阅读说明：本技术 一种聚乳酸膜及其制备方法 (Polylactic acid film and preparation method thereof ) 是由 田子钦 陈加强 袁子丹 崔泽君 赵艳 黄恒辉 谢嘉宜 徐睿杰 雷彩红 于 2019-11-19 设计创作，主要内容包括：本申请属于高分子材料的技术领域,尤其涉及一种聚乳酸膜及其制备方法。本申请还提供了一种聚乳酸膜的制备方法,包括以下步骤：步骤1、将高分子量聚乳酸和低分子量聚乳酸混合,得到聚乳酸混料,高分子量聚乳酸的摩尔质量为100～220kg/mol,低分子量聚乳酸的摩尔质量为1000～5000g/mol,高分子量聚乳酸和低分子量聚乳酸的质量比为(1-10):1；步骤2、将聚乳酸混料由挤出机挤出,再经第一热拉辊进行第一拉伸,然后,经第二热拉辊进行第二拉伸后,热定型成膜得到聚乳酸膜。本申请提供了一种聚乳酸膜及其制备方法,能有效解决现有的聚乳酸在拉伸时容易发生脆性断裂,难以形成聚乳酸薄膜的技术缺陷。(The application belongs to the technical field of high polymer materials, and particularly relates to a polylactic acid film and a preparation method thereof. The application also provides a preparation method of the polylactic acid film, which comprises the following steps: step 1, mixing high molecular weight polylactic acid and low molecular weight polylactic acid to obtain a polylactic acid mixed material, wherein the molar mass of the high molecular weight polylactic acid is 100-220 kg/mol, the molar mass of the low molecular weight polylactic acid is 1000-5000 g/mol, and the mass ratio of the high molecular weight polylactic acid to the low molecular weight polylactic acid is (1-10): 1; and 2, extruding the polylactic acid mixed material by an extruder, performing first stretching by a first hot drawing roller, performing second stretching by a second hot drawing roller, and performing heat setting to form a film to obtain the polylactic acid film. The application provides a polylactic acid film and a preparation method thereof, which can effectively overcome the technical defects that the existing polylactic acid is easy to generate brittle fracture during stretching and is difficult to form a polylactic acid film.)

1. A method for producing a polylactic acid film, comprising the steps of:

step 1, mixing high molecular weight polylactic acid and low molecular weight polylactic acid to obtain a polylactic acid mixed material, wherein the molar mass of the high molecular weight polylactic acid is 100-220 kg/mol, the molar mass of the low molecular weight polylactic acid is 1000-5000 g/mol, and the mass ratio of the high molecular weight polylactic acid to the low molecular weight polylactic acid is (1-10): 1;

and 2, extruding the polylactic acid mixed material by an extruder, performing first-stage stretching by a first hot drawing roller, performing second-stage stretching by a second hot drawing roller, and performing heat setting to form a film to obtain the polylactic acid film.

2. The production method according to claim 1, wherein the mass ratio of the high-molecular weight polylactic acid to the low-molecular weight polylactic acid is 10: 1.

3. The method of claim 1, wherein the first stage hot draw roll is at a temperature of less than 60 ℃.

4. The method for preparing the hot drawing roller as claimed in claim 1, wherein the temperature of the second-stage hot drawing roller is 60-130 ℃.

5. The production method according to claim 1, wherein the first stage drawing has a draw ratio of 0 to 4; the stretching speed of the first section of stretching is 10-50 mm/s; the stretching ratio of the second stretching is 0.2-4; the second stage drawing has a drawing rate of 50 to 300 mm/s.

6. The method according to claim 1, wherein the heat setting temperature is 80 to 110 ℃ and the heat setting time is 3 min.

7. The method of claim 1, wherein the extruder has a die temperature of 150 to 210 ℃.

8. A polylactic acid film comprising the polylactic acid film produced by the production method according to any one of claims 1 to 7, wherein a pre-oriented fiber structure is present in the direction of stretching.

9. The polylactic acid film according to claim 8, wherein the thickness of the polylactic acid film is 60 to 12 μm.

10. The polylactic acid film according to claim 8, wherein the polylactic acid film has a crystallinity of 8 to 35%.

Technical Field

The application belongs to the technical field of high polymer materials, and particularly relates to a polylactic acid film and a preparation method thereof.

Background

The synthetic raw materials of the polylactic acid come from crops, such as corn stalks, potatoes, sugarcanes and the like, are biodegradable environment-friendly materials, and have wide application prospect. However, polylactic acid has a great defect, because the molecular chain is short and the molecular weight rigidity is great, the polylactic acid product prepared conventionally is easy to have brittle fracture during stretching, especially high-speed stretching, and the elongation at break is less than 10%, so that the research on toughening of polylactic acid is of great significance.

In summary, the polylactic acid products of the prior art have the technical defect that brittle fracture is easy to occur during stretching, especially high-speed stretching, so that the polylactic acid film is difficult to produce and apply.

