Unique properties of high viscosity gums

Guar gum, a galactomannan from the seed endosperm of the legume, Cyamopsis tetragonolobus, is an important food stabilizer used in a variety of food products ranging from sauces to ice cream. Two guars having viscosities 13-250% higher than conventional guars were studied. Viscosity, effect of shear rate on viscosity, synergy with xanthan gum, granulation, galactomannan content, molecular weight, and scanning electron microscopy of the guar types were evaluated. At equal usage levels of guar, the high viscosity type showed a higher viscosity alone and in combination with xanthan gum under all conditions tested. The high viscosity products have electron microscopic morphology that is more elongated and molecular weights which are greater than normal guars. These factors are discussed in light of the viscosity differences which exist between these products.     

Preparation,Characterization and Anticoagulant Activity of Guar Gum Sulphate

Guar gum was chemically modified by sulphonation using chlorosulphonic acid (ClSO₃H) as a reagent. Effects of molar ratio of ClSO₃H to glucopyranosic unit (ClSO₃H/GU), reaction time and reaction temperature on the degree of sulphonation (DS) and molecular weight (Mw) of products were studied. The structures of guar gum sulphate were investigated by GPC, FT‐IR and UV‐Visible spectroscopy. Activated partial thromboplastin time (APTT) assay showed that the guar gum sulphate could inhibit the intrinsic coagulant pathway. The anticoagulant activity strongly depended on the DS and Mw of polysaccharides. DS>0.56 was essential for anticoagulant activity. The guar gum sulphate with the DS of 0.85 and the Mw of 3.40×10⁴ had the best blood anticoagulant activity.     

Kinetic investigations on the alkaline hydrolysis of tris-(1,10-phenenthroline)Fe(II) with guar gum–surfactant interactions

The kinetic investigations on the alkaline hydrolysis of tris-(1,10–phenanthroline)iron(II) has been explored spectrophotometrically in microheterogeneous environment at 301?K and ionic strength of 0.13?mol?L^?1. Guar gum, cationic amphiphiles, and their mixtures are used as the reaction environments to carry out the reaction. Guar gum decreases the rate of reaction, which indicates that Fe(II) complex may be trapped in the hydrophobic region of gum. Cationic amphiphile decreases the rate in the presence of guar gum. The extent of interaction between guar gum and amphiphile increases with the hydrophobic carbon chain length. The critical aggregation concentration (CAC) and critical micelle concentration (CMC) of the amphiphiles (cetyl trimenthyl ammonium bromide (CTAB), tetradecyl trimenthyl ammonium bromide (TTAB), dodecyl trimenthyl ammonium bromide (DTAB)) in the presence of guar gum have been determined with conductometry and tensiometry. All observations support either weak or strong interaction of cationic amphiphiles with guar gum. Activation parameters of the reaction in different environments have been determined which corroborate the rate data.     

Graft copolymerisation of acrylamide onto cashew gum

The synthesis of cashew gum-g-polyacrylamide was carried out at 60 °C by a radical polymerisation using potassium persulphate as the redox initiator under N₂ atmosphere. A series of graft copolymers, varying in acrylamide concentration and keeping the concentration of the initiator and polysaccharide constant, was prepared. These graft copolymers were characterised by elemental analysis, infrared and ¹³C NMR spectroscopy, rheological studies, differential scanning calorimetry and thermogravimetric analysis. Comparisons amongst grafting parameters of the reaction of various natural polysaccharides with polyacrylamide (PAM) were carried out. High percentages of acrylamide conversion (%C) and grafting efficiency (%E) were obtained for cashew gum (CG), even with a low acrylamide/gum ratio. All copolymers had intrinsic viscosity and thus the hydrodynamic volume much higher than the CG value and closer to the PAM. The CG-g-PAM solution had an absolute viscosity at 2.5% concentration (wt./vol.) up to 33 and 3.3 times the CG and PAM values, respectively. Grafting of PAM chains onto the polysaccharide enhances its thermal stability.     

