阅读说明：本技术 一种高粘结强度防水淀粉基木材胶的制备方法 (Preparation method of waterproof starch-based wood adhesive with high bonding strength ) 是由 马科 于 2020-07-08 设计创作，主要内容包括：本发明公开了一种高粘结强度防水淀粉基木材胶的制备方法,属于胶粘剂制备技术领域。本发明首先将玉米淀粉和和水混合得到淀粉乳液,再加入酒石酸酸解后通过过氧化氢氧化,得到预处理玉米淀粉,随后配制聚乙烯醇溶液,并将聚乙烯醇溶液和预处理淀粉混合后再加入马来酸酐反应得到改性淀粉,之后将改性淀粉和硅酸钠溶液混合,在盐酸的作用下反应并高温搅拌处理得到反应物,最终将反应物和异氰酸酯以及其他原料混合反应,最终制得高粘结强度防水淀粉基木材胶,本发明制得的胶黏剂中高反应活性的基团数量较多,能和木材表面的活性基团发生化学键合力,粘结强度提高,具有很好的防水性能。(The invention discloses a preparation method of a high-bonding-strength waterproof starch-based wood adhesive, belonging to the technical field of adhesive preparation. The invention firstly mixes corn starch and water to obtain starch emulsion, then adds tartaric acid for acidolysis, and then carries out hydrogen peroxide oxidation to obtain pretreated corn starch, then prepares polyvinyl alcohol solution, and mixes the polyvinyl alcohol solution and the pretreated starch, then adds maleic anhydride for reaction to obtain modified starch, then mixes the modified starch and sodium silicate solution, and carries out reaction under the action of hydrochloric acid and high-temperature stirring treatment to obtain reactant, and finally mixes the reactant with isocyanate and other raw materials for reaction to finally obtain the high-bonding-strength waterproof starch-based wood adhesive.)

1. A preparation method of a waterproof starch-based wood adhesive with high bonding strength is characterized by comprising the following specific preparation steps:

weighing reactants, oxalic acid and isocyanate, putting into a reaction kettle, stirring for reaction, and discharging to obtain the waterproof starch-based wood adhesive with high bonding strength;

the preparation steps of the reactants are as follows:

mixing modified starch and 30% sodium silicate solution by mass to obtain a mixed solution, adjusting the pH of the mixed solution to 2.0-3.0 by using 1mol/L hydrochloric acid, heating to 160-170 ℃, and stirring for reaction for 30-40 min to obtain a reactant;

the preparation steps of the modified starch are as follows:

(1) mixing polyvinyl alcohol and deionized water, putting the mixture into a stirrer, heating the mixture to 80-90 ℃, stirring and mixing the mixture for 30-40 min at a rotating speed of 200-300 r/min until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution;

(2) mixing the polyvinyl alcohol solution and the pretreated starch, putting the mixture into a reaction kettle, heating the mixture to 70-80 ℃, adding maleic anhydride accounting for 8% of the mass of the pretreated starch into the reaction kettle, and stirring the mixture at 60-70 ℃ for reaction for 30-40 min to obtain modified starch;

the preparation steps of the pretreated starch are as follows:

(1) mixing corn starch and water, then placing the mixture into a reaction kettle, starting a stirrer to stir and mix the mixture for 20-30 min at a rotating speed of 200-300 r/min to obtain starch emulsion, adjusting the pH of the starch emulsion to 10-11 by using a sodium hydroxide solution with the mass fraction of 5%, simultaneously adding tartaric acid with the mass fraction of 5% of the starch, heating the mixture to 40-50 ℃, and stirring the mixture for reaction for 1-2 h;

(2) and after the stirring reaction is finished, continuously adding hydrogen peroxide into the reaction kettle, heating to 70-75 ℃, keeping the temperature, stirring and reacting for 30-40 min, filtering and separating after the reaction is finished to obtain filter residues, putting the filter residues into an oven, and drying at 90-100 ℃ for 1-2 h to obtain a dried substance, namely the pretreated starch.

2. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the specific preparation steps of the high-bonding-strength waterproof starch-based wood adhesive, 50-55 parts of reactants, 20-25 parts of oxalic acid and 10-15 parts of isocyanate are counted in parts by weight.

3. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the specific preparation steps of the high-bonding-strength waterproof starch-based wood adhesive, the stirring reaction temperature is 70-80 ℃, the stirring reaction rotating speed is 100-200 r/min, and the stirring reaction time is 1-2 h.

4. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the preparation step of the reactant, the mass ratio of the modified starch to the sodium silicate solution with the mass fraction of 30% is 1: 5.

5. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the preparation step (1) of the modified starch, the mass ratio of the polyvinyl alcohol to the deionized water is 1: 6.

6. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the step (2) of preparing the modified starch, the mass ratio of the polyvinyl alcohol solution to the pretreated starch is 1: 5.

7. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the preparation step (1) of the pretreated starch, the mass ratio of the corn starch to the water is 1: 8.

8. The method for preparing the waterproof starch-based wood adhesive with high bonding strength according to claim 1, wherein the method comprises the following steps: in the preparation step (2) of the pretreated starch, the addition amount of the hydrogen peroxide is 5% of the mass of the starch emulsion.

Technical Field

The invention discloses a preparation method of a high-bonding-strength waterproof starch-based wood adhesive, belonging to the technical field of adhesive preparation.

Background

Starch adhesives are adhesives made using starch gelatinization or starch derivatives. Starch is a high molecular carbohydrate, a polysaccharide composed of a single type of sugar unit.

Amylose starch: is a linear polymer linked by alpha-1, 4-glycosidic bonds. Amylopectin starch: is a highly branched polymer with a side chain structure connected with alpha-1, 6-glucoside bonds on a starch chain. Modified starch: the modification of starch by changing the structure or size of starch molecules by physical, chemical or enzymatic means is called starch denaturation, and the factor responsible for the denaturation is called a denaturing factor (denaturant), and the product after denaturation is called a denatured starch. Oxidized starch adhesive: the oxidant mainly comprises hydrogen peroxide, potassium permanganate and sodium hypochlorite. Potassium permanganate oxidation occurs primarily at the C6 atom in the amorphous region of the starch. Esterified starch adhesive: the esterified starch adhesive belongs to a non-degradable starch adhesive, and is characterized in that the hydroxyl of starch molecules and other substances are subjected to esterification reaction to endow starch with new functional groups, so that the performance of the starch adhesive is improved. The commonly used esterification agents include urea-formaldehyde resin, phosphoric acid, sodium hydrogen phosphate, etc. Grafting starch adhesive: the graft copolymerization of starch is achieved by a free radical reaction. The grafting of starch is that a physical and chemical method is used to make the molecular chain of starch generate free radical, when it meets the high molecular monomer, it forms chain reaction, and a side chain formed by high molecular monomer is generated on the main chain of starch. At present, the starch adhesive is mainly applied to paper, cotton fabrics, envelopes, labels and corrugated boards.

The starch adhesive prepared by the traditional method is actually used for bonding paper products in practice mostly due to low solid content, poor water resistance and poor gluing performance. And the adhesive has high solid content and good water-resistant bonding performance when used for manufacturing the adhesive for wood. For this purpose, the starch has to be modified. The method for modifying starch by adopting more starch is a method of oxidation, grafting and the like, namely oxidizing by using oxidants such as hydrogen peroxide, sodium hypochlorite and the like, and then mixing with organic monomers such as: graft copolymerization of vinyl acetate, acrylic acid, acrylamide, etc. or grafting with aqueous polymers such as PVA, rubber latex, etc.; the water-resistant gluing performance of the starch adhesive is greatly improved by using starch through esterification, crosslinking and other methods. Apparently, the standard requirements can be met from the test results, but the actual production has not been really used due to the complex or high cost of the manufacturing process, the limited use of chemical raw materials, the poor stability of the finished product state, the difficult operation in the actual use process, and the like. Limiting its use in wood adhesives. Chinese patent CN1687279A, "a method for preparing starch glue for wood", proposes a process for preparing starch glue by using starch as a main raw material, performing acidolysis, oxidation, graft copolymerization modification, and finally adding a certain amount of auxiliary agent. The starch glue prepared by the process has the advantages of low cost, environmental protection and the like, the bonding strength of the starch glue reaches the national standard, but the appearance, the bonding strength and the water resistance of the starch glue are still to be improved, so that the starch glue is expected to be applied industrially.

