阅读说明：本技术 一种可生物降解的淀粉基微波炉用保鲜膜及其制备方法 (Biodegradable starch-based preservative film for microwave oven and preparation method thereof ) 是由 袁守汶 李高峰 于 2019-11-12 设计创作，主要内容包括：本发明公开一种保鲜膜,所述保鲜膜包括聚乳酸10-50份、聚己二酸-对苯二甲酸丁二酯10-20份、聚丁二酸丁二醇酯0-20份、淀粉接枝聚合物50-150份、交联剂5-30份、分散剂0-30份,所述淀粉接枝聚合物中含有质量分数为1-15％的硅氮烷化合物,所述硅氮烷化合物包括硅氮烷单体和/或硅氮烷聚合物。所述保鲜膜制备原料中不含增塑剂,可用于高脂类食品的包装,且耐热性好,可用于微波炉加热,另外,所述保鲜膜可生物降解,造成的环境污染小。(The invention discloses a preservative film which comprises 10-50 parts of polylactic acid, 10-20 parts of poly (butylene adipate-terephthalate), 0-20 parts of poly (butylene succinate), 50-150 parts of starch graft polymer, 5-30 parts of cross-linking agent and 0-30 parts of dispersing agent, wherein the starch graft polymer contains 1-15% by mass of silazane compound, and the silazane compound comprises silazane monomer and/or silazane polymer. The preservative film preparation raw material does not contain a plasticizer, can be used for packaging high-lipid food, has good heat resistance, can be used for heating in a microwave oven, and is biodegradable and causes little environmental pollution.)

1. The preservative film is prepared from the following raw materials in parts by mass: 50-150 parts of starch graft polymer, 10-50 parts of polylactic acid, 10-20 parts of poly (butylene adipate-terephthalate), 0-20 parts of poly (butylene succinate), 5-30 parts of cross-linking agent and 0-30 parts of dispersing agent, wherein the starch graft polymer contains 1-15% by mass of silazane compound, the silazane compound comprises silazane monomer and/or silazane polymer,

the silazane compound has the structural formula shown as (I):

wherein R is selected from-H and-CH₃or-C₂H₅；R₁、R₂、R₃、R₄、R₅、R₆Independently selected from-H, C_1-3Straight chain alkyl, C_2-4Alkenyl or C_2-6Alkynyl radical；

And n is an integer between 1 and 12, when n is 1, the compound is a silazane monomer, and when n is 2 to 12, the compound is a silazane polymer.

2. The preservative film according to claim 1, wherein the ratio of the content of the starch graft polymer to the sum of the contents of the polylactic acid, polybutylene adipate-terephthalate and polybutylene succinate in the preservative film is 1-10:1, and the silazane monomer contains at least one unsaturated double bond; the silazane polymer contains at least one unsaturated double bond or unsaturated triple bond.

3. The preservative film according to claim 2, wherein the ratio of the content of the starch graft polymer to the sum of the contents of the polylactic acid, the polybutylene adipate-terephthalate and the polybutylene succinate in the preservative film is 2-5:1, the silazane is a silazane monomer and/or a silazane dimer, and the specific structural formula is shown in the specification

4. The preservative film according to claim 1, wherein the starch graft polymer is prepared from the following raw materials in parts by mass: 100 parts of unsaturated modified starch, 60-120 parts of grafting monomer, 16-45 parts of silazane compound and 0.1-5 parts of initiator, wherein the mass fraction of silazane compound in the starch graft polymer is 10-15%, and the grafting monomer comprises: one or more of ethyl acrylate, methyl methacrylate, ethyl methacrylate and vinyl acetate.

5. The preservative film according to claim 4, wherein the unsaturated modified starch is a modified starch formed by esterification of natural starch and a modifier, and the unsaturated modified starch comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-40 parts of a modifier and 5-10 parts of a catalyst, wherein the modifier is double-bond-containing acid, acyl chloride or isocyanate.

