【作者】 陈谱；

【导师】 张俐娜；

【作者基本信息】 武汉大学 ， 高分子化学与物理， 2006， 博士

【摘要】 石油价格上涨以及非降解塑料造成的环境污染日益严重,直接威胁人类的生存、健康与可持续发展。因此,可再生植物资源将成为21世纪重要化工原料,并已列为高分子科学和材料科学的前沿领域之一。大豆蛋白质是大豆榨油后的副产物,其来源广泛且产量丰富。近二十年,“工业大豆蛋白质塑料”的研究和开发已经成为材料领域中的新兴课题。然而,蛋白质材料的聚集态结构尚不清楚,而且其耐水性较差,从而限制了它的研究、开发及应用。本论文主要从高分子物理的角度研究甘油增塑大豆分离蛋白(SPI)塑料的玻璃化转变行为、微区结构及其相互作用。同时,为了提高其力学性能和耐水性,通过溶液插层、原位生成以及溶液共混等方法制备出SPI/蒙脱土(MMT)、SPI/氧化铝水合物(AlOH)和SPI/羟丙基木质素(HPL)等蛋白质纳米复合物,并研究它们的结构与性能的关系。本论文的主要创新之处包括:(1)首次提出甘油增塑的SPI塑料存在两个玻璃化转变温度,分别归属于材料的富甘油微区和富蛋白质微区;(2)弄清了大气中水份引起的SPI增塑发生在富甘油微区,导致蛋白质-水微区的出现以及材料性能的显著改变;(3)揭示蛋白质分子在富蛋白微区和富甘油微区分别为紧缩盘状和疏松链状构象; (4)用SPI与MMT成功制备出高度剥离的纳米复合材料,其力学性能和热性能显著提高;(5)建立水介质中原位合成SPI /AlOH纳米复合物的新方法;(6)成功制备出性能优良的耐水性SPI塑料,通过反应挤出和模压成型用SPI与ε-己内酯(CL)、甘油发生接枝和交联反应。本论文主要研究内容和结论包括以下几个部分。首先,我们制备出一系列不同甘油含量的SPI塑料。示差扫描量热分析(DSC)结果指出,甘油增塑的SPI塑料存在两个玻璃化转变温度(Tg1和Tg2)。当甘油含量在25 ~ 50 wt%范围内时,位于-28.5 ~ -65.2 oC的Tg1和44 oC左右的Tg2同时存在,分别归属于试片中富甘油微区和富蛋白微区的玻璃化转变。由耐压密封盘示差扫描量热分析(DSC)和傅立叶变换红外光谱(TGA-FTIR)的联用测量结果证明,普通DSC曲线上100 ~ 120 oC范围内的吸热峰主要是试片中残留水份和甘油的挥发引起的,并不是蛋白质的变性。当甘油含量高于25 wt%时,小角X-射线散射(SAXS)测得的富蛋白微区的旋转半径(Rg)大约在60 nm左右,表明富蛋白微区是由紧缩蛋白质链构成的无定形结构。这些实验结果表明,SPI中存在与甘油亲和性差异较大的两类蛋白质,从而导致两个玻璃化转变以及富甘油和富蛋白微区的出现。普通铝盘和密封盘DSC的实验结果证明,在较高的相对湿度(RH)环境下,甘油增塑的SPI塑料试片中存在三个不同的玻璃化转变温度(Tg1、Tg2和Tg3),分别位于-12.7 ~ -83.8 oC、65.8 ~ 53.1 oC和3.7 ~ 1.5 oC的范围内。它们依次对应于富甘油微区、富蛋白微区和蛋白质?水微区。同时,蛋白质?水微区的Tg3在RH值大于35%时出现。空气中的水份主要分布在蛋白质链结构疏松且甘油含量高的富甘油微区。Tg2和Tg3值随着RH值上升而缓慢下降,而且表观Rg值基本稳定,由此表明富蛋白微区和蛋白质?水微区是相对稳定的紧缩蛋白质聚集体结构。动态力学热分析(DMTA)、TGA-FTIR和拉伸测试的结果进一步证实甘油增塑的大豆蛋白质对空气中的水份非常敏感,蛋白质材料吸水后导致Tg1急剧下降和Tg3的出现以及材料热稳定性和力学性能显著改变。我们通过DSC、原子力显微镜(AFM)、透射电子显微镜(TEM)和13C固体核磁共振(13C NMR)系统地研究了甘油增塑SPI塑料中的微区结构和相互作用。实验的结果表明SPI /甘油体系中确实存在两个玻璃化转变温度。它们位于1.5 ~ -47.6 oC和70 oC左右,分别归属于富甘油微区和富蛋白微区。富蛋白微区是紧缩的盘状蛋白质聚集体,而富甘油微区则是疏松的链状结构。随着蛋白质塑料中甘油含量的提高,富甘油微区中的蛋白质分子被迅速地稀释,分子间空隙明显增大。13C NMR的结果表明甘油与蛋白质之间存在强烈的氢键,并且这种键合作用受蛋白质链上氨基酸残基的影响很大。含非极性侧基的蛋白质链段与甘油相容性较差,从而形成富蛋白微区,它保持紧缩的结构。换而言之,富蛋白微区主要由具有较长烷烃侧基或芳环侧基的氨基酸构成,而带极性基团或较短非极性侧基的蛋白质链段则组成富甘油微区。用SPI和MMT通过中性水介质中的溶液插层方法成功制备了具有高度剥离结构或插层结构的可生物降解性纳米复合塑料。TEM结果指出,当MMT含量低于12 wt%时,MMT被剥离成厚度约为1 ~ 2 nm的独立片层;当MMT含量高于12 wt%时,插层结构在SPI/MMT复合物中占主导地位。表面静电势计算的结果表明,大豆蛋白质分子表面正电荷分布的不均匀性引起带负电的蛋白质分子对同样带负电的MMT的插层和剥离作用。基于ζ-电势分析和FTIR的结果表明,SPI /MMT体系中至少存在两种相互作用力,即蛋白质分子表面上正电荷富集区与带负电MMT片层间的静电吸引以及–NH和Si–O基团间的氢键相互作用,它们导致SPI对MMT的插层和剥离。由于MMT片层高度无序的分散及其对蛋白质链段的有效限制,使该SPI纳米复合材料的力学强度和热稳定性明显提高。通过水介质中AlCl3和NH3?H2O原位反应的方法成功制备出SPI/AlOH纳米复合物。FTIR实验结果表明蛋白质肽键与氧化铝水合物之间存在氢键相互作用。它对促进AlOH和SPI之间的高亲和性以及AlOH的均匀分布有重要作用。纳米复合物的结构和性能依赖于AlCl3的加入量。TEM以及力学性能表征的结果证明AlOH形成局部网络状分布,致使AlCl3加入量为8 wt%的SA-8试片显示出较高的透光性,良好的力学性能以及耐水性。当AlCl3加入量低于8 wt%时,AlOH纳米颗粒均匀的分散在大豆蛋白质基质中,其直径为10 ~ 50 nm。然而,当AlCl3加入量高于8 wt%时,体系出现明显的相分离。此外,玻璃化转变温度和α-力学松弛温度升高证明SPI与纳米颗粒间有很强的界面粘力,它有效地限制了蛋白质分子的链段运动。由此,提高了材料的拉伸强度和模量,降低材料在高相对湿度环境中的吸湿性。值得注意的是,SPI/AlOH复合物仍然保持良好的生物降解性。我们以GA为增容剂,利用溶液共混的方法,将纳米尺度的羟丙基木质素(HPL)分散到SPI中,以提高材料的力学性能。在所有试片中,添加3.3 wt% GA以及6 wt%HPL的H-6具有最好的力学性能。FTIR和X-射线衍射(XRD)的结果表明SPI/HPL复合物是无规交联网络结构,包括HPL与SPI之间的物理交联以及由GA引起的化学交联。TEM照片指出,由于GA的增容作用使HPL颗粒的直径稳定在大约为50 nm。该蛋白质塑料试片横截面的结构分析证明SPI/HPL复合物中存在较强的界面粘力。当HPL含量从0 wt%提高到6 wt%时,HPL纳米颗粒对网络结构的限制作用使试片的Tg从62.5 oC提高到70.4 oC。在这里,物理交联和化学交联网络的共同存在对SPI塑料的力学性能和热性能的提高起重要作用。通过反应挤出和模压成型的方法成功制备出CL/甘油二元增塑剂增塑的SPI塑料。FTIR和SEM结果说明CL在高温高剪切力挤出和成型过程中可以与SPI和甘油发生交联和接枝反应,导致各组分间有较好的相容性。当CL含量较低时(< 25 wt%),CL主要分布在富甘油微区中,与甘油发生交联反应;而当它含量较高时(> 25 wt%),CL主要分布在富蛋白微区与蛋白质发生接枝聚合反应。交联和接枝聚合反应形成了网络结构,致使材料的两个玻璃化转变温度和α-力学松弛温度均上升,而且材料的拉伸强度和杨氏模量以及耐水性明显提高。此外,各组分之间的化学反应还使SPI塑料的热稳定性提高,并且试片受热时甘油的挥发以及NH3和CO2的释放明显延缓。以大豆残渣(SD)为原料,在20 MPa和120 oC的条件下,以25 wt%的甘油作为增塑剂,6.8 wt%的GA作为交联剂,成功制得具有生物可降解性的大豆渣蛋白质塑料GSD-3。由于SD中纤维素、多糖和蛋白质之间强烈的相互作用,GSD-3试片显示出略高于SPI试片的拉伸强度、断裂伸长率和热稳定性。同时,GSD-3试片在念珠镰刀霉菌、橄榄毛壳菌和绿色木霉菌的作用下可以完全生物降解。此外,用蓖麻油基聚氨酯/硝化壳聚糖互穿聚合物网络涂层涂覆GSD-3试片,制备出耐水性蛋白质塑料,它们的界面存在较强的化学键合作用,显著改善了试片的拉伸强度和耐水性。上述研究成果不仅提出了大豆蛋白质塑料中微观结构和相互作用的新观点,而且为制备大豆蛋白质纳米复合物提供了一系列简便的新途径。同时,建立了新型大豆蛋白质纳米复合塑料的结构与性能之间的关系。尤其,本工作使用可再生资源——大豆渣为原料,通过绿色的工艺制备环境友好材料。因此,本工作具有理论意义和应用前景,并且符合可持续发展战略。更多还原

