Effects of clay‐modifying agents on the morphology and properties of poly(methyl methacrylate)/clay nanocomposites synthesized via γ‐ray irradiation polymerization

Via γ‐ray irradiation polymerization, poly(methyl methacrylate) (PMMA)/clay nanocomposites were successfully prepared with reactive modified clay and nonreactive clay. With reactive modified clay, exfoliated PMMA/clay nanocomposites were obtained, and with nonreactive clay, intercalated PMMA/clay nanocomposites were obtained. Both results were confirmed by X‐ray diffraction and high‐resolution transmission electron microscopy. PMMA extracted from PMMA/clay nanocomposites synthesized by γ‐ray irradiation had higher molecular weights and narrow molecular weight distributions. The enhanced thermal properties of the PMMA/clay nanocomposites were characterized by thermogravimetric analysis and differential scanning calorimetry. The improved mechanical properties of PMMA/clay were characterized by dynamic mechanical analysis. In particular, the enhancement of the thermal properties of the PMMA/clay nanocomposites with reactive modified clay was much more obvious than that of the PMMA/clay nanocomposites with nonreactive clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3218–3226, 2003     

Synthesis and characterization of polyethylene/clay–silica nanocomposites: A montmorillonite/silica‐hybrid‐supported catalyst and in situ polymerization

A novel approach to the preparation of polyethylene (PE) nanocomposites, with montmorillonite/silica hybrid (MT‐Si) supported catalyst, was developed. MT‐Si was prepared by depositing silica nanoparticles between galleries of the MT. A common zirconocene catalyst [bis(cyclopentadienyl)zirconium dichloride/methylaluminoxane] was fixed on the MT‐Si surface by a simple method. After ethylene polymerization, two classes of nanofillers (clay layers and silica nanoparticles) were dispersed concurrently in the PE matrix and PE/clay–silica nanocomposites were obtained. Exfoliation of the clay layers and dispersion of the silica nanoparticles were examined with transmission electron microscopy. Physical properties of the nanocomposites were characterized by tensile tests, dynamic mechanical analysis, and DSC. The nanocomposites with a low nanofiller loading (<10 wt %) exhibited good mechanical properties. The nanocomposite powder produced with the supported catalyst had a granular morphology and a high bulk density, typical of a heterogeneous catalyst system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 941–949, 2004     

Exfoliated poly(methyl methacrylate) and polystyrene nanocomposites occur when the clay cation contains a vinyl monomer

The bulk polymerization of methyl methacrylate and styrene in the presence of an organically modified clay containing a vinyl group that can be involved in the polymerization produces exfoliated nanocomposites. These nanocomposites have been characterized by X‐ray diffraction, transmission electron microscopy, thermogravimetric analysis, mechanical properties, and cone calorimetry. The onset temperature of thermal degradation increases with the mechanical properties. The peak heat release rate is significantly reduced for nanocomposites containing 3 or 5% clay. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 1124–1135, 2003     

Mechanical properties of polymer‐blend nanocomposites with organoclays: Polystyrene/ABS and high impact polystyrene/ABS

Thirty‐three polystyrene (PS)/acrylonitrile‐butadiene‐styrene (ABS) and high impact PS/ABS polymer blends with organoclay and copolymer additives were prepared by melt processing using different mixing sequences in order to test the putative capability of clay to perform a compatibilizing role in polymer blends. In general, the addition of clay increased the tensile modulus and had little effect on tensile strength. For the blends studied in this work, the addition of organoclays caused a catastrophic reduction in impact strength, a critical property for commercial viability. The polymer‐blend nanocomposites adopted a structure similar to that for ABS/clay nanocomposites as determined by X‐ray diffraction and transmission electron microscopy. It is suggested that clay reinforcement inhibits energy absorption by craze formation and shear yielding at high strain rates. Simultaneous mixing of the three components provided nanocomposites with superior elongation and energy to failure compared to sequential mixing. The clay pre‐treated with a benzyl‐containing surfactant gave the best overall properties among the various organoclays tested and of the two clay contents studied 4 wt % was preferred over 8 wt % addition. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Polymorphic behavior in syndiotactic polystyrene/clay nanocomposites

