Superabsorbent hydrogel composites with a focus on hydrogels containing nanofibers or nanowhiskers of cellulose and chitin

The development of superabsorbent hydrogels (SHs) is a very important issue in both academic and industrial fields because of their applications in several technologies. The impressive number of publications dealing with SH confirms this statement: a quick search in the ISI (Web of Science) database under the words superabsorbent hydrogels revealed more than 600 articles published, with about 80% of those published in last decade. Current studies on the development of SHs have focused on the formulation of highly functional materials with enhanced properties for suitable applications in different fields. In light of this, the incorporation of microsized or nanosized materials in SH formulations has been explored as a very attractive strategy for tailoring desired properties. In this review, we discuss relevant aspects of the current knowledge of SHs and nanocomposite polymer hydrogels, mainly those based on chitin and cellulose nanocrystals (fibers and/or whiskers), bringing to light some structure–property relationships and future trends. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39725.     

Poly(ethylene glycol)‐containing cationic hydrogels with lipophilic character

Not much effort has been focused towards the development of hydrogels that swell in nonpolar solvents. We have synthesized a new set of polyelectrolyte hydrogels and demonstrated their ability to absorb a less‐polar or nonpolar organic solvent, as well as their ability to resist gel‐collapse in a predominantly nonpolar medium. The hydrogels were prepared by free radical polymerization of different molar ratios of poly(ethylene glycol) methyl ether acrylate and (3‐(methacryloylamino)propyl)‐trimethyl ammonium chloride as comonomers in an aqueous medium. Their swelling behavior in organic solvents was studied by varying the dielectric constant of the swelling medium including mixed‐solvent systems. Besides a high degree of swelling (up to 200 times) in polar solvents, some of the hydrogels also exhibited moderate swelling (up to 15 times) in less‐polar organic solvents. Hydrogels samples with high cationic content showed drastic change in swelling extent in some of the mixed‐solvent systems. It was also interesting to note that the retention of significant swelling in dimethyl sulphoxide–toluene mixture with even 90% toluene content for some compositions. These polyelectrolyte hydrogels with improved lipophilicity opens up greater opportunities for the development of even superior soft materials through proper structural optimizations that would successfully function for a wider range of solvents. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39873.     

Development of microbial protective Kolliphor‐based nanocomposite hydrogels

In this scientific work, a novel class of antimicrobial nanocomposite hydrogels were designed and synthesized by chemical and environmentally bioprocess using Kolliphor, acrylamide, and mint leafs in order to achieve antiseptic property for wound applications. In the bioprocess approach, silver nitrate and gold chloride were nucleated with mint leafs in order to obtain effective free individual nano‐inorganic compounds to provide superior antibacterial assets. The formations of dual inorganic nanoparticles were confirmed by transmission electron microscopy, which indicated the size of nanoparticles in the range of approximately 3 ± 2 nm and without agglomeration. The formations of biomaterials were characterized using Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopic–energy dispersive spectrometric studies and their swelling properties were determined. Furthermore, the pure hydrogel and the dual inorganic nanocomposite hydrogels developed were tested for antibacterial activities. When compared with the neat hydrogel, the nanocomposite hydrogels significantly improved their anti‐bacterial activities on Bacillus bacterium. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42781.     

Hydrogels composite of poly(acrylamide‐co‐acrylate) and rice husk ash. I. Synthesis and characterization

