CN111205603B - Biodegradable mulch film and preparation method thereof - Google Patents

Abstract

The invention relates to a biodegradable mulching film and a preparation method thereof, and mainly solves the problems that most agricultural mulching films are not degraded, a small part of mulching films are biodegradable but have poor processability, and the comprehensive properties such as strength, toughness and thickness are difficult to give consideration to in the prior art. The modified polyhydroxyalkanoate material comprises the following components in parts by weight: (1) block type polyhydroxyalkanoate: 10-60 parts; (2) poly (butylene terephthalate) -co-succinate: 30-80 parts of a solvent; (3) a compatilizer: 1-10 parts; (4) chain extender: the technical scheme of 0.1-1 part better solves the problem, and the prepared mulching film meets the requirements of mechanical mulching film laying and comprehensive use, can be completely biodegradable, and can be used in the industrial production of biodegradable mulching films.

Description

Biodegradable mulch film and preparation method thereof

technical field

The invention relates to a biodegradable mulch film and a preparation method thereof.

technical background

As an important means of production in agricultural production, mulch film can improve soil temperature, prevent water evaporation, improve fertilizer efficiency, and prevent weeds, etc., and can effectively improve agricultural productivity. It has been widely used in my country. According to statistics, the amount of plastic film used in my country increased from 6,000 tons in 1982 to 1.44 million tons in 2014, covering an area of more than 18 million hectares. The types of applied crops have gradually developed from economic crops to major food crops. Such as corn, wheat, rice, etc., there is still a lot of room for growth in the application of plastic film in the future. However, with the popularization and application of plastic film mulching technology, it has also brought serious plastic film residual pollution problems. The survey shows that the average residual film amount of plastic film-covered farmland for many years is 71.9-259.1kg/hm ² , and the residual plastic film will hinder the soil moisture. Infiltration, reduce soil permeability; and may hinder root extension, affect crop growth, cause crop yield reduction and other problems, and become "white pollution" in agricultural production.

系列生物降解地膜在德、意、日得到较好的应用，并于2012年进入中国市场，以及法国利马格兰集团的Biolice可降解地膜，主要成分为PBAT/淀粉。The development of biodegradable plastic film is an important technology to solve "white pollution", protect soil and reduce the workload of farmers. For this reason, a lot of energy has been invested in the development of biodegradable plastic film at home and abroad. However, most of the degradable mulch films that have been reported are made of polyethylene plus photosensitizers, starch or calcium carbonate, etc. This mulch film can disintegrate into small fragments within a certain period of time, but the polyethylene in the mulch film does not degrade. , will still cause serious soil pollution. In terms of complete biodegradation, domestic companies such as Kingfa Technology and Xinfu Pharmaceutical have adopted aliphatic copolyester polybutylene adipate-succinate (PBSA), polyterephthalate-adipic acid Butylene glycol ester (PBAT) and others have carried out biodegradable plastic film experiments. Foreign countries are mainly composed of PBAT and polylactic acid (PLA) from BASF in Germany.

A series of biodegradable mulch films have been well used in Germany, Italy and Japan, and entered the Chinese market in 2012, as well as the Biolice degradable mulch film of the French Limagrain Group, the main component is PBAT/starch.

Aliphatic aromatic copolyesters (mainly including polybutylene terephthalate-co-succinate and polybutylene terephthalate-co-adipate) are a class of rapidly developing polymers. The material is usually obtained by random copolymerization of aliphatic diacids, aromatic diacids and aliphatic diols, and can combine the advantageous properties of aliphatic polyesters and aromatic polyesters to obtain practical materials with excellent strength and toughness. Aromatic polyester segments mainly play a role in diluting costs in addition to providing performance support; while aliphatic polyester segments are usually biodegradable on the basis of providing performance support. When the content of aliphatic segments reaches a certain level, the overall aliphatic aromatic copolyester will have biodegradation properties. It has been reported in the literature that when the mole fraction of aliphatic diacids in the total diacids is reduced to 38%, the overall material basically loses Biodegradation properties [N. Honda, I. Taniguchi, M. Miyamoto, Y. Kimura, Macromolecular Bioscience, 2003, 3, 189-197.]. On the other hand, cost is one of the important factors restricting the large-scale application of biodegradable polymer materials. Therefore, in order to reduce the cost of biodegradable aliphatic aromatic copolyester materials, on the basis of ensuring biodegradability, low-cost aromatic The amount of the group diacid should be as large as possible. Taking the above two factors into consideration, the mole fraction of aliphatic diacids in the total diacids in the commercially available biodegradable aliphatic aromatic copolyester materials is mostly between 45% and 60%.