Synthesis and Characterization of an Exopolysaccharide by Antarctic Yeast Strain <Emphasis Type="Italic">Cryptococcus laurentii</Emphasis> AL<Subscript>100</Subscript>

An exopolysaccharide-producing Antarctic yeast strain was selected and identified as Cryptococcus laurentii AL₁₀₀. The physiological properties of the strain and its ability to utilize and biotransform different carbon sources (pentoses, hexoses, and oligosaccharides) into exopolysaccharide and biomass were investigated. Sucrose was chosen as a suitable and accessible carbon source. The biosynthetic capacity of the strain was studied in its dynamics at different sucrose concentrations (20, 30, 40, and 50 g/L) and temperatures (22 and 24 °C). The maximum biopolymer quantity of 6.4 g/L was obtained at 40 g/L of sucrose, 22 °C temperature and 96-h fermentation duration. The newly synthesized microbial carbohydrate was a heteropolysaccharide having the following monosaccharide composition: arabinose, 61.1%; mannose, 15.0%; glucose, 12.0%; galactose, 5.9%; and rhamnose, 2.8%. It was characterized by polydispersity of the polymer molecule, 60% of it having molecular mass of 4200 Da. The exopolysaccharide demonstrated good emulsifying and stabilizing properties with regard to oil/water emulsions and a pronounced synergistic effect with other hydrocolloids such as xanthan gum, guar gum, and alginate.     

Biodegradable stereocomplex materials of polylactide‐grafted dextran exhibiting soft and tough properties in dry and wet states

Water‐swellable biodegradable materials exhibiting mechanically tenacious and tough characters in the wet state were prepared by a simple blend of two enantiomeric polylactide‐grafted dextran copolymers (Dex‐g‐PLLA and Dex‐g‐PDLA). DSC and WAXD analyses demonstrated the formation of SC crystals in the copolymer blend films. SC blend films showed lamellar‐type microphase‐separated structures. When swollen with water, these blend films showed the same level of tensile strengths and Young's modulus as the films in the dry state. SC blend films degraded gradually over a month under physiological conditions with a degradation rate faster than the corresponding Dex‐g‐PLLA films. The SC‐forming enantiomeric mixture of polylactide‐grafted polysaccharides should be a good candidate for an implantable biocompatible material exhibiting favorable mechanical properties and degradation behavior. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Radiation effects on polymers—XIII. The application of cellulose acetate-g-polyacrylamide membranes in the process of water desalination by reverse osmosis

Using computerized programs, the water flux and salt rejection properties in reverse osmosis of cellulose acetate-g-acrylamide membranes are determined. Comparisons are made with ungrafted commercial cellulose acetate membranes, using 0.1 and 1.0 M sodium chloride, sodium sulphate and ammonium sulphate solutions. The grafted cellulose acetates show improved water flux but reduced NaCl rejection. However, they show promising prospects in bigger ion separation as for Na₂SO₄ and (NH₄)₂SO₄ solutions.     

Gelation Studies, 3

Summary: The sol‐gel transition of one thermoreversible gelling mixture made of xanthan gum and locust bean gum has been studied by using in situ time‐resolved dynamic light scattering (DLS) and measuring the spin‐lattice relaxation time T₁ of several protons. A critical dynamical behavior was observed near the sol‐gel transition, which is characterized by the presence of power‐law spectra over four decades of the delay time in the time‐intensity correlation function g₂(t)−1 ∼ t^−μ at 48 °C. The increase in T₁ with increasing temperature becomes steeper at 50 °C indicating a significant change in the local mobility of one anomeric proton of the xanthan side chain and the anomeric protons of the locust bean gum mannose backbone.

Temperature dependence of the spin‐lattice relaxation time T₁ for the equatorial anomeric proton of the mannopyranosic unit located next to the main chain of the xanthan.     

The pyrolysis characteristics of moso bamboo

In the research, thermogravimetry (TG), a combination of thermogravimetry and Fourier transform infrared spectrometer (TG–FTIR) and X-ray diffraction (XRD) were used to investigate pyrolysis characteristics of moso bamboo (Phyllostachys pubescens). The Flynn–Wall–Ozawa and Coats–Redfern (modified) methods were used to determine the apparent activation energy (E_a). The TG curve indicated that the pyrolysis process of moso bamboo included three steps and the main pyrolysis occurred in the second steps with temperature range from 450 K to 650 K and over 68.69% mass was degraded. TG–FTIR analysis showed that the main pyrolysis products included absorbed water (H₂O), methane gas (CH₄), carbon dioxide (CO₂), acids and aldehydes, ammonia gas (NH₃), etc. XRD analysis expressed that the index and width crystallinity of moso bamboo gradually increased from 273 K to 538 K and cellulose gradually degraded from amorphous region to crystalline region. The E_a values of moso bamboo increased with conversion rate increase from 10 to 70. The E_a values were, respectively 153.37–198.55 kJ/mol and 152.14–197.87 kJ/mol based on Flynn–Wall–Ozawa and Coats–Redfern (modified) methods. The information was very helpful and significant to design manufacturing process of bio-energy, made from moso bamboo, using gasification or pyrolysis methods.     

