Biocomposites are being developed for structural applications, particularly in the automotive industry. The use of plant fibers as reinforcement is a first step towards the development of ecomaterials 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.

This paper aims to study the tensile behavior of a woven [0/90]7 hemp/Elium composite after three different conditionings: “Ambient storage”, “Saturated at 60 °C” and “15 wet/dry cycles”. Instrumented repeated progressive tensile loading tests were carried out and showed an unexpected increase in the secant modulus for the aged samples at the end of the test. An in-situ micro-CT tensile test was then performed on a “15 wet/dry cycles” aged sample. The analysis of the tomographic images showed the damage development with interfacial debonding and matrix cracks in the specimen volume, and also the decrease in the curvature radius of the warp yarns during tensile loading facilitated by the plasticization of the resin. Finite element calculations were thus performed and demonstrated that the increase in the modulus is directly linked to the straightening of warp yarns, showing that the evolution of the modulus on a macroscopic scale can be explained by the deformations of the yarns on a microscopic level. These results allow us to better understand the mechanical behavior and the damage mechanisms that occur in biocomposites during tensile testing after water aging.