product is brittle and easy to crack. And because of the low crystallinity of polylactic acid, its heat-resistant temperature is only 60°C.

In order to improve the toughness of polylactic acid products and broaden its application fields, different elastomers are often used to blend with polylactic acid. Now the main elastomers that can be used for toughening are: biodegradable polyester, copolyester, core-shell copolymer, Butyl acrylate-ethyl acrylate-glycidyl methacrylate terpolymer, etc. However, with the addition of the toughening agent, the strength of the polylactic acid material also decreases, especially when the amount of the toughening agent exceeds 30%, the tensile strength of the polylactic acid material will drop significantly. Patent CN104559097A uses lactic acid-dibasic acid diol copolymer as a toughening agent to improve the toughness of polylactic acid, and the addition amount is 5-20wt%, but with the increase of lactic acid-dibasic acid diol copolymer, the material While the elongation at break is increasing, its tensile strength drops rapidly to about 30MPa, and lactic acid-dibasic acid glycol copolymer is not an industrialized product at present. Patent CN102942772A prepares a core-shell copolymer as a toughening agent, which is a core-shell structure with butadiene-styrene copolymer as the core and methyl methacrylate and glycidyl methacrylate copolymer as the shell copolymer. But when the elongation at break of the toughened polylactic acid reaches 200%, its tensile strength has dropped to 40MPa, and the core-shell copolymer is not a completely biodegradable material, so it will affect the degradation ability of polylactic acid. Patent CN105315632A prepared a copolyester based on ethylene terephthalate, and used the copolyester as a toughening modification to improve the toughness of polylactic acid, but the fracture of the modified polylactic acid material The elongation is only 50%, and the toughness is still poor.

In summary, the toughening agent used in the previously disclosed patents to toughen polylactic acid is a non-degradable organic substance or the toughening effect is not good, which will lead to a decrease in the environmental friendliness of the polylactic acid material; or After toughening modification, its strength will be greatly reduced, which limits its use. The invention discloses a high-toughness heat-resistant fully biodegradable polylactic acid material and a preparation method thereof.

Contents of the invention

The technical problem solved by the present invention is to provide a kind of preparation method of toughened polylactic acid with good effect,

The invention provides a high-toughness heat-resistant fully biodegradable polylactic acid material, which is composed of the following raw materials in parts by weight:

Wherein said chain extender is ethylene-methyl acrylate-glycidyl methacrylate

The molecular weight of said D-polylactic acid is 4000-7000g/mol.

The preparation method of above-mentioned a kind of toughened polylactic acid is carried out according to the following steps: poly(butylene terephthalate-co-butylene adipate) of polylactic acid, dextrorotary polylactic acid, poly(butylene terephthalate-co-adipate) ester, chain extender Through the special twin-screw extrusion melt blending, extrusion granulation, the extrusion temperature is 160-195 ℃.

The extruder has been improved, mainly to strengthen the mixing strength of the screw in the melting section and reduce the shear strength of the rear section of the screw. This method can greatly increase the crystallization rate of polylactic acid, increase its crystallinity, refine the grain size of polylactic acid, improve its dimensional stability and heat resistance, and improve the mechanical properties of polylactic acid products. The toughened polylactic acid prepared by this method still has complete biodegradability, which makes the toughened polylactic acid more attractive.

The extruding temperature in the twin-screw is 160-195°C. A special extruder is used. The shearing elements of the screw are recombined, which mainly strengthens the mixing strength of the screw in the melting section and reduces the rear section of the screw. cut.

Beneficial effects of the present invention:

Blending PLA, PDLA and PBAT has both the high toughness of PBAT and the high strength of PLA without compromising the degradation characteristics of the two materials. Compared with the prior art, the invention adds PBAT to improve the toughness of PLA, and also adds PDLA to improve the strength and heat resistance of PLA. The present invention takes PLA as the matrix, adds 15-20% PDLA and 25-30% PBAT, and the temperature of the extruder is set at 160-195°C. In the first three sections of the extruder, when the material temperature is lower than 185 At ℃, PLA, PDLA and PBAT are uniformly plasticized and mixed evenly under the action of strong shear. When the material temperature reaches 190-195 °C, PLA and PDLA form stereocomposite in situ under the action of weak shear field Crystal (SC crystal), the melting temperature of this in-situ formed SC crystal is above 220°C; this in-situ formed SC crystal is a good nucleating agent for PLA, which will increase the crystallinity of PLA, so the total The crystallinity can reach 30%-40%, which will improve the heat resistance of the material; while some PLA segments and PDLA segments that do not participate in the formation of crystals undergo chain extension reactions with PBAT under the action of chain extenders, SC crystals A good physical cross-linking point will be formed, so it will give the material good tensile properties; and the content of PBAT in the blend material exceeds 25%, which ensures the good toughness of the material; PDLA with a lower molecular weight also has two Advantages, one is that the production cost of low molecular weight PDLA is much lower than the production cost of high molecular weight PDLA, and another advantage is that in the case of the same amount of addition, the number of moles of low molecular weight PDLA is more, and the movement ability of molecular chains is stronger. , can form more SC crystals, which is beneficial to improve the heat resistance and tensile strength of the material.

detailed description

The invention provides a preparation method of toughened polylactic acid, which is carried out according to the following steps: 50-60 parts of industrial grade polylactic acid, 15-20 parts of dextrorotatory polylactic acid, poly(butylene terephthalate-co-hexyl 25-30 parts of butanediol dioic acid) and a small amount of chain extender are melt-blended by special twin-screw extrusion, extruded and granulated, and the extrusion temperature is 160-195 ° C. The extruder used in the present invention is adjusted The location of the shearing element, that is, two strong shearing elements are set in the melting zone to improve the mixing effect and the dispersion of PDLA in the PLA matrix; at the same time, there is no shearing element in the homogenization section, and a similar to a plunger is used. way to reduce the shear of the homogenization section and promote the formation of SC crystals. The extruder used had a screw diameter of 35 mm and an aspect ratio of 48.

