Abstract
Detailed analysis of the effects of multiple extrusions on physical, mechanical, micro-structural as well as dynamic mechanical thermal properties of natural fiber high-density polyethylene (HDPE) composites is reported. Composite materials containing HDPE, wood flour, and Maleic Anhydride polyethylene (MAPE) were manufactured and subjected to a recycling process consisting of up to four times grinding and reprocessing under industrial conditions. A wide range of analytical methods including bending tests, modulus of elasticity, impact strength, Scanning electron microscopy (SEM), fiber length measurement, water absorption tests, and dynamic mechanical thermal analysis (DMTA) were employed to understand the effects of recycling on natural fiber-HDPE composites. The results revealed that the recycled composites had lower bending strength and modulus of elasticity values, as compared to the reference counterparts. Also, the once recycled composites showed higher impact strength. Results, as well, indicated that generally the recycled composites had lower water absorption values as compared to the reference ones. The results obtained from DMTA exhibited a decrease in storage modulus and an increase in mechanical loss factor (tan δ) for all composites subjected to recycling. Alterations in phase transition temperatures and intensities were also monitored and the possible reasons were analyzed.
Highlights
Natural fibers offer numerous benefits and challenges in fabrication of natural fiber plastic composites, besides their cost-effectiveness.[1]
The results show that after the first recycling, fibers underwent dramatic length reductions due to the compression and shear stresses existing in different zones of extruder; the length of wood fibers in original high-density polyethylene (HDPE) composites was 463 μm, whereas it reduced to 326 μm after the first recycling
The results of analysis of variance obtained from bending strength test indicated that there was a statistically significant difference between the bending strength values of the studied composite prior to and after recycling at 95% confidence level
Summary
Natural fibers offer numerous benefits and challenges in fabrication of natural fiber plastic composites, besides their cost-effectiveness.[1] One major advantage of such composites over the conventional thermosetting systems is their potential to be recycled either during the manufacturing process (internal recycling) or later after the service life (external recycling). This is an added advantage in terms of the ever-increasing environmental concerns, in particular, the problem of rapidly filling up landfills. The change in mechanical properties was reported to be mostly arising from fiber fracture that occurred during reprocessing, with the subsequent reduction in average fiber length from 2.36 mm for the original fiber to 0.37 mm for the fiber extracted from the composites reprocessed for 8 times.[16,18]
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