Preparation and characterization of sodium alginate/poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide)/clay semi-IPN magnetic hydrogels

pH- and temperature-responsive semi-interpenetrating magnetic nanocomposite hydrogels (NC hydrogels) were prepared by using linear sodium alginate (SA), poly(N-isopropylacrylamide) (PNIPAM) and Fe₃O₄ nanoparticles with inorganic clay as an effective multifunctional cross-linker. The effects of cross-linker and SA contents on various physical properties were investigated. The NC hydrogels exhibited a volume phase transition temperature (VPTT) around 32 °C with no significant deviation from the conventional chemically cross-linked PNIPAM hydrogels (OR hydrogels). The swelling ratios of NC hydrogels were much larger than those of OR hydrogels. Moreover, the swelling ratios of NC hydrogels gradually decreased with increasing the contents of clay and increased with increasing the contents of SA. The pH sensitivity of NC hydrogels was evident below their VPTT. The NC hydrogels had a much better mechanical property than the OR hydrogels. The results showed that the incorporation of clay did not affect the saturation magnetization of the hydrogels.     

Effect of organic modifiers and silicate type on filler dispersion,thermal, and mechanical properties of ABS‐clay nanocomposites

Acrylonitrile–butadiene–styrene (ABS)–clay composite and intercalated nanocomposites were prepared by melt processing, using Na‐montmorillonite (MMT), several chemically different organically modified MMT (OMMT) and Na‐laponite clays. The polymer–clay hybrids were characterized by WAXD, TEM, DSC, TGA, tensile, and impact tests. Intercalated nanocomposites are formed with organoclays, a composite is obtained with unmodified MMT, and the nanocomposite based on synthetic laponite is almost exfoliated. An unintercalated nanocomposite is formed by one of the organically modified clays, with similar overall stack dispersion as compared to the intercalated nanocomposites. T_g of ABS is unaffected by incorporation of the silicate filler in its matrix upto 4 wt % loading for different aspect ratios and organic modifications. A significant improvement in the onset of thermal decomposition (40–44°C at 4 wt % organoclay) is seen. The Young's modulus shows improvement, the elongation‐at‐break shows reduction, and the tensile strength shows improvement. Notched and unnotched impact strength of the intercalated MMT nanocomposites is lower as compared to that of ABS matrix. However, laponite and overexchanged organomontmorillonite clay lead to improvement in ductility. For the MMT clays, the Young's modulus (E) correlates with the intercalation change in organoclay interlayer separation (Δd₀₀₁) as influenced by the chemistry of the modifier. Although ABS‐laponite composites are exfoliated, the intercalated OMMT‐based nanocomposites show greater improvement in modulus. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

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.     

Thermoresponsive nanocomposite hydrogels with high mechanical strength and toughness based on a dual crosslinking strategy

The practical application of thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) hydrogels are severely limited by their poor mechanical properties. Herein, we reported a series of dual crosslinked (DC) PNIPAM hydrogels with superior mechanical properties prepared by simple copolymerization of N-isopropylacrylamide and sodium acrylate (SA) in the laponite RDS suspension, following by a soaking process in multivalent metal cations (e.g., Ca²⁺, Al³⁺, Fe³⁺) aqueous solutions to form ionic coordination interactions with  COO groups of copolymer side chains. The effect of laponite RDS, AANa (sodium acrylate), and metal cation (e.g., Fe³⁺) concentrations on the mechanical properties and deswelling properties of the DC hydrogels are evaluated. The DC hydrogel prepared with 10 w/v% laponite RDS, 0.25 mol/L AANa and 0.45 mol/L Fe³⁺ possesses the best mechanical properties (ca. 1.1 MPa of tensile strength, 9.1 MPa of compression strength at 80% of compression strain, 1.4 MPa of elastic modulus and 1.3 MJ/m³ of toughness). Moreover, we also discovered that the DC hydrogels crosslinked by Fe³⁺ showed better mechanical properties due to the larger charge and ion radius of Fe³⁺.     

