Hygrothermal ageing of recycled polypropylene and rubberwood waste composite for construction material

Ajang, Dalgush Dipak (2022) Hygrothermal ageing of recycled polypropylene and rubberwood waste composite for construction material. Project Report. Universiti Teknikal Malaysia Melaka, Melaka, Malaysia. (Submitted)

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Abstract

This study aims to compare the physical and flexural properties and evaluate the fracture surface of rubberwood(RWF) reinforced recycled polypropylene(rPP) composites caused by hygrothermal ageing. RWF is hydrophilic, absorbs water, and the rPP properties are altered when exposed to high temperatures. Moisture causes the wood polymer composite(WPC) interface to degrade, decreasing the flexural properties. The material with a composition of 37.5wt.% RWF(reinforcement), 50.3wt.% rPP(matrix) and 12.2wt.% additives through hot-pressed and then machined according to ASTM D790. Then, Hygrothermal ageing performs on the specimen for 30 days at 50°C and 90% relative humidity(RH) for the first condition and in water immersion at 50°C for the second condition. The water absorption behaviour result follows the Fickian behaviour. The water absorption rate in water immersion(0.96 m2/s) is higher than exposure at 90%RH(0.95 m2/s). The thickness swelling increase indicates poor dimension stability of composite in a moisture-rich environment. The initial strength of the composite is 30.49 Mpa. It reduces after exposure to vapour(27.85 Mpa) and further after exposure to water immersion(26.61 Mpa), same with the modulus pattern indicating the deleterious effect of moisture on the flexural strength and modulus of the composite. The strain at the break of the composite increases after exposure, showing the composite becomes ductile due to plasticising effect of the rPP. The unaged sample observed failed due to fibre and matrix fractured, causing a brittle fracture upon exposure to the vapour in 90%RH and the water immersion, the presence of the pull-out fibre with the addition of microcracking and a gap between the fibre and matrix. It indicates that the fibre and matrix interface weaken. It was concluded that hygrothermal ageing changes the composite dimension and reduces the flexural properties with SEM images to support the effect caused by hygrothermal ageing.

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