A method for preparing a compostable water-based adhesive

Abstract

A method for preparing a compostable and biodegradable water-based adhesive includes the following steps: S1, esterifying polyacids, polyols, sulfonates, and polyhydroxy organic acids, followed by polycondensation, to form a polyester polyol with a glass transition temperature (Tg) of 38-72℃; S2, dissolving the polyester polyol and polyvinyl alcohol in deionized water, and after all solid particles have dissolved, adding an antifoaming agent and a coupling agent to obtain a water-based adhesive with a solid content of 28-48%. The method for preparing the compostable and biodegradable water-based adhesive of this invention uses polyacids, polyols, sulfonates, and polyhydroxy organic acids to form branched polyester polyols through esterification, then dissolving the polyester polyol and polyvinyl alcohol in water, and adding functional additives such as antifoaming agents and coupling agents to obtain a water-based adhesive with a solid content of 28-48%. The preparation method is simple, easy to implement, and operates under mild conditions, enabling large-scale industrial production.

Description

Technical Field

[0001] This invention relates to the field of polyester compounds, and more specifically to a method for preparing a compostable and biodegradable aqueous adhesive. Background Technology

[0002] With the continuous upgrading of national environmental protection policies, water-based adhesives have become a major development trend. The combination of water-based adhesives and paper has become the most environmentally competitive solution in food packaging. Biodegradable water-soluble resins replace PE lamination, coating paper to form coated paper used to make corresponding daily necessities, such as disposable paper cups, hamburger bags, sunflower seed bags, paper lunch boxes, food paper bags, and airline garbage bags. Consumer products made from this type of material have the advantages of being recyclable, repulped, and reusable, reducing white pollution. It is estimated that the global coated paper market will grow at a CAGR of 4.5% from 2022 to 2029, reaching $6.6 billion. Currently, commercially available water-based adhesives are mainly water-based acrylic emulsions and water-based polyvinyl alcohol, or blends or hybrids of these with water-based ethylene-vinyl acetate copolymer (EVA) emulsions, water-based vinyl acetate-ethylene copolymer (VAE) emulsions, and water-based ethylene-acrylic acid copolymer (EAA) emulsions. Patent CN202010345779.6 discloses a biodegradable coating and its preparation method, but the evaluation of the coating's biodegradability did not specifically assess the resulting coating material (containing EVA resin). Patent CN202210486750.9 discloses a waterborne polyvinyl alcohol-based high-barrier waterborne adhesive. Patents CN202010338340.0 and CN202010515955.6 disclose a waterborne coating formed by modifying polyester resin with acrylic acid, which cannot be used for heat sealing. Polyester compounds are primarily used to prepare waterborne polyurethane emulsions, but there are few reports on their use in preparing biodegradable waterborne adhesives.

[0003] In addition, the adhesive industry has developed extremely rapidly. However, because traditional adhesives are difficult to degrade in the natural environment, they are used in paper products and enter the natural environment after these products are discarded. The "pollution" caused by their inability to degrade has become a major hidden danger to the protection of the natural environment. Solving this problem has gradually become a hot topic in current research and development. Summary of the Invention

[0004] Based on this, the present invention provides a method for preparing a compostable and biodegradable water-based adhesive to solve the technical problems of existing water-based adhesives being difficult to degrade and causing environmental pollution.

[0005] To achieve the above objectives, the present invention provides a method for preparing a compostable and biodegradable water-based adhesive, comprising the following steps:

[0006] S1. Polyesterification reaction of polyacid, polyol, sulfonate and polyhydroxy organic acid, followed by polycondensation reaction to form polyester polyol with glass transition temperature (Tg) of 38-72℃.

[0007] S2. Dissolve polyester polyol and polyvinyl alcohol in deionized water. After all solid particles have dissolved, add defoamer and coupling agent to obtain a water-based adhesive with a solid content of 28-48%.

[0008] As a further preferred embodiment of the present invention, the polyacid includes at least one of terephthalic acid, isophthalic acid, phthalic anhydride, adipic acid, sebacic acid, malic acid, citric acid, and dimer acid.

