阅读说明：本技术 改性聚乙烯醇薄膜及其制备方法与应用 (Modified polyvinyl alcohol film and preparation method and application thereof ) 是由 钱玉英 卢金永 冯晓涛 曲波 邱守季 张彤 于 2021-07-09 设计创作，主要内容包括：本发明涉及一种改性聚乙烯醇薄膜及其制备方法与应用,该改性聚乙烯醇薄膜的制备方法包括：将制备原料混合,得到混合料；将混合料在100℃～150℃熔融造粒,得到改性颗粒；将改性颗粒在120℃～150℃吹膜成型,吹胀比为1:1.2～1:4,牵引比为1:1.5～1:5。按照重量份数计,混合料包括：聚乙烯醇80份～90份及固体增塑剂5份～20份,且制备原料总重量份数为100份；固体增塑剂选自山梨醇、木糖醇、赤藓糖醇、甘露糖醇、异麦芽酮糖醇、麦芽糖醇及乳糖醇中的至少一种。采用固体增塑剂对聚乙烯醇改性,无需复杂的设备,直接将原料混合熔融造粒,然后吹膜成型即可,因而加工设备和工艺简单,可在较低加工温度下制得机械性能良好的改性聚乙烯醇薄膜。(The invention relates to a modified polyvinyl alcohol film and a preparation method and application thereof, wherein the preparation method of the modified polyvinyl alcohol film comprises the following steps: mixing the preparation raw materials to obtain a mixture; melting and granulating the mixture at 100-150 ℃ to obtain modified particles; and (3) blowing the modified particles at 120-150 ℃ for film forming, wherein the blowing-up ratio is 1: 1.2-1: 4, and the traction ratio is 1: 1.5-1: 5. The mixture comprises the following components in parts by weight: 80-90 parts of polyvinyl alcohol and 5-20 parts of solid plasticizer, wherein the total weight parts of the raw materials are 100 parts; the solid plasticizer is at least one selected from sorbitol, xylitol, erythritol, mannitol, isomalt, maltitol and lactitol. The polyvinyl alcohol is modified by the solid plasticizer, complex equipment is not needed, the raw materials are directly mixed, melted and granulated, and then the film is blown for forming, so that the processing equipment and the process are simple, and the modified polyvinyl alcohol film with good mechanical property can be prepared at a lower processing temperature.)

1. A preparation method of a modified polyvinyl alcohol film is characterized by comprising the following steps:

mixing the preparation raw materials to obtain a mixture;

melting and granulating the mixture at 100-150 ℃ to obtain modified particles;

blowing the modified particles at 120-150 ℃ for film forming, wherein the blowing-up ratio is 1: 1.2-1: 4, and the traction ratio is 1: 1.5-1: 5;

wherein, according to the parts by weight, the mixture comprises:

and the total weight part of each preparation raw material is 100 parts;

the solid plasticizer is at least one selected from sorbitol, xylitol, erythritol, mannitol, isomalt, maltitol and lactitol.

2. The method for preparing a modified polyvinyl alcohol film according to claim 1, wherein in the step of mixing the preparation raw materials to obtain the mixture, the mixing speed is 1000rpm to 1500rpm, and the mixing time is 5 minutes to 10 minutes.

3. The method for preparing a modified polyvinyl alcohol film according to claim 1, wherein the step of melt-granulating is performed in a twin-screw extruder, and the rotation speed of the twin-screw extruder is 60rpm to 150 rpm.

4. The method for preparing a modified polyvinyl alcohol film according to any one of claims 1 to 3, wherein the degree of polymerization of the polyvinyl alcohol is 1500 to 3500, and the degree of alcoholysis is 80 to 99%.

5. The method of any one of claims 1 to 3, wherein the stabilizer is at least one selected from zinc stearate, calcium stearate, and barium stearate.

6. The method of any one of claims 1 to 3, wherein the antioxidant is at least one selected from the group consisting of antioxidant 1010, antioxidant 168, antioxidant 1076, and antioxidant 1024.

7. The method of any one of claims 1 to 3, wherein the neutralizing agent is at least one selected from the group consisting of calcium chloride, magnesium chloride, zinc chloride, calcium hydroxide, and magnesium hydroxide.

