Chemical properties of thermally degraded E. dunnii and E. macarthurii

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Stellenbosch : Stellenbosch University
ENGLISH ABSTRACT: Wild fires in South Africa lead to the destruction of an average of 14 000ha of forest plantation annually. In order to reduce the loss of resources the possible recovery of wood after a wildfires was investigated. For this study two eucalyptus species - Eucalyptus dunnii and Eucalyptus macarthurii were selected, as plantations of these species are located in high risk fire regions. The main objective of this study was to determine, at which temperature wood degrades to such an extent that it is no longer suitable for the production of pulp and to find out if differences between different species exist. The aim was to determine whether wood that has been exposed to wildfires can still be used. The change in chemical composition of E. dunnii and E. macarthurii wood was determined before and after exposure to temperatures ranging from 150°C to 220°C. The cellulose, lignin and extractive content, as well as the molecular weight of cellulose were determined as a function of temperature to determine the change in chemical composition that can be expected after exposure to elevated temperatures. The acid insoluble lignin content decreased with increasing temperature, while the acid soluble lignin content increased. As a result, the total lignin content was only reduced by 2%, but the composition of the lignin has clearly changed. The ethanol extractive and water extractive content decreased with increasing temperature for both species. The cellulose content of E. dunnii showed a de facto increase due to the decrease of extractive and lignin content. The cellulose content of E. macarthurii remained relatively unchanged. The molecular weight of both species decreased after exposure to 150°C and reached a low of 160 000 after exposure to 160°C. However, after exposure to a temperature of 170°C the molecular weight began to increase, which was caused by the disintegration of low molecular weight amorphous cellulose. In order to utilise wood from fire damaged trees the wood exposed to a temperature of 160°C and higher must be removed to ensure the wood is suitable for pulp production.
AFRIKAANSE OPSOMMING: Gevolg van wilde brande word jaarliks 'n gemiddelde van 14000 ha bosplantasie verloor. 'N ondersoek na die moontlike herstel van hout uit brandbeskadigde bome is nodig. Vir hierdie studie is twee eucalyptus spesies - Eucalyptus dunnii en E. macarthurii is gekies as plantasies van hierdie spesies in hoërisiko-brandstreke. Die hoofdoel van hierdie studie was om te bepaal, by watter temperatuur hout sodanig degradeer dat dit nie meer geskik is vir die produksie van pulp nie en om uit te vind of daar verskille tussen die verskillende spesies bestaan. Die doel was om te bepaal of hout wat aan veldbrande blootgestel is, nog steeds gebruik kan word. Die verandering in chemiese samestelling van E. dunnii en E. macarthurii hout is bepaal voor en na blootstelling aan temperature tussen 150°C tot 220°C. Die sellulose, lignien en ekstrakstofinhoud, sowel as die molekulêre gewig van sellulose, is bepaal as 'n funksie van temperatuur. Dit is gedoen om die verandering in chemiese samestelling te bepaal wat na verwagting na verhoogde temperature verwag kan word. Die suur-onoplosbare lignieninhoud het met toenemende temperatuur afgeneem, terwyl die suuroplosbare lignieninhoud toegeneem het. As gevolg daarvan is die totale lignieninhoud slegs met 2% verminder, maar die samestelling en lignien het duidelik verander. Die etanol ekstraksie en water ekstraktiewe inhoud verminder met toenemende temperatuur vir beide spesies. Sellulose-inhoud van E. dunnii het 'n effektiewe verhoging getoon weens die afname in ekstraksie en lignieninhoud. Die sellulose-inhoud van E. macarthurii het relatief onveranderd gebly. Die molekulêre gewig van albei spesies het verminder na blootstelling aan 150°C en bereik 'n laagtepunt van 160 000 na blootstelling aan 160°C. Na die blootstelling aan 170°C het die molekulêre gewig egter begin toeneem, wat veroorsaak is deur die disintegrasie van amorfe sellulose met lae molekulêre gewig. Om hout uit brandbeskadigde bome te gebruik, moet die hout wat blootgestel is aan temperature van 160°C en hoër, verwyder word om te verseker dat die hout geskik is vir pulpproduksie. Vir 'n hoë intensiteitsbrand beteken dit 1 cm hout onder die bas vir E. macarthurii en 2 cm vir E.dunnii verwyder moet word.
Thesis (MScFor)--Stellenbosch University, 2019.
Thermal degradation of wood, Eucalyptus dunnii, Eucalyptus macarthurii, Thermal degradation, UCTD