Flow behaviour of polyvinyl alcohol (PVOH) modified blends of polyvinyl acetate (PVAc)/natural rubber (NR) latexes

During compounding processes, polymer latexes are mixed with various colloidal systems (in particular, PVOH) or surface-active agents to modify the flow behaviour in order to suit the manufacturing process. In this study, the flow behaviour of aqueous dispersed PVAc, NR and different mixed dispersions were investigated both in the absence and presence of PVOH as flow modifier, using an Ostwald glass capillary viscometer. The results show an almost linear decrease in the relative viscosity of the NR/PVAc dispersion mixtures in the absence of a modifier, but the presence of different amounts of PVOH gave rise to significant deviations from this behaviour. It was found that these changes in the relative viscosities are governed by a balance between the following four effects: (i) the higher mobility of the NR chains compared to those of PVAc, which generally caused a decrease in the viscosities of the dispersion mixtures; (ii) the physical adsorption of PVOH on the NR chains that slowed down the movement of these chains and caused an increase in relative viscosity; (iii) the chemical interaction between the functional groups on PVAc and PVOH that gave rise to latex thickening and increased the relative viscosity; (iv) a dilution effect which reduced the viscosity, unless counterbalanced by one or more of the other effects.