New polysaccharide-g-polyacrylonitrile copolymers: synthesis and thermal characterization

Various natural and modified polysaccharides (i.e. arabic gum, tragacanth gum, xanthan gum, sodium alginate, chitosan, sodium carboxymethyl cellulose, hydroxyethyl cellulose, methyl cellulose) were modified using ceric-initiated graft polymerization of acrylonitrile under inert atmosphere. Grafting was confirmed using spectral (FT-IR) proofs. The grafting parameters were determined by conventional methods. Thermal characteristics of the homopolymer-free copolymers were studied using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) under nitrogen atmosphere. The major thermal transitions as well as the activation energy of the major decomposition stages were investigated. The polyacrylonitrile (PAN)-grafted polysaccharides were recognized to be thermally stable more than the corresponding non-grafted substrates, although they begin to decompose at relatively lower temperatures than the non-grafted counterparts. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and characterization of guar gum‐graft‐polyacrylonitrile

Cerium(IV) mediated grafting of polyacrylonitrile on to guar gum was studied. Grafting parameters were studied gravimetrically, as a function of temperature, initiator concentration and Guar to acrylonitrile ratio. Higher temperatures resulted in higher monomer conversion and homopolymer formation. Both monomer conversion and extent of grafting increased with increase in cerium ion concentration in the range studied (0.91–9.12 mmol/l). Similar results were obtained with increase in monomer to guar gum ratio from 1 to 5. Grafting with this initiator was found to be generally good with high grafting efficiencies and low homopolymer formation for most experiments. The copolymers obtained were subjected to alkaline hydrolysis to convert nitrile groups in to carboxylic acid groups and the water absorbency of the resulting anionic guar gum was studied. Materials with water absorption up to 300 g/g could be obtained from this study. Copyright © 2003 John Wiley & Sons, Ltd.     

Microwave promoted methylation of plant polysaccharides

O-Methylation is of outstanding importance in structural polysaccharide chemistry. A novel method for the methylation of polysaccharides using microwave (MW) irradiation is described. Seed gum from Cyamopsis tetragonolobus (Guar) was fully methylated with dimethyl sulphate and sodium hydroxide using 100% microwave power for 4 min in 68% yield. The completely methylated seed gum thus obtained was hydrolyzed by 70% formic acid followed by 0.5N H₂SO₄ under full microwave power for 1.16 and 1.66 min, respectively. The partially methylated monosaccharides were separated and identified.     

Xanthan Production on Polyurethane Foam and Its Enhancement by Air Pressure Pulsation

In this study, we evaluated the feasibility of solid-state fermentation (SSF) on polyurethane foam (PUF) for xanthan production. The effects of air pressure pulsation (APP) on biomass accumulation and final xanthan concentration were also studied. Under suitable conditions (15% inoculum, 0.5-cm (side length) PUF cubes, 15 mL medium per gram cubes and 4.5 cm bed depth), the broth was dispersed on the PUF as a film. When the initial glucose concentration in the media was low (20 and 40 g L⁻¹), there was no significant difference between the final xanthan concentration in static SSF and submerged fermentation (SMF). When high initial glucose concentrations (60 and 80 g L⁻¹) were used, the final gum concentrations in SSF were much higher than those in SMF. When the APP technique was applied in xanthan production with a medium containing a high glucose concentration (80 g L⁻¹), the oxygen consumption rate of Xanthomonas campestris was significantly enhanced at the later stages of fermentation, and both the biomass and xanthan concentration were improved. The results indicated that SSF on PUF is suitable for xanthan preparation, especially when the initial glucose concentration ranged from 60 to 80 g L⁻¹. Those results also demonstrated that APP technology can be used to enhance xanthan yields.     

