Amido polylactic acid as well as preparation method, application and application method thereof

Abstract

The invention discloses amido polylactic acid as well as a preparation method, application and an application method thereof. The amido polylactic acid is prepared from polylactic acid, an oxidizing agent, a dicarboxyl amine compound, a hydroxyl-containing acyl chloride monomer and a catalyst. The preparation method comprises the following steps: firstly, respectively preparing a dihydroxy amide monomer and polylactic acid with carboxyl at two ends, then esterifying the dihydroxy amide monomer and the polylactic acid to obtain an amido polylactic acid fiber with an amido group, and blending the amido polylactic acid fiber with a polyethylene fiber to prepare the amido polylactic acid degradation film material. According to the invention, amide groups are introduced into polylactic acid molecules through a chemical method, so that the polylactic acid is endowed with new performance, the heat resistance, chemical stability, biocompatibility and the like of the polylactic acid can be improved, and the formed amido polylactic acid degradable film material has the characteristics of degradability and antibacterial property, is relatively high in heat resistance and mechanical property, and can be widely applied to the field of degradable film materials. The method can be widely applied to the biomedical field.

Description

Technical Field

[0001] This invention belongs to the field of polymer material preparation technology, specifically relating to an amide-based polylactic acid, its preparation method, application, and application method. Background Technology

[0002] With increasing public awareness of environmental protection and strengthened government policies, the demand for biodegradable materials is constantly growing. Polylactic acid (PLA), as a key representative of biodegradable materials, is also experiencing sustained market demand growth. In the biomedical field, it can be used to manufacture medical devices and surgical sutures due to its excellent biocompatibility and biodegradability, reducing secondary harm to the human body. In the packaging materials sector, PLA can replace traditional petroleum-based plastics in the manufacture of food packaging and agricultural mulch films, helping to reduce white pollution. Furthermore, PLA can also be applied in various other fields such as the textile and construction industries.

[0003] Although polylactic acid (PLA) has many advantages, its inherent brittleness limits its application in many fields. Therefore, it is essential to modify PLA. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the present invention aims to provide an amide-based polylactic acid, its preparation method, application, and application method.

[0005] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows: This invention discloses an amide-based polylactic acid, which is prepared by polylactic acid, an oxidant, a dicarboxylic acid compound, a hydroxyl-containing acyl chloride monomer, and a catalyst.

[0006] This invention also discloses a method for preparing amide-based polylactic acid, comprising the following steps: 1) Polylactic acid reacts with an oxidizing agent to obtain polylactic acid with carboxyl groups at both ends; 2) The dicarboxylated amine compound is amidated with a hydroxyl-containing acyl chloride monomer to obtain a dihydroxyamide monomer; 3) Using a catalyst, the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid.

[0007] Furthermore, the weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:2-3.

[0008] Furthermore, the weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 1-2:1-3.

[0009] Furthermore, the catalyst is Zn / Ce-MOF, and the molar ratio of Zn:Ce is 2-3:1.

[0010] The present invention also discloses the application of amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes.

[0011] This invention also discloses a method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes, comprising the following steps: Amide-based polylactic acid, antioxidant, polyethylene and solvent are mixed evenly, then poured into a reaction vessel and stirred and heated. The reaction vessel is then subjected to gradient pressure, and after heat and pressure maintenance, the desired amide-based polylactic acid degradation membrane is obtained by spinning.

[0012] Furthermore, the mass percentages of the amide-based polylactic acid, antioxidant, polyethylene, and solvent are 0.1-1%, 0.1-1%, 1-10%, and 89.8-97%, respectively; the mixture is stirred and heated to 30-80°C at a stirring speed of 200-400 rpm.

[0013] Furthermore, the step of applying gradient pressure to the reactor includes: In the first stage, the reactor is pressurized to 6-7 MPa and heated to 100-110℃, and held for 20-35 minutes to eliminate bubbles in the system. In the second stage, the reactor is pressurized to 8-9 MPa and heated to 150-160℃, and held for 50-60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10-11 MPa and heated to 180-190℃, and held for 30-40 minutes to achieve tightness.