6. The wrap film according to claim 5, wherein the modifier is one or a combination of two or more selected from acrylic acid, acryloyl chloride and isocyano ethyl methacrylate, and the catalyst is one or a combination of two or more selected from pyridine, ethylenediamine and triethylamine.

7. A method for preparing the wrap of any one of claims 1 to 6, comprising the steps of:

(1) preparation of unsaturated modified starch: adding a solvent into natural starch to prepare a starch suspension, adding a catalyst into the suspension, stirring for 0.5-1 hour at room temperature, adjusting the pH value of the solution to 7.5-9.0, slowly dropwise adding a modifier while stirring, reacting overnight, centrifuging, discarding the supernatant, washing for 3-5 times with water or 95% ethanol, drying, crushing, and sieving to obtain unsaturated modified starch;

(2) preparation of starch graft polymer: adding 1-2 times of water into the modified starch prepared in the step (1), gelatinizing at 90-100 ℃ for 20-30 minutes, cooling to room temperature, adding a silazane compound and a grafted unsaturated monomer, stirring at a high speed for pre-emulsification for 0.5-1 hour, dropwise adding an initiator while stirring, reacting overnight, centrifuging, discarding the supernatant, washing with water or 95% ethanol for 3-5 times, and drying to obtain a starch grafted polymer;

(3) preparing a preservative film: putting polylactic acid, poly (butylene adipate-terephthalate), poly (butylene succinate) and starch graft polymer into a high-speed mixer, mixing for 5-10 minutes, adding a dispersing agent, continuously blending for 5-10 minutes, adding a cross-linking agent, mixing for 3-5 minutes to form a mixed raw material, putting the mixed raw material into a double-screw granulator, extruding, granulating and blow-molding to form the preservative film.

8. Use of the wrap of any one of claims 1 to 6 in the field of wrap for microwave ovens.

9. The starch graft polymer of claim 1, wherein the polymer preparation raw material comprises the following raw materials in parts by mass: 100 parts of unsaturated modified starch, 60-120 parts of grafting monomer, 16-45 parts of silazane compound and 0.1-5 parts of initiator;

the unsaturated modified starch is formed by esterification reaction of natural starch and a modifier, and comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-40 parts of modifier and 5-10 parts of catalyst, wherein the modifier is double-bond-containing acid, acyl chloride or isocyanate;

the grafting monomer comprises: one or more of ethyl acrylate, methyl methacrylate, ethyl methacrylate and vinyl acetate;

the initiator is selected from one or the combination of more than two of ammonium persulfate and potassium persulfate;

the silazane compound has the structural formula shown as (I):

wherein R is selected from-H and-CH₃or-C₂H₅；R₁、R₂、R₃、R₄、R₅、R₆Independently selected from-H, C_1-3Straight chain alkyl, C_2-4Alkenyl or C_2-6An alkynyl group;

and n is an integer between 1 and 12, when n is 1, the compound is a silazane monomer, and when n is 2 to 12, the compound is a silazane polymer.

10. The starch graft polymer of claim 9, wherein the modifier is selected from one or a combination of two or more of acrylic acid, acryloyl chloride, and isocyanoethyl methacrylate;

the catalyst is one or the combination of more than two of pyridine, ethylenediamine and triethylamine;

the natural starch is one or the combination of more than two of corn starch, cassava starch, sweet potato starch, wheat starch and bean starch;

the silazane monomer contains at least one unsaturated double bond;

the silazane polymer contains at least one unsaturated double bond or unsaturated triple bond.

Technical Field

The invention belongs to the technical field of starch-based materials, and particularly relates to a biodegradable preservative film for a microwave oven and a preparation method thereof.

Background

Starch is used as a natural polymer material, is the most common storage form of carbohydrates in cells, is widely distributed in the plant world, exists in corn, potato, sweet potato, rice, wheat and the like, has wide sources and low cost, can be completely biodegraded, and is an environment-friendly polymer material with water and carbon dioxide as degraded products.