[0009] As a further preferred embodiment of the present invention, the polyol includes at least one of ethylene glycol, diethylene glycol, 1,3-propanediol, 1,6-hexanediol, 1,2-propanediol, neopentyl glycol, 1,3-pentanediol, glycerol, sorbitol, and xylitol.

[0010] As a further preferred embodiment of the present invention, the sulfonate includes at least one of sodium ethylenediamine sulfonate, terephthalic acid-5-sulfonate and its esters, sodium isophthalic acid-5-sulfonate and its esters, and sulfonates of dicarboxylic acids.

[0011] As a further preferred embodiment of the present invention, the polyhydroxy organic acid includes at least one of 2,2-dihydroxymethylpropionic acid and 2,2-dihydroxymethylbutyric acid.

[0012] As a further preferred embodiment of the present invention, the defoamer includes at least one of DF691, DF677, MO2190, BYK-016, BYK-024, and Beston-1122.

[0013] As a further preferred embodiment of the present invention, the coupling agent includes at least one of CoatOSil MP 200, CoatOSil2287, wetlink-78, KH560, KBM403, A-187, and Z-6040 / OFS6040.

[0014] As a further preferred technical solution of the present invention, in step S2, each raw material, by mass fraction, includes: 15-25 parts of polyester polyol, 10-20 parts of polyvinyl alcohol, 1-2 parts of defoamer and 0.5-1 parts of coupling agent.

[0015] As a further preferred technical solution of the present invention, step S1 specifically includes:

[0016] Polybasic acid and polyol are added to a reaction vessel and heated to 150-160℃ for esterification until water is expelled. Then, sulfonate and polyhydroxy organic acid are added and esterification is continued at 230-280℃ until no more water is expelled. The acid value is measured to be 30-40 mg KOH / g. Then, at 230℃, a vacuum is applied starting from -0.01 MPa for 30 min to remove water, and the temperature is maintained at -0.05 MPa for 0.5-1.5 h. The acid value is measured to be 10-14 mg KOH / g. The vacuum is then continued to -0.1 MPa for polycondensation reaction for 1-3 h. The acid value is measured to be 4-8 mg KOH / g and the hydroxyl value is 2-8 mg KOH / g, yielding a polyester polyol with a glass transition temperature (Tg) of 38-72℃.

[0017] The method for preparing the compostable and biodegradable water-based adhesive of the present invention, by adopting the above technical solution, can achieve the following:

[0018] Beneficial effects:

[0019] 1) In the preparation method of the present invention, polyfunctional compounds such as polyacids, polyols, sulfonates and polyhydroxy organic acids are used to carry out esterification reaction to form branched polyester polyols. Then, the polyester polyols and polyvinyl alcohol are dissolved in water, and functional additives such as defoamers and coupling agents are added to obtain a water-based adhesive with a solid content of 28-48%. The preparation method is simple and easy to implement, the conditions are mild, and it can realize large-scale industrial production.

[0020] 2) The water-based adhesive prepared by this invention can be used for heat sealing of coated paper. It can be applied using a dry laminating machine with a speed of 120-250 m / min and a heat sealing temperature of 90-140℃, meeting the needs of daily and industrial production for heat sealing adhesive.

[0021] 3) The water-based adhesive prepared by this invention has good adhesion to paper, is biodegradable, has no VOC emissions, is pollution-free, easy to apply, saves costs, has high viscosity, and can be widely used for heat sealing of paper products.

[0022] The biodegradability of this invention lies in the introduction of bio-based polyols and acids, including glycerol, sorbitol, xylitol, malic acid, and citric acid, into the prepared polyester polyol. This results in bio-based ester bonds in the adhesive. During composting, the product decomposes into small fragments under composting conditions. Hydrolytic enzymes secreted by microorganisms bind to the surface of these fragments, hydrolyzing the high molecular weight chains into low molecular weight compounds, such as organic acids and sugars. These low molecular weight compounds are then injected into the microorganisms, metabolized, and become microbial biomass or converted into energy for microbial activity, ultimately transforming into water (H2O) and carbon dioxide (CO2). The biodegradability of this invention also lies in the introduction of biodegradable polyvinyl alcohol. Detailed Implementation

[0023] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0024] Unless otherwise defined, the technical terms used in the following embodiments have the same meanings as commonly understood by those skilled in the art to which this invention pertains. Unless otherwise specified, the experimental reagents used in the following embodiments are conventional biochemical reagents; and the experimental methods described are conventional methods.