Polyhydroxyalkanoate (PHA) is a natural polymer biomaterial synthesized by microbial fermentation. It has biocompatibility, biodegradability, thermoplastic processability and gas barrier properties, especially block-type polymer. Hydroxy fatty acid esters can combine the processing and mechanical properties of different segments to significantly improve the overall performance. The research group of Professor Chen Guoqiang of Tsinghua University has done a lot of work in related fields [Chen X, Yin J, Ye, J, et al.Engineering Halomonas bluephagenesis TD01 for non-sterile production of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) [J] Bioresource Technology, 2017, 244: 534.]. However, when used as a biodegradable mulch material, PHA materials still have disadvantages such as poor thermal stability, easy hydrolysis, relatively narrow processing window, difficult processing and molding, slow crystallization speed, poor toughness, and high cost. Patent CN 106589871A uses lignin to modify PHA, and has achieved certain progress in mechanical properties and cost, but it does not specify the thickness of the film. Patent CN102229742A uses plasticizers to modify PHA, and prepares PHA film materials by calendering. However, its thickness is about 0.05-0.3mm, which cannot meet the biodegradable film standard GB13735-92. The film thickness is 0.008 -0.02mm usage requirements. Patent CN104240660A uses polyisobutylene, ethylene ethyl acrylate, etc. to modify PHA, and successfully prepares a film with a thickness of less than 10 microns, the strength is greater than 25MPa, and the elongation at break is greater than 300%. However, the addition of the non-pro-degradation agent described in this paper will have a negative impact on the overall degradation performance of the mulching film material.

In view of the above problems, this patent discloses a biodegradable mulch film prepared and processed through advanced modification technology. The mulch film has good processing performance, adjustable thickness from 3 to 20 microns, tensile elongation at break> 600%, stretchable The breaking strength is >30MPa, and the elastic modulus is >100MPa, which meets the requirements of mechanical film laying and comprehensive use. The plastic film can be completely biodegraded and has broad application prospects.

SUMMARY OF THE INVENTION

One of the technical problems to be solved by the present invention is that most of the agricultural mulch films in the prior art are not degraded, and a small part of the mulch films are biodegradable but their processability is not good, and the comprehensive properties such as strength, toughness and thickness are difficult to take into account. A modified polyhydroxyalkanoate material, the material is prepared by including the following components in a certain proportion: block type polyhydroxyalkanoate, polybutylene terephthalate-co-succinate , compatibilizer, chain extender, blocking agent and other auxiliaries. The biodegradable mulch film prepared from the modified polyhydroxyalkanoate material has good processing performance, the thickness is adjustable from 3 to 20 microns, the tensile elongation at break>600%, the tensile breaking strength>30MPa, the elastic modulus>100MPa, To meet the requirements of mechanical film laying and comprehensive use, the mulch film can be completely biodegraded, which well solves the problems of the prior art.

The second technical problem to be solved by the present invention is to provide a method for preparing a modified polyhydroxyalkanoate material corresponding to one of the technical problems solved.

The third technical problem to be solved by the present invention is that most of the agricultural mulch films in the prior art are not degradable, and a small part of the mulch films are biodegradable but their processability is poor, and the comprehensive properties such as strength, toughness and thickness are difficult to take into account. A biodegradable mulch film is prepared from the modified polyhydroxyalkanoate material described in one of the above technical problems.

The fourth technical problem to be solved by the present invention is to provide a method for preparing a biodegradable mulch film corresponding to the third technical problem.

