CN114163892B - Starch modification method - Google Patents
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- CN114163892B CN114163892B CN202111593986.4A CN202111593986A CN114163892B CN 114163892 B CN114163892 B CN 114163892B CN 202111593986 A CN202111593986 A CN 202111593986A CN 114163892 B CN114163892 B CN 114163892B
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- C—CHEMISTRY; METALLURGY
- C09—DYES; PAINTS; POLISHES; NATURAL RESINS; ADHESIVES; COMPOSITIONS NOT OTHERWISE PROVIDED FOR; APPLICATIONS OF MATERIALS NOT OTHERWISE PROVIDED FOR
- C09D—COATING COMPOSITIONS, e.g. PAINTS, VARNISHES OR LACQUERS; FILLING PASTES; CHEMICAL PAINT OR INK REMOVERS; INKS; CORRECTING FLUIDS; WOODSTAINS; PASTES OR SOLIDS FOR COLOURING OR PRINTING; USE OF MATERIALS THEREFOR
- C09D151/00—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers
- C09D151/02—Coating compositions based on graft polymers in which the grafted component is obtained by reactions only involving carbon-to-carbon unsaturated bonds; Coating compositions based on derivatives of such polymers grafted on to polysaccharides
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08F—MACROMOLECULAR COMPOUNDS OBTAINED BY REACTIONS ONLY INVOLVING CARBON-TO-CARBON UNSATURATED BONDS
- C08F251/00—Macromolecular compounds obtained by polymerising monomers on to polysaccharides or derivatives thereof
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/08—Processes
- C08G18/10—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step
- C08G18/12—Prepolymer processes involving reaction of isocyanates or isothiocyanates with compounds having active hydrogen in a first reaction step using two or more compounds having active hydrogen in the first polymerisation step
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/30—Low-molecular-weight compounds
- C08G18/38—Low-molecular-weight compounds having heteroatoms other than oxygen
- C08G18/3893—Low-molecular-weight compounds having heteroatoms other than oxygen containing silicon
- C08G18/3895—Inorganic compounds, e.g. aqueous alkalimetalsilicate solutions; Organic derivatives thereof containing no direct silicon-carbon bonds
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/40—High-molecular-weight compounds
- C08G18/42—Polycondensates having carboxylic or carbonic ester groups in the main chain
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G18/00—Polymeric products of isocyanates or isothiocyanates
- C08G18/06—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen
- C08G18/28—Polymeric products of isocyanates or isothiocyanates with compounds having active hydrogen characterised by the compounds used containing active hydrogen
- C08G18/67—Unsaturated compounds having active hydrogen
- C08G18/671—Unsaturated compounds having only one group containing active hydrogen
- C08G18/672—Esters of acrylic or alkyl acrylic acid having only one group containing active hydrogen
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
- C08G2150/00—Compositions for coatings
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- C—CHEMISTRY; METALLURGY
- C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
- C08L—COMPOSITIONS OF MACROMOLECULAR COMPOUNDS
- C08L2201/00—Properties
- C08L2201/06—Biodegradable
Abstract
The invention relates to the technical field of starch, in particular to a starch modification method. According to the modification method, starch is subjected to graft modification and an acrylate-terminated polyurethane prepolymer capable of reacting with the starch is prepared, so that a modified starch mixed solution and the polyurethane prepolymer can undergo a free radical polymerization reaction under the action of a second initiator, a cross-linked network structure is formed between the starch and polyurethane molecules, the condition that two phases are incompatible to cause insufficient mechanical properties or insufficient water resistance is avoided, and the cross-linking property of the network structure can be further improved by adding a cross-linking agent, so that the mechanical property and the water resistance of a coating film are better improved.
Description
Technical Field
The invention relates to the technical field of starch, in particular to a starch modification method.