Guarnt® bland,a reduced odor stabilizer and soluble dietary fiber

The odor and flavor of guar gum may emanate from the breakdown of lipid, protein and/or isoflavones. Guar gum is a galactomannan isolated from the annual plant, Cyamopsis tetragonolobus, Guar is widely used as a thickening agent but due to its characteristic off-flavor and odor, its usage level has been limited. GuarNT bland, subjected to a proprietary process to reduce its off-flavor and odor, offers the food formulator more options. GuarNT bland can be subjected to a prehydration process to improve its dispersion and increase hydration rate and avoid lumping problems during large-scale production. It is used as a thickening agent, suspending agent and a “natural” source of soluble dietary fiber (80% minimum, dry basis). Rheological data using a programmable Brookfield rheometer, hexanal levels (index of grassy flavor), PCA analyses (Aroma Scan, Foss NA) and sensory tests by trained panelists were obtained. Prototype formulations using GuarNT Bland are available and usage levels permitted by CFR are included.     

Surface‐initiated atom transfer radical polymerization of a new rhodanine‐based monomer for rapid magnetic removal of Co(II) ions from aqueous solutions

The present study reports synthesis and characterization of a new acrylamide‐based monomer containing rhodanine moiety, N‐3‐amino‐thiazolidine‐4‐one‐acrylamide (ATA). Poly(ATA)‐grafted magnetite nanoparticles (poly(ATA)‐g‐MNPs) were prepared using surface‐initiated atom transfer radical polymerization of the monomer on Fe₃O₄ nanoparticles. The grafted nanoparticles were characterized by Fourier transform infrared analysis, scanning electron microscopy, X‐ray diffraction, and vibrating sample magnetometry. The amount of the grafted polymer was 209 mg g⁻¹, as calculated from thermogravimetric analysis experiment. The capability of poly(ATA)‐g‐MNPs to remove Co(II) cations was shown under optimal conditions of contact time, pH, adsorbent dosage, and initial Co(II) concentration. About 86% of the Co(II) cations were removed over 7 minutes. The adsorption kinetics obeyed the pseudo–second‐order kinetic equation, and the Langmuir isotherm model best described the adsorption isotherm with a maximum adsorption capacity of 3.62 mg g⁻¹. The thermodynamic investigation showed spontaneous nature of the adsorption process (ΔG = −2.90 kJ mol⁻¹ at 25°C ± 1°C). In addition, the poly(ATA)‐g‐MNPs were regenerated by simply washing with an aqueous 0.1M HCl solution. The study of the reusability of the prepared magnetic sorbent revealed that the sorbent can be reused without a significant decrease in the extraction efficiency and be recovered by 95.4% after 7 cycles. These findings suggest that the grafted nanoparticles are stable and reusable adsorbent and can be potentially applied to water treatment in efficient removal of Co(II) cations.     

Hydrophobic guar gum derivatives prepared by controlled grafting processes

Introduction of polyalkoxyalkyleneamide grafts to guar gum produces a new water soluble guar derivative. Modification of either guar gum or hydroxyopropyl guar is achieved in a three‐step process: carboxymethylation with sodium chloroacetate, esterification with dimethyl sulfate (DMS) and amidation with a series of polyalkoxyalkyleneamines. The process was followed using infrared spectroscopy; the grafted guar derivatives were characterized using ¹H NMR. A series of hydroxypropyl guar (HPR) derivatives with degrees of carboxymethylations ranging from 0.2–0.3 were modified with polyalkoxyalkyleneamines with molecular weights ranging from 300 to 3000. The ratio of oxypropylene to oxoethylene units in the polyalkoxyalkyleneamines was varied from 9/1 to 8/58 to adjust the hydrophobicity of the grafts. Aqueous solutions of the graft copolymers exhibit viscosities one to two orders of magnitude lower than the corresponding solutions of the parent guar gum. Copyright © 2007 John Wiley & Sons, Ltd.     

Amorphization of a crystalline active pharmaceutical ingredient and thermoanalytical measurements on this glassy form

Amorphization is nowadays a method that is frequently applied in the pharmaceutical industry. The primary aim of this study is to achieve the amorphization of clopidogrel hydrogen sulphate as an active pharmaceutical ingredient (API) with various solvents and to choose the most suitable one. A secondary aim was to determine the glass-transition temperature (T _g) of this API and to classify it as a good or poor glass former. To investigate the amorphous form, differential scanning calorimetry, X-ray powder diffraction, and FT-IR analysis were applied. The melting point (T _m) was 177.4 °C (450.6 K), and T _g was determined to be 88.9 °C (362.1 K). The quotient T _g/T _m was 0.80, and this API was therefore classified as a good glass former.     