【Abstract】 The increasing price of petroleum and the ever-increasing pollution from non-degraded plastic waste have directly threatened human being’s survival, health and development. Therefore, the natural renewable plant resources have the potential to be used as an alternative to petroleum and become one of the primary chemical materials in the 21st century, which has been one of the fronts of polymer science and material science. Soy protein, a by-product of the production of soy bean oil is a kind of widespread and abundant natural polymers. In the latest decade, developing biodegradable soy protein plastics has been a new topic in material science. However, the condensed structure for soy protein plastics lacks systemic understanding. Meanwhile, the water resistance of soy protein plastics is relative low, which limited their research, development and application. The main objectives of this thesis are to study the glass transition behaviour, microstructure and interaction of glycerol plasticized soy protein isolate (SPI) plastics, and to prepare SPI/montmorillonite (MMT), SPI/alumina hydrate (AlOH) and SPI/ hydroxypropyl alkaline lignin (HPL) nanocomposites via solution intercalation, in situ synthesis and solution blending methods, respectively. The interaction mechanism and the structure-properties correlation for these novel materials are clarified.The innovative achievements of this thesis are as follows. (1) For the first time, we suggested that there were two glass transition temperatures assigned to glycerol-rich and protein-rich domains in glycerol-plasticized SPI plastics. (2) It was clarified that the moisture obviously plasticized the glycerol-rich domains, leading to the occurrence of protein-water domains and the obvious changes of the material properties. (3) The protein-rich and glycerol-rich domains were of compact disk-like structure and loose chain-like structure, respectively. (4) We revealed that there were strong hydrogen bonding and electrostatic interaction between SPI and montmorillonite. These two interactions resulted in the high exfoliation of MMT layers and the significant improvements of mechanical properties and thermal stability. (5) A novel way to prepare the SPI/AlOH nanocomposites in aqueous media via in situ synthesis has been brought out, and it was revealed that the dispersion status of AlOH nanoparticles obviously influenced the material properties. (6) Theε-caprolactone (CL)/glycerol plasticized SPI plastics were successfully prepared through an extruding and compression molding process. It has been shown that grafting and crosslinking reactions occur among CL, glycerol and SPI.The main research contents and conclusions are divided into the following parts. Firstly, two glass transition temperatures (Tg1 and Tg2) of SPI plasticized with glycerol were clearly observed by differential scanning calorimetry (DSC). The results revealed that when glycerol content was in the range from 25 to 50 wt.