Reversible and irreversible changes in physical and mechanical properties of biocomposites during hydrothermal aging

TL;DR

This study investigates how hydrothermal aging affects the physical and mechanical properties of PLA-based biocomposites reinforced with flax fibers, distinguishing between reversible and irreversible effects and their dependence on fiber content and temperature.

Contribution

It provides a detailed analysis of reversible versus irreversible aging effects in biocomposites, highlighting the role of fiber content and temperature in prolonging material lifetime.

Findings

Most property changes are reversible during aging.

Irreversible effects increase with fiber content and temperature.

Fibers significantly extend the biocomposite lifetime.

Abstract

The use of biocomposites on a daily basis for industrial products brings to light the influence of environmental factors on the evolution of mechanical properties. This aging has a major influence in the lifetime of any product based on such materials. Among biobased composites, poly(lactic acid) reinforced with plant fibers are known to be sensitive to hydrothermal aging due to the intrinsic nature of their components. Although some papers studied the influence of temperature and water absorption on such materials, so far the difference between reversible and irreversible effects of aging has been hardly studied. This distinction is the purpose of this study. Poly(lactic acid) samples reinforced with various content of flax fibers (0%, 10%, and 30%) were immersed in water at different temperature (20, 35, and 50{\textdegree}C) up to 51 days. The physical and chemical phenomena responsible for the changes in the mechanical properties of biocomposites were evaluated. It was observed that these changes were mainly reversible. However, irreversible effects of aging turned out to increase drastically with the amount of fiber and the aging temperature. While hydrolysis drastically deteriorated PLA for longer aging times, the lifetime of biocomposites was significantly extended (+ 230% at 50{\textdegree}C from 0% to 10% in fiber content) by the presence of fibers which postponed the failure of PLA.