Shear-thinning and viscosity synergism in mixed solution of guar gum and its etherified derivatives

The flow properties of mixed solution of guar gum and carboxymethyl guar gum, including shear-thinning and viscosity synergism, have been studied at different mixed ratios, shear rates and temperatures using rheometer. The results show that addition of carboxymethyl guar gum enhances shear-thinning behavior and increases viscosity in guar gum solution at a given range of mixed ratios. The temperature-dependence of the mixed solution is markedly different from a single solution. The activation energy of blends with 50 and 75% of guar gum were determined to be 11.02 and 10.39 kJ mol⁻¹, respectively, lower than that of a single solution. These results indicate that the network structure of viscous solution has been changed because carboxymethyl groups branched in galactomannans had changed the interaction among macromolecular chains.     

羧甲基羟丙基瓜尔胶合成新工艺及性能

为解决羧甲基羟丙基瓜尔胶(CMHPG)合成过程中副产物多,容易糊化的问题.以丙酮为反应介质,甲醇钠为催化剂代替乙醇、异丙醇为介质,氢氧化钠为催化剂.探讨了工艺条件对产品的影响,找出了较佳工艺条件.结果表明,合成较佳工艺条件为:环氧丙烷与瓜尔胶质量比为0.2∶1、氯乙酸与瓜尔胶质量比为0.4∶1,反应时间为160 min;前者催化剂与瓜尔胶质量比为0.2∶1、反应温度为45～50℃,后者催化剂与瓜尔胶质量比为0.3∶1,反应温度为65～ 70℃.乙醇、异丙醇为介质,氢氧化钠为催化剂合成产品的羧甲基取代度为0.43,羟丙基取代度为0.36,粘度为1 120mPa·s;以丙酮为反应介质,甲醇钠为催化剂合成产品羧甲基取代度为0.48,羟丙基取代度为0.37,粘度为1 030 mPa·s.     

Barium chloride crosslinked carboxymethyl guar gum beads for gastrointestinal drug delivery

A mild method for microencapsulation of sensitive drugs, such as proteins, employing a suitably derivatized carboxymethyl guar gum (CMGG) and multivalent metal ions like Ca⁺⁺ and Ba⁺⁺ is reported. Initially, guar gum is derivatized with carboxymethyl groups so that it forms durable, self‐standing microbeads when its solution is dropped into CaCl₂ or BaCl₂ solutions. The swelling data of Ca⁺⁺ and Ba⁺⁺ crosslinked beads suggest that Ba⁺⁺ crosslinks CMGG much more efficiently than Ca⁺⁺. The drug loading efficiency of these Ba⁺⁺/CMGG beads, as a function of concentration of both metal ion as well as drug, was then determined using Bovine Serum Albumin as a model drug. The ability of these beads to protect the drug from the acidic environment of the stomach was investigated. It was found that a very little amount of the drug is released from the beads when they are suspended in NaCl–HCl buffer of pH 1.2 for 6 h. The beads were also shown to release almost the entire encapsulated drug when exposed to TRIS–HCl buffer of pH 7.4. Thus, the results indicate that Ba⁺⁺ crosslinked carboxymethyl guar gum beads can be used for gastrointestinal drug delivery. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3084–3090, 2001     

Shear and extensional rheological investigations in solutions of grafted and ungrafted polysaccharides

Many polysaccharides with varying shear stability have been grafted with polyacrylamide branches to enhance their turbulent drag‐reducing and flocculating characteristics. Their aqueous solutions have been studied by shear and extensional rheometric techniques. All the solutions of grafted carboxymethyl cellulose, guar gum, starch, and sodium alginate exhibit shear‐thinning non‐Newtonian behavior. The viscosities are higher than those of ungrafted polysaccharides. The solutions of grafted carboxymethyl cellulose, guar gum and sodium alginate are spinnable. When subjected to uniaxial stretching in a stretching device, the formation of a thread and reduction of the thread diameter with time were observed. The stretching device was used to measure the relaxation time, which was found to be the largest (∼26 ms), on the order of flexible polyacrylamide, for the grafted carboxymethyl cellulose. Though a polyacrylamide solution degrades through nozzle flow and completely loses its extensional properties, a solution of grafted carboxymethyl cellulose retains about half its relaxation time because of the shear stability of polysaccharide chains and their structure. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3200–3209, 2000     