Therefore, the invention of the starch-based wood adhesive with good water resistance and high bonding strength is necessary for the technical field of adhesive preparation.

Disclosure of Invention

The invention mainly solves the technical problem and provides a preparation method of a high-bonding-strength waterproof starch-based wood adhesive aiming at the problems of low solid content, poor water resistance and poor bonding strength of the starch adhesive prepared by the traditional method.

In order to solve the technical problems, the technical scheme adopted by the invention is as follows:

the preparation method of the waterproof starch-based wood adhesive with high bonding strength comprises the following steps:

weighing reactants, oxalic acid and isocyanate, putting into a reaction kettle, stirring for reaction, and discharging to obtain the waterproof starch-based wood adhesive with high bonding strength;

the preparation steps of the reactants are as follows:

mixing modified starch and 30% sodium silicate solution by mass to obtain a mixed solution, adjusting the pH of the mixed solution to 2.0-3.0 by using 1mol/L hydrochloric acid, heating to 160-170 ℃, and stirring for reaction for 30-40 min to obtain a reactant;

the preparation steps of the modified starch are as follows:

(1) mixing polyvinyl alcohol and deionized water, putting the mixture into a stirrer, heating the mixture to 80-90 ℃, stirring and mixing the mixture for 30-40 min at a rotating speed of 200-300 r/min until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution;

(2) mixing the polyvinyl alcohol solution and the pretreated starch, putting the mixture into a reaction kettle, heating the mixture to 70-80 ℃, adding maleic anhydride accounting for 8% of the mass of the pretreated starch into the reaction kettle, and stirring the mixture at 60-70 ℃ for reaction for 30-40 min to obtain modified starch;

the preparation steps of the pretreated starch are as follows:

(1) mixing corn starch and water, then placing the mixture into a reaction kettle, starting a stirrer to stir and mix the mixture for 20-30 min at a rotating speed of 200-300 r/min to obtain starch emulsion, adjusting the pH of the starch emulsion to 10-11 by using a sodium hydroxide solution with the mass fraction of 5%, simultaneously adding tartaric acid with the mass fraction of 5% of the starch, heating the mixture to 40-50 ℃, and stirring the mixture for reaction for 1-2 h;

(2) and after the stirring reaction is finished, continuously adding hydrogen peroxide into the reaction kettle, heating to 70-75 ℃, keeping the temperature, stirring and reacting for 30-40 min, filtering and separating after the reaction is finished to obtain filter residues, putting the filter residues into an oven, and drying at 90-100 ℃ for 1-2 h to obtain a dried substance, namely the pretreated starch.

In the specific preparation steps of the high-bonding-strength waterproof starch-based wood adhesive, 50-55 parts of reactants, 20-25 parts of oxalic acid and 10-15 parts of isocyanate are counted in parts by weight.

In the specific preparation steps of the high-bonding-strength waterproof starch-based wood adhesive, the stirring reaction temperature is 70-80 ℃, the stirring reaction rotating speed is 100-200 r/min, and the stirring reaction time is 1-2 h.

In the preparation step of the reactant, the mass ratio of the modified starch to the sodium silicate solution with the mass fraction of 30% is 1: 5.

In the preparation step (1) of the modified starch, the mass ratio of the polyvinyl alcohol to the deionized water is 1: 6.

In the step (2) of preparing the modified starch, the mass ratio of the polyvinyl alcohol solution to the pretreated starch is 1: 5.

In the preparation step (1) of the pretreated starch, the mass ratio of the corn starch to the water is 1: 8.

In the preparation step (2) of the pretreated starch, the addition amount of the hydrogen peroxide is 5% of the mass of the starch emulsion.

