CN111440426B - Unidirectional stretching polylactic acid stereocomplex and preparation method thereof - Google Patents
Unidirectional stretching polylactic acid stereocomplex and preparation method thereof Download PDFInfo
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Abstract
The invention belongs to the field of polymer composite materials, and particularly relates to a unidirectional stretching polylactic acid stereocomplex and a preparation method thereof. The polylactic acid stereocomplex provided by the invention is prepared by carrying out melt blending and cooling on raw materials and then carrying out unidirectional stretching; the raw materials comprise: 50 parts by weight of L-polylactic acid; 50 parts by weight of dextrorotatory polylactic acid; 15-30 parts by weight of a compatible blend; the compatible blend comprises polyvinyl acetate and/or poly (racemic lactic acid). The invention obviously improves the stereocomplex crystallinity, heat-resistant temperature and mechanical strength of the provided polylactic acid stereocomplex by strictly controlling the dosage ratio of the levorotatory polylactic acid and the dextrorotatory polylactic acid in the raw material and adding a certain amount of compatible blend and adopting a unidirectional stretching process. The polylactic acid stereocomplex provided by the invention has the advantages of simple preparation process, high production efficiency, capability of realizing large-scale industrial production and good market prospect.
Description
Technical Field
The invention belongs to the field of polymer composite materials, and particularly relates to a unidirectional stretching polylactic acid stereocomplex and a preparation method thereof.
Background
Polylactic acid is a polymer material which is obtained by fermenting plant resources as raw materials and then chemically synthesized, can be completely decomposed into water, carbon dioxide and organic matters under the action of microorganisms and the like after being abandoned, does not pollute the environment, and is a typical plant-derived completely biodegradable plastic. Because polylactic acid has the advantages of complete plant sources, complete biodegradability, biocompatibility, bioabsorbable property, easy processing and forming and the like, the polylactic acid is an ideal substitute for petroleum-based high polymer materials, has wide application prospect in the field of biomedical materials and the field of general plastics, and can effectively solve the white pollution brought by traditional materials. In recent years, polylactic acid plastic products have come to the market with an increase in production scale and a decrease in synthesis cost. However, polylactic acid has poor heat resistance due to slow crystallization, and further, polylactic acid has serious brittleness, which limits its wide application.
It was found that stereocomplex of the levorotatory polylactic acid and the dextrorotatory polylactic acid is one of effective ways and methods for improving heat resistance and durability of polylactic acid plastics. Since the L-polylactic acid and the D-polylactic acid can be closely piled up through the hydrogen bond interaction between molecular chains, the stereocomplex polylactic acid with high melting point (220 ℃) is formed. The melting point of the stereocomplex polylactic acid is higher than 220 ℃ and is about 50 ℃ higher than that of the monocomponent (HC) crystal formed by the levorotatory polylactic acid or the dextrorotatory polylactic acid. In addition, the stereocomplex polylactic acid also exhibits more excellent tensile strength and hydrolysis resistance than pure levorotatory polylactic acid and dextrorotatory polylactic acid.
At present, the stereocomplex polylactic acid is generally prepared by adopting a mode of melt blending and then cooling crystallization of the levorotatory polylactic acid and the dextrorotatory polylactic acid, but because the stereocomplex crystallization and the polylactic acid homogeneous crystallization compete with each other in the cooling crystallization process, a certain amount of polylactic acid homogeneous crystallization is inevitably contained in a finally obtained product, the stereocomplex crystallinity is lower, and the heat-resistant temperature and the mechanical property of the product are further affected.
Disclosure of Invention
In view of the above, the present invention aims to provide a unidirectional stretching polylactic acid stereocomplex and a preparation method thereof. The polylactic acid stereocomplex provided by the invention does not contain polylactic acid homogeneous crystallization, has high stereocomplex crystallinity, and has relatively excellent heat-resistant temperature and mechanical properties.
The invention provides a unidirectional stretching polylactic acid stereocomplex, which is prepared by carrying out melt blending and cooling on raw materials and then unidirectional stretching;
the raw materials comprise:
50 parts by weight of L-polylactic acid;
50 parts by weight of dextrorotatory polylactic acid;
15-30 parts by weight of a compatible blend;
the compatible blend comprises polyvinyl acetate and/or poly (racemic lactic acid).
