Preparation of freeze-thaw resistant polyvinyl acetate emulsion adhesive

Abstract : The method of semi-continuous emulsion polymerization was used to screen the emulsifiers and buffers. The copolymerization with unsaturated carboxylic acid monomers was used to synthesize the freeze-thaw resistant polyvinyl acetate emulsion adhesive. The emulsion was frozen at -20°C for 16 hours. . 30 °C melt 2h cycle 5 times to restore the original state, -20 °C frozen 6 months to restore the original state, compression shear strength of up to 12MPa or more.

Keywords :polyvinyl acetate emulsion; freeze-thaw stability; adhesive

Foreword

Environment and health are one of the most important themes of human beings in the 21st century. The development of aqueous emulsions has become a hot topic for researchers because solvent-based products are polluted by the inevitable volatility of solvents. As a water-emulsifiable polyvinyl acetate (PVAc) emulsion, it is widely used in coatings, adhesives, etc. due to its low price, easy production, high bonding strength, and non-toxicity. However, PVAc emulsions have the defect of poor freeze-thaw stability, that is, the gel melts after being frozen in a low-temperature environment and deteriorates in quality and loses its use value, which brings great inconvenience to the application of the emulsion [1]. In northern China, about half an year's worth of emulsions are inventoried each year. Not only do they have to take up warehouses, but they also need to insulate the fuel, which will affect the turnover of funds. Inadvertent storage will also cause serious losses. This issue has not yet been resolved. With the growth of PVAc emulsion production and demand, it is of great significance to improve its stability in storage and transportation, especially during storage and transportation under low temperature environment.

At present, to improve the freeze-thaw stability of polyvinyl acetate emulsion, additives are added, non-polyvinyl alcohol (PVA)-type protective colloids, modified PVA-type protective colloids, and functional monomers containing carboxyl groups are copolymerized [2]. The addition of additives and the use of non-PVA protective colloids not only increase the cost, but also affect the adhesive properties of the emulsion. Therefore, the use of modified PVA-type protective colloids and copolymers containing carboxyl functional monomers to improve the freeze-thaw stability of polyvinyl acetate emulsion is better, but the use of modified acetal modification should pay attention to the problem of residual aldehyde.

Based on the mechanism of emulsion stability, this paper screens the types of emulsifiers and buffers, and by means of copolymerization with unsaturated carboxylic acid monomers, the protective ability of the protective layer is enhanced, and the intermolecular and intermolecular entanglements of protective colloids are reduced, improving Emulsion freeze-thaw stability, synthesis of anti-freeze-thaw poly vinyl acetate emulsion adhesive.

1 Experimental section

1.1 Raw Materials and Basic Formula

The raw material monomer vinyl acetate (industrial product) was distilled at atmospheric pressure before use and 72-73°C fractions were taken; butyl acrylate (BA), acrylic acid (AA) and methacrylic acid (MAA) were used as analytical grades. Colloidal protective agent polyvinyl alcohol (PVA) is an industrial product, non-ionic emulsifier OP-10 is an industrial product, anionic emulsifier sodium dodecyl sulfate (SDS), buffer sodium bicarbonate (NaHCO3), sodium acetate (NaAc ), disodium hydrogen phosphate (Na2HPO4) and initiator potassium persulfate (KPS) were used directly as analytical grade. The basic recipe is shown in Table 1.

1.2 Synthesis of Emulsions

A semi-continuous emulsion polymerization method is used. The flow chart is shown in FIG. 1 .

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