Research On The Technique Of Poplar Wood Dyeing With Reactive Dyes Based On Microwave Treatment

As an important fast-growing and abundant resource wood specie, poplar has some defects, such as monotonous color, poor color sense, poor surface quality, etc. In order to improve the surface quality and visual characteristics of wood, the reactive dyes were selected for dyeing treatment in this study. By using the supercritical CO2 fluid, steam explosion and microwave pretreatment, the fluid permeability of poplar wood has been improved. According to the wood dyeing effect of different processing methods on dyeing rate and fixation rate, the best pretreatment method were selected. The initial moisture content, microwave radiation time and microwave radiation power were chosen as the technical factors in the test. Inquired optimal technology were selected according to orthogonal test, it analysed the change of microstructure, chemical structure, crystallinity and thermal stability of wood by SEM, FTIR, XRD, TG, and it explored to the dyeing mechanism of reactive dyes by a pre-treated means of microwave. Ultrasonic process and pressure process were chosen to dye wood treated by microwave treatment. Time parameter was studied the effect of ultrasonic and pressure process to dye wood. It sought the optimal process for the poplar wood dyed by the reactive dyes. It would service the wood dyeing by the reactive dyes. The results of this study are shown as following:(1) Supercritical CO2 fluids pretreatment, steam explosion pretreatment and microwave pretreatment could remarkably improve the dyeing effect of poplar wood. After supercritical CO2 fluids pretreatment, dyeing rate increased to 25.26%, fixation rate increased to 23.91%. After steam explosion pretreatment, dyeing rate increased to 30.42%, fixation rate increased to 28.95%. After microwave pretreatment, dyeing rate increased to 39.44%, fixation rate increased to 38.31%. CoMPared with supercritical CO2 fluid pretreatment and steam explosion pretreatment, dyeing rate of wood pretreated by microware increased 14.18% and 9.02%, fixation rate of wood pretreated by microware increased 14.4% and 9.36%.Considering the dyeing effect, energy consumption, dimensional, microwave pretreatment was chosen as pretreatment method of successive experiments in this study.(2) Orthogonal test showed that the importance of factors for microwave pretreatment process was:moisture content> processing time> microwave volume density. The optimal process parameters of microwave pretreatment were chosen, for example, moisture content of 25%, microwave pretreatment volume density of 18kW, processing time of 90s. After poplar wood was chosen the microwave pretreatment of the optimal process and dyed with reactive dyes, the dyeing rate of non-sealing specimen was 43.89%, and the dyeing rate of longitudinal sealing specimen was 36.95%, and the dyeing rate of transverse sealing specimen was 31.15%. CoMPared with untreated wood, the dyeing rate of non-sealing specimen increased 26.29%, the dyeing rate of longitudinal sealing specimen increased 22.76%, the dyeing rate of transverse sealing specimen increased 15.32%.(3) After microwave pretreatment, reactive dyes can enter the interior of the wood more smoothly and connect to the chemical composition of the wood more closely. With coMParison to the controls, the structures of the intercellular layer became denser, the size of the vessel became larger, the wall of vessel was broken (or even split along the radial direction), pit membrane was broken off, or even completely fell off, and pit membrane was torn. Therefore, the dye liquor resistance during the penetration process would be smaller than the controls. The FTIR indicated that, after dyeing treatment, the characteristic peak of reactive dyes in wood appeared and shifted. It showed that chemical combination happened between poplar and reactive dyes. The XRD indicated that, after microwave pretreatment, the relative crystallization index of dyed wood increased. The cause may be hydroxyl group had reacted with itself in the amorphous region of cellulose, and formed ether bond. The TG indicated that, after dyeing treatment, the starting point of pyrolysis moved, the residual value of pyrolysis increased. The cause may be chemical combination happened between poplar and reactive dye, the structure of wood became more stable and the thermal stability increased.(4) According to the results of wood dyeing with reactive dyes after microwave pretreatment, it found that, coMParing with conventional dyeing, both the ultrasonic pretreatment and pressure pretreatment could effectively advance the dyeing effect of poplar wood, and they could slightly alter the weathering color fastness of poplar wood. The wood dyeing effect of pressure treatment was better. During the dyeing process, using assisted ultrasonic process of 10,20,30,40,50 minutes. The dyeing result showed that, the optimal process of ultrasonic treatment could be kept 40 mins. During the dyeing processes of pressure, a performing time of 5,10,20,40,60 minutes was chosen. The dyeing result showed that, the optimal process parameters of pressure treatment could be kept 60 mins. Comprehensive evaluation to two selected processes showed that, the chromatic aberration of dyed woodwas small, and can be ignored. According to the dyeing rate and fixation rate, the optimal dyeing auxiliary process was pressure pretreatment of 60 mins.