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     

Synthesis of bio‐based polymeric nanocomposites from acrylated epoxidized soybean oil and montmorillonite clay in the presence of a bio‐based intercalant

Polymeric nanocomposites were synthesized from functionalized soybean‐oil‐based polymer matrix and montmorillonite (MMT) clay using an in situ free radical polymerization reaction. Acrylated epoxidized soybean oil combined with styrene was used as the monomer. Organophilic MMT (OrgMMT) was obtained using a quaternized derivative of methyl oleate, which was synthesized from olive oil triglyceride, as a renewable intercalant. The resultant nanocomposites were characterized using X‐ray diffraction and atomic force microscopy. The effect of increased nanofiller loading on the thermal and mechanical properties of the nanocomposites was investigated using thermogravimetric analysis and dynamic mechanical analysis. It was found that the desired exfoliated nanocomposite structure was achieved when the OrgMMT loading was 1 and 2 wt%, whereas a partially exfoliated or intercalated nanocomposite was obtained for 3 wt% loading. All the nanocomposites were found to have improved thermal and mechanical properties as compared with virgin acrylated epoxidized soybean‐oil‐based polymer matrix. The nanocomposite containing 2 wt% OrgMMT clay was found to have the highest thermal stability and best dynamic mechanical performance. Copyright © 2010 Society of Chemical Industry     

Semi‐IPN carrageenan‐based nanocomposite hydrogels: Synthesis and swelling behavior

Inclusion of nano‐clays into hydrogels is an efficient approach to produce nanocomposite hydrogels. The introduction of nano‐clay into hydrogels causes an increase in water absorbency. In the present work, Nanocomposite hydrogels based on kappa‐carrageenan were synthesized using sodium montmorillonite as nano‐clay. Acrylamide and methylenebisacrylamide were used as monomer and crosslinker, respectively. The structure of nanocomposite hydrogels was investigated by XRD and SEM techniques. Swelling behavior of nanocomposite hydrogels was studied by varying clay and carrageenan contents as well as methylenebisacrylamide concentration. An optimum swelling capacity was achieved at 12% of sodium montmorilonite. The swollen nanocomposite hydrogels were used to study water retention capacity (WRC) under heating. The results revealed an increase in WRC due to inclusion of sodium montmorilonite clay. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Hydrogel‐MWCNT nanocomposites: Synthesis,characterization, and heating with radiofrequency fields

Hydrogel nanocomposites are attractive biomaterials for numerous applications including tissue engineering, drug delivery, cancer treatment, sensors, and actuators. Here we present a nanocomposite of multiwalled carbon nanotubes (MWCNT) and temperature responsive N‐isopropylacrylamide hydrogels. The lower critical solution temperature (LCST) of the nanocomposites was tailored for physiological applications by the addition of varying amounts of acrylamide (AAm). The addition of nanotubes contributed to interesting properties, including tailorability of temperature responsive swelling and mechanical strength of the resultant nanocomposites. The mechanical properties of the nanocomposites were studied over a range of temperatures (25–55°C) to characterize the effect of nanotube addition. A radiofrequency (RF) field of 13.56 MHz was applied to the nanocomposite discs, and the resultant heating was characterized using infrared thermography. This is the first report on the use of RF to remotely heat MWCNT‐hydrogel nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Poly(2‐hydroxyethyl methacrylate) nanocomposites: From a nonionic gel to pH sensitivity

2‐Hydroxyethyl methacrylate (HEMA)‐clay nanocomposites were prepared via in situ free radical polymerization using montmorillonite (MMT) as a crosslinker. The structure and surface morphology of the nanocomposites were characterized by Fourier transform infrared spectroscopy (FTIR), X‐ray diffraction, and scanning electron microscopy. It was found that exfoliated or highly expanded intercalated nanocomposite structure was obtained. The swelling degree was determined in distilled water and various pH buffered solutions. The highest swelling capacity in distilled water was observed for the nanocomposite sample prepared with the MMT amount of 10 % (w). It was seen that the diffusion mechanism was Fickian type in distilled water and also in various pH‐buffered solutions. It is interesting that the swelling degree of nanocomposites in alkaline pH values increased by the increasing of MMT in the polymer structure. This result supports the possibility of future applications of the novel nanocomposite in systems for the controlled released of drugs. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers     