At present, starch is mainly applied to industries such as food, paper making, medicines and the like, but with the technological progress and the demand of people for degradable high polymer materials, in recent years, starch as a green and environment-friendly natural high polymer material has been widely concerned by researchers of degradable plastics at home and abroad. In addition, the aged grain reserve in China is large, in 2013-grade 2014, the corn stock in China only reaches 1.06 hundred million tons, the end-of-year stock consumption ratio reaches 59.73%, and the grain safety standard is far higher than 17% specified by grain and agriculture organization in the United nations. The content of the highly toxic substance aflatoxin in the aged grains is generally seriously exceeded, people and livestock are extremely easy to be poisoned after eating the aged grains, and the existing aged grains are only destroyed to cause serious waste, so that the application and research of the starch have far-reaching significance.

The natural starch has a polyhydroxy structure, large intermolecular force, a microcrystalline structure, difficulty in melting and plasticizing, strong hydrophilicity and poor compatibility with most plastics, and the defects limit the application of the natural starch in production and life. In order to expand the application range of starch in life, the physical and chemical properties of starch need to be fully utilized to modify the starch, the modified starch is mainly prepared by physical, chemical and biological modification methods, composite modification and other methods at present, and the chemical method is one of the most important and widely applied methods for modifying the starch.

The chemical modification method refers to a method of treating natural starch with various chemical agents to obtain modified starch. The starch molecular weight can be divided into two types according to the change of the starch molecular weight before and after modification: one is a modification method in which the molecular weight of starch is reduced after modification such as oxidation and acidolysis, and the other is a method in which the molecular weight of starch is increased by crosslinking, esterification, etherification, grafting, and the like. The graft copolymer of starch is a novel high molecular material, and the research thereof has unique significance in the starch conversion technology. The graft copolymerization refers to graft copolymerization between starch and olefin monomers initiated by a certain method, such as styrene, acrylamide and the like. The starch graft copolymer has the acting force between starch molecules and the mechanical property of the graft polymer. Therefore, the starch graft polymer has good value in the aspects of water absorption materials, biodegradable plastics and the like, and has wider application in the field of food packaging due to low toxicity.

Along with the improvement of living standard, people pay more and more attention to food safety and sanitation, and in daily life, people mostly adopt plastic wrap or freshness protection package to keep fresh food, and along with the popularization of microwave ovens, people use the plastic wrap to plastic envelope food and then the phenomenon of microwave oven heating more and more generally. However, due to the requirement of the production process, a large amount of plasticizer, namely the common plasticizer, is added in the manufacturing process of some preservative films, and the plasticizer is insoluble in cold water but can be dissolved out at the temperature of more than 60 ℃ or in grease. The latest authoritative detection shows that 16 common brand PVC preservative films in the broad market in north and 15 common brand PVC preservative films all contain the DEHA which is a national banned plasticizer, and the plasticizer can permeate into packaged food with high fat content from the preservative films at normal temperature to cause great harm to secretion systems in human bodies. Therefore, the plastic wrap for microwave oven heating is required to be further improved in its preparation composition and heat resistance.

The preservative films on the market at present are mainly divided into two types, one type is a common preservative film and is suitable for the preservation of a refrigerator; one is a microwave oven preservative film which can be used for refrigerator preservation and can also be used for a microwave oven. The ordinary preservative film needs to have proper oxygen permeability and moisture permeability, the content of oxygen and moisture around the preserved product is adjusted, and dust is blocked, so that the preservation period of food is prolonged; the preservative film for the microwave oven is far superior to the common preservative film in the aspects of heat resistance, no toxicity and the like.

Patent document CN201410205371.3 discloses an edible corn starch preservative film, which comprises the following raw materials: 180 portions of corn starch, 35 to 65 portions of soybean protein, 8 to 14 portions of glycerol, 3 to 6 portions of amylase and 0.5 to 3.5 portions of dispersant; the preparation method of the preservative film comprises the following steps: gelatinizing starch; carrying out enzymolysis; and (5) film preparation. The preservative film preparation raw materials seem to be edible materials, the preparation method is simple, but the preservative film prepared by the method has extremely poor mechanical properties and influences normal use.

