Cold flow PVAC

Plasticizers soften the film and increase the adhesion and the setting speed. The most common are phthalates, adipates and benzoates. The amount added can be in a broad range of 10-50%. They affect the swelling and softening of the PVAc emulsion particles, ensure film formation at room temperature, and the tack of the still wet adhesive. They also provide improved moisture resistance of the bond. Disadvantages are the lower resistance of the bond line against heat, possible migration of the plasticizers and enhanced cold flow. 

Cold flow -m PVAc [VINYL POLYMERS - VINYL ACETATE POLYMERS] (Vol 24)... 

Polyvinyl acetate (PVAc) in the pure and solid form is colorless and transparent. It is somewhat brittle unless the degree of polymerization is low. Its softening temperature is between 40 and 90F (4 and 32C), depending on the molecular weight. It shows the phenomenon of cold flow. 

VA, the three copolymers containing 0.37,1.00, and 2.14 mol% AETMC, indicated as PVAcA, PVAcB, and PVAcC, respectively, were prepared by slowly adding a methanol solution of AETMC into a methanol solution of VA at 60°C under nitrogen flow. The polymerization, initiated by AIBN, was continued for 1.5-3 h. Then, the viscous solution was diluted with acetone and poured into excess hexane under stirring. The tacky precipitate was purified by dissolution in methanol and precipitation in cold water. The structure of the three PVAc copolymers is indicated in the scheme below. 

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