Preferably, the weight average molecular weight of the L-polylactic acid is 15 ten thousand to 50 ten thousand; the weight average molecular weight of the dextrorotatory polylactic acid is 15-50 ten thousand.
Preferably, the weight average molecular weight of the polyvinyl acetate is 5 ten thousand to 15 ten thousand; the weight average molecular weight of the poly-racemization lactic acid is 3 ten thousand-10 ten thousand.
Preferably, the raw material further comprises an anti-hydrolysis agent and/or a chain extender.
Preferably, the anti-hydrolysis agent comprises carbodiimide; the chain extender comprises pyromellitic dianhydride and/or dioxybisphenol A diglycidyl ether.
The invention provides a preparation method of a unidirectional stretching polylactic acid stereocomplex, which comprises the following steps:
a) Melt blending 50 parts by weight of L-polylactic acid, 50 parts by weight of L-polylactic acid and 15-30 parts by weight of compatible blend, and cooling to obtain a polylactic acid blend with an amorphous structure;
the compatible blend comprises polyvinyl acetate and/or poly-racemic lactic acid;
b) And carrying out unidirectional stretching on the polylactic acid blend to obtain a unidirectional stretching polylactic acid stereocomplex.
Preferably, the temperature of the melt blending is 220-240 ℃; the time of melt blending is 5-10 min.
Preferably, the temperature of the unidirectional stretching is 65-100 ℃; the stretching rate of the unidirectional stretching is 5-100 mm/min; the stretching multiplying power of unidirectional stretching is 4-10 times.
Preferably, before the polylactic acid blend is uniaxially stretched, the polylactic acid blend is prepared into a sheet to be stretched; the specific steps for preparing the sheet to be stretched include:
and (3) hot-pressing the polylactic acid blend into sheets, and cooling to obtain the sheet to be stretched with an amorphous structure.
Preferably, each of the raw materials is vacuum dried prior to the melt blending.
Compared with the prior art, the invention provides a unidirectional stretching polylactic acid stereocomplex and a preparation method thereof. The polylactic acid stereocomplex provided by the invention is prepared by carrying out melt blending and cooling on raw materials and then carrying out unidirectional stretching; the raw materials comprise: 50 parts by weight of L-polylactic acid; 50 parts by weight of dextrorotatory polylactic acid; 15-30 parts by weight of a compatible blend; the compatible blend comprises polyvinyl acetate and/or poly (racemic lactic acid). The invention obviously improves the stereocomplex crystallinity, heat-resistant temperature and mechanical strength of the provided polylactic acid stereocomplex by strictly controlling the dosage ratio of the levorotatory polylactic acid and the dextrorotatory polylactic acid in the raw material and adding a certain amount of compatible blend and adopting a unidirectional stretching process. The polylactic acid stereocomplex provided by the invention has the advantages of simple preparation process, high production efficiency, capability of realizing large-scale industrial production and good market prospect. The experimental results show that: the polylactic acid stereocomplex provided by the invention does not contain polylactic acid homogeneous crystals, the stereocomplex crystallinity is more than 40%, the tensile strength is more than or equal to 140MPa, and the storage modulus at 180 ℃ is more than 15MPa.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely, and it is apparent that the described embodiments are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
The invention provides a unidirectional stretching polylactic acid stereocomplex, which is prepared by carrying out melt blending and cooling on raw materials and then unidirectional stretching;
the raw materials comprise:
50 parts by weight of L-polylactic acid;
50 parts by weight of dextrorotatory polylactic acid;
15-30 parts by weight of a compatible blend;
the compatible blend comprises polyvinyl acetate and/or poly (racemic lactic acid).
