Morgan法串联测定羟丙基瓜耳胶的取代度

在传统的Morgan法的基础上对羟丙基瓜耳胶的取代度的检测方法进行研究，提出了串连法对羟丙基瓜耳胶的取代度进行检测，提高了实验效率，减小了实验误差。     

Characterization of O-Carboxymethyl Chitosan – Gum Arabic Coacervates as a Function of Degree of Substitution

Three O-carboxymethylated chitosans (O-CMCs) with degrees of substitution (DS) 0.41, 0.51, and 0.83 were synthesized and the effects of the DS of O-CMC on its coacervation with gum Arabic (GA) and partial characteristics of resultant coacervates were investigated. All the O-CMCs exhibited the same optimum pH of 3.0 for coacervation with GA and the O-CMC–GA coacervates displayed similar differential scanning calorimetry (DSC) patterns, thermogravity (TG) profiles, and porous microstructures, but differed markedly in their rheological properties. As the O-CMC DS increased, the elasticity of the coacervates raised accordingly. It was concluded that O-CMC–GA coacervates with desired viscoelasticity can be obtained by varying the DS of O-CMC.     

HS/GC-MS法分析胶基型嚼烟中的挥发性香味物质

运用静态顶空气相色谱-质谱法对22个胶基型嚼烟样品中的挥发性香味物质进行分析,并采用质谱数据库对挥发性香味物质进行定性分析。对顶空分析条件以及GC-MS条件进行了优化,提高了挥发性香味物质的测定灵敏度;对峰面积归一化结果大于0.1%的化合物进行定性分析,通过匹配度限定(≥85%)确认了65种挥发性香味物质;最后对样品进行了相似性分析和聚类分析。结果表明:22个胶基型嚼烟样品中的香味物质主要有酯类(18个化合物)、烯烃类(16个化合物)、醇类(9个化合物)、醛类(8个化合物)、酮类(7个化合物)、酚类(1个化合物)、酸类(1个化合物)、呋喃类(2个化合物)、烷烃类(2个化合物)、硫醚类(1个化合物),共10类化合物;不同胶基型嚼烟样品的品牌识别度高,同时口味对品牌识别有一定的影响作用。方法为进一步开发胶基型嚼烟制品提供了理论基础和技术支持。     

高效原油破乳剂GE-189的制备与应用研究

以分子量大、活泼氢多、具有分支结构的瓜胶作起始剂，与环氧乙烷、环氧丙烷加成，首次合成出具有分支结构的瓜胶类原油破乳剂GE－189，并把这种破乳剂及其与常规破乳剂F3111的复配体系应用于不同油田原油乳状液的室内破乳脱水试验。结果表明，破乳剂复配体系在脱水速率、脱水效果等方面均优于各现场剂，把这种破乳剂与生物表面活性剂复配，于巴西海上油田原油乳状液的破乳脱水，能够显著提高原油乳状液的破乳脱水速率和脱水体积，两者之间表现出明显的协同作用。     

Synthesis of Hydroxypropyl Guar Gum by Phase Transfer Catalysis

HGG (Hydroxypropyl guar gum) was synthesized by phase transfer catalysis for the first time. The effects of alkalinity, phase transfer catalyst, etherification, pH value, temperature,reaction time and stirring speed were investigated. An optimal synthetic reaction technology was established, namely, dose of guar gum is 100 g, propylene oxide 40-50 g, HTAC (hexadecyl trimethyl ammonium chloride ) 1.3-1.7 g, pH value 10-10.5, temperature 45-50~C, and reaction time 3-4 hours. The result shows that the improved HGG has high viscosity. Its dissolution speed, content of insoluble residue, colloid light transparency and stability are apparently superior to guar flour.     

Dynamo-mechanical and rheological characterization of guar gum hydrogels

Polymeric systems gained great interest in the last decades as specialties in the field of drug delivery, being very attractive for their peculiar physico-chemical characteristics. In this paper we report the characterization of a chemical network based on guar gum (GG) cross-linked with glutaraldehyde (Ga). The system was studied at three different temperatures, 7, 25 and 37 °C and at different ageing times in order to evaluate the influence of these two parameters on its stability. The experiments were carried out with a Texture Analyzer thus hardness, cohesion and Young modulus of the hydrogel were evaluated in the different conditions. Furthermore, relaxation experiments were performed and their interpretation, according to the Maxwell generalized model, allowed to describe the mechanical behaviour in terms of materials viscoelasticity theory. The kinetics of the chemical cross-linking was followed at 37 °C by means of rheological measurements, i.e. recording the mechanical spectra of the gelling system. The storage and loss moduli followed a power law, expression of the mechanical and structural self-similarity which evolves during the cross-linking reaction. The critical exponent at the gel point was evaluated, together with the critical time corresponding to the infinity connectivity of the system and the phase angle between stress and strain. Furthermore, also the fractal dimension was evaluated assuming a complete screening of the excluded volume of the chains at the critical point. Information about the release behaviour of the hydrogel, used as a matrix for modified drug delivery of model molecules with different steric hindrance, is also given.     