Preparation of polystyrene–clay nanocomposites via dispersion polymerization using oligomeric styrene‐montmorillonite as stabilizer

This study describes the preparation of polystyrene–clay nanocomposite (PS‐nanocomposite) colloidal particles via free‐radical polymerization in dispersion. Montmorillonite clay (MMT) was pre‐modified using different concentrations of cationic styrene oligomeric (‘PS‐cationic’), and the subsequent modified PS‐MMT was used as stabilizer in the dispersion polymerization of styrene. The main objective of this study was to use the clay platelets as fillers to improve the thermal and mechanical properties of the final PS‐nanocomposites and as steric stabilizers in dispersion polymerization after modification with PS‐cationic. The correlation between the degree of clay modification and the morphology of the colloidal PS particles was investigated. The clay platelets were found to be encapsulated inside PS latex only when the clay surface was rendered highly hydrophobic, and stable polymer latex was obtained. The morphology of PS‐nanocomposite material (after film formation) was found to range from partially exfoliated to intercalated structure depending on the percentage of PS‐MMT loading. The impact of the modified clay loading on the monomer conversion, the polymer molecular weight, the thermal stability and the thermomechanical properties of the final PS‐nanocomposites was determined. Copyright © 2012 Society of Chemical Industry     

Evaluation of different amine‐functionalized polyethylenes as compatibilizers for polyethylene film nanocomposites

The compatibilization effects provided by different amine‐functionalized polyethylenes (PEs) versus those provided by a maleated polyethylene (PEgMA), for forming PE‐based film nanocomposites, were studied. Amine‐functionalized PEs were prepared by reaction of PEgMA with two primary amines, 2‐aminoethanol (EA) and 1,12‐aminododecane (D12), and a tertiary amine, 2‐[2‐(dimethylamino)ethoxy]ethanol (DMAE), in the melt to form the corresponding PEgEA, PEgD12 and PEgDMAE. Nanocomposites were prepared by melt mixing in a twin‐screw extruder PE and these three functionalized compatibilizers with a modified montmorillonite clay. The purpose of the current work was to determine the effect of the various amine‐functionalized PEs on the degree of exfoliation and optical properties of PE–clay nanocomposites in order to obtain nanocomposite films for greenhouse cover applications. Fourier transform infrared analysis confirmed the formation of the amine‐modified PE compatibilizers. Structural, morphological, mechanical, rheological and optical properties of film samples were used to characterize the nanocomposites. All the amine‐modified PE‐compatibilized nanocomposites had better clay exfoliation compared to uncompatibilized PE composites. Results showed that PEgDMAE formed highly exfoliated morphology and a favorable balance between mechanical (stiffness and ductility), optical and thermal insulating film properties even at higher clay contents. It was determined that nanocomposites with greater exfoliated structure showed better optical and thermal insulating film properties. PEgEA and PEgD12 compatibilizers did not provide a better interaction for exfoliation of the organoclay than the PEgMA material. The PEgDMAE compatibilizer led to a highly exfoliated morphology and a favorable balance between mechanical, optical and thermal insulating film properties even at higher clay contents. The PEgDMAE film nanocomposites could be used ideally for greenhouse cover applications. Copyright © 2010 Society of Chemical Industry     

Effects of silane grafting on the morphology and thermal stability of poly(ethylene terephthalate)/clay nanocomposites

An alkylammonium intercalated montmorillonite (A‐MMT) was modified by edge grafting with 3‐glycidoxypropyltrimethoxysilane. In comparison with poly(ethylene terephthalate) (PET)/A‐MMT, the resultant grafted clay, S‐A‐MMT, exhibited improved miscibility with PET matrix and revealed better dispersion state in the melting compounded PET/S‐A‐MMT nanocomposites. As a result, the PET/S‐A‐MMT nanocomposite had slower degradation rate owing to the enhanced clay barrier effect. Meanwhile, the nanocomposite exhibited lower degradation onset temperature under nitrogen because of the clay catalysis effect, which can be explained by the decreasing degradation reaction energy calculated from Coats–Redfern method of degradation kinetics. In the other hand, nanocomposite with better clay dispersion state exhibited increasing thermal oxidative stability due to clay barrier effect of hindering oxygen to diffuse in, which accorded with the continuous and compact char surface formed during polymer degradation. The clay catalysis and barrier effect of silicate layers were presented directly in isothermal oxidative TGA experiment. Furthermore, the mechanical and crystallization properties of PET/clay nanocomposites were investigated as well. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Mechanical and physical properties of polymer‐based nanocomposites containing different types of clay