X‐ray diffraction methods were used in an investigation of the structural changes in syndiotactic polystyrene (sPS)/clay nanocomposites. sPS/clay was prepared by the intercalation of sPS polymer into layered montmorillonite. Both X‐ray diffraction data and transmission electron microscopy micrographs of sPS/clay nanocomposites indicated that most of the swellable silicate layers were exfoliated and randomly dispersed in the sPS matrix. The X‐ray diffraction data also showed the presence of polymorphism in the sPS/clay nanocomposites. This polymorphic behavior was strongly dependent on the thermal history of the sPS/clay nanocomposites from the melt and on the content of clay in the sPS/clay nanocomposites. Quenching from the melt induced crystallization into the α‐crystalline form, and the addition of montmorillonite probably increased heterophase nucleation of the α‐crystalline form. The effect of the melt crystallization of sPS and sPS/clay nanocomposites at different temperatures on the crystalline phases was also examined. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 736–746, 2002     

Poly(cyclohexene oxide)/clay nanocomposites by photoinitiated cationic polymerization via activated monomer mechanism

Poly(cyclohexene oxide) (PCHO)/clay nanocomposites were prepared by in situ photoinitiated activated monomer cationic polymerization. The polymerization of cyclohexene oxide through the interlayer galleries of the clay can provide distribution of the clay layers in the polymer matrix homogenously and results in the formation of PCHO/clay nanocomposites. The exfoliated structures were characterized by X‐ray diffraction spectroscopy, thermogravimetric analysis, transmission electron microscopy, and atomic force microscopy. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5328–5335, 2009     

Zero‐order kinetics of the thermal degradation of polypropylene/clay nanocomposites

The thermal degradation kinetics of polypropylene/clay microcomposites and nanocomposites were studied by thermogravimetric analysis. In comparison with pure polypropylene, the reaction order of the degradation of the composites became zero‐order, and the activation energy increased dramatically. The zero‐order kinetics were associated with the acidic sites (H⁺) created on the clay layers, whereas the increase in the activation energy was coupled with the shielding effect of clay. The kinetic analysis could provide additional mechanistic clues concerning the thermal stability and flammability of polymer/clay nanocomposites. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3713–3719, 2005     

Polypeptide‐based nanocomposite: Structure and properties of poly(L‐lysine)/Na+‐montmorillonite

The feasibility of constructing polymer/clay nanocomposites with polypeptides as the matrix material is shown. Cationic poly‐L‐lysine · HBr (PLL) was reinforced by sodium montmorillonite clay. The PLL/clay nanocomposites were made via the solution‐intercalation film‐casting technique. X‐ray diffraction and transmission electron microscopy data indicated that montmorillonite layers intercalated with PLL chains coexist with exfoliated layers over a wide range of relative PLL/clay compositions. Differential scanning calorimetry suggests that the presence of clay suppresses crystal formation in PLL relative to the neat polypeptide and slightly decreases the PLL melting temperature. Despite lower crystallinity, dynamic mechanical analysis revealed a significant increase in the storage modulus of PLL with an increase in clay loading producing storage modulus magnitudes on par with traditional engineering thermoplastics. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2579–2586, 2002     

Effect of a silicate filler on the crystal morphology of poly(trimethylene terephthalate)/clay nanocomposites

A series of intercalated poly(trimethylene terephthalate) (PTT)/clay nanocomposites were prepared in a twin‐screw extruder by the melt mixing of PTT with either quaternary or ternary ammonium salt‐modified clays. The morphology and structure, along with the crystallization and melting behavior, and the dynamic mechanical behavior of the composites were characterized by X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and dynamic mechanical thermal analysis. The results showed that the PTT chains could undergo center‐mass transport from the polymer melt into the silicate galleries successfully during the blending and extrusion process. More coherent stacking of the silicate layers was reserved at higher clay concentrations and shorter blend times. Compared with conventionally compounded composites, the nanoscale‐dispersed organophilic clays were more effective as crystal nucleation agents. The influence of the nanosilicates on the crystallization and melting behavior of PTT became distinct when the concentration of clay was around 3 wt %. The changes in the crystallization behavior of the polymer/clay nanocomposites depended not only on the size of the silicates but also on the intrinsic crystallization characteristics of the polymers. The resulting nanocomposites showed an increase in the dynamic modulus of PTT and a decrease in the relaxation intensity (both in loss modulus and loss tangent magnitude). © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2275–2289, 2003     