The present invention will be described in detail below in conjunction with various embodiments, but it should be understood that the given embodiments are only for explaining the present invention, rather than limiting the protection scope of the present invention.

Example 1

5kg of dry industrial grade polylactic acid (trade name: NatureWorks PLA4032D, the same below), molecular weight is 7000g/mol dextropolylactic acid 2kg, poly(butylene terephthalate-co-butylene adipate) Ester 3kg and ethylene-methyl acrylate-glycidyl methacrylate 10g are mixed uniformly in a high-speed mixer and then granulated with a twin-screw extruder. The extruder temperature control has 10 zones altogether, and the extruder rotating speed is 200rpm, and the temperature The distribution is as follows:

a district Second District Third District Four districts five districts District six District Seven eight districts District 9 nose temperature 160°C 160°C 180°C 190°C 190°C 195°C 195°C 195°C 195°C 195°C

After drying the extruded particles, use an injection molding machine to inject into a national standard sample, and test the performance. The temperature of the injection machine is divided into four sections, namely 160°C, 190°C, 200°C and 195°C. The mold temperature during injection molding is 100°C, and the holding time is 20s.

Example 2

Dry industrial grade polylactic acid (trade name: NatureWorks PLA4032D, the same below) 6kg, molecular weight is 4000g/mol dextrorotary polylactic acid 1.5kg, poly(butylene terephthalate-co-butylene adipate) ) ester 2.5kg and ethylene-methyl acrylate-glycidyl methacrylate 25g are mixed evenly in a high-speed mixer and then granulated with a twin-screw extruder. The extruder temperature control has 10 zones in total, and the extruder speed is 200rpm , the temperature distribution is as follows:

a district Second District Third District Four districts five districts District six District Seven eight districts District 9 nose temperature 160°C 160°C 180°C 190°C 190°C 195°C 195°C 195°C 195°C 195°C

After drying the extruded particles, use an injection molding machine to inject into a national standard sample, and test the performance. After drying the extruded particles, use an injection molding machine to inject into a national standard sample, and test the performance. The temperature of the injection machine is divided into four sections, namely 160°C, 190°C, 200°C and 195°C. The mold temperature during injection molding is 100°C, and the holding time is 20s.

Example 3

Dry industrial grade polylactic acid (trade name: NatureWorks PLA4032D, the same below) 5kg, molecular weight is 4000g/mol D-polylactic acid 2kg, poly(butylene terephthalate-co-butylene adipate) ) ester 3kg and ethylene-methyl acrylate-glycidyl methacrylate 25g are mixed uniformly in a high-speed mixer and granulated with a twin-screw extruder. The extruder temperature control has 10 zones altogether, and the extruder rotating speed is 200rpm. The temperature distribution is as follows:

a district Second District Third District Four districts five districts District six District Seven eight districts District 9 nose temperature 160°C 160°C 180°C 190°C 190°C 195°C 195°C 195°C 195°C 195°C

After drying the extruded particles, use an injection molding machine to inject them into national standard specimens, and test their properties. The temperature of the injection machine is divided into four sections, namely 160°C, 190°C, 200°C and 195°C. During injection molding, the mold temperature is 100°C, and the holding time is 20s.

The sample performance test results of Examples 1-3 and Comparative Example 1 are shown in Table 1.

*CN104559097A.

Comparative example 1*

Polylactic acid and self-made copolyester elastomer were melt-blended in a Haake mixer, and the blending temperature was 200°C. The rotational speed of the internal mixer was 70 rpm, and the blending time was 9 minutes. The blended samples were directly cooled in air at room temperature. The above blend was pressed into a 1mm thick sheet on a flat vulcanizer at 190°C and 10 MPa. After cooling to room temperature, it was cut into dumbbell-shaped specimens with a knife, and the standard impact strength specimens were pressed at the same time. Use a milling cutter to cut a notch with a bottom radius of 0.25 mm in the middle of the spline, and perform an impact strength test on a cantilever beam impact strength testing machine.

Claims (5)

1. a kind of high-tenacity heat-resistant type full-biodegradable polylactic acid material, it is characterised in that by the raw material group of following parts by weight Into：

PLA 50-60 parts,

15-20 parts of dextrorotation PLA,

It is poly-（Terephthalic acid (TPA) butanediol-co- adipic acid butanediols）Ester 25-30 parts,

A small amount of 0.1-0.25 parts of chain extender.

2. a kind of high-tenacity heat-resistant type full-biodegradable polylactic acid material according to claim 1, it is characterised in that wherein Described chain extender is ethylene-methyl acrylate-glyceryl methacrylate.

3. a kind of high-tenacity heat-resistant type full-biodegradable polylactic acid material according to claim 1, it is characterised in that wherein Described dextrorotation polylactic acid molecule amount is 4000-7000 g/mol.

4. a kind of preparation method of the high-tenacity heat-resistant type full-biodegradable polylactic acid material described in claim 1, its feature exists In carrying out in accordance with the following steps：By PLA, dextrorotation PLA, it is poly-（Terephthalic acid (TPA) butanediol-co- adipic acid butanediols） , by special twin-screw extrusion melt blending, extruding pelletization, extrusion temperature is 160-195 DEG C for ester, chain extender.

5. the preparation method of a kind of high-tenacity heat-resistant type full-biodegradable polylactic acid material according to claim 4, it is special Levy is that screw zones temperature is 160-195^oC, and screw rod, in melt zone You Liangge Strong shears area, it is shallow spiral shell then to be adopted in metering section Groove, without shearing elements.