Background
Starch is a high molecular carbohydrate, a polysaccharide composed of a single type of sugar unit. The starch is basically composed of alpha-D-glucopyranose, and starch molecules are covalent polymers formed by connecting glucose together through glycosidic bonds after water molecules are removed from the glucose. The starch has the advantages of reproducibility, no pollution, low cost, biodegradability and the like, and has the advantages of environmental protection and degradability when being applied to food packaging materials, but the starch film has strong hydrophilicity and poor water resistance, and can be used as a packaging material only through modification treatment. At present, the modified starch film is mainly prepared by adding starch into a connecting material in a physical blending mode to improve the degradability of a film layer, but the sludge blending mode is not beneficial to preparing a high-strength film layer material.
Disclosure of Invention
In order to overcome the defects and shortcomings in the prior art, the invention aims to provide a starch modification method which can prepare high-strength biodegradable coating.
The purpose of the invention is realized by the following technical scheme:
a method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 150-250 parts by weight of water, heating to 70-80 ℃, stirring for 20-30min under heat preservation, then adding 6-10 parts by weight of acrylamide, 10-16 parts by weight of butyl acrylate, 9-11 parts by weight of acrylic acid, 5-9 parts by weight of pentaerythritol tetraacrylate and 0.5-1 part by weight of first initiator, uniformly stirring, heating to 60-70 ℃, and reacting for 2-3h under heat preservation to obtain a modified starch mixed solution;
(2) adding 5-10 parts by weight of nano silicon dioxide into 25-35 parts by weight of isocyanate, adding 30-38 parts by weight of polyester polyol and 0.1-0.3 part by weight of catalyst while stirring, reacting at the temperature of 75-85 ℃ for 2-3h, then adding 5-15 parts by weight of acetone to adjust the viscosity, adding 0.01-0.1 part by weight of polymerization inhibitor and 2.5-4.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 75-85 ℃ for 2-3h, then adding 120-140 parts by weight of deionized water and 2-3 parts by weight of neutralizing agent, removing the acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed solution, polyurethane prepolymer, cross-linking agent, second initiator, flatting agent, defoaming agent and water according to the weight ratio of 100:120-220:23-41:1-2:0.5-1.5: mixing the components in a ratio of 30-50, heating to 65-75 ℃, and reacting for 2-4 hours under the condition of heat preservation to obtain the modified starch coating.
In polyurethane, strong polar and rigid groups such as carbamate groups and the like can form hydrogen bonds among molecules due to large cohesive energy, and the hydrogen bonds are gathered together to form hard segment micro-phase regions which are in glassy paracrystal or microcrystal at room temperature; polyether chain segments or polyester chain segments with weaker polarity are gathered together to form a soft segment phase region. Although the soft and hard segments are somewhat miscible, the hard segment phase region and the soft segment phase region have thermodynamic incompatibility properties, resulting in microphase separation, and the soft and hard segment domains exhibit their respective glass transition temperatures. The soft segment phase region mainly affects the elasticity and low temperature performance of the material. The chain segment attraction between the hard segments is far greater than that between the soft segments, the hard phase is insoluble in the soft phase and distributed in the soft phase to form a discontinuous micro-phase structure, and plays a role of a physical cross-linking point and a reinforcing role in the soft segments at normal temperature; therefore, the polyurethane has the characteristics of high strength and good water resistance as a coating material, and the starch is mixed into the polyurethane, so that the carboxylic acid can be generated in the degradation process to accelerate the degradation, and the polyurethane modified starch film also has good biodegradability.
But if the starch is directly added in a physical blending mode, the starch is not easily and uniformly dispersed in the polyurethane, and the incompatibility of the starch and the polyurethane can cause the remarkable reduction of the mechanical property.
According to the invention, molecular chains of starch are firstly opened through gelatinization, and the starch is subjected to graft modification by using acrylamide, acrylic acid and butyl acrylate under the action of free radical-initiated polymerization reaction, so that the hydrophobicity of the starch can be greatly improved, the dispersibility of the starch in a system is also improved, and pentaerythritol tetraacrylate is added into a graft monomer, so that active sites of reaction can be introduced, and the reaction with an acrylate polyurethane prepolymer is facilitated.
