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     

Comparative studies on the flocculation characteristics of polyacrylamide grafted guar gum and hydroxypropyl guar gum

The synthesis of two polysaccharide‐based graft copolymers with acrylamide, guar gum grafted polyacrylamide (GG‐g‐PAM) and hydroxypropyl guar gum grafted polyacrylamide (HPG‐g‐PAM) is described. The graft copolymers have been characterized by viscometry, infrared spectroscopy and thermal analysis. The flocculation characteristics of the graft copolymers have been studied in kaolin, iron ore, and silica suspensions. For the base polysaccharides guar gum (GG) and hydroxypropyl guar gum (HPG), it is observed that GG exhibits better performance than HPG in all three suspensions. For the graft copolymers, HPG‐g‐PAM shows better performance than GG‐g‐PAM. The flocculation characteristics of the best performing graft copolymer (HPG‐g‐PAM) are compared with various commercially available flocculants in the three suspensions mentioned above. © 2001 Society of Chemical Industry     

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     

Preparation and swelling properties of superabsorbent nanocomposites based on natural guar gum and organo-vermiculite

Vermiculite (VMT) was modified with cetyl trimethylammonium bromide (CTAB). Superabsorbent nanocomposites were prepared by solution polymerization of natural guar gum (GG), partially neutralized acrylic acid (NaA) and organo-vermiculite (CTA⁺-VMT), ammonium persulfate (APS) as initiator and N,N′-methylene-bis-acrylamide (MBA) as crosslinking agent. FTIR spectra confirmed that NaA had been grafted onto GG and the OH groups of CTA⁺-VMT participated in the polymerization reaction. The intercalated-VMT was exfoliated during polymerization and uniformly dispersed in the GG-g-PNaA matrix. Swelling tests show that CTA⁺-VMT improved swelling and swelling rate more remarkably than VMT, and the nanocomposite exhibited distinct kinetic swelling behavior in NaCl and CaCl₂ solution. Organo-VMT improved the gel strength of the nanocomposite compared to VMT, and the maximum storage modulus of the nanocomposite reached 658 Pa (γ = 0.5%, ω = 100 rad/s).     

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     

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     

Carboxymethyl guar: Its synthesis and macromolecular characterization

Guar gum was partially carboxymethylated by the reaction of the base polysaccharide with the sodium salt of monochloroacetic acid in presence of sodium hydroxide. The resulting products (carboxymethyl guar with different degrees of substitution) were characterized by a variety of material characterization techniques, such as intrinsic viscosity measurement, determination of molecular weight, elemental analysis, thermal analysis, ¹³C‐NMR spectra, and Fourier transform infrared analysis. Various grades of carboxymethyl guar gum, which were synthesized in the laboratory, were studied for their suitability as flocculants and viscosifiers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

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.     

瓜尔胶的化学改性

简要介绍了瓜尔胶的结构及其化学改性的原理和方法;综述了国内外瓜尔胶化学改性的研究工作;详细介绍了非离子瓜尔胶、阳离子瓜尔胶、阴离子瓜尔胶、羟烷基阴离子瓜尔胶和羟烷基阳离子瓜尔胶以及两性瓜尔胶的合成方法。瓜尔胶通过改性改善了水溶性、大大降低了水不溶物的含量、提高了电解质的兼容性、增加了黏度的稳定性、从而扩大了瓜尔胶的应用领域,使得改性瓜尔胶广泛应用于化妆品、个人护理品、造纸、油田和增稠剂等众多领域。     

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     

Pentaerythritol encapsulated with boric acid: An efficient composite crosslinker for guar gum fracturing fluid

Commonly used crosslinker agents often have a low crosslinking efficiency with guar gum, the major component of fracturing fluid for crude oil recovery, and it often required a high loading of guar gum for achieving desired recovery from low-permeability reservoir. Nevertheless, a high-loading of guar gum might result in excessive residue and reduce the conductivity of the reservoir. Therefore, boric acid, a commonly used crosslinking agent, was introduced onto the surface of pentaerythritol to afford a composite crosslinking agent denoted as PB. The as-prepared PB crosslinker was characterized by Fourier-transform infrared spectrometry. The guar gum fracturing gel crosslinked with the PB had fantastic viscoelasticity and thermal stability and could reduce the guar gum loading by 16.7%, with boric acid as a control. Besides, the gel-broken liquid had good compatibility with the simulated water and caused reduced damage to rock core, showing potential for hydraulic fracturing of low-permeability reservoirs. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48528.     

