【作者】 耿凤英；

【导师】 于九皋；

【作者基本信息】 天津大学 ， 有机化学， 2010， 博士

【摘要】 淀粉是一种来源广泛,价格低廉,且极具生物降解性的天然可再生高聚物资源,可通过物理、化学改性的方法制得性质各异、适用于不同应用领域的改性淀粉。但在淀粉的化学变性反应中,由于半结晶的淀粉颗粒由交错的结晶区和无定形区组成,结构致密的结晶区限制了化学试剂向淀粉分子内部的渗透,反应只能发生在颗粒表面,从而导致淀粉的反应活性和反应效率较低。因此,研究如何改变淀粉颗粒结构来提高淀粉的反应活性已成为一项极其重要的研究课题。本文在低温条件下用氢氧化钠/尿素对淀粉进行预处理,采用X-射线衍射仪(XRD)、扫描电子显微镜(SEM)及红外光谱(FT-IR)对预处理淀粉进行表征分析,研究了淀粉在预处理过程中其结晶结构、颗粒形貌大小及分子基团的变化规律。研究结果表明氢氧化钠/尿素预处理降低了淀粉的结晶度,改变了其结晶结构,晶型由A型转变为VH型。预处理后淀粉的颗粒形貌发生了变化,由多角形转变为圆球形,颗粒变小,在500nm左右。红外光谱分析表明淀粉在预处理过程中并没有产生新的基团。通过考察氢氧化钠/尿素预处理对玉米淀粉的冷水溶解度、透明度、粘度特性及其热稳定性的影响来研究预处理对淀粉理化性质的影响。研究结果表明,预处理显著提高淀粉的冷水溶解度和淀粉糊的透明度;预处理淀粉糊的粘度降低;热稳定性降低。采用原淀粉及预处理淀粉为原料,以长链脂肪酸、月桂酸甲酯及辛烯基琥珀酸酐为酯化剂,在无溶剂条件下合成淀粉酯,并以取代度为评价指标,通过研究预处理对酯化反应取代度的影响来探讨预处理对淀粉化学反应活性的影响。利用正交试验对淀粉酯的合成工艺进行优化,考察了物料比、反应时间、反应温度对取代度的影响。采用FTIR、13CNMR、SEM、X-射线衍射、TG等技术对产物结构及性能进行表征。研究结果表明,在相同实验条件下,由于预处理淀粉结晶度的降低及比表面积的增大,其取代度比原淀粉高,表明预处理对淀粉的酯化反应有着显著的强化作用,反应活性提高。酯化反应发生在无定形区,其结晶类型保持不变,但结晶度增大。疏水性长碳链的引入减少了淀粉中的羟基数目因而使得淀粉酯的热稳定性提高。月桂酰基团的引入使淀粉酯的疏水性增加,粘度降低,乳化性及乳化稳定性提高。辛烯基琥珀酸基团的引入使得淀粉酯亲水性升高,粘度增大。更多还原

【Abstract】 Starch is an abundant natural polysaccharide that is cheap, and fully biodegradable. It is usually modified physically or chemically to achieve a particular property and cater to the requirements for tailor-made. However, the intact starch granules inhibit chemical reagents from making contact with the molecules in the crystalline region, thus the chemical reactivity and reaction efficiency of native starch is usually low. Therefore, there are many methods destined to modify the structure in the crystalline region, or decrease the size of crystalline regions to increase reactivity of starch.In this thesis, native corn starch (NCS) was pretreated with NaOH/urea/H2O solution at cool temperature, the effects of pretreatment on crystal structure, granular morphology and functional groups were investigated, respectively, by using X-ray diffraction (XRD), scanning electron microscopy (SEM) and Fourier transform infrared (FT-IR) spectroscopy. During the pretreatment, the crystal structure of starch was damaged and the crystallinity decreased. X-ray diffraction revealed that PCS had the VH type crystalline pattern, which was different from NCS. It was found by scanning electron microscopy (SEM) that the PCS was spherical and the size of most PCS was about 500 nm. FT-IR showed that there were no new functional groups produced during the pretreatment process. The pretreatment effects on physicochemical properties of corn starch were investigated by analyzing the influence of pretreatment on cold-water solubility, transparency, viscosity and thermal stability. The pretreatment was evidenced to cause changes of physicochemical properties of corn starch: the degrading of the crystalline regions allowed greater entry of water into the interior of the granule thus led to the greater cold-water solubility and transparency of PCS, the viscosity of PCS decreased. In addition, the PCS also exhibited lower thermal stability.Using long-chain fatty acid, methyl laurate and octenyl succinic anhydride as esterification reagents, NCS and PCS were esterified under solvent-free conditions. Moreover, using the degree of substitution (DS) as an evaluating parameter, the NaOH/urea pretreatment effects on chemical reaction activity of starch were investigated by analyzing the influence of pretreatment on DS. The optimal reaction conditions were confirmed through orthogonal test, effects of molar ratio of the raw material, reaction temperature and reaction time on the degree of substitution (DS) of starch esters were studied. The products are characterized by FT-IR, 13CNMR, SEM, X-ray diffraction and TG. It shown that the smaller size and more amorphous domain of PCS improved the degree of substitution (DS) and reaction efficiency (RE) of PCS. The esterification occurred in the amorphous domain, thus the crystalline pattern did not changed but the crystallinity increased. The introduction of the long alkyl chains led to the better thermal stability of the starch ester. Lauroyl groups in the starch ester led to the better water resistance and emulsifying properties, and also resulted in the drop in viscosity. While the octyl alkenyl succinic acids in the starch ester enhanced the hydrophilicity and thus the viscosity increased.更多还原