8. The modified polyvinyl alcohol film obtained by the method for producing a modified polyvinyl alcohol film according to any one of claims 1 to 7, wherein the modified polyvinyl alcohol film has an elongation at break in the transverse direction of 240% to 270% and an elongation at break in the longitudinal direction of 240% to 265%.

9. Use of the modified polyvinyl alcohol film according to claim 8 for the preparation of packaging materials.

10. A packaging material comprising the modified polyvinyl alcohol film according to claim 8.

Technical Field

The invention relates to the technical field of high polymer material processing, in particular to a modified polyvinyl alcohol film and a preparation method and application thereof.

Background

Polyvinyl alcohol (PVA) is a high molecular polymer formed by alcoholysis of polyvinyl acetate. The oil-resistant and solvent-resistant composite material is soluble in water, biodegradable, non-toxic and free of side effects, has good oil resistance, solvent resistance and gas barrier property, and has good mechanical property and biocompatibility. The polyvinyl alcohol is prepared into a film, and has unique advantages in the aspects of medical treatment, food, toxic contact packaging and the like.

The polyvinyl alcohol has regular structure, small side group volume and high crystallinity; and a large amount of hydroxyl groups on a molecular chain form strong hydrogen bonds, so that the melting temperature and the decomposition temperature of the polyvinyl alcohol are very close, and the polyvinyl alcohol is difficult to process. At present, the production of polyvinyl alcohol films mainly adopts a solution casting method and a plasticizing melting method.

The solution casting method includes dissolving PVA in water solution, adding plasticizer, coloring agent, etc. to prepare water soluble glue, coating on the moving casting belt, drying to evaporate water, stripping film from the casting belt, and post-treatment to obtain PVA film. The plasticizing and melting method is to blend the polyvinyl alcohol with the aid of plasticizer and other additives to lower the melting point of polyvinyl alcohol to below the decomposition temperature of polyvinyl alcohol. The film is prepared by extruding and granulating through a double screw, and then blowing the film for shaping or melting and casting the film.

However, the conventional plasticizing and melting method for preparing the polyvinyl alcohol film usually reduces the mechanical strength of the polyvinyl alcohol film due to the large addition amount of the plasticizer, and needs to be provided with a special feeding device for feeding to perform melting granulation, so that the production cost is high, the process is complex, and the uniformity and stability of the mixed material are difficult to ensure.

Disclosure of Invention

Based on the above, there is a need for a modified polyvinyl alcohol film with high mechanical strength, good isotropy, and simple processing equipment and process, and a preparation method and applications thereof.

In one aspect of the present invention, a method for preparing a modified polyvinyl alcohol film is provided, which comprises the following steps:

mixing the preparation raw materials to obtain a mixture;

melting and granulating the mixture at 100-150 ℃ to obtain modified particles;

blowing the modified particles at 120-150 ℃ for film forming, wherein the blowing-up ratio is 1: 1.2-1: 4, and the traction ratio is 1: 1.5-1: 5;

wherein, according to the parts by weight, the mixture comprises:

and the total weight part of each preparation raw material is 100 parts;

the solid plasticizer is at least one selected from sorbitol, xylitol, erythritol, mannitol, isomalt, maltitol and lactitol.

In some embodiments, in the step of mixing the preparation raw materials to obtain the mixture, the mixing speed is 1000rpm to 1500rpm, and the mixing time is 5 minutes to 10 minutes.

In some of these embodiments, the melt pelletizing step is performed in a twin screw extruder having a speed of 60rpm to 150 rpm.

In some embodiments, the polymerization degree of the polyvinyl alcohol is 1500-3500, and the alcoholysis degree is 80-99%.

In some of these embodiments, the stabilizer is selected from at least one of zinc stearate, calcium stearate, and barium stearate.

In some of these embodiments, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, and antioxidant 1024.

In some of these embodiments, the neutralizing agent is selected from at least one of calcium chloride, magnesium chloride, zinc chloride, calcium hydroxide, and magnesium hydroxide.

In another aspect of the present invention, there is also provided a modified polyvinyl alcohol film obtained by the above method for preparing a modified polyvinyl alcohol film, wherein the modified polyvinyl alcohol film has a transverse elongation at break of 240% to 270% and a longitudinal elongation at break of 240% to 265%.

In another aspect of the invention, the invention also provides the application of the modified polyvinyl alcohol film in preparing packaging materials.

In another aspect of the invention, a packaging material is also provided, which comprises the modified polyvinyl alcohol film.