Morphology and mechanical properties of a novel amorphous polyamide/nanoclay nanocomposite

A novel amorphous polyamide/montmorillonite nanocomposite based on poly(hexamethylene isophthalamide) was successfully prepared by melt intercalation. Wide angle X-ray diffraction and transmission electron microscopy showed that organoclay containing quaternary amine surfactants with phenyl and hydroxyl groups was delaminated in the polymer matrix resulting in well-exfoliated morphologies even at high montmorillonite content. Differential scanning calorimetry results indicated that clay platelets did not induce the formation of a crystalline phase in this amorphous polymer. Tensile tests demonstrated that the addition of nanoclay caused a dramatic increase in Young's modulus (almost twofold) and yield strength of the nanocomposites compared with the homopolymer. The nanocomposites exhibited ductile behavior up to 5 wt % of nanoclay. The improvement in Young's modulus is comparable with semicrystalline aliphatic nylon 6 nanocomposites. Both the main chain amide groups and the amorphous nature of the polyamide are responsible for enhancing the dispersion of the nanofillers, thereby, leading to improved properties of the nanocomposites. The structure-property relationship for these nanocomposites was also explored. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2605–2617, 2008     

Electrical characterization of poly(ethylene oxide)–clay nanocomposites prepared by microwave irradiation

Poly(ethylene oxide) (PEO)–clay (montmorillonite, hectorite, and laponite) nanocomposites were prepared by a melting intercalation procedure induced by microwave irradiation. The influence of parameters such as the time of irradiation, power, amount and relative ratio of the reagents, and relative humidity was investigated. X-ray diffraction, differential scanning calorimetry, elemental microanalysis, Fourier transform infrared, and scanning electron microscopy techniques were applied to characterize the resulting nanocomposites. Techniques involving impedance spectroscopy, thermoelectric power, and electrical polarization in the solid state were used to characterize the electrical properties of the nanocomposites. The electrical behavior of these PEO–silicate nanocomposites, including those containing an excess of alkaline metal salts in comparison with that of similar systems prepared by alternative procedures such as direct intercalation from polymer solutions or melting intercalation, was also examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3249–3263, 2003     

Poly(1‐butene)/clay nanocomposites: Preparation and properties

The preparation and properties of poly(1‐butene) (PB)/clay nanocomposites are described for the first time. Nanocomposites were prepared with the melt‐intercalation technique, using organically modified clay. The X‐ray diffraction patterns portrayed well‐defined diffraction peaks at higher d‐spacing than pristine clay, confirming the intercalation of polymer in silicate layers. Because PB exhibits time‐dependent polymorphism, the effect of clay on the phase transformation of PB was examined with thermal analysis. The phase transformation from a metastable tetragonal form to a stable hexagonal form was enhanced because of incorporation of layered silicates in the polymer matrix. The nanocomposites exhibited about a 40–140% increase in storage modulus depending on the clay content and significantly lower coefficient of thermal expansion. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1014–1021, 2003     

In situ polymerization of ethylene with bis(imino)pyridine iron(II) catalysts supported on clay: The synthesis and characterization of polyethylene–clay nanocomposites

Polyethylene–clay nanocomposites were synthesized by in situ polymerization with 2,6‐bis[1‐(2,6‐diisopropylphenylimino)ethyl] pyridine iron(II) dichloride supported on a modified montmorillonite clay pretreated with methylaluminoxane (MAO). The catalysts and the obtained nanocomposites were examined with wide‐angle X‐ray scattering. The exfoliation of the clay was further established by transmission electron microscopy. Upon the treatment of the clay with MAO, there was an increase in the d‐spacing of the clay galleries. No further increase in the d‐spacing of the galleries was observed with the iron catalyst supported on the MAO‐treated clay. The catalyst activity for ethylene polymerization was independent of the Al/Fe ratio. The exfoliation of the clay inside the polymer matrix depended on various parameters, such as the clay content, catalyst content, and Al/Fe ratio. The crystallinity percentage and crystallite size of the nanocomposites were affected by the degree of exfoliation of the clay. Moreover, when ethylene was polymerized with a mixture of the homogeneous iron(II) catalyst and clay, the degree of exfoliation was significantly lower than when the polymerization was performed with a preformed clay‐supported catalyst. This observation suggested that in the supported catalyst, at least some of the active centers resided within the galleries of the clay. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 304–318, 2005     

