Starches and polylactic acids (PLAs) represent the main biobased and biodegradable polymers with potential industrial availability in the next decades for “bio” foams applications. This paper investigates the improvement of their morphology and properties through processing and materials parameters. Starch foams were obtained by melt extrusion in which water is used as blowing agent. The incorporation of natural fibres (hemp, cellulose, cotton linter, sugarcane, coconut) in the starch foam induced a density reduction up to 33%, a decrease in water absorption, and an increase in mechanical properties according to the fibre content and nature. PLA foams were obtained through single-screw extrusion using of a chemical blowing agent that decomposed at the PLA melting temperature. A void content of 48% for PLA and 25% for cellulose fibre-reinforced PLA foams and an improvement in mechanical properties were achieved. The influence of a fibre surface treatment was investigated for both foams. 1. Introduction Global warming, growing awareness in environmental and waste management issues, dwindling fossil resources, and rising oil prices are some of the reasons why lightweight “bio” products such as “bio” foams are increasingly promoted regarding sustainable development in material applications. In this context, “bio” foams based on starches and biopolyesters such as polylactic acids (PLAs) have a great industrial potential, since starch foams can be considered as good candidates to substitute expanded polystyrene used for food trays in packaging industries. Moreover, PLA foams are promising alternatives to polyolefin-based foams for many automotive parts. They could be also used as efficient carriers for active pharmaceutical ingredients allowing drug release to be controlled and bioavailability to be enhanced. Starches and PLA can be associated to biodegradable fillers leading to commonly named “bio” composites. The poor mechanical properties of starchy materials compared to conventional oil-based polymers can be improved by adding natural fibres. Starches have been yet associated to numerous fibres among which jute fibres [1], ramie fibres [2], flax fibres [1, 2], tunicin, whiskers [3], bleached leafwood fibres [4], wood pulp [5] or microfibrils from potato pulp [6]. Most of these studies showed a high compatibility between starch and natural fibres leading to higher stiffness. A reduction in water absorption was also obtained thanks to the higher hydrophobicity of natural fibres which was linked to the high crystallinity of cellulose. The improvement of the
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