The polylactic acid stereocomplex provided by the invention is prepared by carrying out melt blending and cooling on raw materials and then carrying out unidirectional stretching, wherein the raw materials comprise L-polylactic acid, D-polylactic acid and compatible blend. In the invention, the optical purity of the L-polylactic acid is preferably more than or equal to 95%, and can be particularly 95%, 96%, 97%, 98% or 99%; the weight average molecular weight of the levorotatory polylactic acid is preferably 15 to 50 ten thousand, and may be 15 ten thousand, 16 ten thousand, 17 ten thousand, 18 ten thousand, 19 ten thousand, 20 ten thousand, 21 ten thousand, 22 ten thousand, 23 ten thousand, 24 ten thousand, 25 ten thousand, 26 ten thousand, 27 ten thousand, 28 ten thousand, 29 ten thousand, 30 ten thousand, 31 ten thousand, 32 ten thousand, 33 ten thousand, 34 ten thousand, 35 ten thousand, 36 ten thousand, 37 ten thousand, 38 ten thousand, 39 ten thousand, 40 ten thousand, 41 ten thousand, 42 ten thousand, 43 ten thousand, 44 ten thousand, 45 ten thousand, 46 ten thousand, 47 ten thousand, 48 ten thousand, 49 ten thousand or 50 ten thousand.
In the invention, the optical purity of the dextro polylactic acid is preferably more than or equal to 95%, and can be 95%, 96%, 97%, 98% or 99%; the weight average molecular weight of the dextrorotatory polylactic acid is preferably 15 to 50 ten thousand, and can be 15 ten thousand, 16 ten thousand, 17 ten thousand, 18 ten thousand, 19 ten thousand, 20 ten thousand, 21 ten thousand, 22 ten thousand, 23 ten thousand, 24 ten thousand, 25 ten thousand, 26 ten thousand, 27 ten thousand, 28 ten thousand, 29 ten thousand, 30 ten thousand, 31 ten thousand, 32 ten thousand, 33 ten thousand, 34 ten thousand, 35 ten thousand, 36 ten thousand, 37 ten thousand, 38 ten thousand, 39 ten thousand, 40 ten thousand, 41 ten thousand, 42 ten thousand, 43 ten thousand, 44 ten thousand, 45 ten thousand, 46 ten thousand, 47 ten thousand, 48 ten thousand, 49 ten thousand or 50 ten thousand. In the invention, the content of the L-polylactic acid in the raw material is 50 parts by weight based on the content of the L-polylactic acid in the raw material, namely the mass ratio of the L-polylactic acid to the raw material is 1:1.
In the present invention, the compatible blend comprises polyvinyl acetate and/or poly-racemic lactic acid; the weight average molecular weight of the polyvinyl acetate is preferably 5 ten thousand to 15 ten thousand, and can be particularly 5 ten thousand, 6 ten thousand, 7 ten thousand, 8 ten thousand, 9 ten thousand, 10 ten thousand, 11 ten thousand, 12 ten thousand, 13 ten thousand, 14 ten thousand or 15 ten thousand; the weight average molecular weight of the poly-racemization lactic acid is preferably 3 ten thousand to 10 ten thousand, and can be 3 ten thousand, 4 ten thousand, 5 ten thousand, 6 ten thousand, 7 ten thousand, 8 ten thousand, 9 ten thousand or 10 ten thousand. In one embodiment provided by the invention, the compatible blend comprises polyvinyl acetate and poly-racemic lactic acid, wherein the mass ratio of the polyvinyl acetate to the poly-racemic lactic acid is preferably 1: (0.1-10), which may be specifically 1:0.3, 1:0.5, 1:0.7, 1:1, 1:2, 1:3, 1:4 or 1:5. In the present invention, the content of the compatible blend in the raw material is 10 to 20 parts by weight, specifically 10 parts by weight, 11 parts by weight, 12 parts by weight, 13 parts by weight, 14 parts by weight, 15 parts by weight, 16 parts by weight, 17 parts by weight, 18 parts by weight, 19 parts by weight or 20 parts by weight, based on the content of the levorotatory polylactic acid in the raw material being 50 parts by weight. In the present invention, the addition of the compatible blend may limit the polylactic acid blend from forming homogeneous crystals of polylactic acid during unidirectional stretching.
In the present invention, the raw material preferably further comprises an anti-hydrolysis agent and/or a chain extender; the anti-hydrolysis agent preferably comprises a carbodiimide; the chain extender preferably comprises pyromellitic dianhydride and/or dioxybisphenol A diglycidyl ether. In the present invention, the content of the hydrolysis inhibitor in the raw material is preferably 0.1 to 1 part by weight, and specifically may be 0.1 part by weight, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.6 part by weight, 0.7 part by weight, 0.8 part by weight, 0.9 part by weight, or 1 part by weight, based on the content of the levorotatory polylactic acid in the raw material of 50 parts by weight. In the present invention, the content of the chain extender in the raw material is preferably 0.1 to 1 part by weight, specifically 0.1 part by weight, 0.2 part by weight, 0.3 part by weight, 0.4 part by weight, 0.5 part by weight, 0.6 part by weight, 0.7 part by weight, 0.8 part by weight, 0.9 part by weight or 1 part by weight, based on the content of the levorotatory polylactic acid in the raw material of 50 parts by weight.
