Effects of multiple extrusions on structure-property relationships of hybrid wood flour/poly (vinyl chloride) composites

This study emphasizes on closed-loop recycling of wood flour/poly (vinyl chloride) composites, since there is normally a considerable amount of material waste in wood plastic production lines. Composite materials were produced and subjected to four times reprocessing cycles under industrial conditions. Detailed analytical methods including bending strength, modulus of elasticity, impact strength, scanning electron microscopy, fiber length, water absorption, contact angle, Fourier transform infrared, and dynamic mechanical thermal analysis (DMTA) were conducted to evaluate the effects of recycling on the mentioned composites. Results demonstrated that the recycled composites, except for the four-time recycled ones, had lower bending strength, modulus of elasticity, and impact strength due to fiber-chain scission/fracture resulting from shear stress during reprocessing; however, impact strength remained almost unchanged after the first recycling cycle. Results also revealed that generally the reprocessed composites showed lower water absorption rates due to better fiber wetting and encapsulation. There was also a reduction in hemicellulose hydroxyl groups, rendering the recycled composites less hydrophilic. DMTA results showed an increase in mechanical loss factor (tan delta) for all the reprocessed composites showing a more viscous than elastic nature. The glass transition temperature of Rec4 composites increased due to polymer dehydrochlorination and the resulting cross-linking, which restricted the molecular mobility of the polymer chains.