Mechanical properties, creep resistance, and dimensional stability of core/shell structured wood flour/polyethylene composites with highly filled core layer

To obtain an optimum balance in performance and cost, this study aims to investigate the effect of wood flour (WF) content in both shell and highly filled core layers on the mechanical properties, creep behavior, and dimensional stability of the resulting coextruded WF/high density polyethylene composites (Co-WPCs). Scanning electron microscopy showed good interfacial adhesion between the core and shell layers. The flexural strength and modulus of the Co-WPCs increased with increasing WF content in shell layer, while the flexural strain and impact strength decreased but still higher than those of the core-only controls. Finite element analysis showed that the coextruded flexible shell layer acted as a stress transferring medium avoiding stress concentration and endowed the Co-WPCs with higher toughness. Increasing the content of rigid WF in both the core and shell layers resulted in significant reduction in creep strain. Coating the highly filled core layer with less filled shell layer can markedly reduce the water absorption and thickness swelling. For Co-WPCs with 70 wt% WF in core layer and 20 wt% WF in shell layer, the flexural strength, modulus, and creep strain were comparable to those of the core-only control, but the flexural strain, impact strength, and water resistance were much better. (C) 2019 Elsevier Ltd. All rights reserved.