Study On The Properties Of Taxodium Hybrid ‘Zhongshanshan’ Wood Modified By Combining Impregnation And Heat Treatment

Taxodium hybrid ’Zhongshanshan’ is an excellent clone bred tree from Taxodium,with excellent characteristics of water and moisture resistance,drought resistance,wind resistance,salt and alkali resistance and early rapid growth.After decades of hybridization breeding,seedling promotion and afforestation production,it has accumulated a solid material foundation for its industrial utilization.However,Taxodium hybrid ’Zhongshanshan’ wood has the characteristics of low density,light color and poor low stability.In order to improve the added value of Taxodium hybrid ‘Zhongshanshan’ wood products,this study took Taxodium hybrid‘Zhongshanshan’ wood as the research object and studied the physical,mechanical and chemical properties of Taxodium hybrid ‘Zhongshanshan’ wood before and after treatment by high-temperature heat treatment and impregnation treatment.The aim is to achieve high quality of wood and provide reference for the modification of Taxodium hybrid ‘Zhongshanshan’ wood.The main conclusions of the study are as follows:(1)The effects of high temperature heat treatment on the properties of Taxodium hybrid ‘Zhongshanshan’ wood are as follows:The weight loss rate of Taxodium hybrid ‘Zhongshanshan’ wood raised with the increase of heat treatment temperature.The weight loss rate of Taxodium hybrid ‘Zhongshanshan’ wood was3.06%,3.622% and 5.185% at 175℃-4h,195℃-4h and 215℃-4h,respectively.The weight loss rate of wood raised with the extension of heat treatment time.When the treatment conditions were 215℃-1h,215℃-2h and 215℃-4h,the weight loss rate was 3.903%,4.14% and 5.185%,respectively.This is because the relative contents of hemicellulose and cellulose degraded significantly with the raised of temperature.When the temperature reaches 215℃,the relative contents of hemicellulose and cellulose decrease to 6.625% and 39.248% respectively,which are nearly 65% and 11.47% lower than those of untreated wood.With the raised of treatment temperature and treatment time,the wood color changed from light yellow to dark brown.The lightness L~* decreases gradually,the red-green index a~* raised gradually as a whole,and the yellow-blue index b ~* shows a downward trend as a whole,that is,the wood color of Taxodium hybrid ‘Zhongshanshan’ gradually changes in the direction of red and yellow.The MOR and MOE of Taxodium hybrid ‘Zhongshanshan’ wood decreased with the increase of treatment temperature and time.When treated at 175℃-4h,195℃-4h and 215℃-4h,the MOR of wood decreased by 4.89%,9.42% and 27.61%,respectively.The MOE decreased by12.76%,18.18% and 31.45%,respectively.When treated at 215℃-1h,215℃-2h and 215℃-4h,the MOR of wood decreased by 18.47%,24.88% and 27.74%,respectively.The MOE decreased by 20.03%,27.24% and 31.45%,respectively.(2)Effects of impregnation-high temperature modification and high temperature-impregnation modification on wood properties of Taxodium hybrid‘Zhongshanshan’.After high temperature heat treatment,the WPG of resin impregnation was higher than that of impregnated wood,and with the increase of high temperature heat treatment temperature,the WPG of high temperature-impregnated wood(wet weight gain rate and dry weight gain rate)showed an upward trend.The wet weight gain rate of impregnated material was 155.88% and the dry weight gain rate was 42.02%.The maximum wet weight gain rate of high temperature-impregnated material is 277.16%,and the maximum dry weight gain rate is 52.31%.The wet swelling resistance of impregnated material is 17.88%,and that of high temperature heat treatment material is 45.09%.After the combination of impregnation and heat treatment,the wet swelling resistance of impregnation-high temperature material and high temperature-impregnated material is significantly increased,in which the maximum wet swelling resistance of impregnation-high temperature material is 52.09%,and the maximum wet swelling resistance of high temperature-impregnated material is 56.15%.The MOR of impregnated material is increased by 58.81% and 119.48% compared with that of untreated material and 215℃-4h heat treated material,respectively,while the MOR of impregnation-high temperature material is lower than that of high-temperature impregnated material.When the temperature is 215℃,the MOR of high-temperature impregnated material is57.91% higher than that of impregnated high-temperature material.Similar to the MOR,the MOE of the wood modified by heat treatment is 17.63% larger than that of the wood impregnated before.After 3 months of erosion by brown rot bacteria,the wood of Taxodium hybrid‘Zhongshanshan’ showed different corrosion resistance,among which,high temperature heat treated wood(215℃-4h),impregnated wood,impregnation-high temperature wood and high temperature impregnated wood all reached the strong corrosion resistance grade.(3)Influence mechanism of impregnation-high temperature modification and high temperature-impregnation modification on wood properties of Taxodium hybrid‘Zhongshanshan’:Before treatment,the tracheary wall of Taxodium hybrid ‘Zhongshanshan’ is smooth without resin filling.After impregnation,the cell cavities of the tracheids of the first impregnated wood and the first heat treated wood have been filled with resin,which is evenly distributed and closely combined with the inner wall of the wood cell cavity without obvious gaps.It can be clearly seen from the chord section that the resin on the chord section of the modified material is uniformly filled in the interior of the tracheid cavity,which helps to improve its macroscopic mechanical properties and dimensional stability.The equilibrium water content of high-temperature impregnated materials is lower than that of impregnated high-temperature materials,and the single-layer and multi-layer molecular adsorption water of high-temperature impregnated materials are lower than that of impregnated high-temperature materials.When the temperature is215℃,the contents of hydrated water and dissolved water of impregnated high-temperature materials are 2.72% and 10.15 %,respectively.The contents of hydrated water and dissolved water of high-temperature impregnate d materials are 2.64%and 8.32%,respectively.With the increase of heat treatment temperature or the extension of heat treatment time,the decomposition of hemicellulose leads to a gradual decrease in the absorption peak intensity of hydrophilic hydroxyl and carboxyl groups of materials,and the full solidification of impregnation-high-temperature material leads to a lower characteristic peak intensity of hydroxyl groups of impregnation-high-temperature material than that of high-temperature impregnation-high-temperature material.The higher resin weight gain rate of high-temperature impregnated materials results in stronger hydroxyl characteristic peaks of high-temperature impregnated materials and stronger skeleton characteristic peaks of phenolic resin benzene ring than that o f impregnated high-temperature materials.