A novel superabsorbent composite based on sodium alginate and the inorganic clay kaolin was synthesized via the graft copolymerization of acrylic acid (AA) in an aqueous medium with methylene bisacrylamide (MBA) as a crosslinking agent and ammonium persulfate (APS) as an initiator. The effects of reaction variables, such as the MBA, AA, and APS concentrations and the alginate/kaolin weight ratio, on the water absorbency of the composite were systematically optimized. Evidence of grafting and kaolin interactions was obtained by a comparison of the Fourier transform infrared spectra of the initial substrates with that of the superabsorbent composite, and the hydrogel structure was confirmed with scanning electron microscopy. The results indicated that with an increasing alginate/kaolin weight ratio, the swelling capacity and gel content increased. The effects of various salt media were also studied, along with the swelling kinetics.
A novel approach was developed to prepare a highly porous hydrogel with superior salt-and pH-resisting properties. According to this method, synthetic comonomers, i.e. acrylic acid (AA) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS), were polymerized and crosslinked in the presence of hydrolyzed collagen as a natural backbone. The characterizations of hydrogels were investigated by swelling experiment, Fourier transform infrared (FT-IR) spectroscopy, acid-base titration and thermogravimetric analysis (TGA). Morphology of the samples was examined by scanning electron microscopy (SEM). Experimental results indicate that the hydrogel has an absorbency of 360 and 73-82 g/g for distilled water and saline solutions, respectively. Water absorbency slightly changes from pH 3 to 8 and interestingly is more than of that in distilled water ($ 500 g/g). The hydrogel thus prepared was showing a better salt-and pH-resistance compared to collagen-g-PAA hydrogel due to the introduction of the AMPS segment and therefore is a suitable candidate for horticulture and tissue engineering applications.KEY WORDS: Hydrolyzed Collagen / Hydrogel / Porous / Salt-resisting / pH-Resisting / Hydrogels are an important class of materials have been attracting in many industrial applications because of their response to changing environment conditions such as temperature, 1 pH 2 and solvent composition. 3 Although their attraction in medical and mechanical engineering fields, the technological success of these applications is today limited by their low efficiency and slow rate of response to external stimuli. These are related to the degree of porosity which plays the multiple role of enhancing the total water sorption capability and the rate of response by reducing the transport resistance.4,5 Therefore, creation of porosity in hydrogels has been considered as an important process in many ways.6-8 According to our prior works, 9,10 neutralization of the grafted polymer after gel formation or gas releasing during hydrolyzation create a hydrogel with porous structure.It is desired to develop hydrogels having enhanced absorbency in saline solutions, in various values of pH and good strength of the swollen gel (high absorbency under load), since the requirements of such applications as long-term water holding in horticulture and hygienic products, and the like. So that there have already several studies focusing on improving some hydrogel properties, and further more some modification method seemed effective.11-14 On the basis of our former researches, 9,15 we have been interested in preparing a hydrogel which possess relatively high water absorbency under certain load and at atmosphere pressure in salt solution.Natural-based hydrogels have attracted in medical and pharmaceutical interests since their non-toxicity, biocompatibility and biodegradability. This paper describes the preparation and characterization of a partially neutralized collagen-gpoly(AA-co-AMPS) porous hydrogel, as a new natural-based polymer, which shows salt-and pH-resist...
A series of biopolymer-based superabsorbent hydrogels based on carboxymethyl cellulose has been prepared by free-radical graft copolymerization of acrylamide and 2-acrylamido-2-methylpropan sulfonic acid (AMPS) in aqueous solution using methylenebisacrylamide as a crosslinking agent and ammonium persulfate as an initiator. The effect of variables on the swelling capacity such as: acrylamide/AMPS weight ratio, reaction temperature, and concentration of the initiator and crosslinker were systematically optimized. The results indicated that with increasing the amount of AMPS, the swelling capacity is increased. FT-IR spectroscopy and scanning electron microscope analysis were used to confirm the hydrogel structure. Swelling measurements of the synthesized hydrogels in different salt solutions indicated considerable swelling capacity. The absorbency under load of the superabsorbent hydrogels was determined by using an absorbency under load tester at various applied pressures. A preliminary swelling and deswelling behaviors of the hydrogels were also studied.
A novel superabsorbent hydrogel was synthesized via crosslinking graft copolymerization of acrylamide (AAm) onto kappa-carrageenan (κC) and sodium alginate (Na-Alg) backbones in a homogeneous solution. Methylenebisacrylamide (MBA) and potassium persulfate (KPS) were applied as water-soluble crosslinker and initiator, respectively. FTIR spectroscopy was used for confirming the structure of the final product. A mechanism for superabsorbent hydrogel formation was also suggested. The parameters affecting the swelling capacity of the synthesized hydrogel, i.e., κC-Alg weight ratio, concentration of AAm, MBA and KPS, as well as reaction temperature were systematically optimized for obtaining maximum absorbency. The swelling capacity of hydrogels was also measured in various salt solutions (LiCl, NaCl, KCl, MgCl2, CaCl2, SrCl2, BaCl2, and AlCl3). Due to their high swelling ability in salt solutions, the hydrogels may be referred to as ‘anti-salt superabsorbent’ polymers. The overall activation energy for the graft copolymerization reaction was found to be 374 kJ/mol. The swelling kinetics of the hydrogels in distilled water and in saline solution (0.9 wt.-% NaCl) was investigated.
A novel full-polysaccharide hydrogel was prepared by crosslinking of chitosan with periodateoxidized sucrose. A tetraaldehyde molecule is synthesized via periodate oxidation of sucrose and then applied as a crosslinking agent to form a new hydrogel network. A mechanism for the superabsorbent hydrogel formation via reductive N-alkylation was also suggested. The structure of the hydrogel was confirmed by FTIR spectroscopy, scanning electron microscopy (SEM), and thermogravimetric analysis (TGA). It is shown that crosslinking of chitosan can improve its thermal stability. The effects of crosslinker concentration, pH, and inorganic salt on the swelling behavior of the hydrogel were studied. The results indicate that the hydrogel has good pH sensitivity and pH reversible response. The smart hydrogels may have potential applications in the controlled delivery of bioactive agents and for wound-dressing application
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