Composite hydrogels of poly(acrylamide‐co‐acrylate) with rice husk ash (RHA) were synthesized and studies of the swelling variables were accomplished comparatively with commercial polyacrylamide gel and PAMACRYL, a poly(acrylamide‐co‐acrylate) hydrogel without RHA. FT‐IR and WAXS were the techniques employed for characterizing a series of hydrogel obtained by varying the percentage of RHA (1, 2, 5, 10, and 20 wt %) and the amount of crosslinking agent (0.05, 0.1, and 0.2 mol %) relative to sum of AAm and AAc. Superabsorbent hydrogel with W_eq > 800 g H₂O/g gel was obtained with percentage of 10 wt % of RHA and 0.1 of crosslinking agent mol %. The hydrogel showed to be sensitive to the pH variation and to the presence of salts. The hydrogels, even though submitted through cycles of drying and swelling, preserved their superabsorbent characteristics and demonstrated better water absorbance properties when compared with commercial polyacrylamide gel. The composite hydrogels of poly(acrylamide‐co‐acrylate) with RHA presented good characteristics to be applied as soil conditioner for using in agriculture. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Volume phase transition of a polymer gel induced by phase separation of mixed solvents of water and 2‐butoxyethanol

The occurrence of the volume phase transition triggered by the phase separation of mixed solvents is investigated using polyacrylamide gels in mixtures of water and 2‐butoxyethanol. When the water content of the mixtures is lower than that of the critical composition, the temperature‐dependent swelling curves show a steep change around the phase separation temperatures but remain continuous, although the solvent inside the gel undergoes a discontinuous composition change. This continuous change originates from the critical concentration fluctuation below the spinodal temperature. Hysteresis‐like behavior is also observed for the heating and cooling curves. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46366.     

Equilibrium swelling studies of highly swollen acrylamide/mesaconic acid hydrogels

Acrylamide/mesaconic acid (AAm/MA) hydrogels were prepared by free radical solution polymerization in aqueous solution of acrylamide (AAm) with mesaconic acid (MA) as comonomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of mesaconic acid content in hydrogels was examined. Swelling of AAm/MA hydrogels was increased up to 2301% (for containing 20 mg MA and crosslinked by EGDMA) to 3296% (for containing 80 mg MA and crosslinked by BDMA), while AAm hydrogels swelled up to 1330% (crosslinked by BDMA) to 1400% (crosslinked by EGDMA). The values of equilibrium water content of the hydrogels are 0.9301–0.9706. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Diffusion coefficients of AAm/MA hydrogels were calculated by the short time approximation and found to be from 38.01 × 10^?6 cm² s^?1 to 182.73 × 10^?6 cm² s^?1. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2253–2259, 2005     

Influence of amino group pKa on the properties of stimuli‐responsive piperazine‐based polymers and hydrogels

Linear homopolymers of N‐acryloyl‐N′‐alkyl piperazine (N′‐alkyl: methyl, ethyl, or propyl) and their corresponding crosslinked hydrogels were prepared. The polymers showed good responses to changes in the pH of the medium due to the presence of tertiary amine functions that could be protonated at a low pH. The nature of the N′‐alkyl group attached to the piperazine amino nitrogen greatly affected the pK_a of the amino group. This in turn influenced the solution behavior of the polymers and was studied with light scattering, potentiometry, and viscosity measurements. The basicity of the polymers increased with an increase in the chain length of the N′‐alkyl substituent. The intrinsic viscosity of the polymers in a good polar organic solvent such as dimethylformamide decreased slightly with increasing temperature because of decreased thermodynamic affinity (interaction) at high temperatures. The viscosity behavior of the polymers in sodium chloride solutions was similar to that of classical polyelectrolytes. The swelling property of the hydrogels was studied with water sorption measurements, and the swelling was by anomalous (non‐Fickian) transport. The diffusion coefficient of the gels in solutions of pH 2.6 increased with increasing N′‐alkyl chain length, whereas at neutral pH, the effect was reversed. This behavior was attributed to the increase in both the basicity and hydrophobicity of the gels with an increase in the chain length of the N′‐alkyl groups. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Synthesis of crosslinked superabsorbent carboxymethyl cellulose/acrylamide hydrogels through electron‐beam irradiation

