# Mechanical Property Evolution and Mechanisms of Polyolefins Under Thermo-Oxidative Aging

## TL;DR

This paper studies how heat and oxygen affect the durability of polyolefin materials, revealing a three-stage aging process that impacts their mechanical properties.

## Contribution

The study identifies a three-stage thermo-oxidative aging mechanism in polyolefins, offering insights into material degradation and service life assessment.

## Key findings

- Thermo-oxidative aging of polyolefins occurs in three distinct stages with different structural and mechanical changes.
- Stage I involves increased crystallinity and temporary mechanical improvement due to segmental mobility.
- Stage III is marked by antioxidant depletion, oxidative chain scission, and significant mechanical property loss.

## Abstract

Polyolefin materials are widely used due to their excellent properties and low cost. However, in high-temperature oxygen environments, they are susceptible to thermo-oxidative aging, which reduces mechanical properties and durability. This study systematically analyzed the aging behavior and mechanisms of polyolefins at varying temperatures and exposure durations through accelerated thermal oxidation experiments. The results indicate that the thermo-oxidative aging behavior of polyolefins can be divided into three stages. In Stage I, elevated temperature promotes segmental mobility and chain rearrangement, which increases crystallinity and temporarily improves mechanical properties. In Stage II, antioxidants are progressively consumed and oxygen-containing groups begin to accumulate, resulting in reduced crystallinity, a decline in mechanical performance, and the onset of slight surface yellowing. In Stage III, the antioxidant system is largely depleted and oxidative reactions are intensified, leading to mainchain scission and molecular weight reduction. This causes a further decrease in crystallinity, a significant deterioration in both strength and toughness, accompanied by aggravated yellowing. This study elucidates the thermo-oxidative aging mechanism of polyolefins, providing a theoretical basis for assessing their service life and evaluating the stability of waste plastics.