Patent document CN201710740388.2 discloses a starch/PVA composite antibacterial preservative film and a preparation method thereof, wherein the preservative film is formed by adding a cross-linking agent, a plasticizer, a defoaming agent and a film-forming assistant into a skeleton structure formed by starch, cationic starch and polybutylene adipate-terephthalate. The preservative film has good antibacterial property, but poor heat resistance, is not suitable for heating in a microwave oven, contains a plasticizer, cannot be used for packaging high-lipid articles such as food and the like, and greatly limits the application range of the preservative film.

Patent document CN201410749865.8 discloses a preservative film suitable for microwave oven, wherein the raw materials for preparing the preservative film comprise styrene-acrylonitrile-butadiene copolymer, diphenyl oxide peroxydicarbonate, sodium carboxymethylcellulose, glass fiber reinforced polydecamide, curing agent and catalyst. The preservative film has the beneficial effects that toxic substances which are easy to separate out are not contained, the human body is not damaged, but the preservative film prepared from the materials has poor ductility and does not meet the requirement of the viscosity of the preservative film.

Under the background, in order to overcome the defects of the prior art, the invention provides the biodegradable preservative film for the microwave oven, the preparation raw materials of the preservative film do not contain a plasticizer, the preservative film can be used for packaging high-lipid food, has good heat resistance and can be used for heating the food in the microwave oven, and in addition, the preservative film is biodegradable and causes little environmental pollution.

Disclosure of Invention

The invention aims to provide a biodegradable preservative film for a microwave oven and a preparation method thereof, and the invention also aims to provide a heat-resistant starch graft polymer.

In a first aspect, the invention provides a preservative film, which is prepared from the following raw materials in parts by mass: the high-performance starch graft copolymer comprises, by mass, 50-150 parts of a starch graft polymer, 10-50 parts of polylactic acid, 10-20 parts of poly (butylene adipate-terephthalate), 0-20 parts of poly (butylene succinate), 5-30 parts of a cross-linking agent and 0-30 parts of a dispersing agent, wherein the starch graft polymer contains 1-15% of a silazane compound, and the silazane compound comprises a silazane monomer and/or a silazane polymer.

Preferably, the mass fraction of the silazane compound in the starch graft polymer is 10 to 15%.

The silazane compound has the structural formula shown as (I):

wherein R is selected from-H and-CH₃or-C₂H₅；R₁、R₂、R₃、R₄、R₅、R₆Independently selected from-H, C_1-3Straight chain alkyl, C_2-4Alkenyl or C_2-6Alkynyl.

And n is an integer between 1 and 12, when n is 1, the compound is a silazane monomer, and when n is 2 to 12, the compound is a silazane polymer.

Preferably, the silazane monomer contains at least one unsaturated double bond.

Preferably, the silazane polymer contains at least one unsaturated double bond or unsaturated triple bond.

In a preferred embodiment of the invention, the silazane is a silazane monomer and/or a silazane dimer, and the specific structural formula is

Preferably, the ratio of the content of the starch graft polymer to the sum of the contents of the polylactic acid, the polybutylene adipate-terephthalate and the polybutylene succinate in the preservative film is 1-10:1, preferably 2-5:1, and more preferably 2-4: 1.

In the invention, the starch graft polymer comprises the following preparation raw materials in parts by mass: 100 parts of unsaturated modified starch, 60-120 parts of grafting monomer, 16-45 parts of silazane compound and 0.1-5 parts of initiator.

The grafting monomer comprises: one or more of ethyl acrylate, methyl methacrylate, ethyl methacrylate and vinyl acetate.

The initiator is selected from one or the combination of more than two of ammonium persulfate and potassium persulfate.

The unsaturated modified starch is formed by esterification reaction of natural starch and a modifier, and comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-40 parts of a modifier and 5-10 parts of a catalyst, wherein the modifier is double-bond-containing acid, acyl chloride or isocyanate.

Preferably, the modifier is one or a combination of more than two of acrylic acid, acryloyl chloride and isocyano ethyl methacrylate.

The catalyst is one or the combination of more than two of pyridine, ethylenediamine and triethylamine.