[0014] Furthermore, the pressurized gas environment is one of nitrogen, argon, air, and carbon dioxide; the antioxidant is one or a combination of several of tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168), bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626), tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (antioxidant 1010), and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076); the molecular weight of the polyethylene is 100,000-500,000; and the solvent is one or a combination of several of dimethyl sulfoxide, N,N-dimethylformamide, acetone, benzene, xylene, dichloromethane, and carbon tetrachloride.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention discloses an amide-based polylactic acid (PLA), its preparation method, applications, and application methods. First, a dihydroxyamide monomer and PLA with carboxyl groups at both ends are prepared separately. Then, the two are esterified to obtain amide-based PLA fibers with amide groups. These fibers can be blended with polyethylene fibers to produce amide-based PLA degradable membrane materials. This invention introduces amide groups into PLA molecules through chemical methods, thereby endowing PLA with new properties, improving its heat resistance, chemical stability, and biocompatibility. The resulting amide-based PLA degradable membrane material is degradable and antibacterial, with high heat resistance and mechanical properties, and can be widely used in the biomedical field. Detailed Implementation

[0016] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0017] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0018] This invention discloses an amide-based polylactic acid, which is prepared by polylactic acid, an oxidant, a dicarboxylic acid compound, a hydroxyl-containing acyl chloride monomer, and a catalyst.

[0019] This invention also discloses a method for preparing amide-based polylactic acid, comprising the following steps: 1) Polylactic acid (number average molecular weight of 50,000-100,000) reacts with an oxidizing agent (one or a combination of concentrated sulfuric acid, concentrated nitric acid, hydrogen peroxide, sodium periodate) to obtain polylactic acid with carboxyl groups at both ends. 2) Amidation of a dicarboxylated amine compound with a hydroxyl-containing acyl chloride monomer yields a dihydroxyamide monomer; wherein the weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:2-3; 3) Using a catalyst, the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid; wherein the weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 1-2:1-3.

[0020] In step 3), the catalyst is a zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF), with a Zn:Ce molar ratio of 2-3:1. The zinc-rare earth bimetallic organic framework catalyst can lower the activation energy of the reaction, increase the esterification rate to over 95%, and control the molecular weight distribution of polylactic acid (PDI<1.5). Compared with traditional catalysts, the thermal decomposition temperature of the product is increased by 20℃.

[0021] The present invention also discloses the application of amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes.

[0022] This invention also discloses a method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes, comprising the following steps: Based on a total mass percentage of 100%, 0.1-1% amide-based polylactic acid, 0.1-1% antioxidant, 1-10% polyethylene, and 89.8-97% solvent are mixed evenly and then poured into a reaction vessel. The mixture is stirred and heated to 30-80℃ at a stirring speed of 200-400 rpm. The reaction vessel is then subjected to gradient pressurization in a pressurized gas environment consisting of nitrogen, argon, air, or carbon dioxide. After maintaining the temperature and pressure for 0.5-5 hours, the amide-based polylactic acid degradable membrane is obtained by spinning using a conveyor belt.

[0023] The steps for gradient pressurization of the reactor include: In the first stage, the reactor is pressurized to 6-7 MPa and heated to 100-110℃, and held for 20-35 minutes to eliminate bubbles in the system. In the second stage, the reactor is pressurized to 8-9 MPa and heated to 150-160℃, and held for 50-60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10-11 MPa and heated to 180-190℃, and held for 30-40 minutes to achieve tightness.

[0024] The antioxidant is one or a combination of several of the following: tris[2,4-di-tert-butylphenyl] phosphite (antioxidant 168), bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626), tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (antioxidant 1010), and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076).

[0025] The molecular weight of polyethylene is between 100,000 and 500,000.

[0026] The solvent is one or a combination of several of the following: dimethyl sulfoxide, N,N-dimethylformamide, acetone, benzene, xylene, dichloromethane, and carbon tetrachloride.

[0027] Example 1 An amide-based polylactic acid is prepared by polylactic acid, an oxidant, a dicarboxylic acid compound, a hydroxyl-containing acyl chloride monomer, and a catalyst.