INTERMOLECULAR AND INTRAMOLECULAR INTERACTIONS OF POLYMER GUAR GUM IN SOLUTIONS

The tetrahedral borate ion can crosslink with polymer guar gum in aqueous solutions. If the concentration of guar gum is less than 0.045 g/dL, the intramolecular interaction between guar gum and borate ion increases due to the formation of crosslinks. As a result, the polymer chains of guar gum in solution shrink in size and the reduced viscosity of polymer solution decreases accordingly. On the other hand, if the concentration of guar gum is greater than 0.045 g/dL, the intermolecular interaction becomes apparent due to the same reason. The polymer chains, therefore, associate together and the reduced viscosity of polymer solution increases considerably. According to this technique, the critical concentration c^＊, presented by de-Gennes, is determined successfully.     

黄原胶水凝胶的分子网络模型

本文结合二次采油中作为压裂液的黄原胶水凝胶,从其成胶机理着手分析,以Carreau-Bird模型为基点,在分子网络模型中引进了吸附反应动力学项以及计及流体触变性质的函数f(t),并把自由链、迷向链及破碎网络对应力的贡献模拟成牛顿性,从而导出本构方程。方程中的参数值由凝胶的粘弹性性质及非线性物质函数决定,用有约束的优化方法进行优化后得到,模型计算的结果与实验数据大致相符。     

Ultrasensitive and Selective Detection of Cd(II) Using ZnSe‐Xanthan Gum Complex/CNT Modified Electrodes

This work describes for the first time the employment of water soluble GSH‐ZnSe QDs stabilized by XG and MWCNT for electrode modification in the detection of Cd ions in a highly sensitive and selective manner resulting from the unique structure and surface chemistry of the used QDs. The surface of a glassy carbon (GC) electrode was modified through casting a thin layer of multiwalled carbon nanotubes (MWCNT) followed by a complex layer of ZnSe quantum dots (QDs) stabilized by xanthan gum (XG). Due to the electrocatalytic properties of MWCNT and electroanalytical performance of ZnSe‐XG complex, the new modified electrode significantly improves the sensitivity and selectivity of Cd(II) detection and exhibits enhanced performance in comparison to bare GC, ZnSe/GC and ZnSe/MWCNT/GC electrodes. Strong interactions between ZnSe QDs and XG resulting from hydrogen bonding and complexing association led to stabilization of ZnSe QDs and higher affinity towards Cd(II) ions adsorption compared to a ZnSe QDs film alone. The modified electrode showed linear response in a wide concentration range from 100 nM to 5 μM (R²=0.9967) along with a high sensitivity of 156.6 nA ⋅ mol⁻¹ ⋅ L⁻¹ and a low detection limit of 20 nM. The electrode shows high selectivity to Cd with negligible interference from other metal ions and salts.     

Aqueous polysaccharide blends based on hydroxypropyl guar gum and carboxymethyl cellulose: synergistic viscosity and thixotropic properties

Aqueous polysaccharide blends, formed from 2.5% (w/v) solution of hydroxypropyl guar gum (HPG) and 2.5% (w/v) solution of carboxymethyl cellulose (CMC) according to different blending ratios, were investigated at 20 °C in terms of their shear-dependent viscosity and thixotropic properties. The Cross viscosity equation was found to fit the shear-dependent viscosity data with reasonable accuracy. When the HPG solution with the mass fraction (f _HPG) of 0.87 was mixed, the zero shear viscosity (η _o) of the corresponding blend was found to be 168.5753 Pa s, while the η _o values of component HPG and CMC solutions were found to be 3.3859 and 98.6525 Pa s, respectively. For the aqueous HPG/CMC blends investigated, the resulting zero shear viscosity was observed to be much greater than the combined zero shear viscosity of the component polysaccharide solutions, showing a synergistic viscosity property. The quantitative determination of the hysteresis loop area, developed during viscometer tests on shear rate–shear stress reverse paths, was used to describe the thixotropic behavior. When compared with aqueous solutions of the component polysaccharides, these polysaccharide blends could afford enhanced thixotropic property. Maximum thixotropy synergism was observed for the HPG/CMC blend with the f _HPG of 0.67.