Tensile stress relaxation of wood impregnated with different ACQ formulations at various temperatures

Abstract

Abstract The reactions between constituents of alkaline copper quat (ACQ) and of wood were investigated by a tensile stress relaxation approach. Small samples were stressed and impregnated with various ACQ solutions, in which the ratios of monoethanolamine (MEA), ACQ, and didecyl dimethyl ammonium chloride (DDAC) were varied. The other parameters included temperature and concentration of the treating solutions. The stress relaxation curves of wood were recorded during the impregnation period and the effects of impregnation parameters were investigated by an orthogonal experimental design (OED). The effects of water, MEA, and DDAC on stress relaxation of the samples were also observed. The bulking effect of water was tested separately in samples treated with distilled water without stretching. The results showed that the stress relaxes dramatically in the initial period and then changes slightly over a long period, which is readily visible in double logarithmic plots of f (t)/f (0) versus time (t). There are complex interactions between the components of ACQ solutions and wood matrix: (1) in rapid phase I, the splitting of the easily accessible hydrogen bonds (mainly in the amorphous hemicelluloses) are prevalent by interaction with components of ACQ solution; (2) in slow phase II, Cu penetrates deeper in less accessible regions (e.g., in paracrystalline regions of cellulose) and renders possible further relaxation. The results of range and variance analysis reveal that the molar ratio of Cu to MEA and temperature of ACQ solution have significant effects on the rate of reaction during phase I, whereas in phase II only the temperature of ACQ solution has a significant effect. The stress relaxation curves of samples impregnated in water, MEA, and DDAC all showed a quasi one phase stress relaxation rate, which suggests that phase II is mostly related to Cu in ACQ formulations. It is concluded that the formation of complexes with Cu is still the major reaction in wood although there is competition among ACQ constituents for reaction sites.