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.     

Graft copolymerization of acrylic acid onto guar gum

The graft copolymerization of acrylic acid (AA) onto guar gum (GOH) was carried out by a peroxydiphosphate (PDP)–silver(I) system. Grafting ratio, efficiency, add‐on, and conversion increase upon increasing the concentration of PDP and acrylic acid, whereas they decrease upon increasing the concentration of guar gum. Upon increasing the concentration of silver and hydrogen ions up to 2.0 × 10⁻³ and 4.87 × 10⁻² mol dm⁻³, respectively, the grafting ratio and efficiency increase but decrease upon further increasing the concentration. The increase in temperature from 30 to 45°C increases the grafting ratio but the conversion efficiency decreases. The optimum time period for graft copolymerization was found to be 2 h. The graft copolymers were characterized by infrared spectroscopy and thermogravimetric analysis. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 39–44, 2000     

Synthesis and characterization of a new guar gum 4‐hydroxybenzoic acid resin and its use for the separation of heavy metal ions in industrial effluents

Hydroxybenzoic acid group has been incorporated onto guar gum by modified Porath's method of functionalization of polysaccharides. The newly synthesized guar gum 4‐hydroxybenzoic acid (GHBA) resin was characterized by Fourier‐transform infrared spectroscopy, elemental analysis, ion‐exchange capacity, column reusability, and physicochemical properties. The distribution coefficient (K_d) values and effect of pH on chelation of these metal ions using batch method were studied. The separations of mixture of Fe²⁺, Zn²⁺, Cu²⁺, Cd²⁺, and Pb²⁺ metal ions on GHBA resin on the basis of their distribution coefficient at various pH were also achieved using column chromatography. The effect of experimental parameters such as pH, treatment time, agitation speed, temperature, adsorbent dose, initial metal ion concentration, and flow rate on the removal of metal ions has been also studied. GHBA resin is effective adsorbents for the removal of different toxic metal ions from aqueous solutions and follows the order: Fe²⁺ > Zn²⁺ > Cu²⁺ > Cd²⁺ > Pb²⁺. POLYM. ENG. SCI. 2013. © 2012 Society of Plastics Engineers     

Boric acid incorporated on the surface of reactive nanosilica providing a nano‐crosslinker with potential in guar gum fracturing fluid

Small molecule borate crosslinker widely used in hydraulic fracturing treatment has a low crosslinking efficiency of less than 1%. Thus boric acid was introduced onto the surface of reactive nanosilica (denoted as nano‐SiO₂; size: about 20 nm) containing ? NH₂ group to obtain a nanosilica‐based crosslinker (denoted as nano‐crosslinker) with increased crosslinking efficiency, thereby broadening the application of nano‐SiO₂ in guar gum fracturing fluid. Moreover, the influence of the as‐prepared nano‐crosslinker on the rheological behavior of guar gum gel was investigated with borate crosslinker as a reference. Results show that boric acid chemically reacts with the amino group of the reactive nano‐SiO₂ to form N? B bond, which is beneficial to the formation of the network structure of guar gum gel. The guar gum gel crosslinked with the 57 ppm of borate based on the carrier of nano‐SiO₂ exhibits better temperature tolerance and shear resistance as well as breaking behavior than the counterpart crosslinked with 200 ppm of borate. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 45037.     