A study on the possibility of the preparation of superabsorbent hydrogels based on crosslinked carboxymethyl cellulose polymer and acrylamide monomer through electron‐beam irradiation was carried out. The effects of the irradiation dose and polymer–monomer compositions on the crosslinking density were studied. The hydrophilic properties of the superabsorbent hydrogels were identified by the swelling percentage. The prepared hydrogels had higher swelling in distilled water than in salt solutions. Moreover, the hydrogels exhibited the highest swelling at pH 7. Also, increasing the temperature up to 50°C caused an increase in the swelling. The thermal properties of the hydrogels were characterized with thermogravimetric analysis. The use of the prepared superabsorbent hydrogels for the growth of rice was also investigated through the water‐retention property. The water retention in the soil was enhanced with the hydrogels. Superabsorbent hydrogels based on carboxymethyl cellulose polymer and acrylamide monomer could be considered as water‐managing materials for agriculture and horticulture in desert and drought‐prone areas. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2003–2008, 2007     

Sorption and desorption properties of random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide: Effect of monomer composition

Random copolymer hydrogels of N‐isopropylacrylamide and N‐ethylacrylamide (NEAM) were prepared using different monomer compositions in 1:1 methanol–water mixtures. The samples were characterized by cononsolvency study in methanol‐water mixtures at various temperatures, swelling properties measurements, scanning electron microscopy. With changing ratio of the monomers in the reaction mixture, the thermal, morphological and swelling properties, varied significantly. The change in the properties with monomer composition variation are interpreted based on the different thermoresponsive characteristics and interactions of gels of N‐isopropylacrylamide and NEAM (homo‐ and copolymer gels) in water and different methanol‐water mixtures, their variable compositions in the synthesis mixtures, and their morphologies. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45176.     

Synthesis,characterization and,swelling behavior of semi‐IPN nanocomposite hydrogels of alginate with poly(N‐isopropylacrylamide) crosslinked by nanoclay

pH and temperature responsive nanocomposite hydrogels were synthesized with sodium alginate (NaAlg), N‐isopropylacrylamide (NIPA), and nanoclay. The structure, morphology, thermal behavior, and swelling and deswelling behaviors of the hydrogels were studied. The NaAlgm/PNIPA/Clayn hydrogels revealed a highly porous structure in which the pore sizes decreased and the amount of pores increased with increasing the nanoclay content in the hydrogels. PNIPA retained its own characteristics regardless of the amount of NaAlg and nanoclay. The effect of pH and nanoclay content on the swelling and effect of temperature on the deswelling behavior were investigated. The equilibrium swelling ratios of the nanocomposite hydrogels increased with increasing the pH from 2 to 6. The maximum swelling was attained at pH 6. Deswelling increased with increasing the nanoclay content in the hydrogels. The hydrogels were found to be pH and temperature responsive. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43222.     

Dual pH‐ and temperature‐responsive hydrogels with extraordinary swelling/deswelling behavior and enhanced mechanical performances

pH‐ and temperature‐responsive semi‐interpenetrating nanocomposite hydrogels (NC hydrogels) were prepared with surface‐functionalized graphene oxide (GO) as the crosslinker, N‐isopropylacrylamide (NIPAM) as the monomer, and chitosan (CS) as an additive. The effects of 3‐(trimethoxysilyl)propylmethacrylate‐modified GO sheets and CS content on various physical properties were investigated. Results show that PNIPAM/CS/GO hydrogels undergo a large volumetric change in response to temperature. Swelling ratios of PNIPAM/CS/GO hydrogels are much larger than those of the conventional organically crosslinked PNIPAM hydrogels. The deswelling test indicates that the deswelling rate was greatly enhanced by incorporating CS into the hydrogel network and using the surface‐functionalized GO as the crosslinker. The pH‐sensitivity of PNIPAM/CS/GO hydrogels is evident below their volume phase transition temperature. Moreover, the PNIPAM/CS/GO hydrogels have a much better mechanical property compared with traditional hydrogels even in a high water content of 90%. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41530.     

