Wood Modification By Heat Treatment With Metal Bath And Silicone Oil

The present scarcity of wood species has necessitated research into thermal modification of wood as an alternative method which can modify the properties of wood for a broad application.Thermal modification of wood is achieved by exposing wood to high temperatures ranging between 160 and 230? under controlled conditions.This leads to several modifications that occurred in the wood properties,including reduction in equilibrium moisture,increased natural durability and improved dimensional stability.Over the years,several thermal treatment processes have been developed based on different technologies and treatment media.Treatment temperature and exposure time are two most crucial factors which determine the modification level of treated wood.In this research,two treatments media-silicone oil and tin-based alloy were used for the thermal treatment of some selected wood species.Specifically,the study explored the effects of silicone oil heat treatment(SOHT)and metal bath heat treatment(MBHT)on Chinese fir(Cunninghamia lanceolata L.),Chinese parasol(Firmiana simplex L.)and Chinese pine(Pinus massoniana L.)woods exposed to different treatment temperatures and times.Wood samples were pre-treated in a micro-wave at 150? for 5 minutes before the actual SOHT/MBHT at 150 ?,180? and 210? for2h,4hand8h.The results showed significant effects of SOHT on the physical and chemical properties of Chinese fir and Chinese parasol woods.(1)The shrinkage characteristic of silicone oil treated Chinese fir wood decreased significantly,where the shrinkage values in the tangential,radial and longitudinal directions were 4.34%,2.97%and 0.31%,respectively when treated at 210? for 8 h.(2)The colour of the silicone oil treated wood was darker compared to the untreated wood and the total colour difference(?E*)increased from 21.89 when treated at 150? for 2 h to 61.81 at 210? for 8 h.This is an indication that values have been added to the treated wood.(3)The anti-swelling efficiency(ASE)of thermally treated wood increased from 29.61%to 58.68%in the tangential,12.29%to 49.38%in radial and 21.89%to 61.81%in longitudinal ASE.The ASE results indicated that the dimensional stability of silicone oil treated wood increased with the increase of heat treatment temperature and exposure time.(4)The density of the silicone oil treated wood increased significantly up to 75%(0.98 g/cm3)when treated at 150? for 8 h,followed by gradual decrease to 8%(0.61 g/cm3)at 210? for 8 h.In general the density of the treated wood was higher compared to the untreated wood.(5)The chemical composition of silicone oil treated wood were modified particularly when treated at 210? for 8 h.The extractive and lignin contents of Chinese fir increased to 4.72%and 50.54%respectively,while ashes,cellulose,hemicelluloses and holocellulose contents decreased to 9.02%,35.66%,4.99%and 40.65%respectively when treated at 210? for 8 h compared to the untreated wood.The same trends were observed in the chemical composition of Chinese parasol after SOHT.(6)Changes were observed in the fourier transform infrared(FTIR)spectra of silicone oil treated wood which suggests changes in the wood chemical constituents,mainly due to the degradation of biopolymer components of the wood which might be the cause of wood modification.(7)Thermogravimetric analysis(TGA)showed that silicone oil treated wood presented relatively high thermal stability as the mass loss reduction of the untreated wood was significantly higher.The observed thermal stability of the treated wood is attributed to the resistance of lignin to heat.(8)X-ray diffraction(XRD)showed that crystal structure of the silicone oil treated wood increased.Significant high crystalline index(CI)of 63.78%was achieved at higher heat treatment temperature compared to 38.83%for the untreated wood.Similarly,significant effects of MBHT on the biological,physical and mechanical properties of Chinese fir,Chinese parasol and Chinese pine woods were also observed.(1)The decay resistance of metal bath treated wood increased with the level of modification as regards to the treatment temperature.Low mass losses of 7.32%and 7.32%were achieved for treated F.simplex and 3.89%and 3.57%for C.lanceolata heat treated at 210? for 8 h against Coriolus versicolor and Poria placenta.(2)The ASE of F.simplex(66.20%)and C.lanceolata(69.16%)show that MBHT has contributed to improved dimensional stability of both wood species after thermal treatment at 210? for 8 h.(3)The scanning electron micrograph(SEM)showed that metal bath treated F.simplex and C.lanceolata presented strong resistance against fungal attacks.The cell walls of the treated wood were intact and there was no distinct damage to the cell walls structure.(4)The strength properties of metal bath treated Chinese pine wood declined at different treatment temperatures and exposure time.The bending strength of 87.61 MPa,modulus of elasticity(MOE)of 11299.01 MPa and impact bending of 1.48 MPa were obtained for the treated wood at 210? for 8 h,which were significantly low compared to untreated wood,suggesting that MBHT had remarkable effect on the wood properties.(5)The contact angle of metal bath treated Chinese pine wood increased significantly when treated at 210? for 8 h,with mean contact angle of 130.50° obtained compared to the untreated wood with mean contact angle of 63.51°.(6)The colour of Chinese pine wood showed great difference between the metal bath treated wood with ?E*of 35.31 at 210? for 8 h and darker colour was achieved with the increase of thermal treatments temperature.