OPTIMISING FORMULATION ON WEATHERING RESISTANCE OF RECYCLED POLYPROPYLENE AND RUBBERWOOD FLOUR COMPOSITES

Abstract

The usage of wood–plastic composites (WPCs) in exterior environments was primarily concerned on long-term durability and weatherability when exposed to natural weathering. Discoloration, physical and mechanical properties of WPCs are affected by humidity, sunlight and temperature. The properties of WPCs under service conditions were investigated to optimise the mixture ratios of rubberwood flour and recycled polypropylene using D-optimal mixture design. Effects on physical and mechanical properties of components were analysed. Overall composition significantly affected weathering effects on lightness (L*), discoloration (ΔE), hardness, flexural strength, i.e. modulus of rupture (MOR) and modulus of elasticity (MOE), and maximum strain. L*, ΔE, hardness, MOR and MOE increased with fraction of rubberwood flour. At long weathering exposure times, hardness, MOR and MOE decreased. Fraction of maleic anhydride-grafted polypropylene (MAPP) slightly affected L*, hardness and MOR, while increased ultraviolet stabiliser fraction decreased L* and ΔE but decreased flexural properties. Optimal formulation of WPCs, using the Design-Expert software, based on minimum lightness and discoloration, maximum hardness, MOR, MOE and strain was 61.9 wt% recycled polypropylene, 33.9 wt% rubberwood flour, 3.1 wt% MAPP, 0.2 wt% ultraviolet stabiliser and 1.0 wt% lubricant.