Study on superabsorbent composites. XVIII. Preparation,characterization, and property evaluation of poly(acrylic acid‐co‐acrylamide)/organomontmorillonite/sodium humate superabsorbent composites

A series of novel multifunctional poly (acrylic acid‐co‐acrylamide) (PAA‐AM)/organomontmorillonite (O‐MMT)/sodium humate (SH) superabsorbent composites were synthesized by the graft copolymerization reaction of partially neutralized acrylic acid and acrylamide on O‐MMT micropowder and SH with N,N′‐methylene bisacrylamide as a crosslinker and ammonium persulfate as an initiator in an aqueous solution. The superabsorbent composites were characterized by means of Fourier transform infrared spectroscopy, X‐ray diffraction, scanning electron microscopy, and thermogravimetric analysis. The effect of the relative weight ratio of SH to O‐MMT on the water absorbency was studied, and the results indicated that the best water absorbency of 591 g/g in distilled water was obtained when an O‐MMT content of 20 wt % and an SH content of 30 wt % were incorporated. The superabsorbent composite possessed a good capacity for water retention; even after 30 days, 24.4 wt % of water could still be saved by the sand soil containing 1.0 wt % superabsorbent composite. The results from this study show that the water absorbency of a superabsorbent composite is improved by the simultaneous introduction of O‐MMT and SH into a PAA‐AM network in comparison with the incorporation of only O‐MMT or SH. Also, in comparison with PAA‐AM/MMT/SH, an appropriate amount of O‐MMT can benefit the developed composites with respect to their water absorbency, salt resistance, and capacity for water retention in sand soil. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Preparation and property of starch nanoparticles reinforced aldehyde–hydrazide covalently crosslinked PNIPAM hydrogels

Injectable, de‐crosslinkable, and thermosensitive hydrogels are obtained by hydrazide‐functionalized poly(N‐isopropylacrylamide) and aldehyde‐functionalized dextrin through in situ crosslinked method. Natural based and degradable starch nanoparticles (SNPs) are used as fillers in order to improve mechanical property of hydrogels. Internal morphology, dynamic modulus, thermosensitivity property, de‐crosslinking performance, drug release, and in vitro cytotoxicity of hydrogels are investigated. Results show that SNPs disperse well throughout hydrogel and have no significant influence on gelation time and de‐crosslinking performance. Elasticity property of composite hydrogel prepared from 9.0 wt % precursors with 1.5 wt % fillers is improved significantly by SNPs and maximum storage modulus reaches 399.2 kPa, but 89.6 kPa of unreinforced hydrogels. Hydrogels exhibit good thermosensitive performance at alternating cyclic temperature of 25 and 37 °C. Doxorubicin hydrochloride‐loaded hydrogels can release more than 25 days. No significant cytotoxicity to L929 fibroblast cells is observed through a CCK‐8 assay for hydrogels, precursors, and SNPs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45761.     

Multiporous microstructure for enhancing the water absorption and swelling rate in poly(sodium acrylic acid) superabsorbent hydrogels based on a novel physical and chemical composite foaming system

In this article, we report a novel physical and chemical composite foaming system, which was used to successfully prepare high‐performance and low‐cost composite superabsorbent [poly(sodium acrylic acid) (PAA–Na)] hydrogels based on acrylic acid by free‐radical polymerization in a water bath under a nitrogen atmosphere without the use of any organic solvents. The prepared hydrogels showed superabsorbent properties, high water‐absorption abilities and swelling rates, a lighter packing density, and a multiporous microstructure. Fourier transform infrared spectroscopy and scanning electron microscopy revealed that the sodium dodecyl sulfate surfactant, sodium bicarbonate chemical foaming agent, and 1,1,2‐trifluorotrichloroethane physical foaming agent were evenly distributed and grafted onto the PAA–Na matrix. Water‐absorption, swelling rate, and packing density testing confirmed that the superabsorbent had a high water‐absorption ability and swelling rate and a lighter packing density. Furthermore, we investigated the effects of different foaming agents, including chemical and physical foaming agents, on the swelling and water‐retention capabilities of the superabsorbent hydrogels (SAHs).The results show that the combination of these foaming agents significantly improved the water‐absorbing capacity. With the help of these foaming agents, we obtained PAA–Na hydrogels without any organic solvents for posttreatment or special porogens; this is an environmentally beneficial way to prepare SAHs for hygiene and biomedical products. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 44149.     

