Effect Of Wood Cell Wall Modified By Organic Compound On Its Decay Resistance

Wood is a kind of renewable,natural and environmental friendly building material which is easy to be decayed by wood rot fungi.Wood treated with preservatives usually has an impact on the environment.In recent years,people’s awareness of environmental protection has been gradually strengthened,and many wood preservatives which have impacts on the environment have been banned by the country.Plant preservatives such as salicylic acid and quercetin have good anti-fungal properties,but they could not combine with wood effectively and have poor leaching resistance.The salicylic acid/silica microcapsule（SSM）treated wood,salicylic acid grafted wood and quercetin grafted wood were prepared.The release rules of salicylic acid and quercetin were investigated by loss test.The properties of the three treated wood were evaluated from the aspects of microstructure,chemical composition,decay resistance,bending strength and elastic Modulus.In order to evaluate the potential of microencapsulation and chemical grafting for the fixation of salicylic acid and quercetin in wood,this study provided a theoretical basis for other chemical structure preservatives of plant origin.The main results were as follows:（1）Using salicylic acid as the core material and silica as the wall material,salicylic acid/silica microcapsules（SSM）were successfully prepared by sol-gel method.The size of SSM prepared was between 0.06μm and 0.16μm.The SSM treated wood have leaching resistance,and there were the characteristic peaks of Si-O-Si and Si-OH in FT-IR of SSM treated wood before and after leaching.The flexural strength of SSM was increased slightly,but the elastic modulus remained basically unchanged.The MOE and MOR of SSM were9185.12 MPa and 133.08 MPa,respectively（the untreated wood were 9162.57 MPa and121.24 MPa,respectively）.In addition,the SSM treated wood had decay resistance,and the weight loss rates of the departed SSM treated wood after decay by white and brown rot fungi are 15.87%and 14.42%,respectively（the untreated wood were 62.82%and 42.50%,respectively）.（2）Using salicylic acid and wood as raw materials,salicylic acid grafted wood was prepared through esterification reaction.The reaction yield of 1.5 mol/L salicylic acid with wood cell wall reached the maximum,and the C=O peak at 1635cm^-1 reached the maximum under this condition in FT-IR spectrogram.The elasticity of the grafted wood with salicylic acid was increased,but the mechanical property of the wood was decreased greatly due to the decomposition of its components.The MOE and MOR of the grafted wood with 1 mol/L salicylic acid reached the maximum values,which were 6580.38 MPa and 40.16 MPa,respectively（the untreated wood were 6491.31 MPa and 87.00 MPa,respectively）.The grafted wood with different concentrations of salicylic acid showed decay resistance,and the weight loss rates of the grafted materials with white rot fungi and brown rot fungi were less than 15%（the weight loss rates of the untreated wood were 50.71%and 27.86%,respectively）.（3）Using quercetin,oxalic acid and wood as raw materials,the grafted wood of quercetin was prepared by esterification.Quercetin was successfully grafted onto wood by oxalic acid,and ester groups were formed between quercetin and oxalic acid,and between oxalic acid and wood.The characteristic peaks of C=O appeared at 1620 cm^-1 and 1768cm^-1 in FTIR under different chemical environments.When the ratio of quercetin and oxalid was 1:2,the number of ester groups was the highest and the yield was the highest.With the increase of oxalic acid content,the cell wall thickness was firstly increased and then decreased.The grafting of quercetin made the wood cell wall thickened,and the high oxalic acid concentration would decompose the wood components,which made the wood cell wall thinner.The maximum value of the cell wall was 2.25μm（the wood was 1.65μm）when the quercetin and oxalid ratio was 1:2.The elasticity of the grafted wood was increased,but the mechanical strength was decreased.When the quercetin and oxalic ratio was 1:1,the MOE reached the maximum of 10238.91 MPa（the untreated wood was9162.56 MPa）,and the MOR reached the maximum of 57.05 MPa（the untreated wood was121.24 MPa）when the quercetin and oxalic ratio was 1:2.The grafted quercetin wood prepared by different quercetin and oxalic ratios had decay resistance,and the weight loss rate of the grafted wood treated with white rot fungi decayed quercetin was lower than 15%（the untreated wood was 42.84%,and the quercetin impregnation wood was 48.42%）.（4）Salicylic acid and quercetin,which were two preservatives of plant origin,could be immobilized in wood by microencapsulation and chemical grafting.When using microcapsules to impregnate wood,the treatment conditions are mild,which could improve the leaching resistance of preservatives and mechanical strength,wood decay resistance,but the microcapsule emulsion was difficult to store at room temperature,which was easy to solidify.When chemical grafting was used to modify wood,the process was simple,the leaching resistance of preservatives and the decay resistance of wood could be improved,but the mechanical strength of wood was decreased.