Disclosure of Invention

In view of the above, the present application provides a polylactic acid film and a preparation method thereof, which can effectively solve the technical defects that the existing polylactic acid is easy to brittle fracture during stretching and is difficult to form a polylactic acid film.

The application also provides a preparation method of the polylactic acid film, which comprises the following steps:

step 1, mixing high molecular weight polylactic acid and low molecular weight polylactic acid to obtain a polylactic acid mixed material, wherein the molar mass of the high molecular weight polylactic acid is 100-220 kg/mol, the molar mass of the low molecular weight polylactic acid is 1000-5000 g/mol, and the mass ratio of the high molecular weight polylactic acid to the low molecular weight polylactic acid is (1-10): 1;

and 2, extruding the polylactic acid mixed material by an extruder, performing first stretching by a first hot drawing roller, performing second stretching by a second hot drawing roller, and performing heat setting to form a film to obtain the polylactic acid film.

Preferably, the mass ratio of the high molecular weight polylactic acid to the low molecular weight polylactic acid is 10: 1.

The lactic acid used alone in the above-mentioned polylactic acid may be L-lactic acid, D-lactic acid, or DL-lactic acid.

Preferably, the temperature of the first hot draw roll is less than 60 ℃.

Preferably, the temperature of the second hot drawing roll is 60-130 ℃.

Preferably, the stretching ratio of the first-stage stretching is 0-4, and the stretching speed of the first-stage stretching is 10-50 mm/min; the stretching ratio of the second-stage stretching is 0.5-4, and the stretching speed of the second-stage stretching is 50-300 mm/min.

And controlling the stretching multiplying power of the first section of stretching, the stretching rate of the first section of stretching, the stretching multiplying power of the second section of stretching and the stretching rate of the second section of stretching by adjusting the distance between the axle center of the first hot drawing roll and the axle center of the second hot drawing roll and the rotating speed of the first hot drawing roll and the rotating speed of the second hot drawing roll.

Preferably, the temperature of the die head of the extruder is 150-210 ℃.

Preferably, the heat setting temperature is 80-110 ℃, and the heat setting time is 3 min.

Preferably, the extruder is a twin screw extruder.

The application also provides a polylactic acid film, which comprises the polylactic acid film prepared by the preparation method.

Preferably, the polylactic acid film has a pre-oriented fiber structure along the stretching direction, and the thickness of the polylactic acid film is 60-12 μm.

Specifically, the polylactic acid intermediate sample drawn by the first stage roll has an amorphous structure when its thickness is about 200 μm and a pre-oriented fiber structure (a fiber structure having a large amount of orientation in the drawing direction) when its thickness is less than 60 μm.

Preferably, the final polylactic acid film article has a crystallinity of 8 to 35%.

Wherein the pre-oriented fiber structure is a Shish-like Kebab structure, the Shish width is 1-10 mu m, and the Kebab width is 50-150 mu m.

The purpose of the present application is to solve the technical problems that the conventional polylactic acid is easy to be brittle and broken during stretching and is difficult to form a polylactic acid film. The application provides a polylactic acid film with a pre-oriented fiber structure and a preparation method thereof. According to the preparation method, polylactic acid with two different molecular weights is mixed, low molecular weight polylactic acid is added to plasticize high molecular weight polylactic acid, then, a pre-oriented fiber structure is prepared through casting, and the flexible polylactic acid product with a lamellar structure is prepared through stretching of a casting roller and heat setting. According to experimental data, the polylactic acid film with the pre-oriented fiber structure has high transparency and crystallinity, and the crystallinity can reach as high as 35%; has higher breaking strength and no yielding process; the modulus can reach up to 4.2 Gpa; it rebounds up to 50% (when stretched to 30%).

Drawings

In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below.

FIG. 1 is a surface topography of a product 1 made in example 1 of the present application;

FIG. 2 is a first microscopic view of a product 1 obtained in example 1 of the present application;

FIG. 3 is a second microscopic view of a product 1 obtained in example 1 of the present application;

FIG. 4 is a microscopic view of a product 10 made by comparative example 2 of the present application;

FIG. 5 is a graph showing the results of the production apparatus of example 1 of the present application;

wherein, the reference numerals are extruder 1, die head 2, first hot drawing roll 3, second hot drawing roll 4 and polylactic acid film 5.

Detailed Description

The application provides a polylactic acid film and a preparation method thereof, which are used for solving the technical defects that the existing polylactic acid is easy to have brittle fracture during stretching and is difficult to form a polylactic acid film.

The technical solutions in the embodiments of the present application will be described clearly and completely below, and it should be understood that the described embodiments are only a part of the embodiments of the present application, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present application.

The following examples, in which the raw materials were commercially available or self-made, were prepared using the apparatus of fig. 5, and a polylactic acid film 5 was obtained by melting a polylactic acid compound in an extruder 1, extruding the same from a die 2, first-stage stretching the same by a first hot drawing roll 3, and second-stage stretching the same by a second hot drawing roll 4.