Mechanical Destruction of Isoprene Rubber. Part 6. Comparison of the Kinetics of the Processes in Ultrahigh and Low Molecular Weight Fractions of Isoprene Rubber During its Plasticization

Abstract

Continuation of studies of changes in molecular parameters and kinetics of the processes accompanying the plasticization (P) of SKI-3
isoprene rubber. A comparative study of the kinetics of the processes of mechanodestruction (mechanocreaking), oxidative destruction and
recombination of macromolecules of ultrahigh molecular (UHMF) and low molecular (LMF) fractions of SKI-3 at P in the temperature range
(T) 30–130 °C and time (t) 30–600 s was carried out. As before, P was performed in a laboratory rubber mixer of the company «NFM»; the
determination of molecular characteristics was carried out on a gel chromatograph «Waters». The change in the Mooney viscosity η of both
fractions during the process of P was measured. Regardless of T and t, the value of η is on average 5 times lower in LMF than in UHMF, which
is associated with the difference in O2 diffusion conditions and different shear stress. As a result, the degree of mechanocreaking and oxidative
degradation of the UHMF macromolecules is greater than that of LMF macromolecules. Data on changes in molecular weights and calculated
rate constants K and activation energies Eeff of these processes in the UHMF and LMF at different T and t are compared. The Eeff of the processes
of oxidative destruction, mechanocreaking and recombination in UHMF is higher than that in LMF; the calculated number of acts of oxidative
destruction at high T is comparable, and recombination in LMF at any T proceeds much faster than that in ULMF.