Then, the polyurethane is prepared by the reaction of isocyanate and polyester polyol, and the end capping treatment is carried out by utilizing hydroxyethyl acrylate to provide reaction sites of carbon-carbon double bonds, so that the reaction sites can generate a crosslinking reaction with acrylate modified starch molecules; in addition, the nano silicon dioxide is added in the polyurethane synthesis process, isocyanate reacts with hydroxyl on the surface of the nano silicon dioxide, so that the nano silicon dioxide is introduced into the internal structure of the polyurethane, the problem of dispersibility of the nano silicon dioxide is solved, the mechanical property and the water resistance of a coating film are further improved through the nano silicon dioxide, the nano silicon dioxide is uniformly distributed in a polyurethane continuous body instead of starch with poor plasticity, the silver streak effect can be more actively initiated in the stretching process, energy is consumed, and the toughness of the film layer is better improved.
Finally, the modified starch mixed solution and the polyurethane prepolymer of the invention are subjected to free radical polymerization reaction under the action of a second initiator, so that a cross-linked network structure is formed between starch and polyurethane molecules, the condition of insufficient mechanical property or insufficient water resistance caused by incompatibility of two phases is avoided, and the cross-linking property of the network structure can be further improved by adding a cross-linking agent, so that the mechanical property and the water resistance of the coating film are better improved.
Wherein the first initiator and the second initiator are one or more of ammonium persulfate, potassium persulfate and sodium persulfate.
Wherein the isocyanate is isophorone diisocyanate, and the molecular weight of the polyester polyol is 1000.
Wherein the catalyst is dibutyltin dilaurate.
Wherein the particle size of the nano silicon dioxide is 20-40 nm.
Wherein the neutralizer is triethylamine, and the polymerization inhibitor is hydroquinone.
Wherein the cross-linking agent is trimethylolpropane trimethacrylate.
Wherein the leveling agent is an acrylate leveling agent, and the defoaming agent is a BYK defoaming agent.
The invention has the beneficial effects that:
according to the invention, molecular chains of starch are firstly opened through gelatinization, and the starch is subjected to graft modification by using acrylamide, acrylic acid and butyl acrylate under the action of free radical-initiated polymerization reaction, so that the hydrophobicity of the starch can be greatly improved, the dispersibility of the starch in a system is also improved, and pentaerythritol tetraacrylate is added into a graft monomer, so that active sites of reaction can be introduced, and the reaction with an acrylate polyurethane prepolymer is facilitated.
Then, the polyurethane is prepared by the reaction of isocyanate and polyester polyol, and the end capping treatment is carried out by utilizing hydroxyethyl acrylate to provide reaction sites of carbon-carbon double bonds, so that the reaction sites can generate a crosslinking reaction with acrylate modified starch molecules; in addition, the nano silicon dioxide is added in the polyurethane synthesis process, isocyanate reacts with hydroxyl on the surface of the nano silicon dioxide, so that the nano silicon dioxide is introduced into the internal structure of the polyurethane, the problem of dispersibility of the nano silicon dioxide is solved, the mechanical property and the water resistance of a coating film are further improved through the nano silicon dioxide, the nano silicon dioxide is uniformly distributed in a polyurethane continuous body instead of starch with poor plasticity, the silver streak effect can be more actively initiated in the stretching process, energy is consumed, and the toughness of the film layer is better improved.
Finally, the modified starch mixed solution and the polyurethane prepolymer of the invention are subjected to free radical polymerization reaction under the action of a second initiator, so that a cross-linked network structure is formed between starch and polyurethane molecules, the condition of insufficient mechanical property or insufficient water resistance caused by incompatibility of two phases is avoided, and the cross-linking property of the network structure can be further improved by adding a cross-linking agent, so that the mechanical property and the water resistance of the coating film are better improved.
Detailed Description
The present invention will be further described with reference to the following examples for facilitating understanding of those skilled in the art, and the description of the embodiments is not intended to limit the present invention.
