林木剩余物半纤维素薄膜的制备及性能

Efficient use of forest residues to produce energy and materials with high added value is of great significance worldwide. This is especially true for such countries as China that is short of forest resources. This project aims to the isolation of hemicelluloses from saw dust by using methods including green-liquor pretreatment. The green liquor pretreatment process with respect to hemicellulose yield and composition were optimized. ..In addition, we propose to prepare hemicellulose-based films with improved barrier properties under conditions of high humidity. To this end, films are to be prepared from solution cast of mixture of hemicellulose with addition of various plasticizers, i.e . glycol, xylitol and sorbital.The films will be subsequently subjected to surface modification via grafting of various monomers using either solvent-free vapor-phase photografting or electron beam-induced grafting. Hydrophobic modification of films is to be achieved by incorporating vernolic acid, a fatty acid with long carbon chain, onto modified surface having amino groups through an amide bond which is formed from the reaction of carboxyl of fatty acid and amino of the surface. ..Composite films will be prepared by using either spin coating or by casting mixture solution of hemicellulose and phyllosilicates in polystyrene petri dish. Water vapor transmission rate (WVTR) will be determined using an ASTM E-96 procedure. Oxygen transmission rate (OTR) will be measured on an oxygen permeation analyzer. Composite films will be transformed into dumbbell-shaped samples for measurements of mechanical properties by using an Instron universal tester. A correlation between barrier properties and structure of films is to be addressed. ..The overall and ultimate goal of the project is to develop methodologies for an efficient chemical valorization of forest residues for various applications including green food packing.

我国属于森林资源匮乏的国家，高附加值利用林木剩余物意义重大。本项目采用绿液辅助预处理等方法从林木剩余物中分离提取半纤维素，设计采用多种增塑剂研究半纤维素的成膜性；通过膜表面接枝聚合引入活性官能团，并以此为反应位点用长碳链斑鸠菊酸改性制备半纤维素基疏水性薄膜；研究模型单体丙烯酰胺、丙烯酸和马来酸酐在膜表面的接枝聚合及 XPS探针化合物在表面的键合；通过与蒙脱土等层状硅酸盐共混复合制备高阻隔性半纤维素基薄膜。通过对弹性模量、拉伸强度、断裂伸长率及氧气透过率、水蒸气透过率等的研究，阐明其力学性能和阻隔性能与结构的关系。本项目旨在提高木材的高效增值利用,为其在包装材料等多领域应用提供科学依据。

本项目面向基于生物质材料在绿色包装领域的潜在应用，以林业剩余物杨木木粉为对象，研究了半纤维素的提取、复合膜制备以及疏水改性。.采用响应面法确定了碱解醇沉法提取半纤维素的最优条件；采用物理共混改性方式构筑了半纤维素/纤维素纳米晶复合膜和半纤维素/木质素复合薄膜，研究了复合膜的力学性能、表面疏水性、氧阻隔性能和热稳定性，分析了木质素添加量对复合膜各方面性能的影响效果和机理。研究发现，半纤维素复合膜的表面疏水性随木质素含量的增加而改善，最大平均接触角可达到65.6 °，为不含木质素的原膜的161%。在力学性能方面，复合膜的拉伸强度随木质素添加量不断升高，表明了木质素对体系具有增强作用；采用醚化方式对半纤维素进行一步法化学改性，避免了传统的先提取再改性过程中二次碱解对半纤维素结构的破坏。证实了将环氧氯丙烷直接作为烷基化试剂与半纤维素进行醚化反应的可行性，阐释了反应机理。醚化改性半纤维素薄膜疏水性能、氧气阻隔性能和热稳定性能均明显提升。最优条件下复合膜的拉伸强度为14.6 MPa，表面接触角为71.7°，氧气透过系数为1.9 (cm3•µm)/(m2•d•kPa)； 采用天然无毒的柠檬酸作为酯化剂，在温和条件与半纤维素发生酯化交联反应；探究了柠檬酸添加量对疏水改性复合膜力学、疏水、氧阻隔和热稳定等性能的影响，提出了酯化交联反应机理，阐明了复合膜性能和柠檬酸添加量之间的关系。研究表明，当柠檬酸添加量达到20%时，杨木半纤维素充分酯化交联，形成致密的网状结构，获得最高的拉伸强度和最低的断裂伸长率。进一步添加柠檬酸，可以增强复合膜的韧性、氧阻隔性和表面疏水性，最大接触角达87.5 °，氧气透过系数低至1.9 (cm3•µm)/(m2•d•kPa)。改性半纤维素薄膜疏水性能显著改善，阻隔性能比典型石油基包装材料低密度聚乙烯和可再生高分子材料聚乳酸更优越，在食品包装材料领域极具应用潜力。