‘72杨’韧皮部的构造与理化性能

将‘72杨’、杉木和毛竹的木质部进行对比试验,观察并测试‘72杨’韧皮部的解剖构造以及理化特性,为其高值化利用提供基础数据。使用场发射环境扫描电镜、X射线衍射仪、傅里叶变换红外光谱仪等设备和NREL标准对‘72杨’韧皮部的微观结构、结晶度、化学成分等物化性质进行测定与分析。研究结果表明,‘72杨’韧皮部中韧皮薄壁细胞和筛管分子占细胞总面积的(81.9±1.8)%,结构相对简单。‘72杨’韧皮部气干密度为0.358 g/cm3,绝干密度为0.321 g/cm3;而木质部的相应密度较高,分别为0.497和0.482 g/cm3;‘72杨’韧皮部结晶度仅为19.4%,比木质部低8.7%。‘72杨’韧皮部纤维素、半纤维素、木质素的含量分别为28.7%,11.1%,24.1%,均低于木质部中相应成分的含量,且木质化程度低,半纤维素以木糖为主。此外,由红外谱图发现‘72杨’韧皮部含有单宁、酚类、胼胝质等物质。‘72杨’韧皮部具有低密多孔、结构疏松、结晶度低、木质素含量低、抽提物含量高等特点。因此,‘72杨’韧皮部特别有利于机械(能耗低)或化学(抗降解屏障低)降解以及物化改性(多孔、可及性强),可提取酚类、单宁、胼胝质等物质用于工业应用,研究结果可为‘72杨’韧皮部的高值化利用提供重要的理论依据。

Structure and physicochemical property of‘72 poplar’phloem

Only a small amount of the bark produced in the course of forest harvesting,transportation,storage,wood processing and chemical processing of forest products has been effectively utilized.Most of the bark was directly dis?carded or burned as fuel,causing huge wastes and environmental pollution.Scientists have begun to explore the use of bark,but there were limited research data on its physical structure and chemical composition.The disadvantages of low production efficiency and high cost were found in the utilization of bark.Therefore,the physical and chemical structure of bark needs to be further studied.In this study,the physical structure and chemical composition of‘72 poplar’phloem were studied to provide theoretical basis for achieving the high?value,high?efficiency and low?cost u?tilization of poplar.The anatomic structure,physical and chemical structure of the‘72 poplar’(Populus euramericana cv.‘San Martina I?72/58’)phloem with the xylem of‘72 poplar’,Chinese fir(Cunninghamia lancelata),and moso bamboo(Phyllostachys edulis)were compared in order to provide basic data and services for high?value applications.The field emission environment scanning electron microscope,X?ray diffractometer,Fourier transform infrared spectrometer and other pieces of equipment were used to measure and analyze the microstructure,crystallinity,physical and chemical properties of the‘72 poplar’phloem based on the National Renewable Energy Laboratory(NREL)standards.It was found that the‘72 poplar’phloem was mainly composed of phloem parenchy?ma cells and sieve tube molecules that accounted for(81.9±1.8)%of the total cell area.The structure was relatively simple.The air?dry density of the‘72 poplar’phloem was 0.358 g/cm3,and the oven?dry density was 0.321 g/cm3,while the air?dry density and oven?dry density of xylem were higher,which were 0.497 g/cm3 and 0.482 g/cm3,re?spectively.The crystallinity of the phloem of the‘72 poplar’was only 19.4%,which was 8.7%lower than that of the xylem.The content of cellulose,hemicellulose and lignin in the phloem of the‘72 poplar’were 28.7%,11.1%and 24.1%,respectively,which were lower than the content of the corresponding components in the xylem,and the degree of lignification was low.In addition,xylose was the main component of the hemicelluloses,and other monosac?charides were few.Through the FT?IR detection spectrum analysis,it was found that the phloem of‘72 poplar’con?tained tannin,phenols,callose and other contents.The‘72 poplar’phloem had the characteristics of low density and porosity,loose structure,low crystallinity,low lignin content and high extract content,which was particularly benefi?cial for the mechanical(low energy consumption)or chemical(low anti?degradation barrier)degradation,physico?chemical modification(porous and highly accessible),extraction of phenols,tannins,callose and other substances for industrial applications.The results of this study could provide an important theoretical basis for the high?value utili?zation of the‘72 poplar’phloem.