According to the preparation method of the modified polyvinyl alcohol film, the polyvinyl alcohol is subjected to plastic modification by adding the solid plasticizer, and the plasticizer is solid, so that no complicated feeding equipment is needed, and the polyvinyl alcohol, the solid plasticizer and other preparation raw materials are directly mixed and fed for melting granulation. The solid plasticizer is selected from solid polyols such as sorbitol, xylitol, erythritol, mannitol, isomalt, maltitol, lactitol and the like, and can effectively destroy the intramolecular hydrogen bond acting force of the polyvinyl alcohol, so that the processing temperature of the polyvinyl alcohol can be obviously reduced under the condition of less adding amount of the solid plasticizer, and the modification effect is good. The preparation method of the modified polyvinyl alcohol film has simple processing equipment and processing technology, and lower processing temperature, and the prepared modified polyvinyl alcohol film has good mechanical property, and is particularly suitable for preparing packaging materials.

Drawings

FIG. 1 shows modified polyvinyl alcohol obtained by melt granulation in example 1 of the present invention;

FIG. 2 shows a modified polyvinyl alcohol film obtained by blow molding in example 1 of the present invention.

Detailed Description

To facilitate an understanding of the invention, the invention will now be described more fully with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The terminology used in the description of the invention herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items.

One embodiment of the present invention provides a method for preparing a modified polyvinyl alcohol film, including the following steps S1, S2, and S3.

Step S1: mixing the preparation raw materials to obtain a mixture;

step S2: melting and granulating the mixture at 100-150 ℃ to obtain modified particles;

step S3: blowing the modified particles at 120-150 ℃ for film forming, wherein the blowing-up ratio is 1: 1.2-1: 4, and the traction ratio is 1: 1.5-1: 5;

wherein, according to the weight portion, the mixture includes:

and the total weight part of each preparation raw material is 100 parts;

the solid plasticizer is at least one selected from sorbitol, xylitol, erythritol, mannitol, isomalt, maltitol and lactitol. The solid plasticizer is solid polyhydric sugar alcohol, and hydrogen bonds are easily formed with polyvinyl alcohol molecules, so that the hydrogen bond acting force in the polyvinyl alcohol molecules is weakened, the melting point of the polyvinyl alcohol is reduced, and the processing temperature is reduced.

According to the preparation method of the modified polyvinyl alcohol film, the polyvinyl alcohol is subjected to plastic modification by adding the solid plasticizer, and the plasticizer is solid, so that compared with the traditional processing method using the liquid plasticizer, special equipment is required for auxiliary blanking, and the volume of the screw groove of the liquid plasticizer in a double-screw conveying compression section is reduced, so that the plasticizer is easy to precipitate and gather at a feeding port, and the blanking difficulty is increased. The preparation method does not need complicated feeding equipment, and the raw materials for preparing the polyvinyl alcohol, the solid plasticizer and the like are directly mixed and fed for melting and granulation.

In addition, the processing temperature of the polyvinyl alcohol can be obviously reduced under the condition of less adding amount of the solid plasticizer, and the modification effect is good. The preparation method of the modified polyvinyl alcohol film has the advantages of simple processing equipment and processing technology, lower processing temperature, extremely small degradation amount of polyvinyl alcohol, good mechanical property of the prepared modified polyvinyl alcohol film, and approximate transverse property and longitudinal property of the film obtained by the film blowing forming technology, and is particularly suitable for preparing packaging materials.

In some of these embodiments, step S1 is performed in a high speed mixer at a speed of 1000rpm to 1500rpm for a period of 5 minutes to 10 minutes.

In some of these embodiments, step S2 is performed in a twin screw extruder; the rotating speed of the double-screw extruder is 60 rpm-150 rpm.

In some of these embodiments, the temperatures set for the zones of the twin screw extruder are 120 deg.C, 125 deg.C, 130 deg.C, 135 deg.C, 140 deg.C, 145 deg.C, 150 deg.C, respectively.

In some of these embodiments, step S3 is performed by blown film forming using a single screw extruder. In some of these embodiments, the single screw extruder is set to temperatures of 130 ℃, 140 ℃, 150 ℃, 150 ℃; the rotating speed of the double-screw extruder is 20 rpm-80 rpm.

