Studies On The Dyeing Technology Of Wood With Reactive Dyes

It is of much value to improve low quality wood to high performance with or above precious trees in color, grain and other physical properties, by means of dyeing low-quality plantation wood and re-organizing them.Dyeing mechanism of reactive dyes is reacting one or two reactive groups in dyestuff molecules with hydroxy in cellulose with covalent link. Main chemical composition of wood is cellulose, hemicellulose and lignin, which contain a large number of hydroxy groups, and as a result some problems existing in the present dyeing technology with acid dyes such as color fastness(anti-spillage and light stability) and dyeing depth can be effectively solved with reactive dyes, the reason of which are as follows:(1) Fine color fastness and anti-spillage can be obtained with covalent link by means of combining ractive dyes with cellulose, hemicellulose and lignin in the wood. (2) Dyeing depth and distributing property can be improved and color difference from surface to inner in the dyed wood can also be effectively avoid, because dyeing and fixing are in separate stage and thus dyestuff can be fully diffused and distributed before fixing in the process of dyeing with reactive dyes.Because systematic study in the respect of wood dyeing with reactive dyes is rarely reported at home and abroad, the study in the thesis can make up the insufficiency, and in the mean time the new way of wood dyeing can be opened up.The fast-growing wood such as Poplar and Paulownia were selected in the thesis. The most satisfactory technology of wood dyeing with reactive dyes are expected to be obtained with spectrophotometer and full automatic color difference meter.The results of this study shows as follows:1) Extractive could be all reduced and permeating depth of dyes liquor could all be improved, by separately pretreating the wood with hot water, sodium hydroxide, and hydrogen peroxide, and the best of all was pretreating Poplar with sodium hytroxide. The most satisfactory effect could be obtained under the following pretreating conditions:NaOH at 8 g/L, a temperature between 90-95℃, a time of 2 h. Compared with unpretreated sample, longtitudinal and cross dispersion depth of dyestuffs were increased by 48.0%and 43.7% respectively.2) By bleaching wood with H2O2, pretreated Polar could achieve clear grain, light shade and in coincidence, and natural appearance in beauty. Compared with pretreated wood with sodium hytroxide, although permeating depth of dyes solution could not be effectively improved, color difference cut down and ultimately achieve fairly good dyeing results while employed in making decorating materials in light and natural shade.3) Reactive dyes were susceptible to Polar and Paulownia veneer. In common condition(not in high-temperature pressure dyeing),wood veneer dyed readily.4) Estimated by eye, dyed Polar and Paulownia veneer could completely achieve the natural style of target wood. Because dying and colourfixing are in separate stage, the molecule of dyes could diffuse efficiently before being colourfixed, and different colour could be avoided from surface to inner of the veneer.5) The better dyeing condition with reactive dyes was temperature of 70-80℃, time of 3 h, accelerating agent of Na2SO4·10H2O 40g/L, colorfixing agent of Na2CO320g/L。6) The current cost of reactive dyestuffs is 30-40 yuan/kg. It is a technique worthy of developing and extending that reactive dyes are used to dye the fast-growing wood due to simple technology, easy to operate and low cost.