Properties of Recycled LDPE/Birch Fibre Composites

Abstract

This study investigates how the properties of a wood polymer composite are modified by recycling, especially how the presence of fibres modify polymer degradation. To this end, low density polyethylene was selected as the matrix and yellow birch fibres as the reinforcement. The effect of recycling was simulated via closed-loop reprocessing of the material up to ten times under constant extrusion conditions. For each generation, thermal, rheological and morphological measurements were combined with macromolecular investigations including the complete molecular weight distribution of the polymer. The results revealed that polymer crystallinity increased with the number of composite regeneration, while the zero-shear viscosity decreased with recycling. Elongational rheology also revealed that the behaviour of the polymer changed from strain hardening to strain softening for the composite. From the morphological analysis, a degradation severity coefficient was defined to characterize the impact of operating conditions on fibre length. Finally, macromolecular investigations showed that the number-average molecular weight (Mn) of the polymer was more affected than the weight-average molecular weight (Mw). The relative branching factor and the branching frequency were also modified by the effect of reprocessing with and without the presence of wood fibre.