Properties of wood-plastic composites made from alien invasive tree waste and recycled low-density polyethylene for interior use in social housing

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dc.contributor.advisorMeincken, Martinaen_ZA
dc.contributor.authorMohammed, Abubakar Sadiqen_ZA
dc.contributor.otherStellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.en_ZA
dc.date.accessioned2022-11-03T13:59:42Zen_ZA
dc.date.accessioned2023-01-16T12:42:03Zen_ZA
dc.date.available2022-11-03T13:59:42Zen_ZA
dc.date.available2023-01-16T12:42:03Zen_ZA
dc.date.issued2022-11en_ZA
dc.descriptionThesis (PhD) -- Stellenbosch University, 2022.en_ZA
dc.description.abstractENGLISH ABSTRACTS: Low-cost wood plastic composites (WPCs) were developed from the entire biomass of invasive trees and recycled low-density polyethylene. The aim was to produce affordable building materials for low-cost social housing in South Africa. Both raw materials are regarded as waste materials and the subsequent product development adds value to these resources, while simultaneously reducing the waste stream. The entire biomass of Acacia saligna salvaged from clearing operations was utilised as received, without any prior processing to minimise associated processing costs. Low-grade recycled low-density polyethylene (rLDPE) was used as the matrix to make the WPCs without any additives as an additional cost-cutting measure. The WPCs were at three different biomass content (50, 60 and 70 wt%), with two wood particle sizes (0.3 and 0.5 mm), and at different hot press times (10 and 30 min) and temperatures (150 and 180 °C) to obtain boards with optimum mechanical, physical and insulation properties for use in social housing in South Africa. The water absorption, dimensional stability, moduli of elasticity (MOE) and rupture (MOR), tensile strength and modulus were found to be better at longer press times and higher temperatures for all blending ratios. An increased biomass content and particle size were positively correlated with water absorption and thickness swelling and inversely related to MOR, tensile strength and density due to discontinues plastic matrix formation. A heat flow meter (HFM) and an acoustic impedance tube were designed and built to measure the thermal transmission and sound transmission loss (STL) properties of the WPCs. Boards from larger sized particles generally showed lower conductivity. The boards pressed with 70 wt% biomass and lower press temperature and time had the lowest heat conductivity value (0.044 W/m‧k), which can be attributed to higher incidence of lattice defects and vacancies due to a higher proportion of thermally modified biomass. The boards pressed with 50 wt% biomass at 150 °C for 10 min possessed a higher mass/stiffness ratio, which resulted in improved STL via reflection and absorption of acoustic energy in the mid-frequencies (500-2000 Hz). Boards produced with 60 wt% biomass exhibited the best noise attenuation level (8-14 dB) and thermal insulation with a heat conductivity around 0.048-0.056 W/m‧k, making them best suited as insulation boards to improve living conditions in Reconstruction and Development Programme (RDP) houses. The low proportion of non-woody biomass (leaves and bark) in the WPC formulation did not entirely inhibit mould growth on the WPC surfaces immediatly, even though the growth was slowed across all samples in no particular order. The fire tests showed that the WPCs composed with 70 wt% biomass pose the lowest fire hazard as they possess higher flammability and self-ignition temperatures and are also the most thermally stable with the highest melt-deflection temperature. This study demonstrates the feasibility of utilising low-grade recycled polyethylene and whole-tree biomass of A. saligna to manufacture WPC boards, without the need for pre-processing, or the addition of expensive compatibilisers, to produce boards with properties that satisfy the minimum South African Bureau of Standards (SABS) requirements for interior wall or ceiling cladding.en_ZA
