【作者】 任丽丽；

【导师】 周江； 佟金；

【作者基本信息】 吉林大学 ， 农业机械化工程， 2012， 博士

【摘要】 近二十年来，人们纷纷致力于研发来自于可再生资源的生物降解材料，用其替代石化基不可降解材料。热塑性淀粉因其可生物降解、来自可再生资源、价格相对低廉而受到广泛的关注。热塑性淀粉可以通过现有的合成塑料加工技术进一步加工成各种制品，并在某些领域特别是包装领域成功取代部分合成塑料。但是，淀粉的亲水特性，使得热塑性淀粉的力学性能对环境湿度敏感、阻湿性差。这些缺点极大地限制了热塑性淀粉材料的应用。向热塑性淀粉中添加至少在某一维方向上具有纳米尺度（≤100nm)的填料，制备热塑性淀粉纳米复合材料，是近年来改善热塑性淀粉力学性能和阻隔性能的主要方法之一。在淀粉糊化温度以下，通过酸水解的方法除去原淀粉颗粒中的无定形部分而得到的淀粉纳米晶，由于其呈碟片状，结构致密，刚度大，结晶度高以及透湿性低，使其成为制备热塑性淀粉纳米复合材料以提高其力学性能和阻湿性能的理想增强相。通过酸解蜡质玉米淀粉制备淀粉纳米晶，对其进行交联改性、酯化改性和交联-酯化双重改性，调节淀粉纳米晶的极性。以改性处理的淀粉纳米晶为增强相，用流延法制备热塑性淀粉纳米复合材料。通过淀粉纳米晶改性程度的变化与控制，优化热塑性淀粉纳米复合材料的力学性能和阻湿性能。在水相介质中及淀粉糊化温度以下，淀粉纳米晶可以与六偏磷酸钠、硼砂、戊二醛发生交联反应，交联改性后淀粉纳米晶的结晶结构可以完全或部分保留，交联反应基本只发生在淀粉纳米晶表面。用柠檬酸对淀粉纳米晶进行交联改性，可以在淀粉分子上引入酯基基团；柠檬酸水溶液改性处理的淀粉纳米晶，结晶结构完全被破坏，但用pH值调节为3.5的柠檬酸水溶液或柠檬酸乙醇溶液改性处理，淀粉纳米晶的结晶结构可以部分保留。透射电子显微镜照片显示，交联改性后，淀粉纳米晶的形貌发生了变化，因氢键作用而引起的团聚现象明显减弱。经六偏磷酸钠、硼砂交联改性处理后，淀粉纳米晶之间的团聚现象被有效地抑制，能够均匀稳定地分散在水中；经戊二醛、柠檬酸交联改性处理后，淀粉纳米晶除了可以均匀稳定地分散在水中，还可以在极性比较低的氯仿、二氯甲烷等有机溶剂中分散。通过对交联剂所含官能团的选择，可以在降低淀粉纳米晶极性的基础上，赋予淀粉纳米晶一定的疏水性。在淀粉糊化温度以下，淀粉纳米晶可以与十二烯基琥珀酸酐、辛烯基琥珀酸酐和乙酸酐发生酯化反应，酯化改性将酯基官能团C=O引入到淀粉纳米晶上，淀粉纳米晶的结晶结构可以部分保留。在相同的酯化反应条件下，相比于十二烯基琥珀酸酐，使用烯基碳原子个数少的（即碳链长度短的）辛烯基琥珀酸酐对淀粉纳米晶进行酯化改性，更容易得到高的羟基取代度。酯化改性处理后，淀粉纳米晶的极性降低，能够分散在水以及氯仿、二氯甲烷和甲苯等有机溶剂中，具有两亲性；羟基取代度越高，淀粉纳米晶越容易分散到有机溶剂中。在羟基取代度相近的情况下，相比于乙酸酐，烯基琥珀酸酐酯化改性更有效地降低了淀粉纳米晶的极性，抑制了淀粉纳米晶的团聚。淀粉纳米晶经交联改性处理后仍然可以与十二烯基琥珀酸酐、辛烯基琥珀酸酐和乙酸酐发生酯化反应，而且淀粉纳米晶的结晶结构可以部分保留。交联-酯化双重改性处理后，淀粉纳米晶不仅能够均匀稳定地分散在水中，还可以在氯仿、二氯甲烷、甲苯等有机溶剂中分散，具有两亲性。相比于交联改性，交联-酯化双重改性有效降低了淀粉纳米晶的极性，使其可以在极性比较低的有机溶剂中分散；相比于酯化改性，交联-酯化双重改性在提高淀粉纳米晶羟基取代度的同时，有效降低了淀粉纳米晶的极性。淀粉纳米晶的加入，显著提高了热塑性淀粉复合材料的拉伸强度和弹性模量。交联改性淀粉纳米晶的加入大幅度提高了热塑性淀粉复合材料的拉伸强度和弹性模量，同时也提高了在75%和95%相对湿度环境下的断裂伸长率。相比于淀粉纳米晶自增强热塑性淀粉，交联改性淀粉纳米晶增强热塑性淀粉的拉伸强度和断裂伸长率增加了，但弹性模量变化不大。酯化改性淀粉纳米晶和交联-酯化双重改性淀粉纳米晶的加入提高了热塑性淀粉复合材料的拉伸强度、弹性模量和断裂伸长率，但相比于淀粉纳米晶自增强热塑性淀粉，拉伸强度和弹性模量却大幅度下降了。交联-酯化双重改性淀粉纳米晶增强热塑性淀粉的拉伸强度和弹性模量明显小于交联改性淀粉纳米晶增强热塑性淀粉，但断裂伸长率却大于交联改性淀粉纳米晶增强热塑性淀粉。相比于热塑性淀粉，淀粉纳米晶自增强热塑性淀粉的水蒸气透过量和水蒸气透过系数明显降低，而且随着淀粉纳米晶添加量的增加而减小；相比于淀粉纳米晶，改性淀粉纳米晶的加入更有效地提高了热塑性淀粉复合膜的阻湿性能，而且交联-酯化双重改性淀粉纳米晶增强热塑性淀粉膜的阻湿性明显优于交联改性淀粉纳米晶增强热塑性淀粉膜和酯化改性淀粉纳米晶增强热塑性淀粉膜。在低湿环境下，淀粉纳米晶自增强热塑性淀粉和改性淀粉纳米晶增强热塑性淀粉的饱和吸湿率与热塑性淀粉十分相近，只有在高湿环境下，才明显低于热塑性淀粉的饱和吸湿率。相比于交联改性和酯化改性，交联-酯化双重改性有效降低了淀粉纳米晶增强热塑性淀粉对环境湿度的敏感性。更多还原

【Abstract】 In the last two decades, there have been greater efforts to develop biodegradablepolymers and products from renewable resources for replacing non-degradablepetrochemical-based materials. Thermoplastic starch (TPS) has received considerableattention because of its biodegradability, availability from renewable resources and low cost.Products of TPS can be manufactured using technology already developed for the syntheticplastics and have found applications to replace the synthetic plastics in some marketsespecially in packaging industry. However, the hydrophilic nature of starch leads tomechanical properties of TPS sensitive to humidity and poor moisture barrier. Thesedisadvantages hinder the applications of TPS materials which may be improved by