[0028] A method for preparing amide-based polylactic acid includes the following steps: 1) 10g of polylactic acid with a number average molecular weight of 50,000 was pulverized to a particle size of 0.5mm, dried to remove moisture, and then added to a flask. 100mL of 65% concentrated nitric acid was added, the temperature was raised to 70℃, the stirring speed was 300r, and the reaction was carried out for 7h. After cooling to room temperature, the product was filtered and collected. The product was neutralized to pH 7 with 5% sodium bicarbonate, washed 4 times with deionized water, and finally dried to obtain white powder polylactic acid with carboxyl groups at both ends. 2) The dicarboxylated amine compound is amidated with a hydroxyl-containing acyl chloride monomer to obtain a dihydroxyamide monomer; wherein the weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:3. The dicarboxyamine compound was vacuum dried at 50°C for 12 h, pulverized and passed through a 100-mesh sieve, 1 mol of the dicarboxyamine compound was dissolved in 50 mL of anhydrous THF, cooled to 0°C in an ice bath, and a mixture of 2.2 mol of hydroxyl-containing acyl chloride monomer and 4.4 mol of TEA in THF was slowly added dropwise. The addition was completed in 1 h, the temperature was raised to 25°C, and the reaction was stirred for 5 h. After filtration, the mixture was washed with dilute hydrochloric acid and sodium bicarbonate, dried, concentrated and purified to obtain the desired dihydroxyamide monomer. 3) Using a zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF), the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid; wherein the weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 1:1. 1 mol of polylactic acid with carboxyl groups at both ends, 1.05 mol of dihydroxyamide monomer, 1% of zinc-rare earth bimetallic organic framework catalyst, and 0.2% of PTSA were added to a toluene / DMSO mixed solvent and stirred until homogeneous. The mixture was heated to 100℃ and stirred for 2 hours, then heated to 140℃ and reacted for 8 hours. The acid value was measured every 2 hours, with a target acid value of <5 mg KOH / g. In the last hour, the temperature was raised to 160℃ and vacuum dehydration was performed. The mixture was then filtered, purified, washed with water and alkali, and dried.

[0029] The zinc-rare earth bimetallic organic framework catalyst Zn / Ce-MOF was prepared using the following steps: Using zinc nitrate (Zn(NO3)2·6H2O) and cerium nitrate (Ce(NO3)3·6H2O) as metal sources, with a molar ratio of Zn:Ce=3:1, terephthalic acid as a binder, and methanol as a solvent, zinc nitrate (Zn(NO3)2·6H2O) and cerium nitrate (Ce(NO3)3·6H2O) were dissolved in methanol and stirred until completely dissolved. Then, terephthalic acid was slowly added, and the pH value was controlled at 8. The mixture was then placed in a polytetrafluoroethylene-lined reactor and hydrothermally reacted at 160℃ for 24 hours.

[0030] Zinc (Zn) 2+ ) provides Lewis acid sites, with cerium (Ce) 3+ Synergistically improves thermal stability (increases decomposition temperature by 20-30℃), cerium (Ce) 3+ The redox properties of zinc (Zn / Ce) can enhance catalytic activity and lower the activation energy in esterification reactions. The design of zinc-rare earth bimetallic organic framework catalysts (Zn / Ce-MOF) can significantly improve catalytic activity and stability.

[0031] Application of amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes.

[0032] A method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes includes the following steps: By mass percentage, 1% amide-based polylactic acid, 1% antioxidant, 1% polyethylene and 97% dimethyl sulfoxide are mixed evenly, then poured into a reaction vessel and heated to 50°C with stirring speed of 300 r. The reaction vessel is then subjected to gradient pressurization in a nitrogen atmosphere. After maintaining the temperature and pressure for 0.5 h, the desired amide-based polylactic acid degradation membrane is obtained by spinning.

[0033] The steps for gradient pressurization of the reactor include: In the first stage, the reactor is pressurized to 6MPa, heated to 100℃, and held for 30 minutes to eliminate bubbles in the system. In the second stage, the reactor was pressurized to 8 MPa and heated to 150°C, and held for 60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10 MPa and heated to 180°C, and held for 30 minutes to achieve tightness.