Influence of gamma irradiation on high density polyethylene/ethylene‐vinyl acetate/clay nanocomposites

The study of high density polyethylene (HDPE)/ethylene‐vinyl acetate (EVA)/and organically‐modified montmorillonite (OMT) nanocomposites prepared by melt intercalation followed by exposure to gamma‐rays have been carried out. The morphology and properties of the nanocomposites were studied using X‐ray diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TGA) and cone calorimetry. The purpose of the study focuses on the influence of gamma irradiation on the morphology, thermal stability and flammability properties of the nanocomposites. XRD studies and TEM images verified that the ordered intercalated nanomorphology of the nanocomposites was not disturbed by gamma irradiation. TGA data showed that the nano‐dispersion of clay throughout the polymer inhibited the irradiation degradation of HDPE/EVA blend, which led to the nanocomposites exhibiting superior irradiation‐resistant properties than that of the pure blend. Cone calorimetry results indicated that the improvement in heat release rate (HRR) for irradiated HDPE/EVA blend was suppressed efficiently when clay was present. Increasing clay loading from 2 to 10% was beneficial by improving the flammability properties of the nanocomposites, but promoted a rapid increase in the sub‐peak HRR at high irradiation dose level. Copyright © 2004 John Wiley & Sons, Ltd.     

Efficient photoinduced In situ preparation of clay/poly(glycidyl methacrylate) nanocomposites using hydrogen‐donor silane

Clay/poly(glycidyl methacrylate) nanocomposites (clay/PGMA) were prepared by in situ radical photopolymerization using N,N‐dimethylaminopropyltrimethoxysilane(DMA)‐modified bentonite clay acting as hydrogen donor for benzophenone in solution. This initiating system permits to photopolymerize glycidyl methacrylate between the lamellae of the DMA‐modified clay. The approach provides exfoliated nanocomposites as judged by the measurements of X‐ray diffraction. However, a low fraction of persistent intercalated clay regions was visible by transmission electron microscopy. X‐ray photoelectron spectra analyses indicate that the nanocomposites have PGMA‐rich surface. The clay/PGMA nanocomposites can be readily dispersed in ethanol. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 800–808     

Melt blending of ethylene‐vinyl alcohol copolymer/clay nanocomposites: Effect of the clay type and processing conditions

Ethylene‐vinyl alcohol copolymer (EVOH)/clay nanocomposites were prepared via dynamic melt blending. The effect of the processing parameters on blends containing two clay types in different amounts was examined. The blends were characterized with a Brabender plastograph and capillary rheometer, differential scanning calorimetry, dynamic mechanical thermal analysis (DMTA), X‐ray diffraction (XRD), transmission electron microscopy (TEM), and thermogravimetric analysis (TGA). XRD showed advanced EVOH intercalation within the galleries, whereas TEM images indicated exfoliation, thereby complementing the XRD data. A dilution process with EVOH and clay treatment in an ultrasonic bath before melt blending did not add to the intercalation level. Different trends were observed for the EVOHs containing two different clay treatments, one claimed to be treated for EVOH and the other for amine‐cured epoxy. They reflected the differences in the amounts of the strongly interacting polymer for the two nanocomposites. Thermal analysis showed that the melting temperature, crystallization temperature, and heat of fusion of the EVOH matrix sharply decreased with both increasing clay content and processing times. Significantly higher viscosity levels were obtained for the blends in comparison with those of the neat polymer. The DMTA spectra showed higher glass‐transition temperatures for the nanocomposites in comparison with those of the neat EVOH. However, at high clay loadings, the glass‐transition temperature remained constant, presumably because of an adverse plasticizing effect of the low moleculared mass onium ions treating the clays. The storage modulus improved when clay treated for EVOH was used, and it deteriorated when amine‐cured epoxy clay was incorporated, except for the sonicated clay. TGA results showed significant improvements in the blends' thermal stability in comparison with that of the neat EVOH, which, according to TEM, was greater for the intercalated structures rather than for exfoliated ones. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1741–1753, 2002     

