The reactions between ammoniacal copper quat (ACQ) constituents and wood components were investigated by tensile stress relaxation approach. Small wood samples were stressed and impregnated in ACQ solutions with different formulation including the ethanolamine (MEA) to copper molar ratio, copper (as copper oxide) to quat (as DDAC) weight basis, treatment temperature and also the solution concentration, and during this period the stress relaxation curves were recorded. The effect of different parameters mentioned above on stress relaxation of wood was investigated by orthogonal experiment design (OED). From the stress relaxation curves, some information concerning the reactions between ACQ constituents and wood was obtained since the formation of chemical or physical bonding between ACQ and wood would both release the stress produced in wood and then accelerate the stress relaxation process. The results showed that the stress relaxes dramatically in the initial period and then change slightly even within a long period. There are two reaction mechanisms predicted from the slopes of the regression lines obtained from the double logarithmic plots of modulus f (t) versus time (t) in the initial period of stress relaxation, which are defined as Phase I and PhaseⅡ. They correspond to physical and chemical processes respectively. The molar ratio of Cu to MEA and treatment temperature take the significant effects on the rate of reaction on Phase I, while on Phase Ⅱ, the significant factor is only the treatment temperature based on the results of range and variance analysis. It reveals that although the competitions among ACQ constituents existed, the adsorption of copper is still the major reaction in the wood.

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