[0034] The antioxidant is tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168).

[0035] The molecular weight of polyethylene is 100,000.

[0036] Example 2 An amide-based polylactic acid is prepared by polylactic acid, an oxidant, a dicarboxylic acid compound, a hydroxyl-containing acyl chloride monomer, and a catalyst.

[0037] A method for preparing amide-based polylactic acid includes the following steps: 1) Polylactic acid reacts with an oxidizing agent to obtain polylactic acid with carboxyl groups at both ends; 2) The dicarboxylated amine compound is amidated with a hydroxyl-containing acyl chloride monomer to obtain a dihydroxyamide monomer; 3) Using a catalyst, the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid.

[0038] The weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:3.

[0039] The weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 1:2.

[0040] The catalyst is Zn / Ce-MOF, with a Zn:Ce molar ratio of 3:1.

[0041] Application of amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes.

[0042] A method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes includes the following steps: Mix 0.1% amide-based polylactic acid, 0.1% antioxidant, 10% polyethylene and 89.8% acetone evenly, then pour into a reaction vessel and stir and heat to 80°C at a stirring speed of 400 r. Then apply gradient pressure to the reaction vessel and keep it at the temperature and pressure for 1 hour. The desired amide-based polylactic acid degradation membrane is then obtained by spinning.

[0043] The steps for gradient pressurization of the reactor include: In the first stage, the reactor is pressurized to 6MPa and heated to 100℃, and held for 35 minutes to eliminate bubbles in the system. In the second stage, the reactor was pressurized to 8 MPa and heated to 150°C, and held for 60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10 MPa and heated to 180°C, and held for 40 minutes to achieve tightness.

[0044] The pressurized gas environment is argon.

[0045] The antioxidant is pentaerythritol diphosphite (antioxidant 626).

[0046] The rest is the same as in Example 1.

[0047] Example 3 An amide-based polylactic acid is prepared by polylactic acid, an oxidant, a dicarboxylic acid compound, a hydroxyl-containing acyl chloride monomer, and a catalyst.

[0048] A method for preparing amide-based polylactic acid includes the following steps: 1) Polylactic acid (number average molecular weight of 100,000) reacts with an oxidizing agent (65% concentrated sulfuric acid) to obtain polylactic acid with carboxyl groups at both ends; 2) Amidation of a dicarboxylated amine compound with a hydroxyl-containing acyl chloride monomer yields a dihydroxyamide monomer; wherein the weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:3. 3) Using a catalyst, the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid; wherein the weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 2:1.

[0049] In step 3), the catalyst is a zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF), with a Zn:Ce molar ratio of 3:1. The zinc-rare earth bimetallic organic framework catalyst can reduce the activation energy of the reaction, increase the esterification rate to over 95%, and control the molecular weight distribution of polylactic acid (PDI<1.5). Compared with traditional catalysts, the thermal decomposition temperature of the product is increased by 20℃.

[0050] Application of amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes.

[0051] A method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes includes the following steps: Based on a total mass percentage of 100%, 0.5% amide-based polylactic acid, 0.9% antioxidant, 3.6% polyethylene, and 95% solvent were mixed evenly and then poured into a reaction vessel. The mixture was stirred and heated to 70°C at a stirring speed of 350 rpm. The reaction vessel was then subjected to gradient pressurization in a nitrogen atmosphere. After maintaining the temperature and pressure for 5 hours, the amide-based polylactic acid degradation membrane was obtained by spinning using a conveyor belt.

[0052] The steps for gradient pressurization of the reactor include: In the first stage, the reactor is pressurized to 7MPa, heated to 100℃, and held for 35 minutes to eliminate bubbles in the system. In the second stage, the reactor was pressurized to 8 MPa and heated to 155 °C, and held for 60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10 MPa and heated to 185°C, and held for 30 minutes to achieve tightness.

[0053] The antioxidant is pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] (antioxidant 1010).

[0054] The solvent is dimethyl sulfoxide.

[0055] The rest is the same as in Example 1.