-%, the obvious microphase separation occurred in the SPI/glycerol system. In the meanwhile, Tg1 at -28.5 ~ -65.2 oC and Tg2 at about 44 oC coexisted, assigned to glycerol-rich and protein-rich domains in the SPI sheets, respectively. The results from DSC with O-ring-sealed capsule and thermogravimetric analysis-Fourier transform infrared spectroscopy (TGA-FTIR) evidenced that the endothermal peaks at 100 ~ 120 oC in the DSC curves were assigned to the evaporation of the residual moisture, rather than denature of proteins. The values of gyration radii (Rg) of protein-rich domains estimated by small angle X-ray scattering (SAXS) were around 60 nm when the glycerol contents were higher than 25 wt%, indicating the amorphous protein-rich domains were composed of the compact protein chains. All of the results suggested that there were two kinds of protein chains with relatively high or low compatibility to glycerol in the SPI, leading to two glass transitions as a result of the existence of glycerol-rich and protein-rich domains.On the basis of the results from DSC with the aluminum pan and O-ring-sealed stainless steel capsule, there were three glass transition temperatures (Tg1, Tg2 and Tg3) at -12.7 ~ -83.8 oC, 65.8 ~ 53.1 oC and 3.7 ~ 1.5 oC in glycerol plasticized SPI plastic sheets at high relative humidity (RH). They were assigned to the glycerol-rich, protein-rich and protein-water domains, respectively. Tg3 of the protein-water domain occurred when the RH value was higher than 35%. Moreover, the absorbed water mainly dispersed in the glycerol-rich domain composed of loose protein chains with high glycerol content. With an increase of RH, the slow decrease of the Tg2 and Tg3 values as well as the relative stability of the Rg values indicated that the protein-rich and protein-water domains were relatively stable protein aggregates. The results from DMTA, TGA-FTIR and tensile testing further confirmed that the glycerol-plasticized soy protein sheets easily absorbed the moisture in atmosphere into the glycerol-rich and protein-water domains, leading to the obvious decrease of Tg1, the occurrence of Tg3 and the evident change of mechanical and thermal properties.The domain structure and interaction in the glycerol plasticized SPI plastics were carefully investigated using DSC, atomic force microscropy (AFM) and solid-state 13C nuclear magnetic resonance (13C NMR). The results from DSC indicated that there were exactly two glass transitions in SPI/glycerol systems at 1.5 ~ -47.6 oC and around 70 oC, assigned to glycerol-rich and protein-rich domains, respectively. The protein-rich domains were compact disk-like protein aggregates, and the glycerol-rich domains were loose chain-like structures. With an increase of the glycerol content in the protein plastics, the protein molecules were rapidly diluted, and the free spaces around the molecules are obviously enlarged. In the meanwhile, the protein-rich domains maintained their compact structures. The results from 13C NMR revealed that there was strong hydrogen bonding between glycerol and protein. Such bonding was significantly influenced by the amino acid residues. The protein molecular segments with non-polar residues had a low compatibility with glycerol, which formed protein-rich domains. Namely, the protein-rich