Synthesis And Characterization Of The Polyvinyl Acetate Emulsion With Low Solid Content

Emulsion adhesive is widely used because of their excellent properties. However, the cost of emulsion adhesive is high so that the applications of which was restricted. In this paper, the method of reducing the solid content of polyvinyl acetate (PVAc) emulsion adhesive was applied in order to reduce its cost. In the same processing conditions, the viscosity and bonding strength of the emulsion adhesive would be decreased because of the reducing of the solid content. The study of the influencing factors of the viscosity of the emulsion in order to adapt various application requirements and the methods to enhance the bonding strength of the emulsion would be focused on.PVAc emulsion with the solid content of about 20% was synthesized with the method of semi-continuous seeded emulsion polymerization. The effects of some factors such as the amount of protective colloid polyvinyl alcohol (PVA), comonomers, feeding methods, alkali-thickening and the addition amount of inorganic filler of light calcium carbonate on the viscosity of the emulsion were studied. The results indicated that, with the increasing of the amount of PVA and the pH value, the reducing of the amount of seeded emulsion and being copolymerized with suitable copolymers, the viscosity of emulsion was enhanced. With the increasing of the addition amount of light calcium carbonate, the viscosity of emulsion was decreased and then increased.To enhance the bonding strength of the emulsion, on the one hand, the PVAc emulsion was synthesized with polyvinyl formal (PVF) as the protective colloid. The effects of the type of catalyst (sulfate H2SO4, hydrochloric acid HCl), pH value, the addition amount of formaldehyde, the reaction temperature and the reaction time on the properties of the emulsion were studied. And the orthogonal experiment was applied to optimize the process. The results indicated that, acetal reaction leaded to the increasing of storage modulus and thermal stability of the polymer. The optimization process, i.e. H2SO4 was used as the catalyst, pH value was 3.4, the reaction temperature was 92℃, the reaction time was 75min.On the other hand, urea was added into the emulsion in order to improve the bonding properties. The effects of the addition amount of urea on the properties of the emulsion were studied. The results indicated that, with the increasing of the addition amount of urea, the particle size of the emulsion was increased, but the particle size distribution was little changed, the viscosity was decreased, and the changing rate of which was decreased with the changing of shear rate, and the shear stress of which was also decreased, the bonding strength of the emulsion was increased and then decreased and the maximum value was achieved when the addition amount of urea was 60%, and the storage modulus, thermal stability, water resistance and the stability of the membranes were enhanced. Being modified with carboxyl groups, the particle size of the emulsion was increased, but the particle size distribution was become narrow, the viscosity of the emulsion was improved, and the changing rate of which was increased with the changing of shear rate, and the shear stress of which was also increased. The thermal stability of the carboxyl groups modified polymer was improved, however, the water resistance and stability of the membranes were declined.