[0056] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example uses concentrated sulfuric acid, a conventional catalyst for esterification reactions, instead of the zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF) used in Example 1.

[0057] The rest is the same as in Example 1.

[0058] Comparative Example 2 The difference between this comparative example and Example 1 is that this comparative example uses a zinc metal-organic framework catalyst (Zn-MOF) instead of the zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF) in Example 1.

[0059] The rest is the same as in Example 1.

[0060] Experiments show that the esterification rate of Example 1 was 96%, while the esterification rates of Comparative Examples 1 and 2 were 81% and 87%, respectively. This demonstrates that using the zinc-rare earth bimetallic organic framework catalyst (Zn / Ce-MOF) of the present invention helps to improve the esterification rate.

[0061] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0062] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. An amide-based polylactic acid, characterized in that, It was prepared by polylactic acid, oxidant, dicarboxylic acid compound, hydroxyl-containing acyl chloride monomer and catalyst.

2. The method for preparing amide-based polylactic acid according to claim 1, characterized in that, Includes the following steps: 1) Polylactic acid reacts with an oxidizing agent to obtain polylactic acid with carboxyl groups at both ends; 2) The dicarboxylated amine compound is amidated with a hydroxyl-containing acyl chloride monomer to obtain a dihydroxyamide monomer; 3) Using a catalyst, the dihydroxyamide monomer is esterified with polylactic acid with carboxyl groups at both ends to obtain the desired amide-based polylactic acid.

3. The method for preparing amide-based polylactic acid according to claim 2, characterized in that, The weight ratio of the dicarboxylated amine compound to the hydroxyl-containing acyl chloride monomer is 1:2-3.

4. The method for preparing amide-based polylactic acid according to claim 2, characterized in that, The weight ratio of the dihydroxyamide monomer to the polylactic acid with carboxyl groups at both ends is 1-2:1-3.

5. The method for preparing amide-based polylactic acid according to claim 2, characterized in that, The catalyst is Zn / Ce-MOF, with a Zn:Ce molar ratio of 2-3:

1.

6. The application of the amide-based polylactic acid according to claim 1 in the preparation of amide-based polylactic acid degradable membranes.

7. The method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes according to claim 6, characterized in that, Includes the following steps: Amide-based polylactic acid, antioxidant, polyethylene and solvent are mixed evenly, then poured into a reaction vessel and stirred and heated. The reaction vessel is then subjected to gradient pressure, and after heat and pressure maintenance, the desired amide-based polylactic acid degradation membrane is obtained by spinning.

8. The method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes according to claim 7, characterized in that, The mass percentages of the amide-based polylactic acid, antioxidant, polyethylene, and solvent are 0.1-1%, 0.1-1%, 1-10%, and 89.8-97%, respectively; the mixture is stirred and heated to 30-80°C at a stirring speed of 200-400 rpm.

9. The method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes according to claim 7, characterized in that, The steps for gradient pressurization of the reactor include: In the first stage, the reactor is pressurized to 6-7 MPa and heated to 100-110℃, and held for 20-35 minutes to eliminate bubbles in the system. In the second stage, the reactor is pressurized to 8-9 MPa and heated to 150-160℃, and held for 50-60 min to induce molecular chain orientation. In the third stage, the reactor is pressurized to 10-11 MPa and heated to 180-190℃, and held for 30-40 minutes to achieve tightness.

10. The method for using amide-based polylactic acid in the preparation of amide-based polylactic acid degradable membranes according to claim 7, characterized in that, The pressurized gas environment is one of nitrogen, argon, air, and carbon dioxide; the antioxidant is one or a combination of several of tris[2,4-di-tert-butylphenyl]phosphite (antioxidant 168), bis(2,4-di-tert-butylphenol) pentaerythritol diphosphite (antioxidant 626), tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] pentaerythritol ester (antioxidant 1010), and β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate n-octadecyl alcohol ester (antioxidant 1076); the molecular weight of the polyethylene is 100,000-500,000; the solvent is one or a combination of several of dimethyl sulfoxide, N,N-dimethylformamide, acetone, benzene, xylene, dichloromethane, and carbon tetrachloride.