阅读说明：本技术 一种高强度耐水聚醋酸乙烯酯木工粘合剂的制备方法 (Preparation method of high-strength water-resistant polyvinyl acetate woodworking adhesive ) 是由 汤丽军 万江 叶鹏金 彭奕诚 何琳 于 2021-09-28 设计创作，主要内容包括：本发明公开了一种高强度耐水聚醋酸乙烯酯木工粘合剂的制备方法。该方法通过引入次氯酸钠对淀粉进行氧化生成羧基、醛基和酮羰基等基团,在酸性条件下羧基、醛基等可以与聚乙烯醇(PVA)上的羟基发生酯化反应和缩醛反应生成酯基等疏水基团实现对PVA的接枝改性和减少了PVA分子链段上的羟基数量使得白胶的耐水得以提高,其次氧化淀粉与PVA的接枝增大了PVA的分子量,并与PVA形成部分交联网状结构使得粘接强度得到增强。本发明制得的聚醋酸乙烯酯以水为分散介质,使用方便,对环境无污染与相同固含量的传统聚醋酸乙烯酯相比具有更高的耐水性和强度。其挥发物对人体和环境不会造成危害,生产环境安全。(The invention discloses a preparation method of a high-strength water-resistant polyvinyl acetate woodworking adhesive. According to the method, sodium hypochlorite is introduced to oxidize starch to generate carboxyl, aldehyde, ketocarbonyl and other groups, the carboxyl, aldehyde and other groups can generate esterification reaction with hydroxyl on polyvinyl alcohol (PVA) and acetal reaction to generate ester and other hydrophobic groups under an acidic condition to realize grafting modification of the PVA and reduce the number of the hydroxyl on a molecular chain segment of the PVA so as to improve the water resistance of the white glue, and then the oxidized starch is grafted with the PVA to increase the molecular weight of the PVA and form a partially crosslinked network structure with the PVA so as to enhance the bonding strength. The polyvinyl acetate prepared by the invention takes water as a dispersion medium, is convenient to use, has no pollution to the environment, and has higher water resistance and strength compared with the traditional polyvinyl acetate with the same solid content. The volatile substance does not cause harm to human bodies and the environment, and the production environment is safe.)

1. The preparation method of the high-strength waterproof polyvinyl acetate environment-friendly adhesive is characterized by comprising the following steps of:

(1) adding 0.1-0.2 part by weight of defoaming agent and 60-80 parts by weight of polyvinyl alcohol into 800 parts by weight of 600-plus-800 parts by weight of water, heating to 80-90 ℃, preserving heat for 60-70 minutes, and then cooling to below 50 ℃ to obtain a polyvinyl alcohol solution;

(2) dissolving 3-5 parts by weight of sodium hypochlorite in 10 parts by weight of water to obtain a sodium hypochlorite solution; dissolving 3-5 parts by weight of starch and 0.5-1 part by weight of ammonium persulfate into 10 parts by weight of water to obtain an ammonium persulfate solution; adding the sodium hypochlorite solution and the ammonium persulfate solution into the polyvinyl alcohol solution dissolved in the step (1), heating to 65-75 ℃, and stirring for 30-50 minutes; adding 5-10 parts by weight of borax and 0.1-0.5 part by weight of acrylamide, and stirring for 20-30 minutes;

(3) adding 0.5-1.5 parts by weight of sodium bicarbonate pH regulator and 0.5-2 parts by weight of emulsifier, and emulsifying for 10-20 minutes;

(4) uniformly mixing and stirring 250-300 parts by weight of vinyl acetate and 20-30 parts by weight of acrylic acid to prepare 270-330 parts by weight of mixed monomer solution; dissolving 1.5 parts by weight of ammonium persulfate initiator in 50 parts by weight of water to obtain an ammonium persulfate initiator solution;

(5) heating to 78-80 ℃, keeping the temperature for 10-20 minutes, then dropwise adding the mixed monomer solution and ammonium persulfate initiator solution prepared in the step (4), keeping the temperature for 30-40 minutes, heating to 90 ℃, and keeping the temperature for 60-80 minutes again; and then cooling to below 50 ℃, adding 0.2-0.3 weight part of mildew preventive, 0.5-1.0 weight part of plasticizer and 0.1-1.0 weight part of cross-linking agent, and stirring for 30-40 minutes to obtain the finished emulsion.