Synthesis of guar‐gum‐stabilized nanosized silver clusters with γ radiation

Gamma ray induced synthesis of Ag clusters in the aqueous medium has been carried out using natural polysaccharide guar gum as a stabilizer. The results showed that guar gum is very effective in binding the Ag clusters and restricts their size in the nano region. The surface plasmon resonance band in the wavelength range of 410–425 nm of visible region has confirmed the formation of Ag clusters. The size of the clusters is governed by the concentration of both, i.e. precursor Ag⁺ and guar gum. The clusters were characterized by TEM and XRD, which shows that the size of clusters is in the range of 10–30 nm. The results have shown that silver clusters stabilized by guar gum are stable in acid media and alkaline media is not a desired media for the synthesis. From thermogravimetric analysis it has been demonstrated that incorporation of nano sized Ag clusters within guar gum improves the thermal properties of irradiated guar gum. To the best of our knowledge, the use of guar gum as a stabilizer in the gamma ray induced synthesis of Ag nano clusters is being reported first time in the literature. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Screening of different hydrocolloids for improving the quality of fried papad

Papads prepared from cereals, legumes and combinations thereof are India s contribution to the international menu. They are specially relished as snacks in fried form. In the present study hydrocolloids amounting to 0.25‐1.00% of fried papads prepared from black gram were investigated. The hydrocolloids chosen were guar gum, carrageenan, carboxymethyl cellulose, hydroxypropylmethyl cellulose, gum tragacanth, gum karaya, gum ghatti and gum arabic. It was observed that carboxymethyl cellulose was the most effective in increasing the diametrical expansion of the papads at a concentration of 1.00%, while gum arabic at 1.00% caused a maximum reduction in oil content (26.19% as compared to control). Gum tragacanth at 0.5% gave the best texture, measured as crispness using Steven's LFRA texturimeter.     

有机锆对羧甲基羟丙基瓜胶的交联性能研究

以氧氯化锆和柠檬酸等为原料,合成了适用于羧甲基羟丙基瓜胶在酸性条件下交联的有机锆交联剂,考察了pH值、温度、羧甲基羟丙基瓜胶和交联剂加量等对体系成胶时间的影响,评价了形成冻胶的抗温抗剪切性能、滤失性能和破胶性能.实验发现,在pH值为3.0时,羧甲基羟丙基瓜胶/有机锆体系具有可控的延缓交联特性,质量分数为0.5%和0.6...     

Stabilization of Mineral Suspensions by Guar Gum in Potash Ore Flotation Systems

The adsorption of guar gum on illite and dolomite was studied as a function of polymer concentration and ionic strength. The adsorption results were correlated with colloid stability of aqueous suspensions of these two minerals. The adsorption density of guar gum on illite was not affected by the ionic strength of the system. Guar gum adsorption on dolomite was found to strongly decrease at higher electrolyte concentrations. Low concentrations of guar gum brought about flocculation of the minerals while higher dosages led to steric re‐dispersion. Results presented here are compared with previously published results for carboxymethyl cellulose (Pawlik et al., J. Colloid Interface Sci. 260 , 251‐258 (2003)).     

