Study On The Anti-weathering Of Heat-treated Fir Wood(Cunninghamia Lanceolate) Based On Metal Activation

Heat treated wood is widely used in outdoor environments such as landscaping and decorative architecture because of its good dimensional stability,bio-resistance and dark colour similar to tropical wood.However,heat-treated timber is susceptible to the effects of UV light and moisture,which can lead to photodegradation of the surface of heat-treated timber.When exposed outdoors for long periods of time,the colour of heat-treated timber becomes lighter,greyer,loses its original beautiful dark colour and even causes cracking.Therefore,in-depth development of methods for light ageing resistance of heat-treated wood is important for its targeted modification and service life extension.In this study,the problem that heat-treated wood is prone to deterioration during ageing was addressed by using a high-voltage electrostatic field and metal electrode plate synergistic treatment method to deposit TiO₂and ZnO on the surface of heat-treated wood at a voltage of 60k V,a treatment time of 48 h and a pressure of 0.1 MPa to achieve the effect of UV absorption and mitigation of photodegradation.In this paper,the structural and compositional changes of the heat-treated wood after metal activation were analysed;and the heat-treated wood after metal activation was subjected to an artificial accelerated ageing test for 720h and a natural ageing test for 1 year.The main findings of this study are as follows:（1）Nano-metallic zinc and titanium particles were successfully deposited in situ on the surface of the heat-treated fir wood by a synergistic treatment method of high-voltage electrostatic field and metal electrode plate.The zinc and titanium particles were effectively distributed on the surface of the heat-treated fir,and the zinc particles were more uniformly distributed on the surface of the heat-treated fir.Under the same high voltage electrostatic field conditions,the weight ratios of the metal particles were greater than 10%,with the concentration of the zinc metal particles around 7%and the titanium metal particles around 5%.Under the same polarisation effect,the zinc metal particles have a higher activity,resulting in a higher concentration of particles compared to the titanium metal particles.At the same time,the wettability of the surface of the heat-treated cedar after metal activation is reduced.（2）The O/C ratio of the specimens after metal activation was significantly reduced.The surface chemical groups-OH,-CHO and Zn particles and titanium particles grafted and covered the surface of the heat treated fir.After metal activation,some of the Zn²⁺and Ti⁴⁺reacted with the hydroxyl groups in lignin and hemicellulose,and the main form of the bond was Zn（OH）₂and TiOH,while some of them formed ZnO and TiO₂after high pressure electrostatic oxidation,which were uniformly distributed on the surface of the heat-treated fir.After metal activation,the Zn and Ti particles in the heat-treated cedar wood were of nanoscale and crystalline level,with an average particle size of less than 30 nm.this size is suitable for the Zn particles and Ti particles to penetrate into the microstructure of the heat-treated cedar wood,reducing the possibility of their leaching.（3）In the artificial ageing test,the colour index L^*values of the heat-treated fir surface after metal activation decreased by nearly 14%compared to the control group after ageing;the colour indexes a^*and b^*increased slowly in the later stages of ageing.The metal activation effectively suppressed the reddening and yellowing of the specimen surface,and the colour differenceΔE was always less than 4 during the ageing process,which improved the colour stability.During the artificial ageing process,the static contact angle on the surface of the treated specimens was always greater than 100°,maintaining a good hydrophobicity,and their cell structure remained basically intact without obvious cracks.The lignin photodegradation of the treated specimens was effectively suppressed during the artificial ageing process,and the relative ratio of the infrared peaks(I₁₇₃₀/I₁₃₇₅)was significantly smaller than that of the control group,confirming that metal activation could enhance the photostability of lignin and improve the light ageing resistance of the heat-treated fir wood.（4）In the natural ageing test,the surface of the heat-treated fir remained dark after metal activation,and the colour indexes L^*,a^*and b^*after ageing were reduced by 20%,29%and 34%,respectively,compared with the control group,and the colour differenceΔE was always less than10%,showing better colour stability.The change in surface roughness（R_a）of the heat-treated fir was effectively mitigated after metal activation,with a rate of change of R_aof less than 10%after1 year of artificial ageing.The cell structure on the surface of the specimens remained largely intact with no obvious cracks,but a reduction in cell wall thickness could be observed.The lignin degradation rate I₁₇₃₀/I₁₃₇₅of heat-treated fir after metal activation was still smaller than that of the control group.The results indicate that cellulose,hemicellulose and lignin are all photodegraded to some extent during natural ageing,but metal activation can effectively inhibit the photodegradation of lignin.（5）After metal activation,the leaching rates of surface metal oxides ZnO and TiO₂increased by 5%and 3%respectively after the artificial ageing test compared to those before ageing,and decreased by 35%and 40%respectively after the natural ageing test compared to those before ageing.The metal activation improved the adhesion and loss resistance of ZnO and TiO₂,which provided for the improvement of the light ageing resistance of the heat treated fir wood.