VISCOELASTIC MODELING AND STRAIN-RATE BEHAVIOR OF PLASTICIZED POLY(VINYL CHLORIDE)

The effect of four different types of plasticizers and four strain-rates on the tensile behaviour of poly(vinyl chloride) (PVC) has been studied. di(2-ethylhexyl phthalate), benzyl butyl phthalate, epoxidized soyabean oil and chloroparaffin were mixed at different ratios and were used as plasticizers in concentration levels of up to 77% of the PVC weight. The plasticized and unplasticized PVC were processed into sheets by compression moulding. Tensile tests were conducted at different strain rates. It was found that tensile modulus increases with increasing strain rate while it decreases with increasing plasticizer concentration. The rate of variation of tensile modulus either as a function of strain rate and/or the plasticizer concentration was, in all cases, dependent on the mixing ratio of the different types of plasticizers. Assuming the material to be a linearly viscoelastic one, a simple viscoelastic model along with a least-squares-based computer procedure was applied which enabled us to fit the experimentally obtained curves with the respective theoretical predictions as well as to study the strain-rate effect on the relaxation spectrum, H(tau), of the material under consideration.