In order to solve one of the above-mentioned technical problems, the technical scheme adopted in the present invention is: a modified polyhydroxyalkanoate material, in parts by weight, comprising the following components:

(1) Block type polyhydroxyalkanoate: 10-60 parts;

(2) Polybutylene terephthalate-co-succinate: 30-80 parts;

(3) Compatibilizer: 1 to 10 parts;

(4) Chain extender: 0.1 to 1 part.

In the above-mentioned technical scheme, the structure of the described block type polyhydroxy fatty acid ester is shown in formula (I):

In formula (I), m, n, and l are all integers from 3 to 16, which may be the same or different; R ₁ , R ₂ , and R ₃ are hydrogen atoms, alkyl groups, alkenyl groups, or alkyl groups with a benzene ring , can be the same or different; R ₁ and R ₂ , m and n are not the same at the same time; x, x' are 0 to 200, and are not 0 at the same time. When x=0, R ₂ and R ₃ , and n and l are different when they are different, and when x′=0, R ₁ and R ₃ , and m and l are different when they are different. y and z are the statistical average degree of polymerization, and y and z are 10 to 5000, which may be the same or different.

In the above-mentioned technical scheme, the described block type polyhydroxyalkanoate structure is preferably as shown in formula (II):

In formula (II), x=1-50, x'=1-50, y=50-2000, z=50-2000, and the weight average molecular weight is 100,000-800,000. In formula (II), the mass fraction of the -CH ₂ CH ₂ CH ₂ COO- segment in the whole is preferably 5% to 50%, more preferably 8% to 20%.

In the above technical solution, the mole fraction of succinic acid in the polybutylene terephthalate-co-succinate is 40%-90% of the total diacid, preferably 50%-65%.

In the above technical scheme, the compatibilizer is at least one of maleic anhydride, acrylate, silane coupling agent and titanate coupling agent, preferably a copolymer containing maleic anhydride or acrylate Or at least one of the graft polymers, more preferably ethylene-acrylate-maleic anhydride terpolymer or/and ethylene-methyl acrylate-glycidyl methacrylate.

In the above technical solution, the chain extender is a multifunctional compound or polymer capable of reacting with a hydroxyl group or a carbonyl group, preferably a multifunctional isocyanate or a multifunctional epoxy compound or polymer.

In the above-mentioned technical scheme, the material also preferably includes:

(5) Opening agent: 0.1 to 10 parts;

(6) Other additives: 0-10 parts.

In the above technical scheme, the opening agent is an auxiliary agent that can increase surface roughness or/and reduce surface energy, including inorganic opening agent and organic opening agent, and inorganic opening agent is calcium carbonate, talc, calcium oxide, titanium dioxide, oxide At least one of aluminum, magnesium oxide, boron nitride, silicon oxide, carbon black, mica, and chalk powder, and the organic blocking agent is at least one of oleic acid amide and erucic acid amide.

In the above technical solution, the other auxiliary agents are at least one of anti-hydrolysis agents, ultraviolet absorbers, antioxidants, light stabilizers and the like.

In order to solve the second of the above-mentioned technical problems, the technical scheme adopted in the present invention is: a preparation method of the modified polyhydroxyalkanoate material described in any of the technical schemes for solving one of the above-mentioned technical problems:

Add the required amount of block polyhydroxyalkanoate, polybutylene terephthalate-co-succinate, compatibilizer, chain extender, blocking agent and optional other additives to the twin screw In the extruder, the modified polyhydroxyalkanoate material is obtained by mixing, melting, reacting and extruding.

In the above technical solution, the rotational speed of the twin-screw extruder is preferably 80 to 400 rpm; the extrusion temperature is preferably 130°C to 190°C.

In order to solve the third technical problem above, the technical solution adopted in the present invention is: a biodegradable mulch film containing the modified polyhydroxyalkanoate material described in any one of the technical solutions for solving one of the above technical problems.

In the above technical solution, the thickness of the biodegradable mulch film is preferably 3 to 20 microns, more preferably 3 to 10 microns, and even more preferably 3 to 6 microns; the tensile elongation at break is preferably >600%; The breaking strength is preferably >30 MPa; the elastic modulus is preferably >100 MPa.

