Research On Veneer Dyeing Technology

The purpose of this research is to investigate the improvement effects of pretreatment process on the dyeability of the veneer, analyze the effects of different dyeing methods on the color stability of the dyed veneer, determine the changes of the pH and buffering capacities of the dyed veneer, and explore the existing status of the dye stuff in the dyed wood. Two types of hard wood veneer, namely the Ussuri Poplar and birch, were selected as the sample materials; four types of the dyestuffs, namely the acid dyes, reactive dyes, basic dyes and direct dyes, were applied as the dyeing agents. Accordingly, the determine equipments such as visible light spectrophotometer, pH meter and FTIR spectrum meter were applied in this series experiments. The conclusions of this research would be an important reference for optimizing the veneer dyeing process and for improving the subsequent processing technology of the dyed veneer; it would be also expected to pave the way for further study on wood dyeing mechanism.The research has drawn the following conclusions: 1) pretreatment has a significant improvement on the dye uptake of the acid dyestuff; and the 0.3% NaOH solution pretreatment gives better performance than water pretreatment, while 80 °C pretreatment presents a better effect than room temperature pretreatment. Different pretreatments exhibit no explicit effect on the water-resisting and light-resisting color fastness of the dyed veneer. Also, no clear effect of pretreatments on color difference within the dyed veneer is observed. 2) Dyestuff types has the most significant effect on the color stability of the dyed veneer, the color fastness of water bath resisting of the four dyestuffs is ranged in such order: direct dyestuff> reactive dyestuff> acid dyestuff> basic dyestuff; and the order for color fastness of light resisting is: acid dyestuff > direct dyestuff > reactive dyestuff> basic dyestuff. The color fixing agents do help in improving the color stability of the dyed veneer, and sodium carbonate has a better comprehensive performance than potassium dichromate when serving as the color fixing agent. A good color fixing effect could be achieved when the dosage of the color fixing agent is 0.3% in proportion to the total weight of the dyeing liquor; any higher dosage will not improve the color fixing effect too much, besides, different add in methods present no significant differences in the color fixing effects. 3) The effects of NaOH solution pretreatment and the dyeing process on pH and buffering capacity are similar for the two types of wood. The dyeing process will increase a little bit of the pH of wood and decrease the acid buffering capacity sharply at the same time; pretreatment of NaOH solution would increase the pH of wood significantly and the acid buffering capacity of wood is increased too during the same process. 4) Under all the dyeing conditions of this research, the existing status of the dyestuff in wood is mainly a mechanical filling. The infrared spectrum of the dyed wood basically stays unchanged, and the amount of the functional groups does not change too much, however, the absorbance of certain functional groups were either raised or dropped; no new chemical group is observed, hence no new substance is created in the dyeing process.