On the nature and properties of cellulose acetate and poly(vinyl alcohol) gels

Dilatometric, rheological, and some optical (spectrography, birefringence, light scattering) investigation methods were adopted to study gelation processes in acetyl cellulose (AC), poly(vinyl alcohol) (PVA), and iodopoly(vinyl alcohol) (IPVA) solutions in different solvents. The influence of the molecular and chemical heterogeneity of these polymers upon the gelation temperature and mechanical properties of gels is ascertained. The jumps in the volume versus temperature dependence ΔV(T) of PVA fraction solutions were discovered. The greater the molecular weight of polymer fractions the higher is the temperature of these jumps. It is established that diluted AC solutions in benzyl alcohol as well as its concentrated acetone solutions are nonhomogeneous thixotropic systems with long relaxation times. The results of investigation have been interpreted by means of the conception about gelation as the separation of fractions, which have become insoluble (under changed thermodynamic conditions), from homogeneous polymer solution. These fractions form a second amorphous phase, either as the single whole network, enveloping the solution of the other fractions by its network (gel), or as discrete aggregates (gel suspension). The structure variants, for example, partial crystallization, present the consecutive stages of a thermodynamic transition of a true solution into a non-homogeneous colloid system.