[0025] In this invention, both polyacids and polyols refer to dibasic or higher acids or alcohols.

[0026] Example 1:

[0027] 38.5g adipic acid, 43.7g hexanediol, and 4.4g isophthalic acid were added to a four-necked round-bottom flask. The temperature was raised to 150-160℃ and the reaction was carried out for 4 hours until water excretion was complete. Then, 11.7g terephthalic acid-5-sulfonate and 1.8g 2,2-dimethylolpropionic acid were added to continue the esterification reaction to 230-280℃ until no more water was excreted. The acid value was measured to be 30-40 mg KOH / g. Then, at 230℃, a vacuum was applied starting from -0.01 MPa for 30 minutes to remove water, and the temperature was maintained at -0.05 MPa for 0.5-1.5 hours. The acid value was measured to be 10-14 mg KOH / g. The vacuum was then continued to -0.1 MPa for a polycondensation reaction for 1-3 hours. The acid value was measured to be 7 mg KOH / g, the hydroxyl value was 4 mg KOH / g, and the glass transition temperature (Tg) of the obtained polyester polyol was 43℃.

[0028] Dissolve 25 parts of the above-mentioned polyester polyol A and 13 parts of polyvinyl alcohol in 60 parts of deionized water, then add 1 part of defoamer and 1 part of coupling agent to obtain a water-based adhesive with a solid content of 40%.

[0029] A dry laminating machine was used to apply the water-based adhesive from Example 1 onto the paper. The machine speed was 180 m / min and the amount of adhesive applied was 10.3 g. The pre-coated paper was dried at 70°C for 12 h. The heat sealing temperature of the pre-coated paper was tested to be 110-130°C, and the paper showed signs of fuzzing during the peel test.

[0030] Example 2:

[0031] 53.9 g of adipic acid, 32.0 g of ethylene glycol, and 6.1% terephthalic acid were added to a four-necked round-bottom flask and heated to 150-160 °C for 4 hours until water excretion ceased. Then, 5.5 g of terephthalic acid-5-sulfonate and 2.5 g of 2,2-dimethylolpropionic acid were added to continue the esterification reaction to 230-280 °C. No further water excretion occurred, and the acid value was measured to be 30-40 mg KOH / g. Next, at 230 °C, a vacuum was applied starting at -0.01 MPa for 30 min to remove water, and the temperature was maintained at -0.05 MPa for 0.5-1.5 hours, with an acid value of 10-14 mg KOH / g. The vacuum was then continued to -0.1 MPa for a polycondensation reaction for 1-3 hours, with an acid value of 7 mg KOH / g and a hydroxyl value of 4 mg KOH / g. The glass transition temperature (Tg) of the resulting polyester polyol was 59 °C.

[0032] Dissolve 20 parts of the above-mentioned polyester polyol A and 10 parts of polyvinyl alcohol in 68 parts of deionized water, then add 1 part of defoamer and 1 part of coupling agent to obtain a water-based adhesive with a solid content of 32%.

[0033] A dry laminating machine was used to apply the water-based adhesive from Example 2 onto the paper. The machine speed was 230 m / min and the amount of adhesive applied was 9.6 g. The pre-coated paper was dried at 70°C for 12 h. The heat sealing temperature of the pre-coated paper was tested to be 100-120°C, and the paper showed signs of fuzzing during the peel test.

[0034] Example 3:

[0035] 38.4 g of adipic acid, 32.6 g of ethylene glycol, and 12.5% ​​terephthalic acid were added to a four-necked round-bottom flask. The mixture was heated to 150-160 °C and reacted for 4 hours until water excretion ceased. Then, 11.1 g of isophthalic acid-5-sulfonate and 5.5 g of 2,2-dihydroxymethylbutyric acid were added to continue the esterification reaction at 230-280 °C until no more water was excreted. The acid value was measured to be 30-40 mg KOH / g. Then, at 230 °C, a vacuum was applied starting at -0.01 MPa for 30 min to remove water, and the temperature was maintained at -0.05 MPa for 0.5-1.5 hours. The acid value was measured to be 10-14 mg KOH / g. The vacuum was then continued to -0.1 MPa for a polycondensation reaction for 1-3 hours. The acid value was measured to be 7 mg KOH / g, and the hydroxyl value was 4 mg KOH / g. The glass transition temperature (Tg) of the obtained polyester polyol A is 67℃.