Poly(acrylamide/laponite) nanocomposite hydrogels: Swelling and cationic dye adsorption properties

Super adsorbent polyacrylamide (PAAm)/nanoclay (laponite, Lap) hydrogels were prepared by in situ free radical polymerization of AAm in an aqueous solution with clay as a crosslinker. The swelling properties and water‐soluble cationic dye adsorption behaviors of the PAAm/laponite (PAAm/Lap) nanocomposite (NC) hydrogels were investigated. The parameters of swelling and diffusion of water in dye solutions were evaluated for the PAAm/Lap NC hydrogels. The adsorption behavior of the monovalent cationic dyes such as Basic Blue 12 (BB 12), Basic Blue 9 (BB 9), and Basic Violet 1 (BV 1), were studied on the NC hydrogels. The effects of the clay content of the hydrogel on its cationic dye uptake behavior were studied. The adsorption studies indicated that the rates of dye uptake by the NC hydrogels increased in the following order: BB 9 > BB 12 > BV 1. This order is similar to the swelling results of the PAAm/Lap NC hydrogel in the dye solutions. The equilibrium uptakes of the different dyes by the PAAm/Lap NC hydrogel were nearly the same. In the dye absorption studies, S‐type adsorption in the Giles classification system was found for the BB 12 and BV 1 dyes, whereas L ‐type was observed for the BB 9 dye. After the heat treatment of PAAm/Lap, the rate of dye uptake and equilibrium dye uptake were increased. The NC hydrogels may be considered as a good candidate for environmental applications to retain more water and to remove dyes. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

High clay content nanocomposite hydrogels with surprising mechanical strength and interesting deswelling kinetics

A series of high hectorite content nanocomposite Poly (N-isopropylacrylamide), (PNIPAAm), hydrogels have been successfully synthesized by choosing a special kind of hectorite (Laponite XLS) modified by tetrasodium pyrophosphate. It was found that these hydrogels show surprising mechanical properties (i.e. tensile strength: 1 MPa, elongation at break: 1400%) and complicated deswelling behavior, which are due to the high clay content of the hydrogels and ionic dispersant contained in Laponite XLS, respectively.     

Equilibrium swelling behavior and elastic properties of polymer–clay nanocomposite hydrogels

Nanocomposite hydrogels were prepared by free‐radical polymerization of the monomers acrylamide (AAm), N,N‐dimethylacrylamide (DMA), and N‐isopropylacrylamide (NIPA) in aqueous clay dispersions at 21°C. Laponite XLS was used as clay nanoparticles in the hydrogel preparation. The hydrogels based on DMA or NIPA monomers exhibit much larger moduli of elasticity compared with the hydrogels based on AAm monomer. Calculations using the theory of rubber elasticity reveal that, in DMA‐clay or NIPA‐clay nanocomposites, both the effective crosslink density of the hydrogels and the functionality of the clay particles rapidly increase with increasing amount of Laponite up to 10% (w/v). The results suggest that DMA‐clay and NIPA‐clay attractive interactions are stronger than AAm‐clay interactions due to the formation of multiple layers on the nanoparticles through hydrophobic associations. It was also shown that, although the nanocomposite hydrogels do not dissolve in good solvents such as water, they dissolve in dilute aqueous solutions of acetone or poly(ethylene oxide) of molecular weight 10,000 g/mol, demonstrating the physical nature of the crosslink points. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Composite latex production with high solid content

Poly(methyl methacrylate-co-butyl acrylate) (PMMA-co-PBA) and poly(sytrene-co-butyl acrylate) (PSt-co-PBA) latexes in which solid content (SC) varied from 20% up to 40 wt % armored with laponite clay have been successfully synthesized using a simple method, which does not require modification of the clay particles prior to polymerization. Incorporation of quite high amounts of laponite nanoparticles into PMMA-co-PBA and PSt-co-PBA latexes with a certain amount of solids content was achieved. The nanocomposite latexes and polymer samples were characterized using Fourier transform infrared (FTIR) spectroscopy in attenuated total reflectance (ATR) mode, dynamic light scattering (DLS), X-ray diffraction (XRD), transmission electron microscopy (TEM), thermal gravimetric analysis (TGA), differential scanning calorimetry (DSC), contact angle, zeta potential, viscosimetry and analytical ultracentrifuge (AUC). Zeta potential values showed that stable latex was obtained and precipitation problem of the nanoparticles in the latex was not seen during the storage. Obtained nanocomposite latex showed fine particle size between 88 and 160 nm. TEM images and XRD results pointed out that the exfoliated nanocomposite structure for latexes was obtained. DSC analyzes showed that the glass-transition temperature (T _g) values of nanocomposite films decreased slightly compared with those of pure (PMMA-co-PBA) films. Mechanical properties of laponite clay armored PMMA-co-PBA were tested and compared with those of pure PMMA-co-PBA, indicating that incorporated the Young's modulus and tensile strength are also improved to a noticeable extent after the incorporation of laponite. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47423.     