In some of these embodiments, the blow-up ratio in step S3 is 1:2 and the draw ratio is 1: 3. The longitudinal performance and the transverse performance of the modified polyvinyl alcohol film obtained in the way are close to each other, and the isotropy is good.

In some embodiments, the polymerization degree of the polyvinyl alcohol is 1500-3500, and the alcoholysis degree is 80-99%.

In some embodiments, the mixture comprises 0.1 to 5 parts by weight of the stabilizer. In some of these embodiments, the stabilizer is selected from at least one of zinc stearate, calcium stearate, and barium stearate.

The antioxidant is added, so that the problem of oxidation and aging of polyvinyl alcohol in the processing process and the use of subsequent products can be avoided, the performance of the processed products is improved, and the service life of the processed products is prolonged. In some embodiments, the mixture comprises 0.1 to 0.5 parts by weight of antioxidant. In some of these embodiments, the antioxidant is selected from at least one of antioxidant 1010, antioxidant 168, antioxidant 1076, and antioxidant 1024.

In some of these embodiments, the blend includes 0.1 to 1 part by weight of the lubricant. In some of these embodiments, the lubricant may be selected from at least one of stearic acid, PE wax, pentaerythritol stearate, and oleamide.

The neutralizer is mainly used for absorbing acid generated in the fusion processing process of the polyvinyl alcohol, reducing free acid, removing odor, preventing the degradation of the polyvinyl alcohol and further improving the performance of the polyvinyl alcohol film. In some embodiments, the mixture comprises 0.1 to 2 parts by weight of the neutralizing agent. In some of these embodiments, the neutralizing agent is selected from at least one of calcium chloride, magnesium chloride, zinc chloride, calcium hydroxide, and magnesium hydroxide.

The invention also provides a modified polyvinyl alcohol film obtained by the preparation method of the modified polyvinyl alcohol film, wherein the transverse elongation at break of the modified polyvinyl alcohol film is 240-270%, and the longitudinal elongation at break of the modified polyvinyl alcohol film is 240-265%.

The modified polyethylene film has good mechanical properties, and the transverse properties are close to the longitudinal properties, so that the modified polyethylene film is particularly suitable for preparing packaging materials.

The invention also provides application of the modified polyvinyl alcohol film in preparing packaging materials.

The invention also provides a packaging material which comprises the modified polyvinyl alcohol film.

The packaging material comprises the modified polyvinyl alcohol film, and the modified polyvinyl alcohol film has good mechanical properties, transverse properties close to longitudinal properties, good isotropy, good mechanical properties and good coating property.

The modified polyvinyl alcohol film and the method for producing the same according to the present invention will be further described below with reference to specific examples.

Example 1:

the raw material for preparing the modified polyvinyl alcohol film of example 1 comprises the following components in parts by weight: 83.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 13 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1.5 parts of calcium chloride.

The modified polyvinyl alcohol film of example 1 was prepared as follows:

(1) at normal temperature, adding polyvinyl alcohol, a solid plasticizer, a stabilizer, an antioxidant, a lubricant and a neutralizer into a high-speed mixer for mixing, wherein the set rotating speed is 1200rpm, and the mixing time is 10 minutes, so as to obtain a mixture.

(2) Introducing the mixture into a hopper of a double-screw extruder, starving for feeding, and carrying out melt granulation by using the double-screw extruder, wherein the extrusion temperature of ten areas of the double-screw extruder is set as follows: 120 ℃, 125 ℃, 130 ℃, 135 ℃, 135 ℃, 135 ℃, 135 ℃, 140 ℃, 145 ℃, 150 ℃ and the rotating speed of 100 rpm. And (4) drawing strips, air-cooling and granulating to obtain modified polyvinyl alcohol particles.

(3) Drying the modified polyvinyl alcohol particles at 80 ℃ for 4 hours, and then putting the modified polyvinyl alcohol particles into a hopper of a single-screw extruder for film blowing forming, wherein the temperature of the single-screw film blowing forming is 130 ℃, and the rotating speed of the single-screw extruder is 50 rpm; the blow-up ratio of the blown film forming is 1:2, and the traction ratio is 1: 3. And rolling to obtain the modified polyvinyl alcohol film.

Example 2:

the raw material for preparing the modified polyvinyl alcohol film of example 2 comprises the following components in parts by weight: 86 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 10 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1.5 parts of calcium chloride. The preparation method is the same as that of example 1.