2. The method according to claim 1, wherein the polyvinyl alcohol is preferably one or more of PVA1788, PVA0588 and PVA2488, and is mixed in any proportion.

3. The method according to claim 1, wherein the emulsifier is one or more selected from sodium acrylamido sulfonate, maleic acid derivative, and sodium alkyl sulfosuccinate alkyl ester sulfonate.

4. The method of claim 1, wherein the plasticizer is preferably polyethylene glycol 400(PEG-400), TXIB or DBP.

5. The production method according to claim 1, wherein the crosslinking agent is an aluminum chloride solution having a mass fraction of 50% or an iron chloride solution having a mass fraction of 50%.

Technical Field

The invention relates to a preparation technology of a special performance adhesive, in particular to a preparation method of a high-strength waterproof polyvinyl acetate woodworking adhesive;

Technical Field

Polyvinyl acetate emulsion, produced in 1929, developed rapidly after 70 s of industrial production in 1937. The sale amount of polyvinyl acetate emulsion in China since the eighties is second to that of urea-formaldehyde resin and is second. However, nowadays, our country advocates environment-friendly new materials, and urea-formaldehyde resin has been gradually replaced by water-based polyvinyl acetate (PVAc) emulsion. The polyvinyl acetate emulsion is one of the most widely used and most used environment-friendly adhesive varieties at present, has a series of advantages of convenient use, low price, no toxicity, safety, environmental protection and the like, and is popular in the market. However, polyvinyl acetate emulsions have inherent disadvantages such as poor cold, heat and water resistance, and long curing time, which limit their utility.

PVA plays the role of an emulsifier, a protective colloid and a thickening agent in the polymerization process of vinyl acetate emulsion, and has excellent performances of strong adhesion, toughness, transparency, high adhesive film strength and the like in polyvinyl acetate adhesive. But the PAV also has the defects of soft mechanical property, poor water resistance and the like, so that the application of the PAVc emulsion is greatly limited.

Polyvinyl alcohol strongly exhibits an affinity for water during external changes in humidity and humidity due to a large number of hydrophilic groups contained in the molecule, which is also one of the causes of poor water resistance of PVAc. In the initial stage of dissolving PVA as a protective colloid, the carboxyl, ketocarbonyl and aldehyde groups on oxidized starch molecules C2, C3 and C6 are subjected to dehydration, acetal and other reactions with hydroxyl groups in PVA molecules to convert the hydrophilic hydroxyl groups on the PVA into hydrophobic groups; part of the branched chains of the oxidized starch and PVA can form a cross-linked body type structure; the PVA molecule is hindered from converging by destroying the symmetry of the PVA, the number of hydroxyl groups in the PVA molecule is reduced, and the water resistance of the PVA molecule is enhanced, so that the water resistance of the PVAc is improved, and the polyvinyl acetate adhesive can be suitable for more application environments. Therefore, the method has very important significance for designing the water resistance of the polyvinyl acetate emulsion adhesive.

Disclosure of Invention

The invention aims to provide a preparation method of a high-strength waterproof polyvinyl acetate adhesive aiming at the problem that the traditional polyvinyl acetate adhesive is insufficient in strength and water resistance.

The purpose of the invention is realized by the following technical scheme: a preparation method of a high-strength water-resistant polyvinyl acetate adhesive comprises the following steps: a preparation method of a high-strength waterproof polyvinyl acetate environment-friendly adhesive comprises the following steps:

(1) adding 0.1-0.2 part by weight of defoaming agent and 60-80 parts by weight of polyvinyl alcohol into 800 parts by weight of 600-plus-800 parts by weight of water, heating to 80-90 ℃, preserving heat for 60-70 minutes, and then cooling to below 50 ℃ to obtain a polyvinyl alcohol solution;

(2) dissolving 3-5 parts by weight of sodium hypochlorite in 10 parts by weight of water to obtain a sodium hypochlorite solution; dissolving 3-5 parts by weight of starch and 0.5-1 part by weight of ammonium persulfate into 10 parts by weight of water to obtain an ammonium persulfate solution; adding the sodium hypochlorite solution and the ammonium persulfate solution into the polyvinyl alcohol solution dissolved in the step (1), heating to 65-75 ℃, and stirring for 30-50 minutes; adding 5-10 parts by weight of borax and 0.1-0.5 part by weight of acrylamide, and stirring for 20-30 minutes;

