Chemical Processes - Isoconversional Kinetics of Thermally Stimulated Processes - page 201

Fig. 4.30 E ʱ dependencies
for the thermal degrada-
tion of isotactic polystyrene
(iPS) and atactic polystyrene
(aPS). (Adapted from Chen
et al. [ 89 ] with permission of
Wiley)

D36
L36

α

Fig. 4.31 ln A ʱ dependencies
for the thermal degrada-
tion of isotactic polystyrene
( iPS) and atactic polystyrene
( aPS). (Adapted from Chen
et al. [ 89 ] with permission of
Wiley)

D36
L36

α

reaction models (Table 1.1) to the process of polymer degradation. The issue is due
to the fact that these models were derived for processes that involve solids, whereas
thermal degradation of the majority of polymers takes place in the liquid state. By
way of illustration, the model of a contracting sphere assumes that a reactant is a
solid spherical particle, which decreases in size throughout the process of decom-
position. This can be a reasonable assumption when the reactant is a solid powder,
but not so when the reactant is bulk liquid. Therefore, when the solid-state reaction
models are applied to liquid-state polymer degradation, they rather play a role of in-
terpolating functions than physically meaningful models. That is why one should be
careful in assigning a physical meaning when polymer degradation data are found
to fit one of these models, unless the model is similar to one of the homogeneous
kinetics models. For example, the Mampel model is identical with the first-order
reaction model. As an alternative to the solid-state models, one can use the truncated