Phosphate-bonded composite products : the influence of filler materials, biomass type, and processing method on panel properties

Mngomezulu, Lehlohonolo Benjamin (2019-04)

Thesis (MScFor)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Daar is ‘n hernude poging in die konstruksie sektor om CO2 deur die gebruik van alternatiewe verbindings materiale met gewone Portland sement te verminder. Onder die alternatiewe is fosfaat-gebaseerde verbinders, wat sterkte eienskappe getoon het in die omgewing van sement, en hoër sterkte as kalk-gebaseerde produkte, asook ook 'n laer koolstof-voetspoor as beide materiale. In 'n poging om die koste van die fosfaat verbinders te verminder, verbetering van die prestasie eienskappe van die produkte, sowel as die koolstof-voetspoor verder te verminder, is toevoeg materiale gebaseer op byprodukte van industriële prosesse opgeneem in die verbindings matriks en hul prestasie beoordeel in saamgestelde bord produkte . Die geselekteerde toevoeg materiale het vliegas, silika rook en kalsiumkarbonaat ingesluit. Biomassa monsters wat gebruik is het denne, bagasse en swartwattel (Acacia mearnsii) ingesluit. Fiesiese en meganiese eienskappe, soos digtheid, water-absorpsie (WA), dikte swelling (TS), modulus van skeuring (MOR) en die modulus van elastisiteit (MOE) was getoets volgens BS EN 634-2 (2007). Die produkte was ondersoek vir termiese gedrag deur blootstelling aan hitte. Fisiese en meganiese eienskappe, soos kleurverandering, krimping, gewigsverlies en buig sterkte was ondersoek voor en na hitte blootstelling. Verder meer, paneel produkte is vanuit roterende gesnyde fineer velle van denne (Pinus elliottii) met 'n dikte van 3 mm gelamineer. Die gelamineerde panele is getoets vir modulus van skeuring (MOR), modulus van elastisiteit (MOE) en digtheid, gebaseer op ISO 16893 (2016). Die effek van hout laminering op fosfaat paneel eienskappe was ondersoek. Die digtheid van die borde het gewissel van 0.82 tot 1.16 g/cm3, WA het gewissel van 15.77 tot 48.42%, TS het gewissel van 0.35 tot 4.18%. MOR het gewissel van 2.83 tot 6.16 MPa en MOE het gewissel tussen 410.57 tot 1737.87 MPa. Beduidende verbeterings van bord eienskappe is waargeneem na laminering, met die MOR wat gewissel het van 14.96 tot 56.94 MPa en MOE wat gewissel het tussen 3636.33 tot 6827.65 MPa in vergelyking met borde wat voorberei was sonder laminering. Die digtheid van gelamineerde paneel produkte is gevind om te wissel tussen 0.78 em 0.93 g/cm3. Al die saamgestelde panele verander kleur met toename in temperatuur en krimping het ook toegeneem met toenemende hitte blootstelling. Die sterkte eienskappe het aansienlik verminder na behandeling. Die gewig van denne borde wat gevul is met vullers (vliegas, silica rook of kalsiumkarbonaat) plaasgevind het by 65-85ºC, 199ºC-210ºC en 298ºC-310ºC verminder. Die algemene gevolgtrekking bewys dat kalsium-karbonaat gevulde borde, hoogs uitstaande eienskappe toon teenoor borde gevul met vliegas en silika rook. Dit was as gevolg van die reaksie van kalsiumkarbonaat (CaCO3) met monokaliumfosfaat (KH2PO4) wat CaCO3 veroorsaak om op te los in die KH2PO4's oplossing en vorm 'n chemies gebinde fosfaat sement. Daarbenewens het die biomassa tipe 'n uitwerking op die bord eienskappe gehad. Swartwattel - 'n hardehout – het beter as die ander twee biomassas gevaar as gevolg van die verskille in chemiese samestelling. Die temperatuur het ook 'n invloed op die bord eienskappe tot gevolg gehad, wat die verspreiding van die gom geaktiveer het tot by die bindings areas. Aan die ander kant, die termiese weerstand, fisiese en meganiese eienskappe van die saamgestelde produkte, is beïnvloed deur water verdamping, tipe vullers en die vermindering van 'n hoë volume van biomassa gebruik in die produksie van die saamgestelde borde. Spaanderbord gevul met silika rook het hoër sterkte weerstand teen blootstelling by hoër temperature as borde vol kalsiumkarbonaat en vliegas as gevolg van die ultra-fyn, pozzolanic en reaktiewe deeltjies van silika rook wat versprei in die pasta en sodoende termiese weerstand verbeter. Die reaksie van vliegas met magnesium kaliumfosfaat veroorsaak die vrylating van amorfe verbindings, soos CaO, SiO2, Al2O3, MgO en K2O. Hierdie amorfe massas vul die leemtes en bind die matriks saam en sodoende word hardheid die produk verhoog en die massa verlaag met ‘n toename in temperatuur. Die studie het ook ‘n beduidende meganiese verbetering na die laminering van die borde met fineer getoon. Dit is bevestig dat laminering verbeter die sterkte eienskappe van fosfaat-sement gebinde spaanderborde om aan die standaarde te voldoen vir die gebruik daarvan in meubels, lasdraende en swaar-lasdraende gebruik.

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