The natural starch is one or more of corn starch, cassava starch, sweet potato starch, wheat starch and bean starch.

Preferably, corn starch is selected in the specific embodiment of the present invention.

The cross-linking agent used in the preparation process of the preservative film is one or the combination of more than two of epichlorohydrin, N' -methylenebisacrylamide, diethylenetriamine, triethylenetetramine and divinylbenzene.

The dispersant is selected from one or the combination of more than two of titanate, stearic acid, oleic acid and sodium polyacrylate.

In a preferred embodiment of the invention, the preservative film comprises the following preparation raw materials in parts by mass: 10-20 parts of polylactic acid, 10-20 parts of poly (butylene adipate-terephthalate), 100-150 parts of starch graft polymer and 10-15 parts of cross-linking agent; the starch graft polymer comprises the following preparation raw materials in parts by weight: 100 parts of unsaturated modified starch, 60-80 parts of grafting monomer, 16-25 parts of silazane compound and 1-2 parts of initiator; the unsaturated modified starch comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-40 parts of modifier and 5-10 parts of catalyst.

In another preferred embodiment of the invention, the raw materials for preparing the preservative film comprise the following raw materials in parts by weight: 10-20 parts of polylactic acid, 10-20 parts of poly (butylene adipate-terephthalate), 5-10 parts of poly (butylene succinate), 100-120 parts of starch graft polymer, 10-15 parts of cross-linking agent and 10-20 parts of dispersing agent; the starch graft polymer comprises the following preparation raw materials in parts by weight: 100 parts of unsaturated modified starch, 60 parts of grafting monomer, 20-25 parts of silazane compound and 1-2 parts of initiator; the unsaturated modified starch comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-20 parts of modifier and 5-10 parts of catalyst.

In a second aspect, the present invention provides a method for preparing a plastic wrap, comprising the steps of:

(1) preparation of unsaturated modified starch: adding a solvent into natural starch to prepare a starch suspension, adding a catalyst into the suspension, stirring for 0.5-1 hour at room temperature, adjusting the pH value of the solution to 7.5-9.0, slowly dropwise adding a modifier while stirring, reacting overnight, centrifuging, discarding the supernatant, washing for 3-5 times with water or 95% ethanol, drying, crushing, and sieving to obtain unsaturated modified starch;

(2) preparation of starch graft polymer: adding 1-2 times of water into the modified starch prepared in the step (1), gelatinizing at 90-100 ℃ for 20-30 minutes, cooling to room temperature, adding a silazane compound and a grafted unsaturated monomer, stirring at a high speed for pre-emulsification for 0.5-1 hour, dropwise adding an initiator while stirring, reacting overnight, centrifuging, discarding the supernatant, washing with water or 95% ethanol for 3-5 times, and drying to obtain a starch grafted polymer;

(3) preparing a preservative film: putting polylactic acid, poly (butylene adipate-terephthalate), poly (butylene succinate) and starch graft polymer into a high-speed mixer, mixing for 5-10 minutes, adding a dispersing agent, continuously blending for 5-10 minutes, adding a cross-linking agent, mixing for 3-5 minutes to form a mixed raw material, putting the mixed raw material into a double-screw granulator, extruding, granulating and blow-molding to form the preservative film.

Illustratively, the process temperature of the twin-screw granulator in the step (3) is as follows: the first zone is 80-115 ℃, the second zone is 110-130 ℃, the third zone is 105-140 ℃, the fourth zone is 110-140 ℃, the fifth zone is 100-160 ℃, the sixth zone is 140-155 ℃, the seventh zone is 145-170 ℃, the eighth zone is 140-160 ℃ and the ninth zone is 145-180 ℃; the main machine rotating speed of the double-screw granulator is 100-300 r/min; the feeding speed is 30-70 r/min.

Preferably, the solvent in step (1) is one or a combination of two or more of acetone, chloroform, ethyl acetate, dimethylformamide, ethanol and methanol.