Structure–property relationships of polymer blend/clay nanocomposites: Compatibilized and noncompatibilized polystyrene/propylene/clay

Polymer blends represent an important class of materials in engineering applications. The incorporation of clay nanofiller may provide new opportunities for this type of materials to enhance their applications. This article reports on the effects of clay on the structure and properties of compatibilized and noncompatibilized polymer blends and presents a detailed process for quantitative analysis of the elastic moduli of polymer blend/clay nanocomposites, based on immiscible polystyrene/polypropylene (PS/PP) blends with or without maleated PP as the compatibilizer. The results show that in the noncompatibilized PS/PP/clay nanocomposite clay locates solely in the PS phase, whereas in the compatibilized nanocomposite clay disperses in both phases. The addition of clay to both polymer blends reduces the domain size significantly, modifies the crystallinity and improves the stiffness. The Mori–Tanaka and Christensen's models offer a reasonably good prediction of the elastic moduli of both types of nanocomposites. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Poly(vinylidene fluoride)/clay nanocomposites prepared by melt intercalation: Crystallization and dynamic mechanical behavior studies

The preparation and properties of poly(vinylidene fluoride) (PVDF)/clay nanocomposites are reported for the first time. PVDF/clay nanocomposites were prepared by melt intercalation with organophilic clay. The composites were characterized with X‐ray diffraction, differential scanning calorimetry, and dynamic mechanical analysis. X‐ray diffraction results indicated intercalation of the polymer into the interlayer spacing. PVDF in the nanocomposites crystallized in the β form. Differential scanning calorimetry nonisothermal curves showed an increase in the melting and crystallization temperatures along with a decrease in crystallinity, as evidenced by the melting and crystallization peaks. Isothermal crystallization studies showed an enhanced rate of crystallization with the addition of clay, as evidenced by a reduction in the crystallization time. Dynamic mechanical analysis indicated significant improvements in the storage modulus over a temperature range of ?100 to 150 °C. The tan δ peak signifying the glass‐transition temperature of PVDF shifted to higher temperatures. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1682–1689, 2002     

Silicon‐methoxide‐modified clays and their polystyrene nanocomposites

Silicon‐methoxide‐containing modified clays were obtained through cationic exchange between the sodium clay and the ammonium cation of [3‐(trimethoxysilyl)propyl]octadecyldimethylammonium chloride (Si18). The nanocomposites were prepared through bulk polymerization of styrene in which the Si18 clay was dispersed. The silicon‐methoxide offers the possibility of reaction between the methoxide and a clay hydroxyl group to link together the cation and the clay. The nanocomposites were characterized by X‐ray diffraction, transmission electron microscopy, and atomic force microscopy. Their thermal stability and flame retardancy were measured by thermogravimetric analysis (TGA) and cone calorimetry. Linkage between the silicon and the clay apparently occurs in the clay but is not likely to occur in the nanocomposite, perhaps because of the presence of the polystyrene spreading the distance between the reactive sites, which makes reaction more difficult. The results from TGA and cone calorimetry were similar to those obtained with other nanocomposites. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1498–1503, 2002     

Properties of covalently bonded layered‐silicate/polystyrene nanocomposites synthesized via atom transfer radical polymerization

Covalently bonded layered silicated/polystyrene nanocomposites were synthesized via atom transfer radical polymerization in the presence of initiator‐modified layered silicate. The resulting nanocomposites had an intercalated and partially exfoliated structure, as confirmed by X‐ray diffraction and transmission electron microscopy. The thermal properties of the nanocomposites improved substantially over those of neat polystyrene. In particular, a maximum increase of 35.5 °C in the degradation temperature was displayed by these nanocomposites. Additionally, the surface elastic modulus and hardness of these nanocomposites were more than double those of pure polystyrene. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 534–542, 2005