Durability, mechanical recycling and environmental impacts of poly-lactic acid (PLA) based natural fiber reinforced composites: Effect of reactive agents and fiber surface treatment

This study presents the recyclability analysis of PLA/flax and PLA/bamboo biocomposites comprising silane treated fibers with and without the addition of a chain extender agent. To assess their mechanical recyclability, PLA biocomposites were reprocessed using multiple cycles of hygrothermal ageing, grinding process, followed by injection molding. The environmental impact of producing the biocomposites on a laboratory scale was evaluated by a life cycle assessment (LCA). An ecodesign approach was adopted to identify hotspots in the production process. The influence of fiber treatment with and without the addition of Joncryl ™ as a reactive chain extender agent, on the properties of the biocomposites after reprocessing cycles was evaluated by examining changes in the molecular structure and physico-mechanical properties of the samples. In general, the study showed that all biocomposites exposed to hygrothermal ageing, grinding and the re-injection process underwent a chain scission mechanism which was responsible for the decrease in average molecular weight, thermal stability and tensile properties. However, fiber treatment with silane and the addition of Joncryl™ helped to limit these effects. LCA results showed that fiber treatment was the most impactful stage, followed by PLA production. Despite the fact that it exhibits poorer mechanical properties after recycling cycles, the PLA/bamboo biocomposite has a smaller environmental footprint than the PLA/Flax biocomposite. This discrepancy arises from variations in both the biomass cultivation conditions and the subsequent processing steps, including fiber treatment and compounding in an internal mixer. Recycling PLA/Flax or Bamboo biocomposites beyond the third and second recycling stages, respectively, is not recommended. • The mechanical recycling of two types of biocomposites based on PLA and flax tows and PLA and bamboo shavings is possible • The addition of a chain extender (Joncryl™) combined with silane fiber treatment improve the number of recycling cycles for both biocomposites • The environmental impact of PLA-FF is higher than that of PLA-BF and surface treatment of fibers, significantly increases environmental impact