Abstract: BACKGROUND: As part of an ongoing research and development programme of our laboratory on functional modification of seaweed polysaccharides for preparing hydrogels with improved properties, we report herein the preparation of a robust hydrogel system based on grafting of agar and sodium alginate blend (Agar/Na-Alg) with acrylamide (AAm) to obtain the copolymer Agar/Na-Alg-graft-PAAm.
RESULTS: A robust hydrogel system with superior absorbency and pH resistance has been developed based on a PAAm-grafted seaweed polysaccharide blend of Agar/Na-Alg. The blend (Agar/Na-Alg) and grafted product (Agar/Na-Alg-graft-PAAm) were evaluated using Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, swelling capacity, rheology and scanning electron microscopy. The swelling capacity of the grafted copolymer exhibited an enhancement over that of the blend from 14 to 24 g g-1 in acidic medium. The blend and grafted copolymer produced hydrogels with lower gelling points of 31 and 29 °C and gel strengths were 170 and 120 g cm-2, respectively.
CONCLUSION: This study constitutes an example of value addition of seaweed polysaccharides targeting new applications. The copolymer hydrogel may be useful in health, personal care and agricultural applications.
Abstract: Agar and ï«-carrageenan are seaweed polysaccharides and by virtue of their gelling nature these exhibit excellent film forming properties. We have disclosed recently a novel process for preparation of biodegradable film from semi-refined κ-carrageenan (US Patent No.7,067,568). A new approach of functionalization of seaweed polysaccharide based thin films leading to partial hydrophobization using methyl methacrylate (MMA) was achieved by carrying out grafting reaction prior to casting the films, in the presence of potassium persulphate (KPS) in the film forming dispersions based on agar or ï«-carrageenan under microwave irradiation, instead of using the film directly for this reaction as it is usually done. The hydrophobicity of the films was measured by contact angle and swellability measurements, which showed that the films thus prepared became significantly hydrophobic compared to those of the parent polysaccharides. FT-IR (ATR), SEM-EDAX and ESI-MS/MS analysis confirmed grafting of methyl methacrylate (MMA) on the polysaccharides and films.
The pore size of the films determined from water vapour permeability (WVP) values indicated their potential utility in pervaporation and gas separation membrane applications. The biodegradability of the functionalized films was also studied. This study thus provides a new one-pot method of preparing partially hydrophobic thin films, which would have wider applicability.
Abstract: Gracilaria edulis, G. crassa, G. foliifera, and G. corticata are naturally occurring agarophytes of Indian waters. These agarophytes were evaluated for their agar contents using an improved process recently reported by us (US Patent 2005/0267296A1). The effect of different concentrations of NaOH in the alkali treatment was studied for optimizing the extraction conditions. These Gracilaria species of Indian waters produced agars, both native and alkali treated, with different properties confirming the heterogeneity of the agar polymers in this genera, as one would expect. Among these, G. edulis and G. crassa produced agar polymers having high gel strengths of 490â±â8.16 and 800â±â15.4 g cmâ2, respectively, with 8% NaOH treatment as opposed the low gel strength agars that have been reported in the literature to date.
Abstract: Genipin-fixed kappa-carrageenan was prepared in ambient conditions in aqueous solution using genipin, a naturally occurring crosslinker with kappa-carrageenan (κC). The crosslinked κC showed the greatest swelling capacity in acidic medium having pH 1.2 when compared to those in neutral and alkaline media. Enhanced stability of the crosslinked product with respect to the non-modified κC was confirmed by degradation studies in Ringer's solution, rheological and thermogravimetric measurements. Genipin fixation of κC was confirmed by measuring the bulk density, true density, pore volume, porosity, intrinsic viscosity, UV absorbance and optical rotation of the crosslinked κC, and as well as by optical microscopy, SEM, and MS/MS studies. The crosslinked product may be useful as super absorbent and sustained release formulation in biomedical applications.