addingreinforcing fillers with at least one nanoscale dimension (nanoparticles), formingcomposites.By submitting native starch to acid hydrolysis at temperature below the gelatinizationtemperature of starch, the amorphous regions in starch granules are hydrolyzed allowing theseparation of nanoscale crystalline residues. Because of its unique properties such as thenanoscale platelet morphology, intrinsic rigidity, high crystallinity and low permeability,starch nanocystals (SNC) have been used as ideal reinforcements to prepare TPSnanocomposites to improve mechanical properties and moisture barrier. In this paper, SNCobtained from acid hydrolysis of waxy maize starch were modified through crosslinking oresterification or dual modification of crosslinking and esterification to reduce hydrophilicity of SNC and adjust surface polarity of SNC. TPS nanocomposites were prepared by castingprocess using modified SNC as the fillers in glycerol-plasticized corn starch matrix. Themechanical properties and moisture barrier properties of the SNC reinforced TPSnanocomposites were optimized by controlling the degree of modification of SNC.SNC were successfully modified through crosslinking with sodium hexametaphosphate(SHMP), borax and glutaraldehyde (GA) in water at temperatures below the gelatinizationtemperature of starch. The crystalline structure of SNC was completely or partially preservedafter the crosslinking modification and the crosslinking reaction may only occur on thesurface of SNC. The ester groups were introduced onto the starch molecule throughcrosslinking with citric acid (CA). The crystalline structure of SNC was completelydestroyed after modification with CA aqueous solution, but the crystalline structure could bepartially preserved with the CA aqueous solution adjusting the pH to3.5or CA ethanolsolution. Transmission electron microscopy (TEM) showed that, after crosslinkingmodification, the morphology of SNC changed and the aggregation between SNC due to thehydrogen bonding significantly reduced. The SNC crosslinked with SHMP or borax could bewell dispersed in water. The SNC crosslinked with GA or CA could be well dispersed notnoly in water, but also in lower polarity organic solvents such as chloroform,dichloromethane. These results suggested that it is possible to reduce the hydrophilicity ofSNC and provide it hydrophobicity by selecting crosslinking agents with different functionalgroups to react with SNC.SNC were modified through esterification by using dodecenyl succinic anhydride(DDSA), octenyl succinic anhydride (OSA) and actic anhydride (AA) at temperatures belowthe gelatinization temperature of starch. The ester groups were introduced onto the starchmolecule and the crystalline structure of SNC was partially preserved after esterificationmodification. Esterification modification of SNC with OSA having shorter chain ofn-alkenyl group