Use of naturally durable wood as an alternative to the use of chemical-based wood preservation

Thesis (MScFor)--Stellenbosch University, 2025.

Jayeola, V. A. 2025. Use of Naturally Durable Wood as an Alternative to the use of Chemical-based Wood Preservation. Unpublished masters thesis. Stellenbosch: Stellenbosch University [online]. Available: https://scholar.sun.ac.za/items/1a04c628-4c1e-48af-b258-90635dc3519c

ENGLISH ABSTRACT: Environmental and health concerns surrounding the use of chemical wood preservatives such as chromated copper arsenate (CCA), creosote, pentachlorophenol, among others have led to an urgent search for sustainable alternatives. These preservatives, while effective in protecting wood from decay, pose risks of soil and water contamination, and potential carcinogenic effects on humans. Naturally durable woods have inherent ability to resist attacks from fungi, insects, bacteria, and marine borers. Among the naturally durable species, Eucalyptus species presents unique characteristics such as, fast-growth, and ability to produce significant amount of heartwood (responsible for wood durability) in a short period. This study then focused on evaluating the performance of some Eucalyptus species in a two-year in-ground degradation trial compared to chemically treated and untreated wood. The objectives were: (a) to evaluate degradation performance after exposure based on applicable standards (b) to characterise wood to develop an understanding of the inherent properties that influence performance. A two-year field trial was conducted to assess the in-ground durability of Eucalyptus cladocalyx and Eucalyptus cloeziana compared to chemically treated Pinus radiata wood. Performance was assessed using visual assessment, mass loss measurement, and follow up methods such as density using computed tomography scan (CT scan), scanning electron microscopy SEM, and chemical analysis to provide insights into structural changes and durability mechanisms. Eucalyptus cladocalyx wooden stakes (samples) showed slight to moderate decay, with edge regions of the stakes typically rated as slightly decayed (1) and pith regions rated as moderately decayed (2). Statistical analysis indicated no significant difference in decay ratings between these regions, suggesting uniformity in structural properties. In contrast, Eucalyptus cloeziana exhibited consistent moderate decay (rating 2) across the edge and pith regions. CCA-treated Pinus radiata stakes were consistently used as controls receiving a decay rating of 0 (no attack). The mass loss in Eucalyptus cladocalyx stakes ranged from 6.05% (edge) to 12.81% (pith), which was higher than the 2.85% observed in CCA-treated Pinus radiata, though no significant difference was found (p = 1). Eucalyptus cloeziana demonstrated the highest mass losses, with mean values of 34.07% (edge) and 32.51% (pith), significantly different from E. cladocalyx and CCA-treated Pinus radiata (p < 0.05). For the follow-up tests, a consistent density decrease was observed from below the groundline (604.2 kg/m³) to the groundline (546.3 kg/m³) for E. cloeziana. In contrast, E. cladocalyx showed no clear density trend, with the highest mean density of 1032.1 kg/m³ at the lower middle position, indicating enhanced durability. The fungal presence within the vessels of E. cloeziana was also notably higher, with fungal hyphae detected in the pith region, while the edge region of E. cladocalyx showed no visible fungal presence. Chemical analysis on E. cloeziana revealed changes in wood composition. The reference sample had the highest cellulose content (30.1%), while degraded samples showed a reduction in cellulose and an increase in hemicellulose, extractives, and lignin, particularly in the pith and edge regions. This suggests that cellulose breakdown contributed to the degradation process. These findings reveal that E. cloeziana wood is not suitable for in-ground applications. Eucalyptus cladocalyx on the other hand, shows the potential as a sustainable, non-toxic alternative to chemical wood treatments. Its rapid growth and natural durability make it suitable for agricultural uses, such as vineyard poles, reducing reliance on harmful preservatives. This aligns with South Africa’s bio-economy strategy and global sustainability objectives.