Rheological properties of hydroxypropyl- and sodium carboxymethyl-substituted guar gums in aqueous solution

The aqueous solutions of guar gum and its hydroxypropyl (HP) and sodium carboxymethyl (sod CM) derivatives are pseudoplastic, and the transition from Newtonian to pseudoplastic occurs in the low-shear-rate range at the concentrations of interest to industries. The flow properties of these polysaccharide solutions were studied in the range of low to moderately high shear rates, using a very simple technique and instrument. The flow of these polysaccharide solutions can be described by equation of state based on Cross model, and the basic rheological parameters, like zero shear rate viscosity (η₀), elasticity modulus (G₀), and relaxation time (γ₀), were calculated from simple and established relations. Master viscosity curves indicate that the molecular weight distribution of native guar gum has not been changed by derivatization. The effect of concentration and temperature on rheological parameters (η₀ and γ₀) has been studied, and the relations among these were established by simple equations.     

Synthesis and characterization of acryloyloxy guar gum

Guar gum is a galactomannan commonly used as a viscosity modifier in the food, pharmaceutical, and cosmetics industry. The aim of this study was to synthesize acryloyloxy guar gum via a Schotten‐Bauman reaction in aqueous media. The reaction products were characterized using FTIR, C¹³‐NMR, wide angle X‐ray diffraction techniques to ascertain the effect of acrylation on the structure of guar gum. The acrylation of guar gum was found to be limited to the primary hydroxyl groups on the guar gum molecule. The maximum degree of substitution (DS) was found to be 0.56, which was observed after 3 h of reaction. Since the reaction was carried out in an aqueous medium after 3 h of reaction the DS of the derivatised guar gum was found to decrease, because of hydrolysis of the formed ester linkages. The ester content and intrinsic viscosity of the derivatised guar gums were also evaluated. Thermal analysis showed that a higher DS resulted in products with lower thermal stability and there was no evidence of reaction via the acrylate groups on heating. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of grafted carboxymethyl guar gum

Graft copolymers of carboxymethyl guar gum (CMGG) and polyacrylamide (PAM) have been synthesized by grafting polyacrylamide chains onto carboxymethyl guar gum backbone using a ceric‐ion‐induced solution polymerization technique. By varying the amount of initiator, three different grades of graft copolymers are synthesized. The characterization of graft copolymer is carried out by FTIR, NMR, intrinsic viscosity measurement, SEM, SLS, DTG, and rheology. A comparison of flocculation efficiency of CMGG and its graft copolymer shows that the graft copolymer exhibits better flocculation performance. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies on graft copolymerization of 4‐vinylpyridine onto guar gum

Graft copolymerization of 4‐vinylpyridine (4‐VP) onto guar gum (GOH) using potassium monopersulfate (PMS)/thioacetamide (TAA) as a redox pair was studied in an aqueous medium under inert atmosphere. The concentration of potassium monopersulfate and thioacetamide should be 1.0 × 10^?2 and 5.0 × 10^?3 mol dm^?3, respectively, for highest grafting ratio and efficiency. Efficient grafting was observed at 19.25 × 10^?2 and 4.87 × 10^?2 mol dm^?3 concentration of 4‐vinylpyridine and sulfuric acid, respectively. The optimum temperature for grafting is 30°C. As the time period of reaction is increased, the grafting ratio increases, whereas efficiency decreases. The plausible mechanism of grafting has been suggested. A sample of guar gum and guar‐ g‐4‐vinylpyridine were subjected to thermogravimetric analysis with the objective of studying the effect of grafting 4‐vinylpyridine on the thermal stability of guar gum. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2380–2385, 2002     

Vanadium(V)/mandelic acid initiated graft copolymerization of acrylamide onto guar gum in an aqueous medium

The graft copolymerization reaction of acrylamide onto guar gum with a vanadium(V)/mandelic acid redox pair was carried out in an N₂ atmosphere. The optimum concentrations of vanadium(V), mandelic acid, hydrogen ions, acrylamide, and guar gum for the maximum percentage of grafting were 6.0 × 10^?3, 2.0 × 10^?2, 55.0 × 10^?2, and 20.0 × 10^?2 mol/dm³ and 110.1 × 10^?2 g/dm³, respectively. The optimum time and temperature of reaction were 90 min and 35°C, respectively, and during the study of [H⁺] variation, a prompt change in the value of the grafting parameters was observed. The maximum percentage of swelling of the graft copolymer was achieved at room temperature in 1 h. Studies of the flocculation, viscosity, and metal‐ion absorption capacity were also performed. The synthesized graft copolymer was characterized by Fourier transform infrared spectroscopy and thermogravimetric analyses, which showed that the grafted guar gum was thermally more stable than the ungrafted guar gum. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and characterization of graft copolymer (guar gum–g–N‐vinyl‐2‐pyrrolidone) and investigation of metal ion sorption and swelling behavior