In order to solve the above-mentioned technical problem No. 4, the technical solution adopted in the present invention is: a preparation method of a biodegradable mulch film described in any one of the technical solutions to solve the above-mentioned technical problem No. 3, comprising the following steps:

Add the required amount of block polyhydroxyalkanoate, polybutylene terephthalate-co-succinate, compatibilizer, chain extender, blocking agent and optional other additives to the twin screw In the extruder, after mixing, melting, reacting, extruding, cooling, and granulating, the modified polyhydroxyalkanoate material pellets are obtained, and the modified polyhydroxyalkanoate material pellets are added to the single-screw extruder. In the film blowing machine, the biodegradable mulch is obtained after melting, extrusion, drawing, cooling and shaping;

Or: add the required amount of block polyhydroxyalkanoate, polybutylene terephthalate-co-succinate, compatibilizer, chain extender, blocking agent and optional other auxiliary agents In the twin-screw extruder, after mixing, melting and reacting, it is pressurized by a melt pump and extruded to a film blowing die, and after drawing, cooling and shaping, the biodegradable mulch film is obtained.

In the above technical solution, the rotational speed of the twin-screw extruder is preferably 80 to 400 rpm; the extrusion temperature is preferably 130°C to 190°C.

In the above technical solution, the rotation speed of the single-screw extruder is preferably 30 to 200 rpm; the extrusion temperature is preferably 130°C to 190°C.

In the above technical solution, the ratio (inflation ratio) of the diameter of the film bubble after shaping to the diameter of the die is preferably 2:1 to 6:1.

In the above technical solution, the thickness of the biodegradable mulch film is preferably 3-20 microns, more preferably 3-10 microns, and still more preferably 3-6 microns.

By adopting the technical scheme of the present invention, the obtained modified polyhydroxyalkanoate material can better solve the problems of poor processability of the existing biodegradable mulch film and the difficulty in taking into account the comprehensive properties such as strength, toughness, thickness, etc. Excellent biodegradable mulch film, the thickness of the biodegradable mulch film: 3-20 microns, tensile elongation at break: >600%, tensile breaking strength: >30MPa, elastic modulus: >100MPa, meet the requirements of mechanical film laying and Comprehensive use requirements, with high promotion and application value, and achieved good technical results. The present invention carries out performance measurement by the following method:

Film thickness: Tested according to GB/T 6672-2001, and averaged at 10 points.

Mechanical properties: According to ISO 527-3 standard, measured by INSTRON's 3344 film product testing machine, and the processing software is Bluehill version 2.31. The film was cut into Type 5 in the ISO 527-3 standard, and placed in a Bluepard BPS-100CB constant temperature and humidity box (temperature 23° C., relative humidity 50%) of Shanghai Yiheng Scientific Instrument Co., Ltd. for 24 hours. During the test, the initial clamp spacing was 75mm, the test tensile rate was 500mm/min, each sample was tested 5 times, and the average value was taken.

Detailed ways

The present invention is specifically described by the following examples. It is necessary to point out that the following embodiments are only for further illustration of the present invention, and should not be construed as a limitation on the protection scope of the present invention, and those skilled in the art can make some non-essential improvements and adjustments according to the above-mentioned contents of the invention.

[Example 1]

The block type polyhydroxyalkanoic acid used in the present invention is prepared by biological fermentation, and the specific molecular structure is that 3-hydroxybutyric acid and 4-hydroxybutyric acid are randomly copolymerized first and then block copolymerized with 3-hydroxybutyric acid. (bPHA), the weight average molecular weight is about 500,000, of which the mass fraction of 4-hydroxybutyric acid is about 18%, the mass fraction of block copolymerized 3-hydroxybutyric acid is about 50%, and the random copolymerization of 3-hydroxybutyric acid is about 50%. The mass fraction of hydroxybutyric acid is about 32%.

