Kinetics of the Solid-State Chlorination of High-Density Polyethylene

Abstract

The kinetics of the solid-state chlorination of polyethylene within the temperature range 293 to 353 K was studied using the generalized Avrami-Erofeev equation. The thermally initiated process for heterogeneous chlorination of polyethylene was observed to take place in two stages. The first stage was kinetically controlled, whereas in the second stage the diffusion control of the reaction predominated. The increase of temperature resulted in the reduction of the transition from the “mixed” diffusion–kinetic region of the rate-determining step to the one controlled entirely by diffusion. A temperature increase to over 345 K led to a process controlled by the diffusion phenomena only. A number of kinetic parameters were calculated for each stage such as the apparent rate constants and the corresponding activation energies, the pre-exponential factors in the Arrhenius equation, entropy changes, and steric factors. Based on the observed changes in both the crystallinity and porous structure of polyethylene, predominant chlorination of the amorphous regions in the surface layers of the polymer particles can be assumed at the initial stage. Following that, the reaction proceeded with the simultaneous chlorination of both the amorphous and crystalline regions into the depth of particles, regardless of the hampered diffusion of the gaseous reactant.