Optimization of the physical properties of recycled plastic hybrid composites reinforced with rubberwood flour and crab shell flour for underwater use

This research aimed to optimize the composition and physical properties of recycled high-density polyethylene (rHDPE) hybrid composites reinforced with rubberwood flour (RWF) and crab shell flour (CS) for application in water immersion. The effects of composition and deterioration in physical properties after immersion in different water conditions (distilled water and seawater) were investigated. D-optimal mixture experimental design and response surface methodology were applied. The findings showed that all the physical properties deteriorated with an increase in immersion times. The increasing addition of CS increased the density, water absorption, thickness swelling, and surface roughness of the samples before and after being immersed in distilled water and seawater. Further, the results revealed that the optimal composition for application in water immersion included 60.0 wt% rHDPE, 29.5 wt% RWF, 5.6 wt% CS, 3.5 wt% maleic anhydride-grafted polyethylene, 0.5 wt% ultraviolet stabilizers, and 1.0 wt% lubricant with a desirability score value of 95.80 %. The predicted response of density, color measurement, surface roughness, water absorption, and thickness swelling were 0.89 g/cm3, 10.11, 4.59 mu m, 10.27 %, and 7.73 %, respectively. Based on the findings in this research, the effective application of naturally sourced additives in composite products, and using the optimized rHDPE, RWF, and CS contents would enable the development of alternative materials for applications in water immersion.