The 1,4-succinic acid, terephthalic acid, 1,4-butanediol, tetraisopropyl titanate and pentaerythritol used in the present invention are all CP grade products of Sinopharm Chemical Co., Ltd. In the reaction kettle with complete dehydration and deoxygenation, 1,4-succinic acid and terephthalic acid respectively account for 50% and 50% of the total diacid feeding amount molar ratio, and 1,4-butanediol is divided into two The molar ratio of acid feeding amount is 105%, and pentaerythritol with 0.25% mole number of total diacid is added. After the feeding is completed, under the protection of inert gas, keep stirring, slowly increase the temperature of the reactor from 80 ° C to 215 ° C, and keep the temperature at 215 ° C for about 2.5 hr to ensure that the degree of reaction is more than 90%, then use a vacuum pump to pump air and rise simultaneously. Increase the oil bath temperature to 245°C, keep the pumping for about 2 hr until the stirring torque is constant, and the polymerization step is now complete. After the polymerization reaction, the melt was colorless and transparent, extruded through a die with a diameter of about 5 mm, and was cooled in a water bath at room temperature and cut into cylindrical particles with a length of about 3 mm using a pelletizer. The obtained PBST particles were evacuated in a vacuum drying oven at 60° C. for 4 hr, then cooled and packaged for use (named PBST-S50).

Auxiliaries such as bPHA, PBST-S50, compatibilizer, chain extender, and opening agent were first dried in a vacuum oven at 60°C for 4 hours to remove moisture. Then, according to the parts by mass, it is 10 parts of bPHA, 74.5 parts of PBST-S50, 10 parts of compatibilizer, 0.5 part of chain extender, 4.5 parts of inorganic opening agent, 0.5 part of organic opening agent, and then added into the twin screw for extrusion. granules to obtain biodegradable mulch granules. The twin-screw used is a PolyLab HAAKE Rheomex OS PTW16 co-rotating twin-screw extruder (screw diameter 16 mm, length-diameter ratio L/D=40) from ThermoFisher Technology Company of the United States. The extruder has 11 sections from the feeding port to the die, numbered 1-11, of which the first section only plays the role of feeding and cannot be heated. The temperatures of sections 2-11 of the extruder were: 150°C, 160°C, 170°C, 170°C, 170°C, 170°C, 170°C, 170°C, 170°C and 160°C, respectively, and the screw speed was set at 200 rpm. In steady operation, torque is 40-60% of maximum. The extruder is equipped with a circular die with a diameter of 3 mm. After the splines are extruded from the die and cooled by air, they are cut into cylindrical particles with a set diameter of about 3 mm by a pelletizer. The obtained particles were evacuated in a vacuum drying oven at 60° C. for 4 hours, and then packaged for later use.

[Example 2]

The implementation is the same as in Example 1, but the parts by mass of each component are changed to 20 parts of bPHA, 64.5 parts of PBST-S50, 10 parts of compatibilizer, 0.5 parts of chain extender, 4.5 parts of inorganic blocking agent, and 0.5 part of organic blocking agent. share.

[Example 3]

The implementation is the same as in Example 1, but the parts by mass of each component are changed to 30 parts of bPHA, 64.5 parts of PBST-S50, 10 parts of compatibilizer, 0.5 part of chain extender, 4.5 parts of inorganic blocking agent, and organic blocking agent 0.5 servings.

[Example 4]

The three kinds of biodegradable plastic film pellets prepared in Examples 1-3 were extruded and blown in a single-screw extruder (PolyLab HAAKE Rheomex 252OS) equipped with a film blowing accessory. The single-screw has three heating sections plus There are four heating zones in the die head, the temperature is set to 150°C, 160°C, 160°C and 160°C respectively, and the inflation ratio is controlled to 4:1. The film thickness is controlled by controlling the stretching speed and screw speed. The thinnest pellets in Example 1 can be made into 3-micron films, the thinnest pellets in Example 2 can be made into 4-micron films, and the thinnest pellets in Example 3 can be made into 5-micron films.

[Example 5]

The three films prepared in Example 4 were taken in the thinnest state to carry out the mechanical property test respectively according to the method described above, and the drawing direction (MD) and the vertical drawing direction (CD) were measured respectively. The results are shown in Table 1.