Example 3:

the raw material for preparing the modified polyvinyl alcohol film of example 3 comprises the following components in parts by weight: 79 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 18 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method is the same as that of example 1.

Example 4:

the raw material for preparing the modified polyvinyl alcohol film of example 4 comprises the following components in parts by weight: 85 parts of polyvinyl alcohol (with the polymerization degree of 1700 and the alcoholysis degree of 88%), 12 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1.5 parts of calcium chloride. The preparation method is the same as that of example 1. The preparation method is the same as that of example 1.

Example 5:

the raw material for preparing the modified polyvinyl alcohol film of example 5 comprises the following components in parts by weight: 82 parts of polyvinyl alcohol (with the polymerization degree of 1700 and the alcoholysis degree of 88%), 15 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method is the same as that of example 1.

Example 6:

the raw material for preparing the modified polyvinyl alcohol film of example 6 comprises the following components in parts by weight: 91.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 5 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1.5 parts of calcium chloride. The preparation method is the same as that of example 1.

Example 7:

the raw material for preparing the modified polyvinyl alcohol film of example 7 comprises the following components in parts by weight: 77 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 20 parts of erythritol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method is the same as that of example 1.

Example 8:

the raw material for preparing the modified polyvinyl alcohol film of example 8 comprises the following components in parts by weight: 85 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 12 parts of sorbitol, 0.5 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method is the same as that of example 1.

Example 9:

the modified polyvinyl alcohol film of example 9 was substantially the same as that of example 1 except that the inflation ratio for inflation molding was 1:2, traction ratio 1: 5.

example 10:

the modified polyvinyl alcohol film of example 10 was substantially the same as that of example 1 except that the inflation ratio for inflation molding was 1:4, traction ratio 1: 2.

the injection molding tensile property test of the modified polyvinyl alcohol particles prepared in the examples 1-8 is shown in Table 1, and the test standards of the tensile strength and the elongation at break refer to GB/T1040.2. The performance test results of the modified polyvinyl alcohol films prepared in the examples 1-10 are shown in table 2, wherein MD refers to the longitudinal performance of the film, and TD refers to the transverse performance of the film; the test standard is referred to GB/T1040.3.

TABLE 1

Sample (I)	Tensile strength	Elongation at break
			Example 1	55.5MPa	256％
Example 2	52.3MPa	266％
			Example 3	50.8MPa	272％
Example 4	51.8MPa	276％
			Example 5	52.2MPa	264％
Example 6	60.0MPa	246％
			Example 7	50.2MPa	280％
Example 8	52.3MPa	263％

TABLE 2

Comparative example 1:

the modified polyvinyl alcohol film of comparative example 1 was prepared from the following raw materials in parts by weight: 45 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 40 parts of glycerol, 10 parts of PEG400, 1.5 parts of zinc stearate, 10100.5 parts of antioxidant, 1680.5 part of antioxidant, 1 part of stearic acid and 1.5 parts of calcium chloride.

The modified polyvinyl alcohol film of comparative example 1 was prepared as follows:

(1) adding polyvinyl alcohol, a lubricant (zinc stearate), an antioxidant, a lubricant (stearic acid) and a neutralizer (calcium chloride) into a high-speed mixer at normal temperature, and mixing for 3 minutes at a set rotating speed of 1000 rpm; then adding 50% of plasticizer (glycerol and PEG400), setting the rotating speed to be 1000rpm, and mixing for 3 minutes; finally, the remaining plasticizer was added at a set speed of 1000rpm for 5 minutes.

(2) Introducing the mixture into a hopper of a double-screw extruder with a forced feeder, starving and feeding, melting and granulating by using the double-screw extruder, wherein the temperature of an extrusion ten-zone of the double-screw extruder is set as follows: 160 ℃, 165 ℃, 170 ℃, 175 ℃, 185 ℃, 185 ℃, 190 ℃, 190 ℃, 190 ℃, 195 ℃ and 100 rpm. And (4) drawing strips, air-cooling and granulating to obtain modified polyvinyl alcohol particles.

(3) Drying the modified polyvinyl alcohol particles at 80 ℃ for 4 hours, and then putting the modified polyvinyl alcohol particles into a hopper of a single-screw extruder for film blowing forming, wherein the temperature of the single-screw film blowing forming is 180 ℃, and the rotating speed of the single-screw extruder is 50 rpm; the blow-up ratio of the blown film forming is 1:2, and the traction ratio is 1: 3. And rolling to obtain the modified polyvinyl alcohol film.