[0036] Dissolve 15 parts of the above-mentioned polyester polyol A and 13 parts of polyvinyl alcohol in 68 parts of deionized water, then add 1 part of defoamer and 1 part of coupling agent to obtain a water-based adhesive with a solid content of 30%.

[0037] The water-based adhesive from Example 3 was applied to the paper using a dry laminating machine at a speed of 200 m / min and an adhesive application rate of 9.6 g. The resulting pre-coated paper was dried at 70°C for 12 hours. The heat-sealing temperature of the pre-coated paper was tested to be 130-140°C, and the paper showed signs of fuzzing during a peel test.

[0038] After drying the water-based adhesives of Examples 1-3 above, they were placed in a compost bin for degradation testing according to GBT19277.1-2001 standard, and compared with water-based acrylic acid. The test results are shown in Table 1 below:

[0039] Table 1

[0040]

[0041] As shown in Table 1, the composting degradation rate of the water-based adhesive of the present invention is significantly better than that of the water-based acrylic emulsion adhesive of the prior art. Moreover, the water-based adhesive of the present invention begins to show significant degradation in the compost bin after 60 days, and the degradation rate can reach more than 90% after 180 days. Among them, Example 1 is the optimal solution of the present invention.

[0042] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and various changes or modifications can be made to these embodiments without departing from the principles and essence of the present invention. The scope of protection of the present invention is defined only by the appended claims.

Claims

1. A method for preparing a compostable and biodegradable water-based adhesive, characterized in that, Includes the following steps: S1. Add polyacid and polyol to the reaction vessel, heat to 150-160 ℃ for esterification until water is expelled. Then add sulfonate and polyhydroxy organic acid and continue esterification at 230-280 ℃ until no more water is expelled. The acid value is measured to be 30-40 mg KOH / g. Then, at 230 ℃, vacuum dewatering is carried out starting from -0.01 MPa at -0.01 MPa for 30 min, and the temperature is maintained at -0.05 MPa for 0.5-1.5 h. The acid value is measured to be 10-14 mg KOH / g. Vacuum is continued to be carried out at -0.1 MPa for condensation reaction for 1-3 h. The acid value is measured to be 4-8 mg KOH / g and the hydroxyl value is 2-8 mg KOH / g, resulting in a polyester polyol with a glass transition temperature (Tg) of 38-72 ℃. S2. Dissolve polyester polyol and polyvinyl alcohol in deionized water. After all the solid particles have dissolved, add defoamer and coupling agent to obtain a water-based adhesive with a solid content of 28-48%. The raw materials, by mass fraction, include: 15-25 parts polyester polyol, 10-20 parts polyvinyl alcohol, 1-2 parts defoamer, and 0.5-1 part coupling agent.

2. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The polyacids include at least one of terephthalic acid, isophthalic acid, phthalic anhydride, adipic acid, sebacic acid, malic acid, citric acid, and dimer acid.

3. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The polyols include at least one of ethylene glycol, diethylene glycol, 1,3-propanediol, 1,6-hexanediol, 1,2-propanediol, neopentyl glycol, 1,3-pentanediol, glycerol, sorbitol, and xylitol.

4. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The sulfonate includes at least one of terephthalic acid-5-sulfonate and sodium isophthalic acid-5-sulfonate.

5. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The polyhydroxy organic acid includes at least one of 2,2-dihydroxymethylpropionic acid and 2,2-dihydroxymethylbutyric acid.

6. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The defoamer includes at least one of DF691, DF677, MO2190, BYK-016, and BYK-024.

7. The method for preparing the compostable and biodegradable aqueous adhesive according to claim 1, characterized in that, The coupling agent includes at least one of CoatOSil MP 200, CoatOSil 2287, wetlink-78, KH560, KBM403, A-187, and Z-6040 / OFS6040.

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