In the present invention, the temperature of the melt blending is preferably 220 to 240 ℃, and specifically may be 220 ℃, 225 ℃, 230 ℃, 235 ℃ or 240 ℃; the time of melt blending is preferably 5-10 min, and specifically can be 5min, 6min, 7min, 8min, 9min or 10min; the cooling mode is preferably natural cooling under room temperature air.
In the present invention, the temperature of the unidirectional stretching is preferably 65 to 100 ℃, specifically 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃; the stretching rate of the unidirectional stretching is preferably 5-100 mm/min, and can be specifically 5mm/min, 10mm/min, 15mm/min, 20mm/min, 25mm/min, 30mm/min, 35mm/min, 40mm/min, 45mm/min, 50mm/min, 60mm/min, 70mm/min, 80mm/min, 90mm/min or 100mm/min; the stretching magnification of the unidirectional stretching is preferably 4 to 10 times, and specifically may be 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times.
The invention also provides a preparation method of the unidirectional stretching polylactic acid stereocomplex, which comprises the following steps:
a) Melt blending 50 parts by weight of L-polylactic acid, 50 parts by weight of L-polylactic acid and 15-30 parts by weight of compatible blend, and cooling to obtain a polylactic acid blend with an amorphous structure;
the compatible blend comprises polyvinyl acetate and/or poly-racemic lactic acid;
b) And carrying out unidirectional stretching on the polylactic acid blend to obtain a unidirectional stretching polylactic acid stereocomplex.
In the preparation method provided by the invention, the raw materials are firstly melted and blended in proportion. Wherein the raw materials comprise L-polylactic acid, D-polylactic acid and compatible blend, and preferably further comprise an anti-hydrolysis agent and/or a chain extender; specific information and dosage ratios of the levorotatory polylactic acid, the dextrorotatory polylactic acid, the compatible blend, the hydrolysis inhibitor and the chain extender are described above, and are not described in detail herein; before the melt blending, the raw materials are preferably dried in vacuum, and the water content of the raw materials after the vacuum drying is preferably less than or equal to 200ppm; the temperature of the melt blending is preferably 220-240 ℃, and specifically can be 220 ℃, 225 ℃, 230 ℃, 235 ℃ or 240 ℃; the mixing speed of the melt blending is preferably 40-120 revolutions per minute, and specifically can be 40 revolutions per minute, 50 revolutions per minute, 60 revolutions per minute, 70 revolutions per minute, 80 revolutions per minute, 90 revolutions per minute, 100 revolutions per minute, 110 revolutions per minute or 120 revolutions per minute; the time of melt blending is preferably 5-10 min, and specifically can be 5min, 6min, 7min, 8min, 9min or 10min; the melt blending is preferably performed in a torque rheometer. And after the melt blending is finished, obtaining a blended melt.
In the preparation method provided by the invention, after the blending melt is obtained, the blending melt is cooled to obtain the polylactic acid blend with an amorphous structure. Wherein the cooling mode is rapid cooling at ambient temperature (room temperature).