(3) adding 0.5-1.5 parts by weight of sodium bicarbonate pH regulator and 0.5-2 parts by weight of emulsifier, and emulsifying for 10-20 minutes;

(4) uniformly mixing and stirring 250-300 parts by weight of vinyl acetate and 20-30 parts by weight of acrylic acid to prepare 270-330 parts by weight of mixed monomer solution; dissolving 1.5 parts by weight of ammonium persulfate initiator in 50 parts by weight of water to obtain an ammonium persulfate initiator solution;

(5) heating to 78-80 ℃, keeping the temperature for 10-20 minutes, then dropwise adding the mixed monomer solution and ammonium persulfate initiator solution prepared in the step (4), keeping the temperature for 30-40 minutes, heating to 90 ℃, and keeping the temperature for 60-80 minutes again; and then cooling to below 50 ℃, adding 0.2-0.3 weight part of mildew preventive, 0.5-1.0 weight part of plasticizer and 0.1-1.0 weight part of cross-linking agent, and stirring for 30-40 minutes to obtain the finished emulsion.

Further, the polyvinyl alcohol is preferably one or more of PVA1788, PVA0588 and PVA2488, and is mixed according to any proportion.

Further, the emulsifier is preferably one or more of sodium acrylamido sulfonate, maleic acid derivative and sodium alkyl propenyl succinate sulfonate which are mixed according to any proportion;

further, the plasticizer is preferably polyethylene glycol 400(PEG-400), TXIB or DBP.

Further, the cross-linking agent is an aluminum chloride solution with the mass fraction of 50% or an iron chloride solution with the mass fraction of 50%.

The invention has the beneficial effects that: the invention modifies PVA protective colloid, firstly uses sodium hypochlorite to modify starch C₂、C₃、C₅The hydroxyl on the PVA can be oxidized to generate aldehyde, carboxyl, ketocarbonyl and other groups under the acidic condition₂、C₃、C₅The aldehyde group, carboxyl group and ketone carbonyl group are subjected to esterification reaction, acetal reaction and the like to generate hydrophobic groups, the hydrophobic groups on the PVA are increased to improve the water resistance, the hydroxyl number of the PVA of the protective colloid is reduced to a proper degree and enough active groups are kept, the active groups are mutually subjected to crosslinking polycondensation reaction to form a firm network structure in the curing process of the adhesive, the molecular weight of the PVA is increased due to the grafting of oxidized starch, the bonding strength is improved, and the crosslinking points are provided by the free radical polymerization of acrylamide so that polymer molecules form a crosslinking network structure to improve the bonding strength and the water resistance of the product on the whole. Adding oxidant, ammonium persulfate and the like into polyvinyl alcohol aqueous solution to break chains of partial molecular chains of polyvinyl alcohol, introducing carboxyl or aldehyde groups at the tail ends of the molecular chains, introducing ketone groups into the molecular chains, wherein oxidized starch and PVA are macromolecular compounds with polyhydroxy groups, under certain conditions, the starch and the PVA can be mutually dehydrated to form a certain micromolecular network structure, and then taking the micromolecular network structure as protective colloid to carry out polyvinyl acetate emulsion polymerizationThereby achieving the purpose of high strength and water resistance.

Detailed Description

The present invention is described in further detail below with reference to specific examples.

Example 1

(1) Adding 0.1kg of defoaming agent, 60kg of polyvinyl alcohol (PVA) and 600kg of water into a reaction kettle, heating to 90 ℃, preserving heat for 60-70 minutes, and then cooling to below 50 ℃ to obtain a polyvinyl alcohol solution;

(2) dissolving 3kg of sodium hypochlorite in 10kg of water; dissolving 3kg of starch and 0.5kg of ammonium persulfate into 10kg of water, adding the water into the polyvinyl alcohol PVA solution dissolved in the step (1), heating to 70 ℃, and stirring for 50 minutes; adding 5kg of borax and 0.1kg of acrylamide, and stirring for 20 minutes;

(3) adding 0.5kg of sodium bicarbonate pH regulator and 0.5kg of emulsifier, and emulsifying for 10 minutes;