The beneficial technical effects of the invention are as follows:

(1) firstly mixing corn starch and water to obtain starch emulsion, then adding tartaric acid for acidolysis, then adding hydrogen peroxide for oxidation to obtain pretreated corn starch, then preparing polyvinyl alcohol solution, mixing the polyvinyl alcohol solution and pretreated starch, then adding maleic anhydride for reaction to obtain modified starch, then mixing the modified starch and sodium silicate solution, making reaction under the action of hydrochloric acid and high-temp. stirring treatment to obtain reactant, finally mixing the reactant with isocyanate and other raw materials for reaction to obtain the invented high-adhesive-strength water-proof starch-base wood glue. The molecular weight is reduced, the reaction activity is greatly enhanced, the oxidized corn starch can obtain a polyhydroxy substance with a glucose ethylene glycol glycoside side chain under the action of thermal catalysis by utilizing polyvinyl alcohol, the prepared polyhydroxy product has extremely high chemical reaction activity and can be subjected to cross-linking reaction with maleic anhydride, a polyester type starch adhesive is obtained by polymerization, and then an isocyanate group with high reaction activity is introduced into the polyester type starch adhesive, so that the prepared adhesive has high bonding strength and good water resistance due to the isocyanate adhesive system, and the prepared adhesive has more groups with high reaction activity, can generate chemical bonding force with active groups on the surface of wood, increases the cohesive force between the wood and the wood, and further increases the bonding strength;

(2) the invention also mixes starch and sodium silicate, sodium silicate and sodium silicate react to generate sticky ortho-silicic acid precipitate to be coated on the surface of starch under the action of hydrochloric acid, and the ortho-silicic acid precipitate is heated and hydrolyzed to generate nano silicon dioxide to be attached to the surface of starch under the subsequent high-temperature action, so that the nano silicon dioxide is successfully introduced into a gluing system.

Detailed Description

Mixing corn starch and water according to a mass ratio of 1:8, then putting the mixture into a reaction kettle, starting a stirrer to stir and mix the mixture for 20-30 min at a rotating speed of 200-300 r/min to obtain starch emulsion, adjusting the pH of the starch emulsion to 10-11 by using a sodium hydroxide solution with a mass fraction of 5%, simultaneously adding tartaric acid with a mass fraction of 5% of the starch, heating the mixture to 40-50 ℃, and stirring the mixture for reaction for 1-2 h; after the stirring reaction is finished, continuously adding hydrogen peroxide with the mass of 5% of that of the starch emulsion into the reaction kettle, heating to 70-75 ℃, keeping the temperature, stirring and reacting for 30-40 min, filtering and separating after the reaction is finished to obtain filter residues, putting the filter residues into an oven, and drying for 1-2 h at the temperature of 90-100 ℃ to obtain a dried substance, namely the pretreated starch for later use; mixing polyvinyl alcohol and deionized water according to a mass ratio of 1:6, putting the mixture into a stirrer, heating to 80-90 ℃, stirring and mixing at a rotating speed of 200-300 r/min for 30-40 min until the polyvinyl alcohol is completely dissolved to obtain a polyvinyl alcohol solution; mixing the polyvinyl alcohol solution and the standby pretreated starch according to the mass ratio of 1:5, putting the mixture into a reaction kettle, heating the mixture to 70-80 ℃, adding maleic anhydride accounting for 8% of the mass of the pretreated starch into the reaction kettle, and stirring the mixture at 60-70 ℃ for reaction for 30-40 min to obtain modified starch; mixing the modified starch and 30% sodium silicate solution according to a mass ratio of 1:5 to obtain a mixed solution, adjusting the pH of the mixed solution to 2.0-3.0 by using 1mol/L hydrochloric acid, heating to 160-170 ℃, and stirring for reaction for 30-40 min to obtain a reactant; weighing 50-55 parts of the reactant, 20-25 parts of oxalic acid and 10-15 parts of isocyanate, putting into a reaction kettle, heating to 70-80 ℃, stirring at a rotating speed of 100-200 r/min for reaction for 1-2 hours, and discharging to obtain the waterproof starch-based wood adhesive with high bonding strength.