Study On The Effect Of Air Plasma Treatment On GFRP Used In Wood Structures

Plasma treatment, which is known to modify chemical and physical states of the surface without altering the bulk properties, has become an important technique for the control of interfacial adhesion in composites。This paper employed a kind of atmospheric air low-temperature plasma tereament modifying two types of GFRP to alter the surface wettability, resulting in stronger bonding strength between GFRP and wood. The effect of air plasma on the GFRP surface, the change of GFRP surface wettability, the timeliness of air plasma, and the bonding strength at GFRP-wood interface had been studied.SEM, AFM, FTIR, XPS had been used to characterize the surface topography, chemical constituents and structures. SEM and AFM analysis showed that the GFRP surface became unsmooth after air plasma treatment and its roughness increaed. FTIR analysis showed that air plasma disrupted the chemical groups of the GFRP surface, such as C-H, C-C, C-O, O-C=O and benzene ring. XPS analysis showed that the oxygen content on the GFRP surface increaed, and the avtive groups of C-O, O-C=O increaed. All of these proved that air plasma exhibited etching and oxidation. But due to the lack of the on-line monitoring meas, the complicated modification mechanism of air plasma remain be further studied.Air plasma treatment improved the surface free energy of GFRP, and the ratio of polar component increased obviously, so the water contact angle decreased significantly and the surface wettability improved. Treatment time and power had little effect on the surface free energy, while, with the time prolonging or the power adding, the surface free energy increaed slowly, the water contact angle decreased thereupon. But if the time was too long or the power was too strong, the surface free energy would be decreased and the water contact angle increased. The optimal treatment time and power were 60s and 6.8D.Air plasma treatment enhancd the bonding quality at GFRP-wood interface obviously, and the shear strength increased gradually depending on the treatment time prolonging or the power adding, the maximum value occurred under the condition of 60s or 6.8D. The kind of adhesive also affected the bonding strength. Before air plasma treatment, the average shear streagth of GFRP 1-wood shear test specimens bonded with epoxy adhesive and isocyanate adhesive was 2.786MPa and 3.194MPa, the bonding quality of isocyanate adhesive was slightly better than that of epoxy adhesive; after air plasma treatment, the average shear streagth of specimens with epoxy adhesive and isocyanate adhesive enhanced 1.63～2.17 times and 2.12～2.86 times respectively, the bonding quality of isocyanate adhesive was much higher than that of epoxy adhesive, therefore isocyanate adhesive was suitable for the bonding of GFRP. The types of GFRP had influence on the shear strength too, the average shear streagth of GFRP2-wood specimens was higher 3-4MPa than that of GFRP1-wood specimens approximately.Air plasma treatment was accompanied with timeliness, the contact angle of treated GFRP would increased with the elapsing time, and the better the modification effect of treated GFRP was, the more notable the timeliness displaied. The evolution of timeliness was different corresponding with different type of GFRP. In practice, the material and plasma parameter should be chosen carefully based on the fact.