Example 1
A method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 200 parts by weight of water, heating to 75 ℃, keeping the temperature and stirring for 25min, then adding 8 parts by weight of acrylamide, 13 parts by weight of butyl acrylate, 10 parts by weight of acrylic acid, 7 parts by weight of pentaerythritol tetraacrylate and 0.7 part by weight of first initiator, uniformly stirring, heating to 65 ℃, and keeping the temperature and reacting for 2.5h to obtain a modified starch mixed solution;
(2) adding 7.5 parts by weight of nano silicon dioxide into 30 parts by weight of isocyanate, adding 34 parts by weight of polyester polyol and 0.2 part by weight of catalyst while stirring, reacting at the temperature of 80 ℃ for 2.5h, then adding 10 parts by weight of acetone to adjust the viscosity, adding 0.05 part by weight of polymerization inhibitor and 3.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 80 ℃ for 2.5h, then adding 130 parts by weight of deionized water and 2.5 parts by weight of neutralizer, removing the acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed solution, polyurethane prepolymer, cross-linking agent, second initiator, flatting agent, defoaming agent and water according to the weight ratio of 100:170:32:1.5:1: 40, heating to 70 ℃, and reacting for 3 hours in a heat preservation manner to obtain the modified starch coating.
Wherein the first initiator and the second initiator are ammonium persulfate.
Wherein the isocyanate is isophorone diisocyanate, and the molecular weight of the polyester polyol is 1000.
Wherein the catalyst is dibutyltin dilaurate.
Wherein the particle size of the nano silicon dioxide is 30 nm.
Wherein the neutralizer is triethylamine, and the polymerization inhibitor is hydroquinone.
Wherein the cross-linking agent is trimethylolpropane trimethacrylate.
Wherein the leveling agent is an acrylate leveling agent, and the defoaming agent is a BYK defoaming agent.
Example 2
A method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 150 parts by weight of water, heating to 70 ℃, keeping the temperature and stirring for 20min, then adding 6 parts by weight of acrylamide, 10 parts by weight of butyl acrylate, 9 parts by weight of acrylic acid, 5 parts by weight of pentaerythritol tetraacrylate and 0.5 part by weight of first initiator, uniformly stirring, heating to 60 ℃, and keeping the temperature and reacting for 2h to obtain a modified starch mixed solution;
(2) adding 5 parts by weight of nano silicon dioxide into 25 parts by weight of isocyanate, adding 30 parts by weight of polyester polyol and 0.1 part by weight of catalyst while stirring, reacting at the temperature of 75 ℃ for 2 hours, then adding 5 parts by weight of acetone to adjust viscosity, adding 0.01 part by weight of polymerization inhibitor and 2.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 75 ℃ for 2 hours, then adding 120 parts by weight of deionized water and 2 parts by weight of neutralizer, removing acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed solution, polyurethane prepolymer, cross-linking agent, second initiator, flatting agent, defoaming agent and water according to the weight ratio of 100:120:23:1:0.5: 30, heating to 65 ℃, and reacting for 2 hours under the condition of heat preservation to obtain the modified starch coating.
Wherein the first initiator and the second initiator are potassium persulfate.
Wherein the isocyanate is isophorone diisocyanate, and the molecular weight of the polyester polyol is 1000.
Wherein the catalyst is dibutyltin dilaurate.
Wherein the particle size of the nano silicon dioxide is 20 nm.
Wherein the neutralizer is triethylamine, and the polymerization inhibitor is hydroquinone.
Wherein the cross-linking agent is trimethylolpropane trimethacrylate.
Wherein the leveling agent is an acrylate leveling agent, and the defoaming agent is a BYK defoaming agent.
