Crystallisation in films of polar vinyl polymers Part III: Kinetics of the crystal growth in polyvinyl alcohol films prepared by evaporation of concentrated aqueous solutions

Abstract

This paper describes studies on the kinetics of crystallisation of polyvinyl alcohol films, prepared by the controlled slow evaporation of concentrated aqueous solutions; the initial polymer volume fraction (Vp)0 was 0.2 and the initial evaporation rates (Re)0 were varied from −0.0003 to 0.0150 vol fraction hr−1. The main crystal growth started after prolonged induction periods(t) at polymer contents\(\bar V_p \) =0.66 to 0.82, well beyond the gelation (nucleation) composition. The growth rates reached maximum values (Rg max) at polymer contents (Vp)max = 0.82 to 0.92 and then decreased again to very low values in the viscous systems at the glass transition composition. Growth rates at any polymer content were expressed approximately by the relation, $$R_g = 4R_g \max U(1 - U),$$ , where $$U = \frac{{(V_p - \bar V_p )}}{{2[(V_p )\max - \bar V_p ]}}.$$ (Vp)max andRgmax values did not vary markedly over the fifty-fold range of evaporation rates. (Vp)max values increased andRg max values decreased with rise in crystallisation temperature.