Graft copolymer of N‐vinyl‐2‐pyrrolidone with guar gum was synthesized and its reaction conditions were optimized for better yield using potassium peroxymonosulfate (PMS) and glycolic acid (GA) as a redox initiator. The effect of PMS, GA, hydrogen ions, guar gum, and N‐vinyl‐2‐pyrrolidone (NVP) along with reaction time and temperature were studied by determining the grafting parameters: grafting ratio, efficiency, conversion, add‐on, homopolymer, and rate of grafting. It was observed that the maximum yield occurred at with a time of 120 min at a temperature of 45°C and a guar gum concentration of 0.4 g/L concentration. The graft copolymer was characterized by infrared spectroscopy and thermal analysis. The activation energy for the grafted and ungrafted gum was calculated. It was observed that the graft copolymer was thermally more stable than the pure gum. The swelling and metal ion sorption behavior of guar gum and guar gum‐g‐N‐vinyl‐2‐pyrrolidone also were studied. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 2480–2489, 2006     

瓜尔胶的改性及其透光性能研究

瓜尔豆片为原料,经羟丙基提纯后阳离子改性,得到透明性较好的阳离子瓜尔胶（CGG）。经分析碱法水解除蛋白质最优工艺为：豆片25g,NaOH5g,98℃下反应3h：蛋白质去除率为98．24％,透光率达77％。羟丙基化较优工艺为：环氧丙烷8mL。60℃反应4h;羟丙基取代度为0．2650,透光率为89％e阳离子化最优工艺为：醚化剂10mL,60℃反应3～5h,取代度（DS）为0．1701,透光率达97％。用IR对产蹦结构进行了表征,用TG和DSC对瓜尔胶、羟丙基瓜尔胶和阳离子瓜尔胶的对比研究表明,接枝的阳离子基团对瓜尔胶的相态稳定温度有影响,阳离予瓜尔胶的水分含量和结合水含量有所降低,利于储存。此产品用于对透光率要求较高的领域。     

Ultraviolet‐radiation‐induced graft copolymerization of methyl acrylate onto the sodium salt of partially carboxymethylated guar gum

In an attempt to modify the sodium salt of partially carboxymethylated guar gum (Na‐PCMGG; degree of substitution = 0.291), we studied the ultraviolet‐radiation‐induced graft copolymerization of methyl acrylate with ceric ammonium nitrate as a photoinitiator. The influence of the grafting yield was studied as a function of the different reaction parameters, and the optimum reaction conditions for photografting were determined. The various reaction parameters included the photoinitiator, nitric acid, and monomer (methyl acrylate) concentrations, the reaction time, the temperature, and the amount of the substrate. A kinetic scheme for photografting copolymerization was proposed, and the results were in good agreement with the kinetic scheme. The graft copolymerization of methyl acrylate onto Na‐PCMGG (degree of substitution = 0291) in the presence and absence of ultraviolet radiation was also carried out for the study of the efficiency of the photoinitiator. The influence of carboxymethyl groups added to the guar gum molecule on its behavior toward ultraviolet‐radiation‐induced grafting with methyl acrylate was also investigated. The evidence of photografting was ascertained with IR spectroscopy and scanning electron microscopy techniques. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 1977–1986, 2005     

Curing kinetics of epoxy-anhydride systems using quaternary ammonium guar and hydroxyethyl guar as catalysts

The kinetic parameters for the curing reactions of initially uncured and partly cured samples of the diglycidyl ether of bisphenol-A (DGEBA) with phthalic anhydride and quaternary ammonium compounds of guar gum or quaternary ammonium compounds of hydroxyethyl guar gum as catalyst, with or without n-butanol as diluent, were determined using the differential scanning calorimetry technique with a dynamic scan. To evaluate the kinetic parameters, four different computational methods were applied. The reaction was found to be first-order, with activation energy in the range 65-96 kJ mol^?1.     

