Influence of polyesterurethane plasticizer on the kinetics of poly(vinyl chloride) decomposition process

Poly(vinyl chloride) (PVC), plasticized by di(2-ethylhexyl) phthalate (DEHP), medium molecular mass polyesterurethane (PU) or by both plasticizers, was thermally degraded under dynamic thermogravimetric conditions and the kinetics of decomposition was studied by isoconversional methods and by non-linear regression. It has been found that the initial decomposition temperature is higher for PVC plasticized with PU, as compared with PVC plasticized with di(2-ethylhexyl) phthalate (DEHP) or plasticized with PU/DEHP, and thermal degradation shows features of a multi-step complex process. Application of polymeric plasticizer leads to the increase and a 'smoothing' effect in the course of energy of activation and pre-exponential factor at the initial stage of decomposition indicating thus the hindered migration of medium molecular mass compound from PVC matrix (in comparison with PVC containing monomeric DEHP) due to steric hindrances as well as due to specific interactions between C=O and Cl groups along the macrochains. Kinetic model function of the decomposition process of PVC/DEHP and PVC/DEHP/PU blends was found to be a two-stage autocatalyzed reaction of n(th) order; autocatalytic effect is associated most likely with the role of HCl formed during PVC decomposition. For PVC/PU blend best fit was found by non-linear regression for a two-stage scheme in which first stage was Prout-Tompkins model and the second was autocatalytical model of n(th) order - the first one involves particle disintegration, which was promoted by product generation at branching PVC 'pseudo-crystals' nuclei, thus exposing more surface on which decomposition reaction proceeds.