Epoxy‐clay nanocomposites based on diglycidyl ether of bisphenol A (DGEBA) epoxy reinforced with 2 wt% of four different types of clay were prepared by high shear mixing (HSM) technique. The resultant nanocomposites were investigated to determine the effects of clay addition and clay types on their mechanical, thermal, and physical properties. The XRD and TEM analyses revealed that good dispersions of nanoclay within the epoxy matrix have been achieved especially for the samples prepared with I.30E clay where a combination of disordered intercalated and exfoliated morphology was observed. The structure of samples synthesized with other types of clay was dominated by intercalated morphologies. The tensile results illustrated that the nanocomposite containing I.30E clay has the best mechanical properties as compared to other nanocomposites. This is mainly due to better dispersion of I.30E nanoclay in the epoxy matrix for this nanocomposite. The increase or decrease in the glass transition temperatures of nanocomposites were found to be dependent on the type of clay used. The effect of clay addition on the barrier properties was examined using water exposure test which demonstrated that the addition of 2% of I.30E and C10A clays resulted in 60% reduction in diffusivity. Noticeable reduction in maximum water uptake was also observed for all nanocomposites. The improvement in these physical properties was attributed to the tortuosity effect, where water molecules have to move around clay layers during diffusion in nanocomposites. POLYM. COMPOS., 36:1998–2007, 2015. © 2014 Society of Plastics Engineer     

Systematic study of interfacial interactions between clays and an ionomer

To study the interfacial interactions between an ionomer [poly(ethylene‐co‐acrylic acid) neutralized by zinc salts (PI)] and clays, PI–clay nanocomposites were prepared using a solution method. Two types of commercially available montmorillonite clays respectively K10 and KSF were used, and were modified with organic modifiers with chain lengths of 12–18 carbons. The interactions between the PI, clays, and modifiers were evaluated through study of the structure, morphology, and properties of the PI–clay nanocomposites. We found that the modifiers were successfully intercalated into the clay layers (Fourier transform infrared spectroscopy). The clay modified with a long‐chain agent showed an exfoliated nature in the nanocomposite. The thermal stability and storage modulus of PI were improved greatly by the addition of the clays, especially when the long‐chain modifier was used (thermogravimetric analysis and dynamic mechanical analysis). The differential scanning calorimetry results show that clay layers are inserted into the clusters because of solvent‐directed morphological evolution, so the transition of the ionic domains and the crystallinity of PI are changed. The interaction between PI, the modifier, and the silicate layer played an important role in the determination of the properties of the nanocomposites. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effect of both silane‐grafted and ion‐exchanged organophilic clay in structural,thermal, and mechanical properties of unsaturated polyester nanocomposites

Unsaturated polyester (UPE) resin including styrene monomer was mixed with organophilic montmorillonite (MMT) clay and its crosslinking polymerization reaction was done in the presence of free‐radical initiator. MMT clay was modified with cetyl trimethly ammonium bromide and trimethoxy vinyl silane. The nanocomposites were characterized by X‐ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), thermogravimetric and dynamic mechanical analyses (TGA and DMA). The exfoliated nanocomposite structure was obtained when the MMT clay was modified in the presence of both modifiers, whereas individual modifications all resulted in intercalated structures. The exfoliated UPE nanocomposite exhibited better thermal and dynamic mechanical properties when compared with pure UPE and other composites, even with 3 wt% clay loading. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

A new model for estimation of the thermal conductivity of polymer/clay nanocomposites