Abstract: Agarose was prepared from a red alga Gracilaria dura occurring in the Arabian Sea at the west coast of India. The agarose has been characterized by studying its physicochemical properties as well as by FTIR, 13C NMR and CP-MAS spectra, inductively coupled plasma (ICP) spectrophotometric and rheological measurements. This agarose had gel strength 2200 g cmâ2, gelling temperature 35 °C, sulphate content 0.25%, and Mw 1.25 à 105 g molâ1. These properties were benchmarked against those of the commercially available agarose products of Sigma (A0576) and Fluka, and were found to be comparable.
Abstract: Turbidity measurements performed at 450 nm were used to follow the process of complex formation, and phase separation in gelatinâagar aqueous solutions. Acid (Type-A) and alkali (Type-B) processed gelatin (polyampholyte) and agar (anionic polyelectrolyte) solutions, both having concentration of 0.1% (w/v) were mixed in various proportions, and the mixture was titrated (with 0.01 M HCl or NaOH) to initiate associative complexation that led to coacervation. The titration profiles clearly established observable transitions in terms of the solution pH corresponding to the first occurrence of turbidity (pHC, formation of soluble complexes), and a point of turbidity maximum (pH, formation of insoluble complexes). Decreasing the pH beyond pH drove the system towards precipitation. The values of pHC and pH characterized the initiation of the formation of intermolecular charge neutralized soluble aggregates, and the subsequent formation of microscopic coacervate droplets. These aggregates were characterized by dynamic light scattering. It was found that Type-A and -B gelatin samples formed soluble intermolecular complexes (and coacervates) with agar molecules through electrostatic and patch-binding interactions, respectively.
Abstract: Seventeen agar samples were extracted from Gelidiella acerosa (Forsskal) Feldmann and Hamel (Rhodophyta, Gelidiales) specimens collected from nine different sites on the Indian coastâfive from southeast coast and four from the west coast. The agar samples were analysed. The stability characteristics of the gels of selected agar samples were studied by rheometry under applied stress conditions, i.e. variation of the storage (Gâ²) and loss moduli (Gâ³) were studied under varying frequency and duration (time) of the stress applied. Yield, apparent and dynamic viscosities, gelling and melting temperatures, 3,6-anhydrogalactose (3,6-AG), sulphate contents and TGA (Thermogravimetric Analysis) measurements of the products were done. It was observed that the best quality agar was produced by G. acerosa occurring in the Gulf of Mannar region in the southeast coast. The gel strengths and the viscosities of agars extracted from Gelidiella acerosa occurring in the Gulf of Mannar ranged from 500 to 700 g cmâ2 and 33 to 45 cP for 2001 collections and for 2002 collections the corresponding values were 450 to 845 g cmâ2 and 55 to 67 cP respectively. On the other hand, for the agar samples extracted from the west coast of India, the gel strength and viscosities values ranged from 225 to 400 g cmâ2 and from 15 to 30 cP, respectively. The agars obtained from G. acerosa collected from southeast coast have been found to be suitable for bacterial culture and molecular biology. This is the first report of superior quality of agar from the Indian agarophytes.
Abstract: Genipin, a naturally occurring crosslinker, was employed to modify agarose in aqueous medium at pH 7 at ambient conditions. The physical and rheological properties were studied. The genipin-fixed agarose hydrogel (0.8 wt % genipin with respect to the polysaccharide) having the maximum swelling capacity was obtained after 85-h crosslinking reaction. The reaction mixture developed a dark blue color with the passage of time, indicating thereby the progress of the crosslinking reaction in presence of genipin. The maximum swelling of the genipin-fixed agarose hydrogel in acidic medium at pH 1.2 was 48 g/g, whereas the parent polysaccharide agarose achieved equilibrium swelling state at 6 g/g. The genipin-fixed agarose showed 30% weight loss in Ringer's solution, while the agarose polysaccharide exhibited 50% weight loss in the same medium, both after 60 days. The thermogravimetric analysis studies revealed enhanced thermal stability of the genipin-fixed agarose hydrogel. In view of the enhanced stability and swelling capacity of the genipin-fixed agarose compared to agarose, the value added polysaccharide may be useful in new applications as super absorbents and in biomedical applications.
