Water Resistant Study Of Polyvinyl Acetate Emulsion Adhesives

In this paper, a new type of PVA as protective colloid was used to prepare water-resistant polyvinyl acetate emulsion adhesive. A semi-continuous emulsion polymerization method using tartaric acid/hydrogen peroxide as redox initiator system without emulsifiers was applied.Firstly, this PVA was dissolved and dried to prepare PVA film which was characterized and evaluated by water absorption, FITR and DSC. We found that the water resistance and heat resistance of this PVA film would improve after its interaction with AlCl3. Then this PVA was used in PVAc emulsion polymerization to prepare waterproof polyvinyl acetate emulsion adhesive. With tartaric acid/hydrogen peroxide as redox system, the instant conversation rate of emulsion was up to80%and the polymerization process was stable. Rotational rheometer, particle size laser analyzer, SEM,DSC, universal electronic tensile machine were used to measure the influence of this PVA on the PVAc emulsion. The results showed that the emulsion has good storage stability when m (PVA):m (VAc)=7%～9%. And as the increasing amount of PVA, the viscosity of emulsion increased while the emulsion maintained as a pseudoplastic fluid. And as the increasing amount of PVA, the viscosity of emulsion increased while the emulsion maintained as a pseudoplastic fluid. When (new PVA):(total PVA)=0.5,the wet shear strength of this emulsion adhesive reach to2.8MPa (25℃water) and0.9MPa (100℃water). The proportion of the new type PVA increased and then the wet shear strength raised.Secondly, N-methylol acrylamide was used as comonomer to prepare water-resistant polyvinyl acetate emulsion adhesive. Semi-continuous emulsion polymerization method using persulfate as initiator was applied. The emulsion viscosity and particle morphology were measured by Viscometer and SEM. While the thermal and mechanical properties of the polymer film were evaluated by FTIR, TG, DSC and UTM. The results showed that the VAc/NMA copolymer emulsion particles were spherical and the particle diameter was about800nm. At room temperature, the emulsion was stable, but its viscosity would increase rapidly as the temperature increase. With the increasing amount of NMA, the viscosity of emulsion will increase and the water absorption rate of polymer film will increase either. Nevertheless, the water absorption rate of polymer film can be reduced to around5%when AlCl3and other additives added. When applied to wood bonding, the dry tensile strength of the copolymer emulsion adhesive was a little higher than a pure VAc emulsion and the wet tensile strength would increase to at least2MPa. The tensile strength of this adhesive can be further improved in a high temperature circumstance.