High density polyethylene– and polypropylene–clay nanocomposites are synthesized by melt blending, in which polyethylene glycol and polypropylene glycol are used as compatibilizers to increase the space of galleries. The morphology properties of nanocomposites are explored by X‐ray diffraction and transition electron microscopy. The thermal conductivity coefficient (K) of nanocomposites is also measured along with the thermal stability. A conventional model based on developed Maxwell‐Garnett formula is also established to predict the thermal conductivity of polymer/clay nanocomposites with clay loading. Morphology results indicate that two intercalated and exfoliated structures are formed. The established model satisfactorily predicts the K values of nanocomposites for low range of clay content. Thermogravimetric analysis shows remarkable thermal stability of nanocomposites with 10 wt % of clay content. The deviation of our model from experimental result for 10 wt % of clay can be attributed to the intercalated structure of layered silicates into the matrices. Although the K values do not considerably increase in 5 wt % with respect to the increase occurs for 10 wt % of clay, but it increases about 28 and 37% at 50°C for high density polyethylene– and polypropylene–clay nanocomposites, respectively. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Effects of swelling agents on the crystallization behavior and mechanical properties of polyamide 6/clay nanocomposites

Montomorillonite was organically modified with three different swelling agents: n‐dodecylamine, 12‐aminolauric acid, and 1,12‐diaminodecane. These organoclays and polyamide 6 (PA6) were blended in a formic acid solution. X‐ray diffraction analysis showed that the clay still retained its layer structure in the PA6/clay nanocomposite. Consequently, these materials were intercalated nanocomposites. The effects of the swelling agent and organoclay content on the crystallization behavior of the PA6/clay nanocomposites were studied with differential scanning calorimetry. The results showed that the position and width of the exothermic peak of the PA6/clay nanocomposites were changed during the nonisothermal crystallization process. The clay behaved as a nucleating agent and enhanced the crystallization rate of PA6.The crystallinity of PA6 decreased with an increasing clay content. Different swelling agents also affected the crystallization behavior of PA6. The effects of the type and content of the swelling agent on the tensile and flexural properties of PA6/clay nanocomposites were also investigated. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1686–1693, 2003     

In situ photopolymerization of PEGDA‐protein hydrogels on nanotube surfaces

Peptide nanotubes were used as templates for the growth of poly(ethylene glycol) diacrylate‐based nanoscale hydrogels via photopolymerization. A Rose Bengal di‐amine derivative comprised of a photoactivator and coinitiator within the same molecule was used as the photoinitiator to increase photopolymerization efficiency. The nanotubes were covalently bound to the protein BSA before formation of the hydrogels. We also examined the photopolymerization efficiency in reactions involving nanotubes in the absence of BSA. Although photopolymerization occurred efficiently under both conditions, higher yields of highly crosslinked nanostructures were obtained for the protein bound nanotube‐PEGDA hydrogels. It was observed that the swelling ratios were also dependent upon whether or not BSA was bound to the nanotubes before photopolymerization. The thermal properties of the nanocomposite hydrogels were investigated using differential scanning calorimetry analyses and the morphologies were examined using TEM, SEM, and AFM analyses. Such nanocomposites prepared by low cost, mild methods could be extremely efficient for the in situ preparation of three‐dimensional arrays of peptide nanotube grafted hydrogels. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Flammability and thermal stability studies of ABS/Montmorillonite nanocomposite

Acrylonitrile–butadiene–styrene (ABS)/montmorillonite nanocomposites have been prepared using a direct melt intercalation technique by blending ABS and organophilic clay of two different particle sizes: OMTa (5 µm) and OMTb (38 µm). Their structure and flammability properties were characterized by X‐ray diffraction, high resolution electronic microscopy (HREM), thermogravimetric analysis (TGA) and cone calorimeter experiments. The results of HREM showed that ABS/5 wt% OMTa nanocomposite was a kind of intercalated–delaminated structure, while ABS/5 wt% OMTb nanocomposite was mainly an intercalated structure. The nanocomposites showed a lower heat release rate peak and higher thermal stability than the original ABS by TGA and cone calorimeter experiments. Also, the intercalated nanocomposite was more effective than an exfoliated–intercalated nanocomposite in fire retardancy. Copyright © 2003 Society of Chemical Industry     

Crystal transformation and thermomechanical properties of poly(vinylidene fluoride)/clay nanocomposites