Table 1 Mechanical properties of biodegradable films

sample Thickness/μm Tensile strength/MPa Elongation at break/% Elastic modulus/MPa Example 1-MD 3 37 415 140 Example 1 - CD 3 35 765 128 Example 2-MD 4 35 375 127 Example 2 - CD 4 34 704 120 Example 3-MD 5 34 343 121 Example 3 - CD 5 32 669 112

Claims (10)

1. The modified polyhydroxyalkanoate material comprises the following components in parts by weight:

(1) block type polyhydroxyalkanoate: 10-60 parts;

(2) poly (butylene terephthalate) -co-succinate: 30-80 parts of a solvent;

(3) a compatilizer: 1-10 parts;

(4) chain extender: 0.1-1 part;

wherein, the structure of the block type polyhydroxyalkanoate is shown as the formula (II):

formula (II);

in the formula (II), x = 1-50, x' = 1-50, y = 50-2000, z = 50-2000, and the weight average molecular weight is 10-80 ten thousand; in the formula (II) — CH₂CH₂CH₂The mass fraction of COO-chain links in the whole is 5-50%;

the mol fraction of succinic acid in the poly (terephthalic acid) -co-butylene succinate is 40-90 percent of the total diacid;

the compatilizer is at least one of copolymers containing maleic anhydride or acrylic ester.

2. The modified polyhydroxyalkanoate material of claim 1, wherein the polybutylene terephthalate-co-succinate comprises 50% to 65% by mole of the total diacid.

3. The modified polyhydroxyalkanoate material of claim 1, wherein the compatibilizer is an ethylene-acrylate-maleic anhydride terpolymer or/and an ethylene-methyl acrylate-glycidyl methacrylate terpolymer.

4. The modified polyhydroxyalkanoate material of claim 1, wherein the chain extender is a multifunctional isocyanate or a multifunctional epoxy compound or a polymer.

5. The modified polyhydroxyalkanoate material of claim 1, characterized in that the material further comprises:

(5) an opening agent: 0.1-10 parts;

(6) other auxiliary agents: 0-10 parts;

the opening agent is an auxiliary agent capable of increasing the surface roughness or/and reducing the surface energy; the other auxiliary agent is at least one of hydrolytic resistance agent, antioxidant and light stabilizer.

6. The modified polyhydroxyalkanoate material of claim 5, wherein the opening agent comprises an inorganic opening agent and an organic opening agent.

7. The modified polyhydroxyalkanoate material of claim 6, wherein the inorganic opening agent is at least one of calcium carbonate, talc, calcium oxide, titanium dioxide, alumina, magnesium oxide, boron nitride, silica, mica, chalk powder, and the organic opening agent is at least one of oleamide, erucamide.

8. A method for preparing the modified polyhydroxyalkanoate material of any one of claims 1 to 7, comprising the steps of:

adding required amount of block type polyhydroxyalkanoate, poly (terephthalic acid) -co-butylene succinate, a compatilizer, a chain extender, an optional opening agent and optional other auxiliary agents into a double-screw extruder, and mixing, melting, reacting and extruding to obtain the modified polyhydroxyalkanoate material.

9. A biodegradable mulch film comprising the modified polyhydroxyalkanoate material of any one of claims 1 to 7.

10. A method for preparing the biodegradable mulch film according to claim 9, comprising the steps of:

adding required amount of block type polyhydroxyalkanoate, poly (terephthalic acid) -co-butylene succinate, a compatilizer, a chain extender, an optional opening agent and optional other auxiliary agents into a double-screw extruder, mixing, melting, reacting, extruding, cooling and granulating to obtain modified polyhydroxyalkanoate material granules, adding the modified polyhydroxyalkanoate material granules into a single-screw extrusion film blowing machine, and melting, extruding, drafting, cooling and shaping to obtain the biodegradable mulching film;

or: adding required amount of block type polyhydroxyalkanoate, poly (terephthalic acid) -co-butylene succinate, a compatilizer, a chain extender, an optional opening agent and optional other auxiliary agents into a double-screw extruder, mixing, melting, reacting, pressurizing by a melt pump, extruding to a film blowing die, drafting, cooling and sizing to obtain the biodegradable mulching film.