Abstract: -Carrageenan-graft-PAAm, a copolymer hydrogel of -carrageenan (kC) and acrylamide (AAm), has been synthesized in aqueous medium at pH 7 in the presence of the initiator potassium persulfate (KPS), using microwave irradiation. The reaction conditions were optimized by varying the concentration of AAm and KPS to obtain copolymer hydrogels having different nitrogen contents e.g., %N 6.35, 10.56, and 11.05. It was observed that copolymer hydrogel having %N 11.05 gives superior adhesive properties whereas copolymer hydrogel with %N 10.56 produces superior absorbent properties in the presence of optimized concentrations of AAm (0.87 and 1.1428 mol/L respectively) and KPS (0.022 and 0.0296 mol/L respectively). The product with %N 6.35 is a soft gel (2-5% gel in 1% KCl) exhibiting low gel strength (135 g cm-2). The one with %N 10.56 showed superior swelling property and maximum swelling was observed in the alkaline pH (22 g/g). The swelling behaviors of the hydrogels were studied at different pHs (pH 1.2-12.5) as well as in 1% aqueous solutions of NaCl, KCl, and CaCl2. The 5% dispersion of the hydrogel having %N 11.05 in water had good binding properties with papers, polyethylene sheets, and wood pieces. To evaluate the measure of adhesive property, the viscosity and solid and liquid weights of the applied adhesive were measured. Characterization of the copolymer hydrogels was done by TGA, X-ray diffraction, 13C-NMR, FT-IR, elemental analyses, and rheological studies.
Abstract: -Carrageenan-g-PMMA copolymer has been synthesized by copolymerizing -carrageenan with methyl methacrylate (MMA) in aqueous medium at about pH 7. The copolymerization was carried out under microwave irradiation in the presence of a water-soluble initiator potassium persulphate. Optimum microwave irradiation conditions for obtaining maximum yields are described. The structural characteristics and thermal stability of -carrageenan-g-PMMA was studied by FTIR, NMR, and thermo gravimetric (TGA) measurements. Crystallinity of the copolymer was studied by powder X-ray diffraction. TGA, IR, and XRD data indicated that the -carrageenan was considerably modified. Optical micrograph of the copolymer was also studied. A probable mechanism of formation of the copolymer is proposed.
Abstract: Physicochemical and rheological properties of agars extracted from 20 samples of Gelidiella acerosa collected from Gujarat coast in various seasons have been evaluated. The agar yields varied significantly (8.5â40.4%). The gel strength values were in the range of 200-700 g cm-2 (1.5% gel at 20oC) having gelling temperatures 36-41oC. It was observed that agar obtained from Gelidiella acerosa of Okha, in almost all seasons has superior physicochemical and rheological properties than the rest of the samples. The 3,6-anhydrogalactose (3,6-AG) and sulphate content too varied significantly among the agar of each place. It was observed that the better quality agar has relatively lower sulphate and higher 3,6-anhydrogalactose contents. Therefore, Gelidiella acerosa of Okha can be used as a good source of agar. Rheological data of the best agar of the lot were also in good agreement with the other physicochemical data e.g., high gel strength agar showed higher G¢ value and vice versa.
Abstract: Grafting of agar and -carrageenan with polyvinylpyrrolidone (PVP, average molecular weight 10,000 D) in an aqueous medium at a pH of about 7 produced agar-graft-PVP and -carrageenan-graft-PVP blends capable of forming hydrogels. The reaction was carried out with microwave irradiation in the presence of a water-soluble initiator, potassium persulfate. Optimum microwave irradiation conditions for obtaining hydrogels of the grafted products were achieved. The structural characteristics and thermal stability of the grafted blends were studied by Fourier transform infrared, 13C-NMR, and thermogravimetric analyses. Appearance of new IR bands at 1661, 1465, and 1426 cm-1 in the grafted products indicated the insertion of PVP into the polysaccharide structure. Powder X-ray diffraction studies revealed the enhanced crystallinity in the products compared to in the control polysaccharides as well as PVP. Agar and -carrageenan were grafted to a considerable degree, with 62.5 E % and 125 G % for agar-graft-PVP and 65.5 E % and 131 G % for -carrageenan-graft-PVP. Optical micrographs of the grafted blends indicated considerable changes in the morphology of the agar and the -carrageenan, substantiating the X-ray diffraction data. A plausible mechanism for the crosslinking of PVP to agar and -carrageenan is proposed. These hydrogels exhibited enhanced water-holding capacity despite weaker gel strength than that in the respective control polysaccharides.
