Research On Mechanism Of Modified Hydrophobic Wood By DBD Plasma Treatment

Wooden products will absorb moisture in the air during the applied process, especially for outdoor wooden products which are susceptible to rain erosion. Water absorption causes deformation, cracking and other drawbacks, which limits the application of wood, and the hydrophobic modification process is essential for wood. At present, the modification methods of wood industry spent large resource and have serious pollution to environment. With the development of surface modification, surface hydrophobic modification of wood material has become a popular research point in wood industry.This paper study on Poplar which is a fast-growing wood as research object. The influence of plasma exposure time, plasma power and gages pressure for hydrophobicity of wood surface were explored, as well as got optimization parameter and modification mechanism. In the best plasma parameter, the commonality of plasma treatment for Larch and Oak was researched. Likewise, the hexane and ethyl acetate plasma were explored for wood surface hydrophobicity. Finally, hydrophobicity layer timeliness of wood surface after hexamethyldisiloxane plasma was explored.Contact angles, surface energy were tested to analysis plasma treatment influence on wood surface hydrophobicity in macroscopic scale. Scanning electron microscope(SEM) and atomic force microscope(AFM) were used to explore morphology of plasma treated wood surface. Scanning electron microscopy and energy dispersive spectrum(SEM-EDS), fourier transform attenuation total reflection infrared spectroscopy(ATR-FTIR) and X-ray photoelectron spectroscopy(XPS) were used to explore chemical element composition of wood surface with plasma treatment. According to the research on this experiment, it provides a new idea for the plasma treatment for wood surface hydrophobicity, and it has practical significance to promote the industrialization of plasma modified technology for hydrophobicity.The results are shown as following:In the hexamethyldisiloxane(HMDSO) gage, the contact angle value comes to the maximum(130°) when plasma power is 60 W, exposure time is 75 s and pressure is 20 kPa. The contact angle value of the above situation is 4.33 times as that from the untreated Poplar. Meanwhile, the water drops cannot permeate the treated Poplar wood surfaces. In this moment, the surface free energy is lowest(2.9mJ/m2). The optimum plasma parameter is 60 W power, 75 s exposure time, 20 kPa pressure, respectively. Such conclusion can be found through the analysis of surface contact angles and the free surface energy: firstly, contact angles will increases at first and then remain basically unchanged; secondly, the angles increase first and then decrease when plasma power increase; thirdly, with the increasing of the plasma reaction chamber pressure the contact angles increase and then decrease. The microstructure of the samples surface under different treatment parameters were observed by SEM and AFM. After depositing a hydrophobic layer, the microstructure of wood surface determines the contact angles and surface energy. Hydrophobic groups deposited on wood surface increased at first and then unchanged can be found through SEM-EDS, ATR-FTIR and XPS analysis when plasma modification time increased. Besides, enhancing plasma power, the surface elements will increase and decrease repeatedly, which is the because of interaction between plasma depositon and etching. Furthemore, when reaction cavity pressure increased, monomer concentration increased, which is good for the deposition of Si elements.The mechanism of HMDSO plasma treatment for wood surface is presented as follow: HMDSO is atomized in reaction chamber and re-polymerized or grafted onto wood surface. Such process could form a structure with saturated alkane outer and Si-O-Si and Si-O-C crosslinked core.Three different wood(Larch, Poplar and Oak) had been treated by hexamethyldisiloxane plasma at a best parameter and the result shown that contact angles value of different specimens were basically equal. The angles value of Larch and Oak are 136 degree and Poplar's is 130 degree. Surface element analysis of three treated wood surface shown that there are a lot of hydrophobic groups on the surface, although there were some different functionalize groups in wood surfaces before treatment.Wood specimens had been treated with plasma at three different gages(HMDSO, n-hexane and ethyl acetate). The experiment result indicate that HMDSO plasma treated wood surface have the best hydrophobicity(130 degree), next one is ethyl acetate gage(118 degree), the hydrophobicity effect of plasma with n-hexane gage is the worst(105 degree).All the specimens were treated with HMDSO plasma, some specimens were tested after put into the air for nine months, the others were tested with the specimens directly. It turned out that those specimens still have high contact angles(about 128 degree) after 9 months and composition of specimens surfaces basically not change.