Investigation of the aging process of a polyvinyl chloride gel by the measurement of its dynamic moduli

Abstract

During the aging process of a 10%-solution of polyvinyl chloride in di-(2-ethylhexyl)phthalate at temperatures between −20 and 110°C its storage and loss moduli were measured in a frequency range from 1.6×10−4 to 40 cycles/sec. The specially defined rate of aging plotted against the aging temperature closely resembles the crystallization curve of a normally crystallizable polymer. Although the internal structure of the system changes, when the temperature is changed, the time-temperature reduction could still be applied provided some precautions were taken.Bueche's theory for networks, combined withFlory's post-gelation treatment, has been used to calculate some gel parameters: the molecular weight between cross-links, the sol fraction, the monomeric friction coefficient etc. It is shown that the aging process strongly depends on the thermal history. The cross-links formed by crystallites, differ very much in functionality. Continued aging, after previous aging at lower temperature, causes, after a first melting of unstable crystallites, a recrystallization process. During this process entanglements are formed. This results in a pseudo-equilibrium rubber plateau at higher frequencies, followed by a dispersion region and a lower equilibrium rubber plateau at lower frequencies.