Degradation of poly(N-vinylcarbazole) by annealing under iodine pressure

After room temperature doping of poly(N-vinylcarbazole) by iodine, the powders are annealed at different temperatures (370, 470, and 570 K) for 24 h under vacuum or under iodine pressure. The obtained powders were studied by infrared absorption, x-ray photoelectron spectroscopy, x-ray diffraction, and nuclear magnetic resonance. Annealing of pure PVK powder increases the crystallization quality of the sample. Annealing with iodine induces progressive polymer degradation. At 570 K under iodine pressure the PVK is totally destroyed. The aromatic rings and the C(SINGLEBOND)N bonds have disappeared. NH₄I crystallites have formed, embeded in a degraded, cross-linked polymer matrix. © 1996 John Wiley & Sons, Inc.     

Succinic or glutaric anhydride modified linear unsaturated (epoxy) polyesters

A series of N-alkyl-N-alkyl′-pyrrolidinium-bis(trifluoromethanesulfonyl) imide (TFSI⁻) room temperature ionic liquids (RTILs) has been investigated by means of thermogravimetric analysis (TG), differential scanning calorimetry, FT-IR spectroscopy, and X-ray diffraction analysis. These compounds exhibit a thermal stability up to 548–573 K. The mass loss starting temperature, T _ml, falls in a narrow range of temperatures: 578–594 K. FT-IR spectra, performed before and after 24 h isothermal experiments at 553 and 573 K, have confirmed their great thermal stability. Below the ambient temperature, these compounds exhibit a complex behavior. N-methyl-N-propyl-pyrrolidinium-TFSI is the sole liquid which crystallizes without forming any amorphous phase even after quenching in liquid nitrogen. Its crystalline phase has a melting point, T _m, of 283 ± 1 K. When the amorphous solid is heated, the N-butyl-N-ethyl-pyrrolidinium-TFSI presents a glass transition temperature, T _g, at 186 K followed by a cold crystallization, T _cc, at 225 K, and a final T _m at 262 K. The N-butyl-N-methyl-pyrrolidinium-TFSI exhibits a T _g between 186 and 181 K, its cold crystallization leading to two different solid phases. Solid phase I has a melting point T _I,m = 252 K and phase II, T _II,m = 262 K. When the amorphous phase is obtained at a cooling rate of 10 K/min, its T _cc is 204 K, and a metastable solid phase (III) is obtained which transforms into the phase II at 226 K. However, when the sample is quenched, the amorphous phase transforms into phase II at T _cc = 217 K and phase I at 239 K. P₁₅-TFSI exhibits the most complicated pattern as, on cooling, it leads to both a crystallized phase at 237 K and an amorphous phase at 191 K. On heating, after a T _g at 186 K and a T _cc at 217 K, two solid–solid phase transitions are observed at 239 K and 270 K, the final T _m being 279 K.     

Morphology of polysaccharide blend fibers shaped from NaOH, <Emphasis Type="Italic">N</Emphasis>-methylmorpholine-<Emphasis Type="Italic">N</Emphasis>-oxide and 1-ethyl-3-methylimidazolium acetate

The aim of this study was to find newly structured biopolymer blends bearing those adjustable features able to produce innovative materials. Apart from cellulose derivatives (cellulose carbamate and carboxymethyl cellulose), mannans (guar gum, locust bean gum, and tragacanth gum), xylan, starch (cationized), ι-carrageenan, and xanthan were chosen as blend polysaccharides for cellulose as matrix. In order to study their integration into the cellulose skeleton, fibers were shaped from three different solvents: NaOH by a special wet-spinning process, as well as N-methylmorpholine-N-oxide (NMMO) and 1-ethyl-3-methylimidazolium acetate (EMIMac) via Lyocell technology. The structure and morphologies of the fibers were analyzed by X-ray wide-angle scattering and atomic force microscopy. Hydrophilic/hydrophobic properties were determined by means of a contact angle, as well as moisture content and water retention values, while the surface properties throughout zeta-potential measurements. Being very different processes, the wet spinning in NaOH solution and the dry–wet spinning are deeply impacted by the types of solvent and polysaccharide. The X-ray results for NMMO fibers revealed the highest orientation compared with EMIMac having the lowest orientation of NaOH fibrous types. AFM images also show the lowest surface roughnesses for NMMO and EMIMac fibers. The moisture content and water retention values support these trends, while the water contact angle results show insignificant differences between the samples from EMIMac and NaOH, even though the values calculated for NMMO fibers were the lowest.