Example 3
A method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 250 parts by weight of water, heating to 80 ℃, keeping the temperature and stirring for 30min, then adding 10 parts by weight of acrylamide, 16 parts by weight of butyl acrylate, 11 parts by weight of acrylic acid, 9 parts by weight of pentaerythritol tetraacrylate and 1 part by weight of first initiator, uniformly stirring, heating to 70 ℃, and keeping the temperature and reacting for 3h to obtain a modified starch mixed solution;
(2) adding 10 parts by weight of nano silicon dioxide into 35 parts by weight of isocyanate, adding 38 parts by weight of polyester polyol and 0.3 part by weight of catalyst while stirring, reacting at 85 ℃ for 3 hours, then adding 15 parts by weight of acetone to adjust viscosity, adding 0.1 part by weight of polymerization inhibitor and 4.5 parts by weight of hydroxyethyl acrylate, continuing to react at 85 ℃ for 3 hours, then adding 140 parts by weight of deionized water and 3 parts by weight of neutralizer, removing acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing the modified starch mixed solution, the polyurethane prepolymer, the cross-linking agent, the second initiator, the leveling agent, the defoaming agent and water according to the weight ratio of 100:220:41:2:1.5:1.5:50, heating to 75 ℃, and carrying out heat preservation reaction for 4 hours to obtain the modified starch coating.
Wherein the first initiator and the second initiator are sodium persulfate.
Wherein the isocyanate is isophorone diisocyanate, and the molecular weight of the polyester polyol is 1000.
Wherein the catalyst is dibutyltin dilaurate.
Wherein the particle size of the nano silicon dioxide is 40 nm.
Wherein the neutralizer is triethylamine, and the polymerization inhibitor is hydroquinone.
Wherein the cross-linking agent is trimethylolpropane trimethacrylate.
Wherein the leveling agent is an acrylate leveling agent, and the defoaming agent is a BYK defoaming agent.
Comparative example 1
This comparative example differs from example 1 in that:
a method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 200 parts by weight of water, heating to 75 ℃, keeping the temperature and stirring for 25min, then adding 8 parts by weight of acrylamide, 13 parts by weight of butyl acrylate, 10 parts by weight of acrylic acid and 0.7 part by weight of first initiator, uniformly stirring, heating to 65 ℃, and keeping the temperature and reacting for 2.5h to obtain a modified starch mixed solution;
(2) adding 7.5 parts by weight of nano silicon dioxide into 30 parts by weight of isocyanate, adding 34 parts by weight of polyester polyol and 0.2 part by weight of catalyst while stirring, reacting at the temperature of 80 ℃ for 2.5h, then adding 10 parts by weight of acetone to adjust the viscosity, adding 0.05 part by weight of polymerization inhibitor and 3.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 80 ℃ for 2.5h, then adding 130 parts by weight of deionized water and 2.5 parts by weight of neutralizer, removing the acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed liquor, polyurethane prepolymer, flatting agent, defoaming agent and water according to the weight ratio of 100:170:1: 40, heating to 70 ℃, and reacting for 3 hours in a heat preservation manner to obtain the modified starch coating.
Comparative example 2
A method of modifying starch comprising the steps of:
(1) adding 100 parts by weight of starch into 200 parts by weight of water, heating to 75 ℃, keeping the temperature and stirring for 25min, then adding 8 parts by weight of acrylamide, 13 parts by weight of butyl acrylate, 10 parts by weight of acrylic acid, 7 parts by weight of pentaerythritol tetraacrylate and 0.7 part by weight of first initiator, uniformly stirring, heating to 65 ℃, and keeping the temperature and reacting for 2.5h to obtain a modified starch mixed solution;
(2) adding 34 parts by weight of polyester polyol and 0.2 part by weight of catalyst into 30 parts by weight of isocyanate while stirring, reacting at the temperature of 80 ℃ for 2.5 hours, then adding 10 parts by weight of acetone to adjust the viscosity, adding 0.05 part by weight of polymerization inhibitor and 3.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 80 ℃ for 2.5 hours, then adding 130 parts by weight of deionized water and 2.5 parts by weight of neutralizer, removing the acetone, cooling, and adding 7.5 parts by weight of nano silicon dioxide to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed solution, polyurethane prepolymer, cross-linking agent, second initiator, flatting agent, defoaming agent and water according to the weight ratio of 100:170:32:1.5:1: 40, heating to 70 ℃, and reacting for 3 hours in a heat preservation manner to obtain the modified starch coating.