Abstract: Sugar reactivity was observed within the sugarâagar complexes in presence of sucrose and glucose with agars of Indian agarophytes viz. Gelidiella acerosa, Gracilaria edulis, Gracilaria crassa and Gelidium pusillum. The sugar reactivity was more pronounced in presence of sucrose than glucose. Oxoid agar was used as the reference material. Control agar gel contained 1.12% agar (w/w) in water. Sucroseâagar and glucoseâagar gels in water consisted of 50% (w/w) sucrose and 50% (w/w) glucose, respectively along with 1.12% (w/w) agars of the four seaweeds mentioned above. Addition of sucrose resulted in increase (ca. 25â45%) in gel strength; increase (2â3 °C) in gelling and melting temperatures was observed in the gels prepared with agars from all the agarophytes and Oxoid agar. On the other hand, addition of glucose resulted in increase (19â34%) in the gel strength and gelling and melting temperatures of the agar gels of Oxoid as well as of all other agars decrease (2â3 °C). Maximum sugar reactivity was observed with the 50% level of sucrose and glucose in agar gels. Rheological and thermogravimetric characteristics of these gel samples were studied. The latter showed two patterns e.g. control agar gel of Oxoid agar was thermally less stable than the four control agar samples studied; in sugarâagar gel samples it followed a reverse pattern. To our knowledge, this is the first report of âsugar reactivityâ of agar of Indian agarophytes. Sugar reactivity of agar in presence of glucose is also reported for the first time. The results of this study will be useful in bioprospecting as well as in exploring new applications.
Abstract: Four saturated (C12:0âC18:0) and one unsaturated fatty acid (C18:1) were allowed to react with agar and the resulting agar-fatty acid inclusion complexes were investigated. The bound fatty acids present in agar-fatty acid complexes were isolated and estimated by HPLC using UVâvis detector. Subsequently, confirmatory analysis of these fatty acids were done using TOF LCâMS technique. It was observed that the presence of fatty acids in the agar-fatty acid complexes affected the physical (e.g. gel strength, viscosity, swelling behaviour, syneresis and surface tension) and rheological behaviour (e.g. dynamic viscosity and viscoelasticity) of agar sol and gel.
Abstract: Rheological and thermal properties of agar sol and gel in presence of various cationic, anionic and non-ionic surfactants are reported. The agar used was from the red seaweed Gelidiella acerosa. The gel strength, viscosity, rigidity (Gâ²), gelling temperature and melting temperature were observed to decrease in presence of non-ionic surfactants whereas these were enhanced in presence of ionic surfactants. TGA studies showed that 1.5% agar gels containing non-ionic surfactants lose water at a lower temperature than the control agar gel whereas gels containing ionic surfactants hold on to water more tenaciously. DSC studies, on the other hand, show that the gel to sol transition occurs at lower temperatures in presence of non-ionic surfactants and at higher temperature in presence of ionic surfactants when compared with the control gel. The non-ionic surfactants, Triton X-100 and Brij 35, enabled relatively concentrated agar extractive to be filtered readily, as a result of which water usage in the process could be reduced by 50%. The surfactant was subsequently removed through freezeâthaw operations to restore the gelling capacity of the agar. The finding that 0.3â0.4% (w/v) sodium lauryl sulfate (SLS) lowers the solâgel transition temperature from 41 to 36 °C without adversely affecting gel strength is another useful outcome of the study that may enable better formulations of bacteriological agar to be prepared.