AFRIKAANSE OPSOMMING: Omgewings- en gesondheidsorg rondom die gebruik van chemiese houtpreserveermiddels soos gechromeerde koperarsenaat (CCA), kreosoot, pentachloorfenol, onder andere, het gelei tot 'n dringende soeke na volhoubare alternatiewe. Hierdie preserveermiddels, terwyl dit effektief is om hout teen verval te beskerm, hou risiko's in van grond- en waterbesoedeling, en potensiële karsinogene effekte op mense. Natuurlik duursame houtsoorte het 'n inherente vermoë om aanvalle van swamme, insekte, bakterieë en seeboorders te weerstaan. Onder die natuurlik duursame spesies bied Eucalyptus spesies unieke eienskappe soos vinnige groei en vermoë om aansienlike hoeveelheid kernhout (verantwoordelik vir hout duursaamheid) in 'n kort tydperk te produseer. Hierdie studie het toe gefokus op die evaluering van die prestasie van sommige Eucalyptus spesies in 'n twee-jaar in-grond degradasie proef in vergelyking met chemies behandelde en onbehandelde hout. Die doelwitte was: (a) om afbraakprestasie na blootstelling te evalueer gebaseer op toepaslike standaarde (b) om hout te karakteriseer om 'n begrip te ontwikkel van die inherente eienskappe wat prestasie beïnvloed. 'n Twee jaar veldproef is uitgevoer om die in-grond duursaamheid van Eucalyptus cladocalyx en Eucalyptus cloeziana te bepaal in vergelyking met chemies behandelde Pinus radiata hout. Prestasie is geassesseer deur gebruik te maak van visuele assessering, massaverliesmeting en opvolgmetodes soos digtheid deur gebruik te maak van rekenaartomografieskandering (CT-skandering), skandeerelektronmikroskopie SEM en chemiese analise om insigte in strukturele veranderinge en duursaamheidsmeganismes te verskaf. Eucalyptus cladocalyx houtpale (monsters) het effense tot matige verval getoon, met randstreke van die pale wat tipies as effens verval (1) gegradeer is en mergstreke as matig verval (2). Statistiese analise het geen betekenisvolle verskil in vervalgraderings tussen hierdie streke getoon nie, wat dui op eenvormigheid in strukturele eienskappe. In teenstelling hiermee het Eucalyptus cloeziana konsekwente matige verval (gradering 2) oor die rand- en pitstreke getoon. CCA-behandelde Pinus radiata-stake is konsekwent gebruik as kontroles wat 'n vervalgradering van 0 (geen aanval) ontvang het nie. Die massaverlies in Eucalyptus cladocalyx-stake het gewissel van 6.05% (rand) tot 12.81% (pit), wat hoër was as die 2.85% wat in CCA-behandelde Pinus radiata waargeneem is, alhoewel geen betekenisvolle verskil gevind is nie (p = 1). Eucalyptus cloeziana het die hoogste massaverliese getoon, met gemiddelde waardes van 34.07% (rand) en 32.51% (pit), betekenisvol verskillend van E. cladocalyx en CCA-behandelde Pinus radiata (p < 0.05). Vir die opvolgtoetse is 'n konsekwente afname in digtheid waargeneem vanaf onder die grondlyn (604.2 kg/m³) na die grondlyn (546.3 kg/m³) vir E. cloeziana. Daarteenoor het E. cladocalyx geen duidelike digtheidstendens getoon nie, met die hoogste gemiddelde digtheid van 1032.1 kg/m³ by die laer middelste posisie, wat verbeterde duursaamheid aandui. Die swam teenwoordigheid binne die vate van E. cloeziana was ook noemenswaardig hoër, met swamhifes wat in die merggebied opgespoor is, terwyl die randgebied van E. cladocalyx geen sigbare swam teenwoordigheid getoon het nie. Chemiese ontleding op E. cloeziana het veranderinge in houtsamestelling aan die lig gebring. Die verwysingsmonster het die hoogste sellulose-inhoud (30.1%) gehad, terwyl afgebreekte monsters 'n vermindering in sellulose en 'n toename in hemisellulose, ekstrakteermiddels en lignien getoon het, veral in die merg- en randgebiede. Dit dui daarop dat sellulose-afbraak bygedra het tot die afbraakproses. Hierdie bevindinge toon dat E. cloeziana-hout nie geskik is vir in-grond toedienings nie. Eucalyptus cladocalyx aan die ander kant, toon die potensiaal as 'n volhoubare, nie-giftige alternatief vir chemiese houtbehandelings. Sy vinnige groei en natuurlike duursaamheid maak dit geskik vir landbougebruike, soos wingerdpale, wat die afhanklikheid van skadelike preserveermiddels verminder. Dit strook met Suid-Afrika se bio-ekonomiestrategie en globale volhoubaarheidsdoelwitte.

Masters