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 nth
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 nth
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.