In a preferred embodiment of the invention, the twin-screw granulator process temperature is: a first zone of 110 ℃, a second zone of 130 ℃, a third zone of 130 ℃, a fourth zone of 130 ℃, a fifth zone of 145 ℃, a sixth zone of 155 ℃, a seventh zone of 166 ℃, an eighth zone of 155 ℃, a ninth zone of 175 ℃; the main machine rotating speed of the double-screw granulator is 300 revolutions per minute; the feeding speed was 70 rpm.

In a third aspect, the invention provides an application of a preservative film in the field of microwave oven preservative films.

In a fourth aspect, the invention provides a starch graft polymer, which comprises the following preparation raw materials in parts by mass: 100 parts of unsaturated modified starch, 60-120 parts of grafting monomer, 16-45 parts of silazane compound and 0.1-5 parts of initiator.

The unsaturated modified starch is formed by esterification reaction of natural starch and a modifier, and comprises the following preparation raw materials in parts by weight: 100 parts of natural starch, 10-40 parts of a modifier and 5-10 parts of a catalyst, wherein the modifier is double-bond-containing acid, acyl chloride or isocyanate.

Preferably, the modifier is one or a combination of more than two of acrylic acid, acryloyl chloride and isocyano ethyl methacrylate.

The catalyst is one or the combination of more than two of pyridine, ethylenediamine and triethylamine.

The natural starch is one or more of corn starch, cassava starch, sweet potato starch, wheat starch and bean starch.

The grafting monomer comprises: one or more of ethyl acrylate, methyl methacrylate, ethyl methacrylate and vinyl acetate.

The initiator is selected from one or the combination of more than two of ammonium persulfate and potassium persulfate.

The silazane compound has the structural formula shown as (I):

wherein R is selected from-H and-CH₃or-C₂H₅；R₁、R₂、R₃、R₄、R₅、R₆Independently selected from-H, C_1-3Straight chain alkyl, C_2-4Alkenyl or C_2-6Alkynyl.

And n is an integer between 1 and 12, when n is 1, the compound is a silazane monomer, and when n is 2 to 12, the compound is a silazane polymer.

Preferably, the silazane monomer contains at least one unsaturated double bond.

Preferably, the silazane polymer contains at least one unsaturated double bond or unsaturated triple bond.

In a preferred embodiment of the invention, the silazane is a silazane monomer and/or a silazane dimer, and the specific structural formula is

In a fifth aspect, the present invention provides a method for preparing a starch graft polymer, comprising the steps of:

(1) preparation of unsaturated modified starch: adding a solvent into natural starch to prepare a starch suspension, adding a catalyst into the suspension, stirring for 0.5-1 hour at room temperature, adjusting the pH value of the solution to 7.5-9.0, slowly dropwise adding a modifier while stirring, reacting overnight, centrifuging, discarding the supernatant, washing for 3-5 times with water or 95% ethanol, drying, crushing, and sieving to obtain unsaturated modified starch;

(2) preparation of starch graft polymer: adding 1-2 times of water into the modified starch prepared in the step (1), gelatinizing at 90-100 ℃ for 20-30 minutes, cooling to room temperature, adding a silazane compound and a grafted unsaturated monomer, stirring at a high speed for pre-emulsification for 0.5-1 hour, dropwise adding an initiator while stirring, reacting overnight, centrifuging, discarding the supernatant, washing with water or 95% ethanol for 3-5 times, and drying to obtain a starch grafted polymer;

preferably, the solvent in step (1) is one or a combination of two or more of acetone, chloroform, ethyl acetate, dimethylformamide, ethanol and methanol.

The invention has the beneficial effects that: 1, the preservative film preparation raw material does not contain a plasticizer, so that no toxic substance is dissolved out even in the packing of high-fat food or in a heating state, the preservative film can be used for food packing, and the application range is wide; 2, the preservative film contains a heat-resistant starch graft polymer, so that the preservative film has good heat resistance and can be used for heating in a microwave oven; 3, the preservative film has good biodegradability, meets the environmental protection requirement and has less environmental pollution.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only some embodiments of the present invention, 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 invention.