The crystal transformation and thermomechanical properties of melt‐intercalated poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported in this study. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were used to study the thermal properties of PVDF and its nanocomposites with various clay concentrations. The incorporation of clay in PVDF results in the formation of β‐form crystals of PVDF. DSC study of melting behavior suggested the presence of only α‐phase crystals in neat PVDF and both α‐ and β‐phase crystals in the nanocomposite. This conclusion was corroborated by findings from Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD). Dynamic mechanical analysis (DMA) indicated significant improvements in storage modulus over a temperature range of 20–150 °C. The coefficient of thermal expansion (CTE) decreases with increasing clay loading. Copyright © 2004 Society of Chemical Industry     

Comparison the properties of PVA/Na+‐MMT nanocomposite hydrogels prepared by physical and physicochemical crosslinking

A novel physicochemical crosslinked nanocomposite hydrogel based on polyvinyl alcohol (PVA) and natural Na‐montmorillonite (Na⁺‐MMT) was synthesized by chemical crosslinking of nanocomposite hydrogel followed by a freezing‐thawing process. The effects of physical crosslinking, as well as physicochemical crosslinking, on the structure, morphology, and properties (thermal, mechanical, swelling, and deswelling) of nanocomposite hydrogels were investigated and compared with each other. The structure and morphology of nanocomposites were studied by Fourier transform infrared, X‐ray diffraction, field emission scanning electron microscopy, and transmission electron microscopy techniques. The thermal and mechanical properties of nanocomposites that were affected by physical and physicochemical crosslinking were evaluated by thermogravimetric analysis, differential scanning calorimeter, dynamic mechanical analysis, hardness test, and Water vapor transmission rate (WVTR) experiments. The results showed that the physicochemical crosslinking of a PVA nanocomposite leads to a reduction in crystallinity and melting temperature, as well as an increase in the Hardness and WVTR compared to a physically crosslinked PVA nanocomposite hydrogel. The swelling and deswelling experiments were performed using a gravimetric method, and it was shown that controlled crosslinking of PVA nanocomposite hydrogel with glutaraldehyde causes the swelling ratio to increase and the cumulative amount of water loss to decrease. The swelling (sorption) and deswelling (desorption) kinetics data for physically and physicochemical crosslinking of nanocomposite hydrogels were fitted with a fickian model. It is concluded that through control crosslinking of PVA nanocomposite can lead to a hydrogel with higher swelling capacity than that is in conventional PVA nanocomposite hydrogel. POLYM. COMPOS., 37:897–906, 2016. © 2014 Society of Plastics Engineers     

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     

Development of high‐performance epoxy/clay nanocomposites by incorporating novel phosphonium modified montmorillonite

Novel organoclays were synthesized by several kinds of phosphonium cations to improve the dispersibility in matrix resin of composites and accelerate the curing of matrix resin. The possibility of the application for epoxy/clay nanocomposites and the thermal, mechanical, and adhesive properties were investigated. Furthermore, the structures and morphologies of the epoxy/clay nanocomposites were evaluated by transmission electron microscopy. Consequently, the corporation of organoclays with different types of phosphonium cations into the epoxy matrix led to different morphologies of the organoclay particles, and then the distribution changes of silicate layers in the epoxy resin influenced the physical properties of the nanocomposites. When high‐reactive phosphonium cations with epoxy groups were adopted, the clay particles were well exfoliated and dispersed. The epoxy/clay nanocomposite realized the high glass‐transition temperature (T_g) and low coefficient of thermal expansion (CTE) in comparison with those of neat epoxy resin. On the other hand, in the case of low‐reactive phoshonium cations, the dispersion states of clay particles were intercalated but not exfoliated. The intercalated clay did not influence the T_g and CTE of the nanocomposite. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effect of clay content on the ultraviolet-curing and physical properties of urethane-acrylate/clay nanocomposites

The effect of clay content on the ultraviolet (UV)-curing behavior and physical properties of a urethane-acrylate/clay nanocomposite system was studied. The UV-curing behavior of the nanocomposite system was investigated by monitoring the change of a characteristic IR absorption peak for acrylate groups. The UV-curing rate and final conversion of the nanocomposite system increased with increasing clay content and affected the physical properties of the nanocomposites. The thermal, mechanical and optical properties of the nanocomposites were affected by clay content. The X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) image showed that the nanocomposites had an intercalated structure. POLYM. COMPOS., 28:325–330, 2007. © 2007 Society of Plastics Engineers