Modeling of the Kinetics of Polyoxymethylene Decomposition under Oxidative and Non-Oxidative Conditions.

Tomasz M Majka,Witold Żukowski,Gabriela Berkowicz-Płatek

doi:10.3390/ma14092281

Abstract

Research on the thermal and thermo-oxidative degradation of polyacetals allows for the development of effective methods of utilization of the waste of these polymers towards the recovery of monomers. For this purpose, in addition to qualitative analysis, it is necessary to understand the mechanisms of chemical reactions accompanying the decomposition process under the influence of temperature. Therefore, in this article, with the experimental results from the thermal analysis of the POM homopolymer of three various stages of life—POM-P—unprocessed sample; POM-R—recycled sample, and POM-O—sample waste—we took steps to determine the basic kinetic parameters using two well-known and commonly used kinetic models: Friedman and Ozawa-Flynn-Wall (OFW). Knowing the values of the course of changes in apparent activation energy as a function of partial mass loss, theoretical curves were fitted to the experimental data. The applied calculation models turned out to be consistent in terms of the nature of the curve changes and similar in terms of Ea in the entire range of mass loss. Both kinetic models showed a very similar course of the Ea curves. The samples that decompose under oxidative conditions obtained the best fit for the reaction of nth order with autocatalysis by product B model and the samples that decompose under inert conditions for the n-dimensional nucleation according to the Avrami–Erofeev model.

Highlights

IntroductionPolyoxymethylene (polyacetal, polyformaldehyde, and POM), is a popular thermoplastic engineering polymer due to its good mechanical properties
Polyoxymethylene, is a popular thermoplastic engineering polymer due to its good mechanical properties
POM has a tendency to decompose from these unstable end-chain groups by a chain-cracking process, and in consequence, oxymethylene units are removed from these terminals

Summary

Introduction

Polyoxymethylene (polyacetal, polyformaldehyde, and POM), is a popular thermoplastic engineering polymer due to its good mechanical properties. The starting point for kinetic analysis of the processes taking place in a polymeric material in the glass state is thermo-analytical measurements, i.e., those in which the measured signal, changing in the course of chemical processes, reflects the kinetic nature of the changes taking place [10,11,12,13]. For this purpose, it is necessary to perform several measurements at different sample heating rates [12,14]. Model-less methods are not suitable for characterizing complex transformations in competitive reactions, where the final result is closely dependent on the heating rate [11,15]

Methods

Results

Conclusion