In the preparation method provided by the invention, after the polylactic acid blend with an amorphous structure is obtained, the polylactic acid blend is subjected to unidirectional stretching. The polylactic acid blend is preferably prepared into a sheet to be stretched with an amorphous structure, and then subjected to unidirectional stretching. In the present invention, the specific steps for preparing the sheet to be stretched preferably include: and (3) hot-pressing the polylactic acid blend into sheets, and cooling to obtain the sheet to be stretched with an amorphous structure. Wherein the temperature of the hot pressing is preferably 220-240 ℃, and specifically can be 220 ℃, 225 ℃, 230 ℃, 235 ℃, 240 ℃, 245 ℃ or 250 ℃; the pressure of the hot pressing is preferably 5-20 MPa, and can be specifically 5MPa, 10MPa, 15MPa or 20MPa; the hot pressing is preferably performed on a press vulcanizer; the thickness of the sheet obtained by hot pressing is preferably 0.5-2 mm, and can be specifically 0.5mm, 1mm, 1.5mm or 2mm; the temperature of the cooling is preferably ambient temperature (room temperature); the cooling is preferably carried out in a cold press, the pressure of which is preferably 5 to 20MPa, in particular 5MPa, 10MPa, 15MPa or 20MPa. In the present invention, the temperature of the unidirectional stretching is preferably 65 to 100 ℃, specifically 65 ℃, 70 ℃, 75 ℃, 80 ℃, 85 ℃, 90 ℃, 95 ℃ or 100 ℃; the stretching rate of the unidirectional stretching is preferably 5-100 mm/min, and can be specifically 5mm/min, 10mm/min, 15mm/min, 20mm/min, 25mm/min, 30mm/min, 35mm/min, 40mm/min, 45mm/min, 50mm/min, 60mm/min, 70mm/min, 80mm/min, 90mm/min or 100mm/min; the stretching magnification of the unidirectional stretching is preferably 4 to 10 times, and specifically may be 4 times, 5 times, 6 times, 7 times, 8 times, 9 times or 10 times. In the unidirectional stretching process, molecules of the polylactic acid blend with an amorphous structure are orderly arranged under the action of the directional external force, so that the polylactic acid blend is converted from an amorphous state (amorphous state) to a crystalline state (stereocrystal), namely, oriented crystallization; after unidirectional stretching is finished, cooling to room temperature to obtain the unidirectional stretching polylactic acid stereocomplex provided by the invention.
The invention obviously improves the stereocomplex crystallinity, heat-resistant temperature and mechanical strength of the provided polylactic acid stereocomplex by strictly controlling the dosage ratio of the levorotatory polylactic acid and the dextrorotatory polylactic acid in the raw material and adding a certain amount of compatible blend and adopting a unidirectional stretching process. More specifically, the product and the preparation method thereof provided by the invention have at least the following advantages:
1) According to the invention, through optimizing the design of the raw material formula and selecting a proper preparation process, the provided polylactic acid stereocomplex does not contain polylactic acid homogeneous crystallization, and the stereocomplex crystallinity is improved, so that the polylactic acid stereocomplex provided by the invention has relatively excellent heat resistance and mechanical properties.
2) The polylactic acid stereocomplex provided by the invention has the advantages of simple preparation process, high production efficiency, capability of realizing large-scale industrial production and good market prospect.
3) The invention provides a technical foundation for further improving the heat resistance of the polylactic acid, improving the tensile mechanical property, crystallization property and hydrolysis resistance of the polylactic acid and further expanding the application field of the polylactic acid.
The experimental results show that: the polylactic acid stereocomplex provided by the invention does not contain polylactic acid homogeneous crystals, the stereocomplex crystallinity is more than 40%, the tensile strength is more than or equal to 140MPa, and the storage modulus at 180 ℃ is more than 15MPa.
For clarity, the following examples are provided in detail.
Example 1
50 parts by weight of levorotatory polylactic acid (weight average molecular weight 15 ten thousand, optical purity 99%) and 50 parts by weight of dextrorotatory polylactic acid (weight average molecular weight 15 ten thousand, optical purity 99%) are mixed in a torque rheometer at a mixing temperature of 240 ℃ at a rotation speed of 40 revolutions per minute for 10 minutes with 0.1 part by weight of carbodiimide and 1 part by weight of pyromellitic dianhydride. The blended sample was cooled in air at room temperature and cut into small pieces, then pressed into 1mm thick sheet at 250℃and 10MPa on a flat vulcanizing machine, and then rapidly placed in a cold press under 10MPa for pressure maintaining and cooling to room temperature. Stretching the pressed sheet to 10 times at the stretching rate of 20mm/min at the temperature of 65 ℃, and cooling the stretched sheet to room temperature to obtain the unidirectional stretching polylactic acid stereocomplex product.
