Phosphate bonded wood composite products from invasive Acacia trees occurring on the Cape Coastal plains of South Africa

The feasibility of manufacturing phosphate bonded wood composite board products from four locally occurring invasive acacia tree species (Acacia cyclops, A. saligna, A. mearnsii and A. longifolia) was studied using a formulated magnesium oxide (MgO) and monopotassium phosphate (KH2PO4) binder system. The optimization for the manufacturing process was studied using a central composite statistical design, whereupon the following factors were considered, i.e. KH2PO4: MgO ratio, the fly ash content as partial replacement for the binder and the wood content as a ratio of wood to the total inorganic content. A fitted response surface plot was used to show the effect of the main factors and their interactions on the measured board properties. A response surface model was developed to predict the parameters leading to the best board properties. All physical properties evaluated met or exceeded the minimum requirements for low density particleboards. The results showed that the variables considered have significant effects on the physical properties of the boards. The optimum composite manufacturing process for making durable products within the scope of the studied species was found to be a KH2PO4/MgO ratio of 1.66, an ash content of 2.7% and a wood/inorganic ratio of 0.96 for the selected wood species.