Study on a new polymer/graphene oxide/clay double network hydrogel with improved response rate and mechanical properties

pH‐ and temperature‐responsive double network hydrogels (DN hydrogels) were prepared by using poly (N‐isopropylacrylamide) (PNIPAM) as a tightly crosslinked network (1st network), polyacrylic acid (PAA) as a loosely crosslinked network (2nd network), with clay and graphene oxide as effective crosslinkers and reinforcing fillers. The structure and morphology of the hydrogels were characterized by SEM, FTIR, DSC, and TGA. The synergetic effects of clay, GO and DN structure on various physical properties were investigated. With the increasing of crosslinking densities, the swelling ratios of DN hydrogels gradually decreased by increasing the contents of graphene oxide and PAA. While the DN hydrogels had much better mechanical properties than that of the conventional chemically cross‐linked PNIPAM hydrogels. POLYM. ENG. SCI., 55:1361–1366, 2015. © 2015 Society of Plastics Engineers     

Chitosan‐modified nanoclay–poly(AMPS) nanocomposite hydrogels with improved gel strength

BACKGROUND: Making (nano)composite structures is one of the efficient approaches for strengthening hydrogels extended in recent years. The present paper deals with the synthesis and properties of novel nanocomposite hydrogels based on 2‐acrylamido‐2‐methylpropane‐1‐sulfonic acid (AMPS). Initially, a bio‐modified clay, chitosan‐intercalated montmorillonite (chitoMMT), was prepared. Then, this was incorporated into the polymerization of AMPS in the presence of a macro‐crosslinker, i.e. poly(ethylene glycol) dimethacrylate, to yield super‐swelling nanocomposite hydrogels. The swelling capacity as well as some structural, rheological and thermomechanical properties of the hydrogels were studied and compared with those of the clay‐free counterpart. RESULTS: ChitoMMT exhibited no toxicity, which was confirmed using cell‐culture testing. A chitoMMT content of ca 6% was found to be the most favourable content of the bio‐modified clay for achieving a product with improved properties (i.e. the highest gel content, the highest gel strength and optimal thermal stability). Based on a dynamic mechanical thermal analysis study, an increased glass transition temperature (98.2 °C) and improved rubbery modulus (up to 238% higher than that of the clay‐free counterpart) were recorded. Thermogravimetric analysis verified that the thermal stability of nanocomposite samples was higher than that of clay‐free samples. CONCLUSION: Owing to the non‐toxicity of the incorporated chitoMMT, the strengthened hydrogels may be considered as potential candidates for bio‐applications. Copyright © 2009 Society of Chemical Industry     

Novel Thermoreversible Injectable Hydrogel Formulations Based on Sodium Alginate and Poly(N-Isopropylacrylamide)

Novel injectable thermoreversible hydrogel compositions with semi-interpenetrating network structure were prepared through the addition of sodium alginate (SA) to poly(N-isopropylacrylamide) (PNIPAM) aqueous solutions. The addition of the hydrophilic alginate strongly improved the stability against syneresis of the 15 wt% PNIPAM hydrogels formed at 37°C from less than 15 min in the absence of alginate to more than 7 days in the presence of 4 wt% SA. Besides the SA concentration, the hydrogel stability depended on the molecular weight and polydispersity of PNIPAM, being lower when a high molecular weight fraction was present. The phase transition temperature (T_ph) of the PNIPAM aqueous solutions decreased with alginate concentration, while the dynamic viscosity and elastic modulus of the hydrogels increased. By decreasing the PNIPAM molecular weight and polydispersity, the dynamic viscosity and elastic modulus of the PNIPAM–alginate hydrogels formed above T_ph diminished, while their viscoelastic behavior changed from predominantly elastic to predominantly viscous.     

Bottle‐to‐bottle recycling of PET via nanostructure formation by melt intercalation in twin screw compounder: Improved thermal,barrier, and microbiological properties

Attempts have been made to modify the properties of the injection processing‐scraped PET (denoted as RPET) via intercalation with different levels of organically modified nanoclay (montmorillonite) by melt blending in a corotating twin screw compounder. The clay platelets dispersion state has been qualitatively correlated with the melt linear viscoelastic as well as tensile and barrier properties of the prepared nanocomposites. Oxygen permeation of the nanocomposite PET films showed significant reduction compared with the pristine PET polymer. All the PET/nanoclay composites exhibited no bacterial growth, with no potentiality to generate acetaldehyde, as measured by GC/Mass analyzer. X‐ray diffractometry and transmission electron microscopy performed on the scraped PET/organoclay nanocomposite samples showed increase in d₀₀₁ spacing of the clay layers and their dispersion throughout the PET matrix. Differential scanning calorimetry analysis showed higher crystallization temperature as well as crystallization enthalpy (ΔH_c) for the nanocomposite samples, compared with the unprocessed virgin PET. The RPET nanocomposite samples composed of 3 and 5% of nanoclay exhibited enhanced melt elastic modulus and pseudosolid‐like behavior at low shear frequencies measured by rheomechanical spectroscopy than the unfilled pristine‐scraped PET, indicating the formation of nanoscopic network structure by the clay platelets, which leads to the development of nanostructured resin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Preparation of antimicrobial polycarboxybetaine‐based hydrogels for studies of drug loading and release

