A circular economy use of recovered sludge cellulose in wood plastic composite production: Recycling and eco-efficiency assessment.

This paper presents a novel development of sludge cellulose plastic composite (SPC) in line with the circular economy concept by using recovered sludge cellulose from wastewater treatment plant (WWTP). Bearing the aim of replacing the wood in wood plastic composite (WPC) with sludge cellulose, WPC was developed in parallel for determining the substitution potentials. In order to maximise the integration of properties, maleic anhydride (MA) and vinyltrimethoxysilane (VTMS) coupling agents were employed to refine the interfacial bonding of both SPC and WPC. In line with the main aim of circular economy - to decouple the economic value from the environmental impact, eco-efficiency analysis was performed for the developed process. The results showed that the tensile and flexural strength of the composites were substantially enhanced after both treatments, while MA appeared to be more efficient than VTMS in the refinery of interfacial bonding. Scanning electron microscope (SEM) analysis confirmed the improvement of interface by identifying well embedded and firmly bonded wood flour or sludge cellulose in the matrix. WPC was marginally more thermally stable than SPC, while SPC suggested comparable flexural properties. Eco-efficiency assessment results showed that the SPC had better environmental and economic performance than the WPC. The latter turns sludge cellulose as a promising sustainable alternative to wood or natural fibres in the production of WPC.