Utilisation of Waste Powder Coating as a Binder in the Manufacture of Composite Boards

Abstract

Wide public disquiet about plastics going to landfills is based on the fact that they degrade very slowly and should be recycled. A more fundamental issue is that plastics disposal represents a waste of a valuable, non-renewable petrochemical resource. This problem is also faced by powder coatings, and this study focuses on the powder coating industry and the reuse of waste powder coating powder and fines. These are estimated to be over 5% of production quantities and are generated during the manufacturing process, as old stock unfit for sale and as overspray from the coating applicator. Waste powder coatings are of mixed colours and curing chemistries. The annual world manufacture of powder coating is estimated to be about 1,466,000 tonnes; 5% of this figure equates to over 70,000 tonnes that is sent to landfills each year. Landfilling this quantity of material is an obvious waste of resources and presents a real threat to the environment in years to come. The main focus of this research was to utilise waste powder coating powder (WPCP) as a binder (matrix), in a composite board using wood fibre in the form of sawdust. Although WPCP is a thermoplastic; it Crosslirdcs to form a thermosetting polymer when heated, providing increased strength to composite structures compared to thermoplastic analogues. Natural fibres, paper and wood are hydrophilic. To make a composite out of WPCP and a hydrophilic reinforcing component requires formulating the binder so that wood fibres are fully wetted by the matrix. This factor was instrumental in the success of this project. This resulted in the design of a new type of particleboard. This project also has obvious environmental advantages. Minimising the wastes sent to landfills is a key objective, another is to try and extend the life cycle of material that has already been produced, so easing the pressure of demand for virgin raw materials. Other waste streams identified were evaluated and selected for use. Sawdust waste from the lumber/construction industry was utilised as the main reinforcing material. Waste paint was used as a ςcompatibilizer, between the matrix (powder coating powder) and the sawdust reinforcement. Powder coating and paint have resin, pigments, fillers and additives in their composition. For this study three thermosetting powders were evaluated. The materials were mixed in predetermined ratios and compression moulded into boards under precisely controlled conditions. DSC, SEM, EDX, XRF and FTIR were used to characterise the composition of the resulting composites. The composite boards resembled particleboards and were tested for their mechanical properties according to prescribed standards (ASZNZS 1895.1:2004 for Reconstituted Wood Based Panels) providing very satisfactory results. Physical and mechanical tests include the determination of IBS, MOE, MOR, swelling, moisture and density of boards. SEM confirmed good coating of the polymeric matrix over the sawdust particles. Ruptured samples showed breaking of the sawdust particles (against being pulled) indicating good board construction. The boards have been patented and commercialised by Orica Powder Coatings Ltd. Commercialisation will extend the Iife cycle of these industrial wastes by value addition, generate additional income, save dumping charges and ease the pressure on the environment.