Degradation in the mechanical and thermo-mechanical properties of natural fiber filled polymer composites due to recycling

To manage the plastic waste, recycling is recognized as the most environment-friendly and non-destructive method. The aim of this research is to investigate the recyclability of oak wood flour (WF) filled high density polyethylene (HDPE) composites. Two different composite formulations (30 and 50 wt% filler) were considered, each with 3 wt% coupling agent maleic anhydride (MA). Both composites were individually reprocessed six times by extrusion. Test samples were injection molded, to measure mechanical and thermo-mechanical properties. Fiber length measurement and gel permeation chromatography (GPC) were performed respectively to examine the change on fiber length and molecular weight of polymer. Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), Scanning Electron Microscopy (SEM), and Fourier Transform Infra-Red Spectroscopy (FTIR) were also carried out to better understand the impact of recycling on composite properties. After reprocessing six times, WF-HDPE composites showed relative decrease in strength and stiffness properties and slight increase in strain properties as compared to corresponding virgin composite. The strain properties saw an increase in their value with recycling. The crystallinity of HDPE decreased but thermal stability of the composite increased with reprocessing.