The unidirectional stretching polylactic acid stereocomplex product prepared in the embodiment is subjected to performance evaluation, and specific evaluation indexes are as follows:
1) Crystallinity:
heating a sample to be tested to 250 ℃ for melting by adopting a Differential Scanning Calorimeter (DSC) at a speed of 10 ℃/min, wherein the melting point is 160-180 ℃ for homogeneous crystallization, and the melting point is 200-230 ℃ for stereocrystal. If all samples do not show cold crystallization peaks, it is indicated that the polylactic acid is completely crystallized under the processing conditions.
2) Tensile strength:
cutting a sample to be measured into long strips with the length of 150mm and the width of 15mm plus or minus 0.1mm along the direction to be measured, wherein the distance between clamps is 100mm, and the test speed is 100mm/min plus or minus 10mm/min. The longitudinal and transverse samples were each tested 5 times, and their average values were taken.
3) Heat resistance:
on the DMA storage modulus-temperature curve (storage modulus decreases continuously with increasing test temperature) of the sample to be tested, the corresponding storage modulus at 180 ℃.
The performance evaluation results are as follows: heating a sample to 250 ℃ by using a Differential Scanning Calorimeter (DSC) at a speed of 10 ℃/min to melt the sample, so as to obtain a single melting point of 230 ℃, wherein no polylactic acid is homogeneously crystallized, and the degree of stereocomplex crystallization is 45%; the tensile strength is 160MPa; the corresponding storage modulus at 180℃is 21MPa.
Example 2
50 parts by weight of levorotatory polylactic acid (weight average molecular weight 50 ten thousand, optical purity 95%) and 50 parts by weight of dextrorotatory polylactic acid (weight average molecular weight 50 ten thousand, optical purity 98%) are mixed in a torque rheometer at a mixing temperature of 240 ℃ at a rotation speed of 120 r/min for 5min, wherein 15 parts by weight of poly-racemic lactic acid (weight average molecular weight 3 ten thousand) and 1 part by weight of carbodiimide are mixed. The mixed sample is cooled in the room temperature air state, cut into small pieces, pressed into 1mm thick sheets on a flat vulcanizing machine at 220 ℃ and 10MPa, and then rapidly placed into a cold press for pressure maintaining and cooling to room temperature under 10 MPa. Stretching the pressed sheet to 4 times at 100 ℃ at a stretching rate of 100mm/min, and cooling the stretched sheet to room temperature to obtain the unidirectional stretching polylactic acid stereocomplex product.
The unidirectional stretching polylactic acid stereocomplex product prepared in this example was subjected to performance evaluation by the evaluation method of example 1, and the result is: heating a sample to 250 ℃ by using a Differential Scanning Calorimeter (DSC) at a speed of 10 ℃/min to melt the sample, so as to obtain a single melting point of 220 ℃, wherein no polylactic acid is homogeneously crystallized, and the degree of stereocomplex crystallization is 49%; tensile strength is 140MPa; the corresponding storage modulus at 180℃is 18MPa.
Example 3
50 parts by weight of levorotatory polylactic acid (weight average molecular weight 25 ten thousand, optical purity 98%), 50 parts by weight of dextrorotatory polylactic acid (weight average molecular weight 25 ten thousand, optical purity 98%), 10 parts by weight of polyvinyl acetate (weight average molecular weight 5 ten thousand), 10 parts by weight of poly-racemized lactic acid (weight average molecular weight 10 ten thousand), 0.5 part by weight of carbodiimide and 0.5 part by weight of bisepoxybisphenol A-diglycidyl ether are blended in a torque rheometer, the blending temperature is 240 ℃, the rotating speed is 40 revolutions per minute, and the blending time is 10 minutes. The mixed sample is cooled in the room temperature air state, cut into small pieces, pressed into 1mm thick sheets on a flat vulcanizing machine at 220 ℃ and 10MPa, and then rapidly placed into a cold press for pressure maintaining and cooling to room temperature under 10 MPa. Stretching the pressed sheet to 6 times at the stretching rate of 5mm/min at the temperature of 75 ℃, and cooling the stretched sheet to room temperature to obtain the unidirectional stretching polylactic acid stereocomplex product.
The unidirectional stretching polylactic acid stereocomplex product prepared in this example was subjected to performance evaluation by the evaluation method of example 1, and the result is: heating a sample to 250 ℃ by using a Differential Scanning Calorimeter (DSC) at a speed of 10 ℃/min to melt the sample, so as to obtain a single melting point of 225 ℃, wherein the polylactic acid is not homogeneously crystallized, and the three-dimensional composite crystallinity is 42%; tensile strength is 148MPa; the corresponding storage modulus at 180℃is 23MPa.
