Study On The Effects Of Adhesive Properties Of Larch Treated By Atmospheric Plasma Jet/ASD Flame Retardant

In order to manufacture structural glulam made of larch with good flame retardant property and bonding performance, ASD flame retardant was added into larch by using the method of vacuum pressure. The results show that the THR and TSP of larch significantly decreases after adding ASD flame retardant, the flame retardant performance improves with the increase of ASD flame retardant mass fraction. Considering the comprehensive effect and cost of the flame retardant, the best mass fraction of ASD flame retardant is 50%. The initial decomposition temperature of larch is advanced by ASD flame retardant treatment, the residual carbon rate increased from 18.26% to 41.06%. The effect of ASD flame retardant is mainly attributed to the catalytic effect of char forming. Compared with untreated larch, the flexural strength and flexural modulus of larch treated with ASD flame retardant decreased slightly, the largest decline is about 5%. The compressive strength of the grain improved slightly, the maximum increase is 4.5%.The contact angles of water and diiodomethane of larch treated with ASD flame retardant became larger obviously, the free energy and wettability of larch surface decreased significantly, the compressive shear strength measured with the aqueous polymer isocyanate adhesive (API) decreased by 43.65%. Cold atmospheric plasma jets were used in order to solve the problem of poor adhesion performance of larch after ASD flame retardant treatment. The surface contact angle of larch treated by cold atmospheric plasma jets decreases significantly, the free energy and wettability of larch surface increased significantly. The treatment effect is related to the height of treatment and the treatment time. With the prolonging of treatment time, the overall change of surface contact angle of larch decreased rapidly at the beginning, and then the decline slowed down and finally tended to be stable. Under the premise that the jet is not burned directly to the surface of wood, the treatment effect increased with the decrease of the height of treatment, this is due to the reduction of the processing height lead to the increase the of the strength of the treatment effect. According to the jet length of jet plasma and comprehensive consideration of the effect and cost of treatment, in terms of a sample whose processing section is 30mm×25mm, the optimal processing condition of cold atmospheric plasma jet are:nitrogen gas processing time of 20s and processing height of 15mm; oxygen gas processing time of 20s and processing height of 25mm; air processing time of 20s and processing height of 15mm; argon processing time of 20s and processing height of 10mm.The results of SEM shows that compared with untreated wood, the surface of larch has obvious etching trace and the surface roughness increases after the plasma treatment. The results of FTIR and XPS show that the relative peak area of C1 in the surface of larch decreases after plasma treatment, the relative peak area of C2 and C3 increases and C4 appears. The quantity ratio of oxygen to carbon atoms increases obviously which indicates the increase of oxygen functional groups on the surface of larch. Oxygen-related functional groups that strengthen the hydrophilia of larch surface increases, which is conducive to the enhancement of the wettability of larch surface. Compared with untreated larch, the bonding performance of larch increases significantly after plasma treatment, increase from large to small is as follows: oxygen gas 120.81%; nitrogen gas 43.40%; air 39.09%; argon 28.93%. The adhesion properties of larch treated by ASD flame retardant improves obviously after plasma treatment, the maximum rate of increase is 45.18%(oxygen), which is consistent with the jet effect of plasma treatment on the wettability of larch.The surface free energy which is modified by four kinds of plasma gas including nitrogen, oxygen, argon and air decreases gradually with the passage of time. Compared with larch without flame retardant treatment, the ageing effect of ASD flame retardant larch treated by jet plasma weakens, treatment effect is more remarkable. In order to obtain the best modification effect, wood treated by plasma should be glued in a timely manner in the actual production.