【作者】 孙少敏；

【导师】 郑强； 宋义虎； John R.Mitchell；

【作者基本信息】 浙江大学 ， 材料加工工程， 2009， 博士

【摘要】 由于合成高分子塑料的大量应用造成日益严重的白色污染，生物可降解材料的开发在国际上备受关注。小麦蛋白质来源丰富、价格低廉、可降解，在生物可降解环境友好材料的制备与应用方面有着巨大的潜在应用价值。本论文第一部分以小麦蛋白质粉为主要原料，以甘油为增塑剂，采用模压或浇铸法制备小麦蛋白质热压塑料、醇溶蛋白塑料与浇铸膜。研究了交联剂类型、模压温度以及甘油含量对热压蛋白质塑料结构与吸湿性、力学性能以及热降解性能等的影响，考察了交联剂用量和pH值对醇溶蛋白膜拉伸性能、吸湿性与透湿性的影响。第二部分采用70％（v／v）乙醇／水混合溶剂或50％（v／v）正丙醇／水混合溶剂从小麦蛋白质粉中提取醇溶蛋白，制备醇溶蛋白70％（v／v）乙醇／水溶液或50％（v／v）正丙醇／水溶液，并在适当条件下制备了醇溶蛋白凝胶。研究了醇溶蛋白溶液与凝胶的流变行为，考察了蛋白质浓度（C）、温度、pH值、金属离子浓度等对醇溶蛋白溶液与凝胶流变行为的影响。研究发现，交联剂类型、模压温度以及甘油含量显著影响蛋白质塑料的形态、玻璃化转变与力学性能。二硫键交联使体系相分离程度增大，导致蛋白质富集区玻璃化转变温度（T_g）升高。相比之下，醛类化合物交联可在一定程度上抑制相分离，降低蛋白质富集区的T_g，提高塑料的拉伸强度，同时降低杨氏模量与断裂伸长率。未添加任何交联剂时，仅将模压温度从25℃升高到125℃，可提高蛋白质网络的二硫键交联密度，导致拉伸强度和杨氏模量增高、松弛时间延长。甘油含量增高导致蛋白质富集区与甘油富集区T_g同时降低，醇溶蛋白塑料拉伸强度与杨氏模量降低，断裂伸长率增大。酸碱处理使醇溶蛋白膜的吸湿率稍有增大，但其拉伸强度显著增大。pH值显著影响醇溶蛋白溶液粘度与特征松弛时间。零剪切粘度（η₀）与力学松弛时间（τ_M）均随pH值增大而减小。在50％（v／v）正丙醇／水溶液中，醇溶蛋白溶液的动态流变行为符合杂化（Hybrid）模型，蛋白质分子受静电力作用而伸展，呈半柔性链。50℃、pH=9.3时，醇溶蛋白溶液（蛋白质浓度C=13 wt％）形成杂化程度较低的分子凝胶，凝胶时间为175 min，其平台模量（G_N）=434.4±13.7 Pa，对应有效弹性链段密度（ν_e）=（1.06±0.03）×10²³ m^-3。20 g L^-1～200 g L^-1醇溶蛋白50％（v／v）正丙醇／水溶液呈牛顿流体特性，流动活化能（E_a）为23.5～27.3 kJ mol^-1，特性粘数[η]随温度升高而增大。戊二醛、正十二硫醇与金属离子(Na⁺、K⁺、Mg²⁺、Ca²⁺)均可提高醇溶蛋白溶液粘度。在一定浓度范围内，Ca²⁺可促进C≥200 g L^-1醇溶蛋白溶液形成粒子网络凝胶。更多还原

【Abstract】 Nowadays, much more attention has been paid to white pollution caused bynonbiodegradable synthetically polymers attracting worldwide concern on biodegradablepackage films and plastics made from renewable agricultural resource. Wheat proteinsexhibit the advantage for biodegradable materials because of their low cost, abundantresources and good biodegradability.In the first part of this dissertation, thermo-molded wheat gluten plastics, gliadinplastics and solution-casting films were prepared based on glycerol-plasticized wheatproteins. The influences of crosslinking type, molding temperature and glycerol contenton morphology, moisture absorption, mechanical and thermal properties of wheat proteinplastics were studied. In addition, influences of cross-linker concentration and pH of thefilm-forming solution on tensile properties, water absorption and water vaporpermeability of gliadin films were investigated. In the second part, gliadins wereextracted using 70% （v/v） aqueous ethanol and 50% （v/v） aqueous propanol to preparegliadin solutions. Gliadin gels were prepared through heating alkaline solution of 50%（v/v） aqueous propanol at pH = 9.3 and 50℃. Ca²⁺ induced wheat gliadin gels were alsoprepared. Effects of protein concentration （C）, temperature, pH and metal ions onrheological behavior of gliadin solutions or gels were examined.Experiment results reveal that morphology, glass transition and mechanical propertiesof thermo-molded wheat protein plastics are related to crosslinking type, moldingtemperature and glycerol content. Crosslinking through disulphide bonding leads to ahigh degree of phase-separation and a high glass transition temperature T_g of thegluten-rich phase. Aldehyde-induced crosslinking reduces the degree of phase- separationand lowers T_g of the protein-rich phase, resulting in higher tensile strength and lowerYoung’s modulus and elongation at break in comparison with the disulphide crosslinking.In the absence of additional cross-linker, increasing molding temperature from 25 to 125℃significantly enhances crosslinking density of the three-dimensional proteinnetwork through disulphide bonding, leading to increase of tensile strength, Young’smodulus and relaxation time. For gliadin plastics, increasing glycerol content causesdecrease of both T_g of gliadin-rich and glycerol-rich domains, which lowers tensilestrength and Young’s modulus but improves ductility at room temperature. Gliadin filmscasting from acid or alkaline solutions exhibit higher tensile strength than that of thosefrom neutral solution. Meanwhile, acid or alkali treatment of the gliadin solutions slightlyincreases water absorption of the resulted films.pH significantly influences viscosity and characteristic relaxation times of wheatgliadin solutions. As far as gliadins in 50% （v/v） propanol/water solutions are concerned,both zero-rate viscosity and mechanical relaxation time decrease with increasing pH ofthe solution. The hybrid model is applicable to account for the dynamic data, suggestingthat gliadin macromolecules are partially flexible and are highly elongated due toelectrostatic interaction. Wheat gliadin in 50% （v/v） aqueous propanol solutions at 20 gL^-1 to 200 g L^-1 behave as Newtonian fluids with activity energy of flow E_a = 23.5～27.3kJ mol^-1. The intrinsic viscosity （[η]） tends to increase with temperature due to improvedsolvation. The plateau modulus （G_N） of the alkaline gliadin gel is 434.4±13.7 Pa,corresponding to density of elastically effective chains v_e = （1.06±0.03）×10²³ m^-3.Morphological observation of dried gliadin gel reveals a very low degree of structuralheterogeneity involving in protein aggregation during the formation of the gel networkcomposing of crosslinked strands. Additions of glutaraidehyde, n-dodecanethiol or metalion (Na⁺, K⁺, Mg²⁺ or Ca²⁺) bring increase of apparent viscosity of gliadin solutions.Additions of Ca²⁺ in gliadin solutions (C＞200 g L^-1) lead to the formation of fractalweak gels containing abundant filaments as observed by scanning probe microscopy（SPM）.更多还原