In vitro silver ion release kinetics from nanosilver/poly(vinyl alcohol) hydrogels synthesized by gamma irradiation

A nanosilver (nano‐Ag)/poly(vinyl alcohol) (PVA) hydrogel device was synthesized with γ irradiation because it is a highly suitable tool for enhanced nano‐Ag technologies and biocompatible controlled release formulations. The amount of the Ag⁺ ions released in vitro by the nano‐Ag/PVA hydrogel device was in the antimicrobial parts per million concentration range. The modeling of the Ag⁺ ion release kinetics with the elements of the drug‐delivery paradigm revealed the best fit solution (R² > 0.99) for the Kopcha and Makoid–Banakar's pharmacokinetic dissolution models. The term A/B, derived from the Kopcha model, indicated that the nano‐Ag/PVA hydrogel was mainly an Ag⁺‐ion diffusion‐controlled device. Makoid–Banakar's parameter and the short time approximated Ag⁺‐ion diffusion constant reflected the importance of the size of the Ag nanoparticles. However, it appeared that the cell oxidation potential of the Ag nanoparticles depended on the diffusion characteristics of the fluid penetrating into the Ag/PVA nanosystem. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40321.     

Preparation and application of sulfadiazine surface molecularly imprinted polymers with temperature‐responsive properties

Novel, temperature‐responsive molecularly imprinted polymers (TMIPs) based on potassium hexatitanate whiskers for selectively adsorbing sulfadiazine (SDZ) from aqueous media were prepared with methacrylic acid (MAA) and 4‐vinylpyridine (4‐VP) as cofunctional monomers and N‐isopropyl acrylamide (NIPAM) as a temperature‐responsive monomer. The template–monomer interactions were studied by molecular simulation. In particular, the effects of different kinds of crosslinkers on the selective recognition ability of the TMIPs in water media were investigated. The temperature–responsive adsorption performance and phase behavior of the molecularly imprinted polymers were studied by batch‐mode binding experiments, swelling experiments, and contact angle testing. The results demonstrate that the combination of MAA, 4‐VP, and NIPAM was a favorable temperature‐responsive imprinted system for SDZ in water, and the cocrosslinking agent of ethylene glycol dimethacrylate (EGDMA) and N,N′‐methylene bisacrylamide (MBA) was more suitable compared with either pure EGDMA or MBA. The adsorption kinetics and adsorption isotherms were analyzed by the fitting of different adsorption models. Also, the effect of the temperature on the recovery was investigated by the determination of the spiked SDZ in real‐water samples with solid‐phase extraction and high‐performance liquid chromatography. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41769.     

Improving blood compatibility of natural rubber by UV‐induced graft polymerization of hydrophilic monomers