Preparation and swelling characteristics of a superabsorbent nanocomposite based on natural guar gum and cation‐modified vermiculite

A series of novel superabsorbent nanocomposites were prepared by the solution radical polymerization of natural guar gum (GG), partially neutralized acrylic acid [sodium acrylate (NaA)], and cation‐exchanged vermiculite (Mⁿ⁺‐VMT) with ammonium persulfate as the initiator in the presence of the crosslinking agent N,N′‐methylene‐bis‐acrylamide. Fourier transform infrared analysis revealed that NaA was grafted onto the GG chains and that Mⁿ⁺‐VMT participated in the polymerization. X‐ray diffraction results showed that the occurrence of the cation‐exchange process changed the interlayer gap of vermiculite (VMT) and that Mⁿ⁺‐VMT was exfoliated during polymerization to form a nanocomposite. The exfoliated VMT led to better dispersion in the GG‐g‐poly(sodium acrylate) matrix, as shown by scanning electron microscopy and transmission electron microscopy analysis. Mⁿ⁺‐VMT improved the water absorption of the nanocomposite more remarkably than raw VMT, and Al³⁺‐VMT enhanced the water absorption to the highest degree. The nanocomposite exhibited intriguing overshooting swelling characteristics in a multivalent saline solution and acidic pH solution and showed switching pH‐responsive behaviors in buffer solutions between pH 2 and pH 7.2. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies of graft copolymerization of acrylamide onto guar gum using peroxydiphosphate–metabisulphite redox pair

The effect of reaction conditions on the grafting parameter during grafting of acrylamide onto guar gum has been studied using peroxydiphosphate–metabisulphite redox pair at 35 °C. Grafting ratio, efficiency and add‐on all increase as the concentrations of peroxydiphosphate and acrylamide increase up to 40.0 × 10⁻³ mol dm⁻³ and 40.0 × 10⁻² mol dm⁻³, respectively. It has been observed that the optimum concentrations of metabisulphite and guar gum for obtaining high grafting ratio, efficiency, add‐on and conversion are 6.0 × 10⁻³mol dm⁻³ and 91.7 × 10⁻² g dm⁻³, respectively. © 2000 Society of Chemical Industry     

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.     

The cholesterol-lowering effect of guar gum is not the result of a simple diversion of bile acids toward fecal excretion

The effects of partially hydrolyzed, nonviscous, guar gum (PHGG) on cholesterol metabolism and digestive balance have been compared with those of native guar gum (GUAR) in rats adapted to 0.4% cholesterol diets. Both types of guar gum elicited acidic fermentations in the large intestine, but only GUAR effectively lowered plasma cholesterol (P<0.001), chiefly in the triglyceride-rich lipoprotein fraction. The biliary bile acid excretion was significantly enhanced in rats fed GUAR (P<0.05), as well as the intestinal and cecal bile acid pool (P<0.001). In rats fed GUAR and to a lesser extent in those fed PHGG, the fecal excretion of bile acids and neutral sterol was higher than in controls (P<0.01). The digestive balance (cholesterol intake-steroid excretion) was positive in control rats (+47 μmol/d), whereas it was negative in rats fed GUAR (−20 μmol/d), which could involve a higher rate of endogenous cholesterol synthesis. In rats fed PHGG, the steroid balance remained slightly positive. Liver 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase activity was very low (22 pmol/min/mg protein), owing to cholesterol supplementation, in control rats or in rats fed PHGG, whereas it was markedly higher (+463%) in rats fed GUAR. In conclusion, even if PHGG does alter some parameters of the enterohepatic cycle of cholesterol and bile acids, its effects are not sufficient to elicit a significant cholesterol-lowering effect. The intestinal (ileal or cecal) reabsorption of bile acids was not reduced, but rather increased, by GUAR; nevertheless the intestinal capacities of reabsorption were overwhelmed by the enlargement of the digestive pool of bile acids. In the present model, induction of HMG-CoA reductase probably takes place in the presence of elevated portal bile acid concentrations.