(4) 250kg of vinyl acetate and 20kg of acrylic acid are mixed and stirred uniformly to prepare 270kg of mixed monomer solution; 1.5kg of ammonium persulfate initiator is dissolved in 50kg of water to obtain ammonium persulfate initiator solution;

(5) heating the reaction kettle to 78-80 ℃, keeping the temperature for 10 minutes, then gradually dripping the mixed monomer solution prepared in the step (4) and the ammonium persulfate initiator solution by using a constant flow pump, controlling the dripping within 4 hours, keeping the temperature for 30 minutes after the dripping of the monomer and the potassium persulfate solution is finished, heating to 90 ℃, and keeping the temperature for 60 minutes again; then cooling to below 50 ℃, adding 0.2Kg of mildew preventive and 0.5Kg of plasticizer, and stirring for 30 minutes by 0.1Kg of cross-linking agent to obtain the finished emulsion.

Example 2

(1) Adding 0.2Kg of defoaming agent, 80Kg of polyvinyl alcohol (PVA) and 800Kg of water into a reaction kettle, heating to 90 ℃, keeping the temperature for 60-70 minutes, and cooling to 50 ℃ after dissolution to obtain a polyvinyl alcohol solution;

(2) dissolving 5Kg of sodium hypochlorite in 10Kg of water; dissolving 5Kg of starch and 1Kg of ammonium persulfate into 10Kg of water, adding the dissolved PVA solution in the step (1), heating to 70 ℃, and stirring for 50 minutes; adding 10Kg of borax and 0.5Kg of Acrylamide (AM) and stirring for 20 minutes;

(3) adding 1.5Kg of sodium bicarbonate PH regulator and 2Kg of emulsifier, and emulsifying for 15 minutes;

(4) 300Kg of vinyl acetate and 30Kg of acrylic acid are mixed and stirred evenly to prepare 330Kg of mixed monomer, and 1.5Kg of potassium persulfate initiator is dissolved in 50Kg of water;

(5) heating the reaction kettle to 78-80 ℃, keeping the temperature for 10 minutes, then gradually dripping the solution prepared in the step (4) by using a constant flow pump, controlling the monomer and the initiator to drip off within 4 hours, keeping the temperature for 40 minutes after the monomer and the potassium persulfate solution drip off, heating to 90 ℃, and keeping the temperature for 70 minutes again; then cooling to below 50 ℃, adding 0.3Kg of mildew preventive, 1Kg of plasticizer and 1Kg of crosslinking agent, and stirring for 35 minutes to obtain the finished emulsion.

Example 3

(1) Adding 0.15Kg of defoaming agent, 70Kg of polyvinyl alcohol (PVA) and 700Kg of water into a reaction kettle, heating to 90 ℃, preserving the heat for 60-70 minutes, and cooling to 50 ℃ after dissolution;

(2) 4Kg of sodium hypochlorite is dissolved in 10Kg of water; dissolving 4Kg of starch and 0.75Kg of ammonium persulfate into 10Kg of water, adding the dissolved PVA solution obtained in the step (1), heating to 70 ℃, and stirring for 50 minutes; adding 7.5Kg of borax and 0.25Kg of acrylamide, and stirring for 25 minutes;

(3) adding 1Kg of sodium bicarbonate PH regulator and 1Kg of emulsifier, and emulsifying for 20 minutes;

(4) mixing 280Kg of vinyl acetate and 25Kg of acrylic acid, and uniformly stirring to prepare 305Kg of mixed monomer solution; 1.5Kg of ammonium persulfate initiator is dissolved in 50Kg of water to obtain ammonium persulfate initiator solution;

(5) heating the reaction kettle to 78-80 ℃, keeping the temperature for 10 minutes, then gradually dripping the mixed monomer solution prepared in the step (4) and the ammonium persulfate initiator solution by using a constant flow pump, controlling the monomer and the initiator to drip off within 4 hours, keeping the temperature for 30 minutes after the monomer and the potassium persulfate solution drip off, heating to 90 ℃, and keeping the temperature for 60 minutes again; then cooling to below 50 ℃, adding 0.25Kg of mildew preventive, 0.75Kg of plasticizer and 0.5Kg of cross-linking agent, and stirring for 40 minutes to obtain the finished emulsion.

