Effect of irradiation on the molecular weight and structure and rheological behaviour of xanthan gum | 辐照对黄原胶分子量、结构及流变性能的影响

Chinese. 目的探讨辐照剂量对黄原胶分子量、分子量分布、结构、流变性能的影响，为辐照技术在黄原胶及其它多糖分子修饰上的应用提供理论依据。方法以60Co-γ射线对固态黄原胶进行不同剂量 (0―400 kGy) 的辐照，采用凝胶渗透色谱（GPC）、X-射线衍射(XRD)、红外扫描(FTIR)、紫外-可见光扫描(UV-vis)以及流变仪等对样品的分子量、分子量分布、结构以及流变性能进行表征和测定。结果低于10 kGy剂量的辐照使黄原胶分子量增大，分子量分布变窄；辐照剂量高于10 kGy后，分子量随剂量增大而降低，而分子量分布先变宽，在50 kGy时达到最大后，又趋于变窄。X-射线衍射、红外及紫外分析表明，辐照造成黄原胶分子上的部分糖苷键发生断裂，引起结晶度的变化，并在链端产生少量羰基，但其基本化学结构和晶体结构保持稳定。辐照处理后，黄原胶溶液的表观黏度与剪切速率、剪切时间和温度之间的关系均发生了显著变化。结论γ射线可同时作用于黄原胶的结晶区和无定形区，引发聚合和降解两种辐照效应，并对其分子量、分子量分布造成显著影响，进而使其流变性能发生改变。

English. Objective The effects of irradiation dose on the molecular weight, molecular weight distribution, structures and rheological behaviour of xanthan gum were investigated for the purpose of applying irradiation technique to molecular modification of xanthan gum and even other polysaccharides. Method Xanthan gum was irradiated in dry state at different doses (0-400 kGy) of 60Co γ-rays to investigate the changes of the molecular weight, molecular weight distribution, structures and rheological behaviour of irradiated xanthan gum by using gel permeation chromatography (GPC), X-ray diffraction (XRD), fourier-transform infrared spectra (FTIR), ultraviolet-visible spectral (UV-vis) and rheometer. Result Results showed that the molecular weight and crystallinity of xanthan gum increased at 10 kGy, then decreased gradually with increasing irradiation dose. Contrary to it, molecular weight distribution of irradiated xanthan gum decreased at 10 kGy, then increased gradually to maximum value at 50 kGy, and then decreased with irradiation dose. FT-IR spectra and XRD indicated that γ-irradiation introduced no significant changes into the structure and crystal texture but UV spectra showed a distinct absorption peak at about 265 nm, increasing with irradiation dose, which was attributed to the formation of carbonyl groups or double bond. The relationship between apparent viscosity of xanthan gum solution and shearing rate, shear time and temperature were varied significantly. Conclusion γ-irradiation can act simultaneously on crystallization area and amorphous area of xanthan gum, and cause polymerization or degradation of xanthan gum molecule, thus the molecular weight and molecular weight distribution, and then the rheological behaviour of irradiated xanthan gum were obviously changed.