This thesis reports investigations into the use of a biocide and resin system for
the prevention of wood decay. The resins were used to modify Corsican pine and
European beech. The resins used were urea formaldehyde, melamine
formaldehyde and melamine urea formaldehyde. The three resins were used to
modify the wood alone, and with the biocide, delivered both sequentially and in a co-delivery system. The resin modified wood was subjected to EN 113 type pure
culture decay tests which utilised the fungi Coniophora puteana (Schumacher ex
Fries) Karsten (BAM 15), Coriolus versicolor (Linnaeus) Quelet (CTB 863A),
and Phanerochaete chrysosporium (S 179). It was found that the biocide had a
significant impact on the decay resistance of the wood when modified to a low
resin weight percent gain. However, the biocide did not provide any additional
decay resistance at high weight percent gains. Threshold values for the
modification of timber with resin were found to be ∼30% for Corsican pine and
∼22% for beech. The threshold value did not change with increased fungal
virulence, indicating that the decay resistance mechanism was a physical and not biocidal. The decay resistance of both acetic and hexanoic anhydride modified wood was investigated as a model for cell wall modification. Threshold values for each modification were found to be 15% for the acetic anhydride and 22% for the hexanoic. The threshold values were found to be independent of wood species, fungal species and virulence again indicating that that the decay
resistance is due to a physical mechanism and not a biocidal one. Cell wall
swelling due to resin or anhydride modification was determined using helium
pycnometry, a technique never before applied in such studies. Cell wall swelling
due to modification as determined by helium pycnometry did not correlate with
that determined by external dimensions (a new finding). Cell wall accessibility
was determined using solute exclusion. Anhydride modification reduced fibre
saturation point (as determined by solute exclusion). This reduction correlated
with the volume occupied in the cell wall by the bonded adduct. Resin treatment
presented a more complex picture due to resin filling the lumen and the cell wall.