Abstract: The interaction of CTAB (Cetyl trimethyl ammonium bromide) with the agar has been investigated by surface tension and fluorescence measurements. The plots of the surface tension vs concentration of the surfactants for different polymer concentrations shows interesting feature of the polymer surfactant binding. It was observed that the binding capacities of CTAB are dependent on the polysaccharide concentrations. These results are interpreted in terms of a polymer surfactant complex or micelle formed by binding between the surfactant ions and the polymer. The surface tension experiment shows that the 218 mmol CTAB could be bound to the galactose-anhydrogalactose unit of agar. Fluorescence measurements using pyrene as a photophysical probe were carried out for agar and CTAB mixtures. The interactions between the neutral agar and cationic CTAB leads to formation of pre-micelles at surfactant concentration lower than CMC (0.9585 mM/L) of CTAB. The aggregation process is amused to be electrostatic attraction. It has been proved, using pyrene fluorescence measurements methods, that CTAB form induced micelles at concentrations smaller than those needed to form micelles in aqueous solution.
Abstract: The main aim of the work is to study the physicochemical and rheological behaviour of agar gel extracted from a red seaweed Gelidiella acerosa collected from various locations and seasons in southeast coast and west coast of India. The thesis also deals with the rheological studies of agar gels in presence of various additives including surfactants and fatty acids as well as agar and carrageenan based film-forming dispersions. The observed shear viscosity values were correlated with existing rheological models. It was observed from the shear viscosity studies that agar gel become more gel thinning in presence of non ionic surfactants as well as in presence of fatty acids. Oscillation sweep measurements revealed that the agar gel become liquid like in presence of nonionic surfactants and opposite is true in presence of ionic surfactants. The film forming dispersions prepared from agar and plasticizers had inferior rheological behaviour in comparison to k-carrageenan based thin film forming dispersions. All the agar gel samples collected from various locations displayed different rheological behaviours.
Abstract: The present invention relates to use of inexpensive semi-refined kappa carrageenan as a seaweed polysaccharide in preparation of tough, biodegradable films exhibiting improved performance over films obtained from refined kappa carrageenan. The formulation requires no gelling salt and the only other essential components of the film are glycerol and water, the former being used as plasticizer as reported in the prior art. The films can be recycled and reprocessed if required. The performance of the films can be further enhanced by incorporating polyvinyl alcohol that lends toughness and clarity as also natural rubber latex that imparts greater elasticity and barrier properties. Films of optimum composition can be pulse heat sealed immediately after casting and used for preparation of soft capsules and pouches. It is possible to store solvents and oils in the pouches. In view of the more eco-friendly processing of semi-refined kappa carrageenan compared to refined kappa carrageenan, films made with the former would also effectively be "greener".
Abstract: An integrated method is developed to utilize to a maximum extent the fresh biomass of seaweeds such as Kappaphycus alvarezii that can be crushed to release sap and where the sap is useful as a potent liquid fertilizer after suitable treatment with additives and dilution while the residue is a superior raw material for extraction of .kappa.-carrageenan, thereby enhancing the value of the seaweed. Other advantages of the invention include a reduced drying time and drying area to obtain the raw material for .kappa.-carrageenan production in dry and storable form, a reduced cost of transporting and storing this raw material because of its lesser bulk, easier handling due to its free flowing granular nature, and its direct use for gel preparation in certain applications.
Abstract: The present invention relates to a simple, direct and cost-effective process for the preparation of agarose of high gel strength and low gelling temperature from naturally occurring or cultivated Gracilaria spp. more particularly Gracilaria dura, said process comprising steps of pre-treating the dry seaweed with alkali, rinsing the pre-treated seaweed until the washing shows a pH ranging between 7 and 8, adding water, autoclaving to obtain extractive, treating the extractive with charcoal and Celite to obtain hot extractive, vacuum-filtering the hot extractive over a Celite bed, freezing the filtrate into a mass and thawing the mass, redissolving the mass in water by heating in an autoclave, repeating the freeze-thaw cycle, straining the product to remove thawed liquid and thereafter squeezing to expel residual liquid to the extent possible to obtain agarose, and an agarose thereof.