Modified guar gum: An alternative source for printing of cotton fabric with reactive dye

The alginate thickener is the thickener frequently used for reactive printing of textile. The thickener responds with reactive pigments and thus does not lead to the fabric composition becoming stiffer. In this study, we prepared oxidised natural guar gum with hydrogen peroxide, sodium hypochlorite and sodium hydroxide. All other polysaccharides comprise reactive hydroxyl units with a stronger reactivity that must be replaced if they are to be used in reactive printing. Guar derivatives were synthesised and verified using Fourier-transform infrared (FTIR) spectroscopy. Natural thickeners, synthetic guar gum derivatives, have been employed in textile printing technique. In comparison to other synthetic thickeners, modified environmental guar gum polymer has been shown to be an ecologically friendly and low-cost thickener. Cotton fabric printed with modified guar thickening with hydrogen peroxide has even stronger colour strength than fabric printed with sodium alginate thickener, which is highly favourable. Penetration properties, colour value, colour strength, colour fastness to washing, light and rubbing was compared with alginate thickener (readily available on the market). Guar gum thickeners showed enhanced features versus sodium alginate for reactive printing. Partially replaced guar gum is an appropriate option due to the colour and physical properties.     

两性离子型瓜尔胶的制备及稀溶液性质

以瓜尔胶(GG)为原料,2,3-环氧丙基二甲铵基乙酸盐(ECDH)为两性醚化剂,在碱催化剂作用下干法合成了新型两性离子型瓜尔胶(ZGG)。采用酸碱滴定法测定了ZGG的等电点,并借助乌氏黏度计研究了等电点范围内ZGG的稀溶液性质,考察了外加盐浓度和不同外加盐对ZGG的影响。结果发现,随着氯化钠溶液浓度的增大,其特性黏度增大,表现出明显的反聚电解质溶液行为,二价金属离子对ZGG的影响大于一价金属离子对其的影响,即CaCl2>MgCl2>NaCl。     

Cotton linter nano-fibers as the potential reinforcing agent for guar gum

Cotton linter nano-fibers (CLNFs) were prepared from cotton linters by a refining process. The prepared CLNFs were characterized for morphology, crystallinity and degree of polymerization. CLNF was used as a reinforcing agent in guar gum to improve its performance properties. Guar gum/CLNF nanocomposite films were prepared by a solution-casting process. CLNF was added in concentrations of 0.1, 0.25, 0.5 and 1.0 % (w/w) in guar gum. The prepared guar gum/CLNF nano-composite films were characterized for mechanical, thermal, rheological, crystallinity, water vapor transmission rate (WVTR) and light transparency properties. The enthalpy of melting and melting temperature of guar gum increased with increased concentration of CLNF; but up to 0.25 % (w/w) concentration, above which they started decreasing. Tensile strength and Young’s modulus of guar gum increased by 32 and 35 %, respectively, by 0.25 % (w/w) addition of CLNF; however, it decreased on further increase in the concentration of CLNF. The percentage elongation at break and WVTR decreased by 58 and 57 % for 0.25 % (w/w) CLNF-added guar gum. The observed improvements in the properties were due to better interaction between CLNF and guar gum. CLNF was found to have uniformly dispersed in guar gum on addition up to 0.25 % concentration; however, it started forming aggregates at higher concentration, as evident from scanning electron microscopy. Viscosity increased, whereas transparency decreased with increased concentration of CLNF in guar gum.