A series of cationic poly(N‐isopropyl acrylamide) (PNIPAM)‐g‐poly(carboxybetaine ester) (PCBMAE) hydrogels were prepared by reversible addition–fragmentation chain‐transfer polymerization with PCBMAE precursors reacting with N‐isopropyl acrylamide in the presence of N,N′‐methylene bisacrylamide. These hydrogels exhibited excellent antimicrobial activities against Staphylococcus aureus and could switch to nontoxic zwitterionic hydrogels after hydrolysis. Nonionic tetracycline hydrochloride (TCHC) and anionic sodium salicylate (SA) were selected to evaluate the loading capacities and release kinetics of the cationic hydrogels. We found that the loading efficiencies of TCHC in the PNIPAM‐g‐PCBMAE hydrogels were approximately twice as high as those of SA. However, the cumulative release amount of TCHC was lower than that of SA from the corresponding cationic hydrogel at 37°C. In addition, the PNIPAM‐g‐PCBMAE hydrogels exhibited accelerated release rates of both TCHC and SA with increasing content of (2‐carboxymethyl)?3‐acryloxyethyldimethylammonium chloride methyl ester. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39839.     

Functionalization of hybrid poly(n‐isopropylacrylamide) hydrogels for Escherichia coli cell capture via adsorbed intermediate dye molecule

Poly(n‐isopropylacrylamide) Laponite (PNIPAM‐Lap) hybrid hydrogels, which use the synthetic clay Laponite as a crosslinker, permanently adsorb cationic laser dyes out of solution. This proof‐of‐concept expounds on this capability by adsorbing an intermediate dye molecule and using it as the foundation for successfully conjugating microbial antibodies to the surface of a PNIPAM hydrogel. The study involves using acriflavinium chloride molecules, adsorbed by a PNIPAM‐Lap hydrogel from an acriflavine laser dye solution, as an intermediate molecule to attach antibodies raised against E. coli to the hydrogel and demonstrate cell capture. Furthermore, this system exemplifies a novel biotechnological platform for greatly expanding PNIPAM hydrogels' capabilities and applicability through conjugation chemistry to surface‐bound molecules. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41557.     

Synthesis of amphoteric nanocomposite hydrogels with ultrahigh tensibility

Amphoteric nanocomposite hydrogels (NC gels) were synthesized by in situ copolymerization of acrylic acid (AA) and N[‐3(dimethylamino)propyl] methacrylamide (DMAPMA) in an aqueous dispersion of laponite XLG. Mechanical analyses demonstrated that this type of hydrogels had a combination of high tensile strength and excellent stretchability. The tensile strength was increased by 5 times up to 316 kPa when the laponite content was increased from 0.1 wt% to 20 wt%, and a maximum fracture strain of 2,317% was achieved for hydrogels containing 3 wt% laponite. Additionally, the marked improvements in strength were achieved with minimal sacrifice of the tensibility. This work provided a continuation to previous efforts of the preparation and properties of ionic NC gels. POLYM. COMPOS. 36:538–544, 2015. © 2014 Society of Plastics Engineers     

Poly(sodium 4-styrene sulfonate) and poly(2-acrylamidoglycolic acid) nanocomposite hydrogels: montmorillonite effect on water absorption,thermal, and rheological properties

A systematic study of water absorbency, thermal, and rheological properties was performed on nanocomposite hydrogels of poly(sodium 4-styrene sulfonate) (PSSNa) and poly(2-acrylamide glycolic acid) (PAAG). Montmorillonite was used as clay filler and was previously modified to hydrogel synthesis by addition of (3-acrylamide propyl)trimethylammonium chloride. Syntheses were carried out by in situ radical polymerization, using N,N-methylen-bis-acrylamide as crosslinker reagent. Nanocomposites showed an exfoliated morphology, confirmed by transmission electron microscopy and X-ray diffraction. The water absorption capacity (WAC) of unloaded PSSNa hydrogel was three times higher than for PAAG; due to clay addition, absorption capacity increased for PSSNa nanocomposites and decreased for PAAG. Finally, rheological properties of nanocomposite hydrogels were studied by both dynamic oscillatory test and shear creep analysis. Results showed improvements on mechanical properties, such as yield point, elastic recovery, and storage modulus as consequence of montmorillonite addition.     