domains were composed of the amino acids bearing long alkyl or aromatic groups, and the glycerol-rich consisted of those having polar or short non-polar groups.The biodegradable SPI/MMT plastics with highly exfoliated or intercalated structures were successfully prepared via a solution intercalation process in neutral aqueous medium. The structures of both the SPI/MMT nanocomposites powders and the plastics were strongly depended on the MMT content. When the MMT content was lower than 12 wt%, the MMT were highly exfoliated into single layers with a thickness of approximately 1~2 nm, whereas the intercalation structure predominated in the SPI/MMT nanocomposites when the MMT content was higher than 12 wt.%. The electrostatic surface potential calculation revealed that the heterogeneous distribution of the surface positive charges provided the possibility for negatively charged soy protein to intercalate and exfoliate MMT. In view of the results from theζ-potential measurement and Fourier transform infrared spectroscopy (FTIR), two kinds of interactions existed in this protein/MMT system, that is, the surface electrostatic interaction between the positive-charge-rich domains of soy protein and the negatively charged MMT layers as well as the hydrogen bonding between the–NH and Si–O groups. Such two interactions resulted in the intercalation and delamination of the MMT layers in the soy protein matrices. The mechanical strength and thermo-stability of the SPI/MMT plastics were significantly improved as a result of the fine dispersion of the MMT layers and the strong restriction effects on the interfaces.The SPI / AlOH nanocomposites were successfully prepared via an in situ reaction between AlCl3 and NH3?H2O in aqueous media. The hydrogen bonding interaction between the peptide bond and alumina hydrate played a key role in the high affinity between AlOH and SPI matrices as well as the homogeneous dispersion of nanoparticles. The structures and properties of the SPI/AlOH nanocomposites were strongly depended on the amount of AlCl3 addition. The results from TEM and tensile testing suggested that the local network-like dispersion of AlOH nanoparticles resulted in high transparence, good mechanical performance and elevated water resistance for the SA-8 sheets with the AlCl3 addition of 8 wt%. When the AlCl3 content was lower than 8 wt%, the alumina hydrate were homogenously dispersed in soy protein matrices with a dimension of about 10~50 nm, whereas the phase separation occurred in the nanocomposites when the AlCl3 addition was more than 8 wt%. Additionally, the increase of the glass transition andα-relaxation temperature evidenced the effective confinement of the protein molecules by the strong interfacial adhesion. Meanwhile, this kind of confinement significantly lowered the water uptake, and enhanced the tensile strength and modulus of the composite plastics even at high RH environments. Especially, the composite plastics still maintain relatively good biodegradability.The hydroxypropyl alkaline lignin (HPL) has been homogeneously dispersed in soy protein isolate (SPI) as nano-particle with glutaraldehyde (GA) as compatibilizer to improve the mechanical properties. The H-6 plastic sheets with 3.3 wt% GA and 6 wt% HPL exhibited the best mechanical properties in this case. The results from FTIR and X-ray diffraction (XRD) indicated that SPI/HPL composites were of amorphous network structure resulted from the physical crosslinking between HPL and SPI as well as the chemical crosslinking caused by GA. TEM micrographs demonstrated that the compaibilization of GA led a small dimension of the dispersed HPL particles to be about 50 nm in diameter. The cross section structures of the plastic sheets confirmed that there was a good interfacial adhesive in the SPI/HPL composites. The restricting effects of nano-scale HPL particles on the network structures in the SPI/HPL sheets are responsible for the increase of Tg from 62.5 to 70.4 oC when HPL content increase from 0 to 6 wt%. On the whole, the coexistence of the physical and chemical crosslinking networks significantly improved the mechanical and thermal properties of the SPI plastics.The SPI plastics with CL and glycerol as plasticizers were successfully prepared through reactive extruding and compression molding. The results of FTIR and SEM revealed that the high temperature and high shearing process could cause the occurrence of the grafting and crosslinking reactions among CL, glycerol and SPI, which was responsible for the good compatibility among each component. When the CL content was relatively low (< 25 wt%), the CL was mainly dispersed in the glycerol-rich domains and formed crosslinking with glycerol. When the CL content was relatively high (> 25 wt%), the dispersion of CL was mainly in protein-rich domains and grafted onto the protein chains. The crosslinking and grafting polymerization reactions built the network structures in soy protein matrices, leading to the increase of the glass transition andα-relaxation temperatures. Such chemical reactions enhanced the tensile strength, Young’s modulus and water resistance. Furthermore, the thermal stability was elevated, and the evaporation of glycerol and the emission of NH3 and CO2 during heating were retarded.Biodegradable plasticses (GSD-3) were prepared from soy dreg (SD) with 25 wt% glycerol as the plasticizer and 6.8 wt% GA as the cross-linker under a pressure of 20 MPa at 120 oC. Compared with the sheets based on SPI, the GSD-3 sheets exhibited good tensile strength, breaking elongation and thermostability because of the strong interaction between cellulose, polysaccharide, and protein in the SD. Moreover, the GSD-3 sheets were fully biodegraded by the strains of Fusarium moniliforme, Chaetomium divaceum and Trichoderma viride. The water resistant SD plastics were prepared by coating the castor-oil-based polyurethane/nitrochitosan interpenetrating polymer networks (IPNs) on GSD-3 plastic sheets. The strong interfacial bonding between the GSD-3 sheet and the coating layer elevated the tensile strength and water resistance of the GSD-3 sheets.The achievements mentioned above not only brought out new viewpoints for the microstructure and interaction in soy protein plastics, but also provided convenient ways to prepare soy protein nanocomposites. And the correlation of structure and properties for the novel soy protein nanocomposite plastics were established. Additionally, a novel renewable recourse, soy dreg has been applied to prepare eco-friendly materials via green process. Therefore, this thesis possesses academic value and application perspective, and well accords with the strategy of sustainable development.更多还原