Comparative example 2:

the modified polyvinyl alcohol film of comparative example 2 was prepared from the following raw materials in parts by weight: 46.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 50 parts of glycerol, 1 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method was the same as in comparative example 1.

Comparative example 3:

the raw material for preparing the modified polyvinyl alcohol film of comparative example 3 comprises the following components in parts by weight: 46.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 50 parts of PEG400, 1 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method was the same as in comparative example 1.

Comparative example 4:

the raw material for preparing the modified polyvinyl alcohol film of comparative example 4 comprises the following components in parts by weight: 76.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 20 parts of glycerol, 1 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method was the same as in comparative example 1.

Comparative example 5:

the raw material for preparing the modified polyvinyl alcohol film of comparative example 5 comprises the following components in parts by weight: 76.5 parts of polyvinyl alcohol (with polymerization degree of 3500 and alcoholysis degree of 88%), 20 parts of PEG400, 1 part of zinc stearate, 10100.25 parts of antioxidant, 1680.25 parts of antioxidant, 1 part of stearic acid and 1 part of calcium chloride. The preparation method was the same as in comparative example 1.

Comparative example 6:

the modified polyvinyl alcohol film of comparative example 6 is substantially the same as example 1 except that the inflation ratio for inflation film forming is 1:2, traction ratio 1: 6.

comparative example 7:

the modified polyvinyl alcohol film of comparative example 7 is substantially the same as example 1 except that the inflation ratio for inflation film forming is 1:4, the traction ratio is 1: 6.

the injection molding tensile property test of the modified polyvinyl alcohol particles prepared in the comparative examples 1-5 is shown in Table 3, and the test standard of the tensile strength and the elongation at break refers to GB/T1040.2. The performance test results of the modified polyvinyl alcohol films prepared in the comparative examples 1-7 are shown in Table 4, wherein MD refers to the longitudinal performance of the film, and TD refers to the transverse performance of the film; the test standard is referred to GB/T1040.3.

TABLE 3

Sample (I)	Tensile strength	Elongation at Break (%)
			Comparative example 1	18.0MPa	166％
Comparative example 2	17.2MPa	170％
			Comparative example 3	17.6MPa	160％
Comparative example 4	19.2MPa	45％
			Comparative example 5	19.8MPa	40％

TABLE 4

Referring to fig. 1 and 2, the modified polyvinyl alcohol prepared by melt granulation and the modified polyvinyl alcohol film obtained by film blowing molding in example 1 are shown, respectively, and it can be seen that the prepared modified polyvinyl alcohol and the film have better uniformity. As can be seen from the data in Table 2, the transverse performance and the longitudinal performance of the modified polyvinyl alcohol films prepared in examples 1-10 are similar, the isotropy of the films is good, the mechanical performance of the modified polyvinyl alcohol films is good, the tensile strength is 34.6-37.9 MPa, and the elongation at break is 240-269%. As can be seen from the data in Table 4, the modified polyvinyl alcohol films of comparative examples 1 to 5 modified with liquid plasticizers such as glycerin or PEG400 have poor mechanical properties, 14.2MPa to 16.5MPa of tensile strength and 45% to 165% of elongation at break. Compared with the comparative examples 6 and 7, the film blowing process has the advantages that the blowing ratio and the traction ratio are changed, the tensile strength and the breaking strain rate of the film are obviously reduced, the forming window of the film blowing is extremely narrow, and the film blowing performance is poor.

The technical features of the embodiments described above may be arbitrarily combined, and for the sake of brevity, all possible combinations of the technical features in the embodiments described above are not described, but should be considered as being within the scope of the present specification as long as there is no contradiction between the combinations of the technical features.

The above-mentioned embodiments only express several embodiments of the present invention, so as to understand the technical solutions of the present invention specifically and in detail, but not to be understood as the limitation of the protection scope of the invention. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. It should be understood that the technical solutions provided by the present invention, which are obtained by logical analysis, reasoning or limited experiments, are within the scope of the present invention as set forth in the appended claims. Therefore, the protection scope of the present invention should be subject to the content of the appended claims, and the description and the drawings can be used for explaining the content of the claims.