Time-dependent Properties of HDPE with Hybrid Wood/Graphene reinforcement

For centuries, wood is used as a structural material while wood fibers are used to reinforce polymers. Recent advances in material science lead to development of nano-scale reinforcements such as Graphene (GN) and its derivatives. Combining nano-reinforcements with micro-sized fibers resulted in a remarkable positive impact on the properties of conventional composites. Although extensive research on effects of nano-reinforcement on properties of composites is ongoing, the time-dependent behavior, crucial for structural applications, is often neglected.  This is due to the complicated and time-consuming tests for the characterization of the long-term performance. The objective of this work is to study the effect of GN on the long-term performance of wood fiber/HDPE composite by using short-term creep tests with more efficient, accelerated data analysis. Previously, it was shown that addition of GN at 15wt% into HDPE reduces the viscoplastic (VP) strain developed during 2h creep by ≈50%. The current study shows that 25wt% and 40wt% wood content in HDPE reduces the VP-strains developed during 2h time interval by >75% with no noticeable effect of the increased wood content. However, further addition of only 7-10wt% of GN results in more than 90% reduction in the VP-strains. The development of the VP-strains in hybrid composites follows Zapas’ model which is used in this study. Viscoelastic (VE) response of these materials is nonlinear and thus described by Chapery’s model to extract VE-parameters. The combination of the two sets of parameters allows predicting the time-dependent performance under any type of loading.