Abstract
This thesis aims at developing new fully biosourced and biodegradable composite materials from agricultural residues in the frame of the European project NoAW (https://noaw2020.eu). All the components are derived from agro-wastes: polyhydroxyalkanoates (PHA, bacterial biopolyester and biodegradable in natural conditions) produced by anaerobic digestion of agricultural effluents are used as matrix and vine shoot fibers as fillers. Biocomposites are prepared by melt extrusion. The objective of this thesis is to bring new knowledge on the relationships between the processes used to produce the fillers and the biocomposites, the resulting structure of biocomposites and their functional properties. Biocomposites are developed considering a balance between performance and environmental cost. For this purpose, the thesis focuses on 2 major scientific questions: (i) study of the impact of the filler/matrix interface on the functional properties of biocomposite materials via surface pre-treatments of lignocellulosic particles; (ii) study of the durability of such materials by assessment from the design of the environmental impacts. Thus, special attention is given to the filler/matrix interface, identified as a key factor for the final properties of the composite. A solvent-free surface pretreatment of fibers (chromatogeny) is adapted to modulate the filler/matrix interface. This new method of gas-phase esterification is first studied on micrometric particles of cellulose. Once the proof of concept is established, it is applied to lignocellulosic fibers that are more complex. The vine shoots, agricultural waste abundant in Occitania region, are studied as a potential resource for the production of fillers for composites. Once collected and dried, they are milled using dry fractionation to obtain micrometric sized particles. The variability of the raw material being one of the bottlenecks concerning the use of lignocellusoic biomass by manufacturers, different grape species over several years are studied. In a biorefinery approach, the extraction of molecules of interest, e.g. polyphenols, is considered before using the residue, namely exhausted shoots, as a reinforcing fillers. The environmental impact of the produced biocomposites is evaluated to guide strategic choices and obtain materials displaying a good balance between performance and environmental footprint. A life cycle assessment in the context of a food rigid tray application is carried out, collecting data from sector’s players. In addition, a study of the biodegradability of the final materials is conducted. This thesis encompasses multidisciplinary fields in order to have a decompartmentalized overview of the developed composite materials.