Influence of Hygrothermal Aging on Mechanical Properties and Damage Mechanisms of Hemp-Reinforced Biocomposites

Abstract

Biocomposites are being developed for structural applications, particularly in the automotive industry. The use of plant fibers as reinforcement is a first step toward the development of eco-materials, but it is necessary to use also a more eco-friendly matrix. In this paper, woven hemp composites impregnated with two different eco-polymers are compared: hemp/Greenpoxy and hemp/Elium. Greenpoxy is a partially bio-based thermoset resin, and Elium is a recyclable thermoplastic polymer. The influence of various hygrothermal aging conditions on the mechanical properties of these composites is studied, and results are compared with the behavior of samples stored at ambient temperature and humidity. Water immersion was carried out at three different temperatures: 21°C, 60°C and 70°C. A Fick’s law was used to model the water uptake. Modulated DSC was performed to measure the evolution of the glass transition temperatures. Repeated progressive tensile loading tests were carried out and instrumented with acoustic emission monitoring. The evolution of the damage factor, the residual strains and the acoustic events was analyzed. Fracture surface analysis and microtomography observations were also performed. Damage mechanisms are discussed. Results show that mechanical properties are highly affected by the hygrothermal aging whatever the matrix, but the increase in temperature affects the two composites differently.

Keywords

• woven composites
• water aging
• acoustic emission
• tomography
• damage factor
• fracture surface