HES-HEMA nanocomposite polymer hydrogels: swelling behavior and characterization

Organophilic sodium montmorillonite (Na-MMT) and Laponite-RD clays were incorporated into photopolymerizable hydroxyethyl starch (HES) modified with 2-hydroxyethyl methacrylate (HEMA). Swelling, mechanical properties and thermal stability of obtained crosslinked nanocomposite polymers were evaluated. A camphorquinone-amine system was used as photoinitiating system in visible light. The interaction between nano-sized filler particles and polymer hydrogel was evaluated by FT-IR spectroscopy and the platelet distribution was investigated by SEM. An increased thermal stability of nanocomposite polymers upon addition of clay was observed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) indicating interaction between the clay platelets and the polymer chains. The crosslinking density for HES-HEMA/MMT nanocomposite hydrogels as investigated by swelling measurements increases with increasing the organo-clay content. The mechanical properties of virgin hydrogels were improved by the introduction of organo-clay as evidenced by oscillation rheology measurements. Whereas, the increase in crosslink density and storage modulus with clay content for laponite was found to be increasing for all concentrations investigated, for MMT there is an optimum content of ca. 1.5 wt%.     

Antipolyelectrolyte superabsorbing nanocomposites: Synthesis and properties

Novel polyampholytic superabsorbing nanocomposites based on the zwitterionic sulfobetaine monomer [3‐(methacrylamido)propyl)]dimethyl(3‐sulfopropyl)ammonium hydroxide were synthesized through in situ polymerization in aqueous solution with different contents of an organo‐modified clay (OMMT, Cloisite 30B). Structural and thermomechanical properties of hydrogels were characterized by FT‐IR, XRD, and DMTA, respectively. Swollen gel strength of hydrogels was determined by a rheological method. Storage modulus of the hydrogels was considerably improved in comparison with its the clay‐free counterpart. The nanocomposite hydrogel containing 15% OMMT possessed the highest gel strength. The glass transition temperature was increased from 58.4 to 67.0°C for the clay‐free and nanocomposite hydrogel containing 8% OMMT, respectively. The swelling behavior of the hydrogel in various salt solutions was investigated. Antipolyelectrolyte behavior was observed with enhancement of concentration of mono‐ and multivalent salts. Swelling in the various pH media was nearly pH‐independent over a wide range of pH. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dual stimuli responsive neutral/cationic polymers/clay nanocomposite hydrogels

In this work, a thermodynamic-based equilibrium-swelling model was proposed to predict the swelling process of neutral/cationic polymers-clay nanocomposite hydrogels sensitive to dual stimuli temperature and pH. Indeed, the new swelling model can estimate the effect of the rigid clay nanoparticles component on swelling behavior of blend nanocomposite hydrogels. The mixing term in model was developed based on lattice theory by considering the effects of solvent-polymers, solvent-clay, and polymer-clay interaction parameters. The influence of the ionic groups of the clay layers and cationic polymer on the swelling was also taken into account in the proposed model. The model was verified by preparation of polyvinyl alcohol/chitosan/montmorillonite intelligent nanocomposite hydrogel by tripolyphosphate crosslinking method followed by freezing–thawing process. It was found that it could give good prediction for the equilibrium swelling of polymer-clay nanocomposite hydrogels in the case of phantom network, especially where the swelling temperature and clay loading level are high and the pH of swelling medium is low. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020 , 137, 48797.     

Microwave‐assisted preparation of temperature sensitive poly(N‐isopropylacrylamide) hydrogels in poly(ethylene oxide)‐600

In this article, a series of poly(N‐isopropylacrylamide) (PNIPAM)‐based hydrogels were prepared under microwave irradiation using poly(ethylene oxide)‐600 (PEO‐600) as reaction medium and microwave‐absorbing agent as well as pore‐forming agent. All of the temperature measurements, gel fractions, and FTIR analyses proved that the PNIPAM hydrogels were successfully synthesized. Within 1 min, the PNIPAM hydrogel with a 98% yield was obtained under microwave irradiation. The PNIPAM hydrogels thus prepared exhibited controllable properties such as pore size, equilibrium swelling ratios, and swelling/deswelling rates when changing the feed weight ratios of monomer (N‐isopropylacrylamide, NIPAM) to PEO‐600. These properties are well adapted to the different requirements for their potential application in many fields such as biomedicine. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102:4177–4184, 2006