Impact of water saturation on the tensile and thermal properties of heat-treated mangrove/high-density polyethylene composites

Abstract

The main barrier in the use of natural fiber (NF) as a reinforcing material in thermoplastic composites meant for outdoor applications is NF’s hydrophilicity. Thus, heat treatment of vacuum-dried mangrove was conducted at 120°C in order to reduce the hydrophilic nature of mangrove. The untreated and heat-treated mangrove particles were compounded with high-density polyethylene (HDPE) at 10, 20, and 30 wt% in a twin-screw extruder and injection molded into dog-bone-shaped test pieces for tensile tests and thermal analysis (thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC)). Test pieces were immersed in distilled water for 1440 h at ambient temperature (approximately 27°C) and a relative humidity of 60–65%. The results revealed that the earliest and latest water saturation were observed at 480 and 792 h for 10 wt% treated and 30 wt% untreated composites, respectively. The dry composites maintained higher tensile strength and modulus but lower tensile strain than the water-saturated composites irrespective of treatment. Scanning electron microscopy of tensile fractured surfaces confirmed an improved mangrove-HDPE interfacial interaction of treated composites in both dry and water-saturated conditions. The TGA and DSC data showed that the maximum degradation temperature of dry composites is higher than the wet composites. Overall, the treated composites at dry and water-saturated conditions indicated better tensile and thermal stability than the untreated mangrove-filled HDPE composites; these are possible indications of better performance during outdoor applications.