The tensile strength, elongation at break and contact angle measurements were carried out according to GB/T1040.3 and according to GB/T30693 for example 1, comparative example 1 and comparative example 2, with the following results:
| tensile Strength (MPa) | Elongation at Break (%) | Contact angle (°) | |
| Example 1 | 11.6 | 128 | 63.3 |
| Comparative example 1 | 7.4 | 106 | 45.1 |
| Comparative example 2 | 8.3 | 89 | 56.7 |
As can be seen from comparative example 1, the problem of incompatibility of starch and polyurethane cannot be solved well by directly mixing the starch and the polyurethane in a physical blending manner, so that the mechanical property is obviously reduced, and the water resistance is also reduced due to the uneven distribution of the starch and the phase separation of the starch and the polyurethane, so that the water contact angle is also obviously reduced; as can be seen from comparative example 2, when the nano-silica is directly added after the polyurethane synthesis, the nano-silica is still easy to agglomerate, so the elongation at break is more obviously reduced, but the film layer filled with the nano-silica still has higher tensile strength because the starch and the polyurethane still have better dispersibility.
The above-described embodiments are preferred implementations of the present invention, and the present invention may be implemented in other ways without departing from the spirit of the present invention.
Claims (8)
1. A method for modifying starch, characterized by: the method comprises the following steps:
(1) adding 100 parts by weight of starch into 150-250 parts by weight of water, heating to 70-80 ℃, stirring for 20-30min under heat preservation, then adding 6-10 parts by weight of acrylamide, 10-16 parts by weight of butyl acrylate, 9-11 parts by weight of acrylic acid, 5-9 parts by weight of pentaerythritol tetraacrylate and 0.5-1 part by weight of first initiator, uniformly stirring, heating to 60-70 ℃, and reacting for 2-3h under heat preservation to obtain a modified starch mixed solution;
(2) adding 5-10 parts by weight of nano silicon dioxide into 25-35 parts by weight of isocyanate, adding 30-38 parts by weight of polyester polyol and 0.1-0.3 part by weight of catalyst while stirring, reacting at the temperature of 75-85 ℃ for 2-3h, then adding 5-15 parts by weight of acetone to adjust the viscosity, adding 0.01-0.1 part by weight of polymerization inhibitor and 2.5-4.5 parts by weight of hydroxyethyl acrylate, continuing to react at the temperature of 75-85 ℃ for 2-3h, then adding 120-140 parts by weight of deionized water and 2-3 parts by weight of neutralizing agent, removing the acetone, and cooling to obtain an acrylate-terminated polyurethane prepolymer;
(3) mixing modified starch mixed solution, polyurethane prepolymer, cross-linking agent, second initiator, flatting agent, defoaming agent and water according to the weight ratio of 100:120-220:23-41:1-2:0.5-1.5: mixing the components in a ratio of 30-50, heating to 65-75 ℃, and reacting for 2-4 hours under the condition of heat preservation to obtain the modified starch coating.
2. A method of modifying starch according to claim 1, wherein: the first initiator and the second initiator are one or more of ammonium persulfate, potassium persulfate and sodium persulfate.
3. A method of modifying starch according to claim 1, wherein: the isocyanate is isophorone diisocyanate, and the molecular weight of the polyester polyol is 1000.
4. A method of modifying starch according to claim 1, wherein: the catalyst is dibutyltin dilaurate.
5. A method of modifying starch according to claim 1, wherein: the particle size of the nano silicon dioxide is 20-40 nm.
6. A method of modifying starch according to claim 1, wherein: the neutralizer is triethylamine, and the polymerization inhibitor is hydroquinone.
7. A method of modifying starch according to claim 1, wherein: the cross-linking agent is trimethylolpropane trimethacrylate.
8. A method of modifying starch according to claim 1, wherein: the leveling agent is an acrylate leveling agent, and the defoaming agent is a BYK defoaming agent.
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| CN117050536B (en) * | 2023-10-13 | 2024-02-09 | 广州市瑞合新材料科技有限公司 | Liquid silicone rubber for infants and preparation method thereof |
| CN117089210B (en) * | 2023-10-18 | 2024-02-09 | 广州市瑞合新材料科技有限公司 | Silicon rubber for medical protection and preparation method thereof |
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