dc.description.abstractAFRIKAANS OPSOMMINNG: Laekoste-houtplastiek-komposiete (WPC's) is ontwikkel uit indringerbome en herwonne lae-digtheid poliëtileen. Die doel was om bekostigbare boumateriaal vir laekoste maatskaplike behuising in Suid-Afrika te vervaardig. Beide grondstowwe word as afvalmateriaal beskou en die daaropvolgende produkontwikkeling voeg waarde tot hierdie hulpbronne toe, terwyl dit terselfdertyd die afvalstroom verminder. Die produksiekoste is tot die minimum beperk deur die hele biomassa van Acacia saligna wat van skoonmaakbedrywighede gered is, sonder enige voorafgaande verwerking, en laegraadse herwinde laedigtheid poliëtileen (rLDPE) te gebruik om WPC's sonder enige bymiddels te maak. Die WPC's is verwerk teen drie verskillende vermengingsverhoudings (50, 60 en 70 gew.% biomassa), met twee houtdeeltjiegroottes (0.3 en 0.5 mm), en teen verskillende warmperstye (10 en 30 min) en temperature (150 en 180) °C) om planke met optimale meganiese, fisiese en isolasie-eienskappe te verkry vir gebruik in maatskaplike behuising in Suid-Afrika. Daar is gevind dat die waterabsorpsie, dimensionele stabiliteit, elastiese en breukmoduli, treksterkte en modulus beter is by langer perstye en hoër temperature vir alle mengverhoudings. Dit word toegeskryf aan die kristallisasie van die lignosellulose materiaal en termies-geïnduseerde kruisbinding in die poliëtileen. 'n Verhoogde biomassaverhouding en deeltjiegrootte was positief gekorreleer met waterabsorpsie en dikteswelsel en omgekeerd verwant aan MOR, treksterkte en digtheid as gevolg van 'n onvolledige inkapseling van die biomassa deur die plastiekmatriks. 'n Hittevloeimeter (HFM) en 'n akoestiese impedansiebuis is ontwerp en gebou om die termiese transmissie en klankoordragverlies (STL) eienskappe van die WPC's te meet. Planke van groter grootte deeltjies het oor die algemeen laer geleidingsvermoë getoon. Die planke wat met 70 gew.% biomassa gepars is en laer perstemperatuur en tyd het die laagste hittegeleidingswaarde (0.044 W/m•k) gehad, wat toegeskryf kan word aan hoër voorkoms van roosterdefekte en leë plekke as gevolg van 'n hoër proporsie termies gemodifiseerde biomassa . Die planke wat vir 10 minute met 50 gew.% biomassa by 150 °C gedruk is, het 'n hoër massa/styfheidverhouding gehad, wat gelei het tot verbeterde STL deur weerkaatsing en absorpsie van akoestiese energie in die middelfrekwensies (500-2000 Hz). Planke wat met 60 gew.% biomassa vervaardig is, het die beste geraasdempingsvlak (8-14 dB) en termiese isolasie met 'n hittegeleidingsvermoë rondom 0,048-0,056 W/m‧k getoon, wat hulle die beste geskik maak as isolasieborde om lewensomstandighede in HOP-huise te verbeter. Die lae proporsie nie-houtagtige biomassa (blare en bas) in die WPC-formulering, wat die meeste van die antifungale verbindings in A. saligna bevat, was nie genoeg materiaal om vormgroei op die WPC-oppervlaktes heeltemal te inhibeer nie, al was die groei vertraag oor alle monsters in geen spesifieke volgorde nie. Die WPC's wat met 70 gew.% biomassa saamgestel is, hou die laagste brandgevaar in aangesien hulle hoër vlambaarheid en selfontbrandingstemperature het en ook die mees termies stabiele is met die hoogste smelt-afbuigingstemperatuur. Hierdie studie demonstreer die haalbaarheid van die gebruik van laegraadse herwonne poliëtileen en heelboombiomassa van A. saligna om WPC-borde te vervaardig, sonder die behoefte aan voorafverwerking, of die byvoeging van duur versoenbaarheidsmiddels, om borde te produseer met eienskappe wat aan die minimum voldoen. vereistes vir binnemuur- of plafonbekleding.af_ZA
dc.description.versionDoctoralen_ZA
dc.format.extentxv, 106 pages : illustrationsen_ZA
dc.identifier.urihttp://hdl.handle.net/10019.1/125936en_ZA
dc.language.isoEnglish (British)en_ZA
dc.publisherStellenbosch : Stellenbosch Universityen_ZA
dc.rights.holderStellenbosch Universityen_ZA
dc.subjectEngineered wood -- South Africaen_ZA
dc.subjectPolyethylene -- South Africaen_ZA
dc.subjectBiomass -- South Africaen_ZA
dc.subjectBuilding materials -- Thermal properties -- South Africaen_ZA
dc.subjectUCTDen_ZA
dc.titleProperties of wood-plastic composites made from alien invasive tree waste and recycled low-density polyethylene for interior use in social housingen_ZA
dc.typeThesisen_ZA
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