|dc.contributor.author||Le Roux, Cornelius Johannes||
|dc.description||Thesis (M.Sc. (Chemistry))--North-West University, Potchefstroom Campus, 2007||
|dc.description.abstract||The feasibility of impregnating two types of wood (pine, poplar) with two different
preservatives (creosote, CCA) by means of supercritical carbon dioxide (sc-CO2) as
carrier was investigated in view of the actuality of treatment of wooden poles in
electricity distribution networks and in the agricultural sector.
Two important quantities were determined prior to performing impregnation runs. The
impregnation capacity of the two types of wood was measured by estimating
gravimetrically the amount of water and mercury porosimetrically the amount of mercury
that can be taken up by the wood. The results were highly comparable and could be
used to predict the amount of preservative that could potentially be impregnated. These
figures Served as benchmark for efficient impregnation. The solubility of the
preservatives in sc-CO2 was measured by means of a supercritical extractor (Isco) in
static mode as this quantity was expected to play an important role in the mechanism of
The impregnation of specially prepared wood samples was performed in a locally
manufactured sample holder which fitted an existing supercritical extractor (Varian).
The impregnation experiments on laboratory scale were extended to pilot plant scale by
using a larger supercritical extractor (Swiss Nova).
The wood samples could be impregnated only to a limited extent (creosote: 12% m/m
for poplar, 25% m/m for pine; CCA: 7% m/m for poplar, 19% m/m for pine), since
microscopic analysis revealed that neither of the two preservatives was capable of
occupying the pores of the wood but bound to the wood vessels instead. The pressure
dependence of the impregnation suggested that the process determining parameters
were pressure and solubility for creosote impregnation and pressure only for CCA
impregnation. This conclusion could be supported by surface response graphs. A break
strength test was applied to all impregnated samples in order to confirm that the
ultrastructure of the wood was not damaged by the high pressures involved.
Impregnation was repeated with N2 as carrier, and the results confirmed the superiority
of sc-CO2 as an impregnating agent.||
|dc.title||Sc-CO2 impregnering van houtpreserveermiddels||en