was more easily to yield a higher degree of substitution of hydroxyl groupsthan with DDSA at the same reaction conditions. After esterification modification, thepolarity of SNC reduced and SNC can be well dispersed in water and organic solvents suchas chloroform, dichloromethane and toluene, suggesting that the esterified SNC has amphiphilicity. Esterified SNC with higher degree of substitution of hydroxyl groups wasmore easily dispersed in organic solvents. Esterification modification of SNC with ASA wasbetter than with AA for reducing the hydrophilicity of SNC and the aggregation betweenSNC at similar degree of substitution of hydroxyl groups.The crosslinking SNC were further modified through esterification with AA, DDSA orOSA. The crystalline structure of SNC was partially preserved after the dual modification ofcrosslinking and esterification. Dual modification of SNC through crosslinking andesterification was better than single crosslinkng modification for reducing the polarity of theSNC, and was more easily to yield a higher degree of substitution of hydroxyl groups andmore effectively to reduce the the polarity of the SNC than single esterification modification.The addition of SNC significantly improved the tensile strength and Young’s modulusof TPS composites. The addition of crosslinked SNC significantly increased the tensilestrength and Young’s modulus of TPS composites and the elongation at break at75%RHand95%RH. Compared to SNC self-reinforced TPS composites, the tensile strength andelongation at break of crosslinked SNC reinforced TPS composites increased, but theYoung’s modulus was almost unchanged. The addition of esterified SNC or dual modifiedSNC improved the tensile strength, Young’s modulus and elongation at break of TPScomposites, but compared to SNC self-reinforced TPS composites, it led to a drasticdecrease of tensile strength and Young’s modulus. The tensile strength and Young’s modulusof dual modified SNC reinforced TPS composites were significantly less than those ofcrosslinked SNC reinforced TPS composites, but elongation at break was greater. Thepresence of SNC or modified SNC decreased the rate of water vapor transmission (WVT)and the water vapour permeability (WVP) of TPS composites. Moisture barrier properties ofdual modified SNC reinforced TPS composites were significantly better than crosslinkedSNC reinforced TPS composites and esterified SNC reinforced TPS composites. In the lowRH area, the equilibrium moisture contents of SNC self-reinforced TPS composites andmodified SNC reinforced TPS composites were very similar to those of TPS, but in the highenvironment, the equilibrium moisture contents of them were lower than those of TPS. Dualmodification was better than crosslinking modification and esterification modification for reducing the sensitivity of SNC reinforced TPS composites to ambient humidity.更多还原