Comparative example 1

(1) Adding 0.1Kg of defoaming agent, 60Kg of polyvinyl alcohol (PVA) and 600Kg of water into a reaction kettle, heating to 90 ℃, preserving heat for 60-70 minutes, and then cooling to 50 ℃;

(2) adding 0.5Kg of sodium bicarbonate PH regulator and 0.5Kg of emulsifier, and emulsifying for 10 minutes;

(3) 250Kg of vinyl acetate and 20Kg of acrylic acid are mixed and stirred evenly to prepare 270Kg of mixed monomer solution; 1.5Kg of ammonium persulfate initiator is dissolved in 50Kg of water to obtain ammonium persulfate initiator solution;

(4) heating the reaction kettle to 78-80 ℃, keeping the temperature for 10 minutes, then gradually dripping the mixed monomer solution prepared in the step (4) and the ammonium persulfate initiator solution by using a constant flow pump, controlling the dripping within 4 hours, keeping the temperature for 30 minutes after the dripping of the monomer and the potassium persulfate solution is finished, heating to 90 ℃, and keeping the temperature for 60 minutes again; then cooling to below 50 ℃, adding 0.2Kg of mildew preventive, 0.5Kg of plasticizer and 0.1Kg of cross-linking agent, and stirring for 30 minutes to obtain the finished emulsion.

Comparative example 2

(1) Adding 0.2Kg of defoaming agent, 80Kg of polyvinyl alcohol (PVA) and 800Kg of water into a reaction kettle, heating to 90 ℃, preserving heat for 60-70 minutes, and cooling to 50 ℃ after dissolution;

(2) adding 1.5Kg of sodium bicarbonate PH regulator and 2Kg of emulsifier, and emulsifying for 10 minutes;

(3) 300Kg of vinyl acetate and 30Kg of acrylic acid are mixed and stirred evenly to prepare 330Kg of mixed monomer, and 1.5Kg of potassium persulfate initiator is dissolved in 50Kg of water;

(4) heating the reaction kettle to 78-80 ℃, keeping the temperature for 10 minutes, then gradually dripping the solution prepared in the step (4) by using a constant flow pump, controlling the monomer and the initiator to drip off within 4 hours, keeping the temperature for 30 minutes after the monomer and the potassium persulfate solution drip off, heating to 90 ℃, and keeping the temperature for 60 minutes again; then cooling to below 50 ℃, adding 0.3Kg of mildew preventive, 1.0Kg of plasticizer and 1Kg of cross-linking agent, and stirring for 30 minutes to obtain the finished emulsion.

Test example 1

1. Detecting physical performance indexes of the detected emulsion according to HJ/T220-2005, GB/T185832008 and HG/T2727-2010 standards; dry strength was measured according to EN204D3 test standard;

2. the water-resistant comparison was as follows:

the glass plates were coated with the test glue using a 150g applicator bar and left to cure for 4 hours with complete drying. The prepared dry film was peeled off the glass, cut into 3cm by 3cm squares of about 3 parts, and M was weighed separately₁；

Soaking the glue film in pure deionized water for 60 min, taking out, sucking water on the surface of the glue film with filter paper, weighing M again₂；

Water absorption rate (M2-M1)/M1 × 100% (the larger the water absorption rate, the worse the water resistance); the results were averaged for 2 out of 3 parts each (error between water uptake less than 5% indicates the results are valid).

The test results are shown in Table 1

TABLE 1

Sample (I)	Example 1	Example 2	Example 3	Comparative example 1	Comparative example 2
						Appearance of the product	Milky white sticky	Milky white sticky	Milky white sticky	Milky white sticky	Milky white sticky
pH value	3-5	3-5	3-5	3-5	3-5
						Solid content	48±1％	48±1％	48±1％	48±1％	48±1％
Water absorption (Water-resistant)	1.3％	1.6％	1.1％	15.6％	17.8％
						Shear strength MPa	16.1	18.2	15.8	11.3	10.8
Shelf stability period (d)	180>	180>	180>	90>	90>

As shown in the above table 1, the polyvinyl acetate environment-friendly adhesive prepared by the embodiment of the invention has a shear strength as high as about 15-20 MPa through detection; the water absorption rate is low and is about 1-2%; the storage stability period is longer, more than 180 days. Therefore, the product prepared by the method has the advantages of high strength, water resistance and long-term stable storage.