Diluent Dispersion in Poly(vinyl chloride)—Plasticizer Systems

Abstract

Dynamic mechanical and dielectric measurements were carried out on plasticized poly(vinyl chloride) (PVC). The complex shear moduli (G′ and G″) in the temperature range −196—+10°C were measured by means of a free-oscillating torsional pendulum at about 0.3 Hz. The viscoelastic behavior of plasticizers was studied by the TBA method. The added plasticizers were tricresyl phosphate (TCP), butyl benzyl phthalate (BBP), dioctyl phthalate (DOP), dibutyl sebacate (DBS), and dioctyl sebacate (DOS).The effects of plasticizers on the α-, β-, and γ-dispersions of PVC appear in different ways. The α-dispersion due to the glass transition shifts to a lower temperature as the plasticizer content increases. The β-dispersion is completely suppressed by the presence of a small amount (16 wt%) of plasticizers. A new dispersion labeled as γ, which is not observed for both unplasticized PVC and pure plasticizers, appears in these mixed systems with the exception of the PVC—TCP system. This is an example of the so-called “diluent dispersion”. The intensity of the γ-dispersion increases with increasing plasticizer content and shows a saturation tendency. The appearance of this dispersion is highly sensitive to the nature of the additives and the ability of plasticizers to provoke this dispersion is in the order of DBS > DOS > DOP > BBP. The γ-dispersion is also observed in the dielectric results and the activation energy is estimated to be 6.5±0.5 kcal/mol.