Browsing by Author "Mngomezulu, Lehlohonolo Benjamin"

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    Phosphate-bonded composite products : the influence of filler materials, biomass type, and processing method on panel properties
    (Stellenbosch : Stellenbosch University, 2019-04) Mngomezulu, Lehlohonolo Benjamin; Tyhoda, Luvuyo; Meincken, Martina; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
    ENGLISH ABSTRACT: There is renewed effort in the construction sector to reduce CO2 emissions through the use of alternative binding materials to conventional Portland cements. Among the alternatives are phosphate-based binders, which have been shown to have strength properties comparable to cement, and higher strength than lime-based products, while also having a lower carbon footprint than both materials. In an effort to reduce the cost of the phosphate binder, improving performance properties of the products, as well as further reducing the carbon footprint, filler materials based on by products from industrial processes were incorporated in the binder matrix and their performance assessed in composite board products. The selected filler materials included fly ash, silica fume and calcium carbonate. Biomass samples used included pine, bagasse and black wattle(Acacia mearnsii).Physical and mechanical properties, such as density, water absorption (WA), thickness swelling (TS), modulus of rupture (MOR) and modulus of elasticity (MOE) were tested according to BS EN 634-2 (2007). The products were alsoinvestigatedfor thermal behaviour through exposure to heat. Physical and mechanical properties, such as colour change, shrinkage, weight loss and flexural strength were studiedbefore and after heat exposure. Furthermore, panel products were laminated with rotary cut veneer sheets of pine (Pinus elliottii) with a thickness of 3 mm. The fabricated laminated panels were tested for modulus of rupture (MOR), modulus of elasticity (MOE) and density, based on ISO 16893 (2016).The effect of wood lamination on phosphate panel properties was investigated. The density of the boards produced ranged from 0.82 to 1.16 g/cm3, WA ranged from 15.77 to 48.42%, TS ranged from 0.35 to 4.18%, MOR ranged from 2.83 to 6.16 MPa and MOE ranged from 410.57 to 1737.87 MPa. Significant improvements of boards’ properties were observed after lamination, with the MOR ranging from 14.96 to 56.94 MPa and MOE ranging from 3636.33 to 6827.65 MPa compared with boards prepared without lamination. The density of laminated panel products was found to range between 0.78 to 0.93 g/cm3.All composite panels changed colour with increasing temperature and shrinkage also increased with increasing exposure to heat. The strength properties decreased significantly after treatment. The weight loss of pine board filled with fillers (fly ash, silica fume or calcium carbonate) occurred at 65–85ºC, 199ºC-210ºC and 298ºC–310ºC. The general conclusion proved that calcium carbonate-filled boards had highly superior properties to boards filled with fly ash and silica fume. This was due to the reaction of calcium carbonate (CaCO3) with monopotassium phosphate (KH2PO4) which allows CaCO3 todissolve in the KH2PO4’ssolution and form a chemically bonded phosphate cement. Additionally, the biomass type had an effect on the board properties. Black wattle – a hardwood – performed better than the other two biomasses because of the differences in chemical composition. The temperature also had an influence on the board properties which activated the distribution of adhesives to the bonding site. On the other hand, the thermal resistance,physical and mechanical properties of the composites were influenced by water evaporation, type of fillers and the degradation of high volume of biomass utilised in the production of the composite boards. Particleboard filled with silica fume had higher strength resistance to exposure atelevated temperatures than boards filled with calcium carbonate and fly ash due to the ultra-fine, pozzolanic and reactive particles of silica fume that disperse in the paste and improve thermal resistance. The reaction of fly ash with magnesium potassium phosphate results in the release of amorphous compounds, such as CaO, SiO2, Al2O3, MgO and K2O. These amorphous masses fill the voids and bond the matrix together, thus increasing hardness of the product and reducingmass loss of boards with temperature increase.The study also showed the significant mechanical improvement after the lamination of boards with veneer. It was confirmed that lamination improves the strength properties of phosphate cement-bonded particleboards to meet the standards for its use in furniture, load bearing and heavy-duty load bearing.