Natural rubber (NR) latex films surface‐grafted with hydrophilic monomers, poly(ethylene glycol) methacrylate (PEGMA), N‐vinylpyrrolidone (VPy), and 2‐methacryloyloxyethyl phosphorylcholine (MPC), were prepared by UV‐induced graft polymerization using benzophenone as a photosensitizer. The grafting yield increases of vulcanized NR latex films as a function of time and monomer concentration were of lesser magnitude than those of the unvulcanized NR latex films. This can be explained as a result of the crosslinked network generated during vulcanization acting as a barrier to the permeation of the photosensitizer and the monomer. The appearance of a characteristic carbonyl stretching in the attenuated total reflectance‐Fourier transform infrared spectroscopy (ATR‐FTIR) spectra of NR latex films after the surface grafting of PEGMA and MPC indicates that the modification has proceeded at least to the sampling depth of ATR‐FTIR (∼ 1–2 μm). According to the water contact angle of the modified NR latex films, the surface grafting density became higher as the grafting time and monomer concentration increased. The complete absence of plasma protein adsorption and platelet adhesion on the surface‐modified NR latex films having grafting yield above 1 wt % is a strong indication of improved blood compatibility. Results from tensile tests suggest that graft polymerization does not cause adverse effects on the mechanical properties of vulcanized NR latex films. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Thermoresponsive hydrogels based on sucrose 1‐O′‐methacrylate and N‐isopropylacrylamide: Synthesis,properties, and applications

Chemically crosslinked hydrogels composed of carbohydrate‐based and thermoresponsive monomers, sucrose 1‐O′‐methacrylate (SMA), sucrose dimethacrylate, and N‐isopropylacrylamide, respectively, were synthesized by free radical polymerization. These materials were characterized with respect to their composition, thermoresponsiveness, porosity, degradability, and as drug and protein delivery systems. Swelling studies, thermomechanical analysis, and differential scanning calorimetry showed that the lower critical solution temperature behavior of the hydrogels can be controlled by the SMA amount in the copolymers. On the other hand, thermoporometry showed that the pore size is somewhat dependent on the composition, which is confirmed by scanning electron microscopy. Hydrolytic degradation studies indicated that SMA side chains, as well as the crosslinker (sucrose dimethacrylate), are hydrolysable at corporeal temperature and pH 10, and the water swelling capability of the resulting materials increases as the hydrolysis degree increases. Finally, protein delivery studies revealed that the kinetics of release can be tailored by the copolymer composition. The results of this study suggest the potential application of these hydrogels in drug delivery systems and tissue engineering. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45495.     

Photoinduced surface crosslinking of superabsorbent polymer particles

Superabsorbent polymer particles, consisting of partly neutralized, slightly crosslinked poly(acrylic acid), have been surface‐crosslinked photochemically. Surface crosslinking is required for many applications of superabsorbent polymers, such as disposable diapers, to control the flow and absorption of liquids in the gel bed. Photoinduced surface crosslinking has been achieved under UV irradiation (200–300 nm) with (NH₄)₂S₂O₈ as a photoactivated crosslinking agent. In comparison with the currently used thermal ester bridging method for surface crosslinking, the new photochemical method generates superabsorbent particles with superior properties, such as an improved flow of liquid through the gel bed, which utilizes the entire gel bed. These improved properties have been shown by water absorption capacity studies, fluid flow dynamics, environmental scanning electron microscopy, and low‐energy ion‐scattering studies. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

PCL microsphere/PEG-based composite hydrogels for sustained release of methadone hydrochloride

Hydrogels have increasingly received considerable attention for local opioids delivery in order to sustained wound pain relief. However, burst release of drugs is a critical problem of hydrogels. To this aim, a local drug delivery system consisting of polycaprolactone (PCL) microspheres containing methadone hydrochloride/polyethylene glycol (PEG)-based hydrogels were developed to prolong drug release with potential utilization in pain treatment. Four different drug delivery systems, including methadone hydrochloride/PEG-(N₃)₄-based hydrogel, methadone hydrochloride/PEG-(N₃)₂-based hydrogel, methadone hydrochloride/PCL/PEG-(N₃)₄, and methadone hydrochloride/PCL/PEG-(N₃)₂ composite hydrogels, were fabricated to investigate drug release profiles of these systems. The results showed that drug released can be controlled by both the double-barrier matrix (hydrogel/microsphere), and the crosslinking density of hydrogels. Therefore, methadone hydrochloride/PCL/PEG-(N₃)₂ composite hydrogel with high crosslinking density has great potential application in sustained release systems for wound pain relief. © 2020 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48967.