Comparative example 1
50 parts by weight of levorotatory polylactic acid (weight average molecular weight 15 ten thousand, optical purity 99%) and 50 parts by weight of dextrorotatory polylactic acid (weight average molecular weight 15 ten thousand, optical purity 99%) are mixed in a torque rheometer at a mixing temperature of 240 ℃ at a rotating speed of 40 revolutions per minute for 10 minutes, wherein 0.1 part by weight of carbodiimide and 1 part by weight of pyromellitic dianhydride are mixed. The mixed sample is cooled in the air state at room temperature, cut into small pieces, pressed into a sheet with the thickness of 1mm on a flat vulcanizing machine at the temperature of 250 ℃ and the pressure of 10MPa, and then rapidly placed into a cold press for pressure maintaining and cooling to the room temperature under the pressure of 10 MPa. Stretching the pressed sheet to 10 times at the stretching rate of 20mm/min at the temperature of 65 ℃, and cooling the stretched sheet to room temperature to obtain the unidirectional stretching polylactic acid stereocomplex product.
The unidirectional stretching polylactic acid stereocomplex product prepared in this comparative example was subjected to performance evaluation by the evaluation method of example 1, and the result is: heating a sample to 250 ℃ by using a Differential Scanning Calorimeter (DSC) at a speed of 10 ℃/min to melt the sample to obtain a polylactic acid homogeneous melting point of 178 ℃, a polylactic acid stereocomplex melting point of 230 ℃, and a polylactic acid homogeneous crystallinity of 30% and a stereocomplex crystallinity of 10%; tensile strength is 158MPa; the corresponding storage modulus at 180℃is 1.1MPa.
The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.
Claims (3)
1. A method for preparing a unidirectional stretching polylactic acid stereocomplex, which comprises the following steps:
a) Melt blending the raw materials, and cooling to obtain a polylactic acid blend with an amorphous structure;
the raw material comprises 50 parts by weight of L-polylactic acid, 50 parts by weight of L-polylactic acid and 15-30 parts by weight of compatible blend; the compatible blend comprises polyvinyl acetate and/or poly-racemic lactic acid; the weight average molecular weight of the L-polylactic acid is 15-50 ten thousand; the weight average molecular weight of the dextrorotatory polylactic acid is 15-50 ten thousand; the weight average molecular weight of the polyvinyl acetate is 5-15 ten thousand; the weight average molecular weight of the poly-racemization lactic acid is 3 ten thousand-10 ten thousand;
the raw material also comprises an anti-hydrolysis agent and/or a chain extender; the anti-hydrolysis agent comprises carbodiimide; the chain extender comprises pyromellitic dianhydride and/or dioxybisphenol A-diglycidyl ether;
the temperature of the melt blending is 220-240 ℃; the time of melt blending is 5-10 min;
b) Carrying out unidirectional stretching on the polylactic acid blend to obtain a unidirectional stretching polylactic acid stereocomplex;
the temperature of the unidirectional stretching is 65-100 ℃; the stretching rate of the unidirectional stretching is 5-100 mm/min; the stretching multiplying power of unidirectional stretching is 4-10 times.
2. The method of claim 1, wherein the polylactic acid blend is formed into a sheet to be stretched prior to unidirectional stretching; the specific steps for preparing the sheet to be stretched include:
and (3) hot-pressing the polylactic acid blend into sheets, and cooling to obtain the sheet to be stretched with an amorphous structure.
3. The method according to any one of claims 1 to 2, wherein each raw material is vacuum-dried before the melt blending.
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| JP4693365B2 (en) * | 2004-05-17 | 2011-06-01 | 三井化学東セロ株式会社 | Polylactic acid stretched film and method for producing the same |
| EP2098551B1 (en) * | 2006-12-28 | 2018-08-01 | Musashino Chemical Laboratory, Ltd. | Process for producing polylactic acid block copolymer |
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| JP2013060532A (en) * | 2011-09-14 | 2013-04-04 | Mitsui Chemicals Tohcello Inc | Stretched film composed of polylactic aid-based composition |
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