Study On Wood And Fiber Characteristics And Comprehensive Utilization Of Taxodium ‘Zhongshanshan’

Taxodium.’Zhongshanshan’is a hybrid cultivar with stress resistance,rapid growth and high reproduction efficiency,which is bred by artificial hybridization of Taxodium distichum,Taxodium mucronatum or Taxodium ascendens Brongn.At present,T.’Zhongshanshan’is mainly used as ornamental material for greening,and has not been industrialized.In this study,the chemical composition,wood and fiber properties of the trunk and branch wood of T.’Zhongshanshan’were analyzed comprehensively,and explore the feasibility of the pulping and papermaking by kraft and chemica-mechanical processes of T.’Zhongshanshan’.In addition,the effect of biotransformation to fermentable monosaccharide from the pretreated branches of T.’Zhongshanshan’was evaluated.The main research contents and results are as follows:1.The chemical composition,wood and fiber properties of T.’Zhongshanshan’were analyzed.The results showed that the basic density of the hybrid cultivar ranged from 0.24 to0.33 g/cm³,which was slightly lower than that of T.mucronatum（0.33 g/cm³）and T.distichum（0.34 g/cm³）.The arithhmetic average and weighted length of hybrid cultivar fiber were1.09～1.31 mm and 1.52～1.73 mm,respectively,which were between T.mucronatum and T.distichum.The fiber length-width ratio is similar to that of T.mucronatum,but lower than that of T.distichum.The total polysaccharide content of the hybrid was similar to that of the parents,accounting for about 60%of the dry weight of the wood.The lignin content was about31.0%～33.2%of the dry weight of wood,which was slightly lower than that of the parents.The ash content of both the hybrid cultivar and Taxodium were less than 1%,but the ash content of hybrid cultivar was significantly higher than that of the parents.Typical coniferous tracheids could be seen on the cross section of hybrid and backcross breeding samples.The parenchyma cells were scattered and a large number of traumatic resin canals could be seen at the junction of early and late wood.The tangential section presented an uniserial wood ray,consisting of 2-22 cells.2.The pulping properties of T.’Zhongshanshan’by KP and APMP were evaluated.The process conditions of kraft pulping were as follows:18%alkali（calculated as Na₂O）,25%sulfidity,liquid ratio 1:4,maximum temperature 170℃,holding time 2 h.When the cooking yield is 44%～46%,the kappa number of T.Zhongshanshan pulp is about 38,which is lower than that of T.distichum（43.3）and T.mucronatum（45.6）.The pulp was subjected to oxygen delignification.The process conditions were pulp concentration 10%,temperature 100℃,60min,NaOH 2.5%,MgSO₄0.1%,and oxygen pressure 0.7 MPa,the delignification rate of lignin was about 64%.The oxygen delignification pulp is bleached by DED,when the beating degree is about 13°SR,the brightness can reach 75%～78%ISO,the tensile index is 17.04～21.26N·m·g^-1,and the tearing index is 11.16～14.17 mN·m²·g^-1.3.Under the condition that the amount of NaOH is 6%and the amount of H₂O₂is 6%,the APMP pulps with different physical strength can be obtained by changing different pretreatment,grinding and bleaching processes.When the freeness of T.’Zhongshanshan’is320～570 mL,the yield is 87.90%～88.47%,the brightness is about 60%ISO,the tensile index is 22.03～27.04 N·m·g^-1,the maximum burst index is 1.51 k Pa·m²·g^-1,and the post colour value is about 1.4.The chemical composition,wood and fiber properties of the branches of Taxodium and16 species of T.‘Zhongshanshan’were analyzed.The results showed that,the content of benzyl alcohol extract of branches was lower than that of trunks.The lignin content of the branches of T.‘Zhongshanshan’ranged from 31.0%to 35.7%,which was close to or slightly higher than that of the trunks.The lignin content of the branches of T.‘Zhongshanshan’was lower than that of the trunks when the trees were about 10 years old.The ash content of branches ranged from0.37%to 0.76%,which was slightly lower than that of trunks.The fiber length of branches is larger than that of trunks,but the fiber width is smaller than that of trunks.5.Dilute acid pretreatment,green liquid pretreatment and green liquid combined with oxygen delignification pretreatment were carried out for the branches of two T.Zhongshanshan respectively,and then cellulase hydrolysis was carried out to evaluate the conversion efficiency of glycan to fermentable monosaccharide in these branches.The results showed that the samples pretreated by green liquid combined with oxygen delignification were enzymatically hydrolyzed for 48 hours at the enzyme dosages of 5 FPU/g and 10 FPU/g,and the total sugar conversion and extraction rates reached the highest 51.5%and 37.8%.