Use of acrylic based surfmers for the preparation of exfoliated polystyrene–clay nanocomposites

Two polymerizable cationic surfactants, (11-acryloyloxyundecyl)dimethyl(2-hydroxyethyl)ammonium bromide (hydroxyethyl surfmer) and (11-acryloyloxyundecyl)dimethylethylammonium bromide (ethyl surfmer), were used for the modification of montmorillonite (MMT) clay. The modification of MMT dispersions was carried out by ion exchange of the sodium ions in Na⁺-MMT by surfactants in aqueous media. Modified MMT clays were then dispersed in styrene and subsequently polymerized in bulk by a free-radical polymerization reaction to yield polystyrene–clay nanocomposites. An exfoliated structure was obtained using the ethyl surfmer-modified clay, whereas a mixed exfoliated/intercalated structure was obtained using the hydroxyethyl surfmer-modified clay. Nanocomposite structures were confirmed by small angle X-ray scattering (SAXS) and transmission electron microscopy (TEM). The nanocomposites exhibited enhanced thermal stability and an increase in glass transition temperature, relative to neat polystyrene. The nanocomposites also exhibited enhanced mechanical properties, which were dependent on the clay loading. Intercalated polystyrene–clay nanocomposites were obtained using the non-polymerizable surfactant-modified clay (cetyltrimethylammonium bromide). Nanocomposites made from mixtures of surfmer-modified and CTAB-modified clays were also prepared, showing intermediate properties. However, when the nanocomposites were prepared in solution only intercalated morphologies were obtained. This was attributed to the competition between the solvent molecules and monomer in penetrating into clay galleries. These nanocomposites also exhibited enhanced thermal stability relative to the virgin polystyrene prepared by the same method. Similar temperatures of degradation (at 50% decomposition) were found for these nanocomposites relative to those prepared by bulk polymerization.     

Synthesis and properties of polystyrene–clay nanocomposites via in situ intercalative polymerization

Organophilic montmorillonite (MMT) was prepared by ion exchange between Na⁺ ions in the clay and twin benzyldimethyloctadecylammonium bromine cations in an aqueous medium. The organophilic MMT particles were easily dispersed and swollen in styrene monomer. Polystyrene–MMT nanocomposites were prepared by the free‐radical polymerization of styrene containing dispersed clay. The intercalation spacing in the nanocomposites and the degree of dispersion of these composites were investigated with X‐ray diffraction and transmission electron microscopy, respectively. The nanocomposites had higher weight‐average molecular weights, lower glass‐transition temperatures, and better thermal stability (the decomposition temperature was improved by ca. 70°C) than the virgin polystyrene. The rheological behavior of the polystyrene–MMT nanocomposites was also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 201–207, 2005     

Effect of clay modification on the morphological,mechanical, and thermal properties of polyamide 6/polypropylene/montmorillonite nanocomposites

Polyamide 6/polypropylene (PA6/PP = 70/30 parts) blends containing 4 phr (parts per hundred resin) of organophilic montmorillonite (OMMT) were prepared by melt compounding. The sodium montmorillonite (Na‐MMT) was modified using three different types of alkyl ammonium salts, namely dodecylamine, 12‐aminolauric acid, and stearylamine. The effect of clay modification on the morphological and mechanical properties of PA6/PP nanocomposites was investigated using x‐ray diffraction (XRD), transmission electron microscopy (TEM), tensile, flexural, and impact tests. The thermal properties of PA6/PP nanocomposites were characterized using thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), and heat distortion temperature (HDT). XRD and TEM results indicated the formation of exfoliated structure for the PA6/PP nanocomposites prepared using stearylamine modified montmorillonite. On the other hand, a mixture of intercalated and exfoliated structures was found for the PA6/PP nanocomposites prepared using 12‐aminolauric acid and dodecylamine modified montmorillonite. Incorporation of OMMT increased the stiffness but decreased the ductility and toughness of PA6/PP blend. The PA6/PP nanocomposite containing stearylamine modified montmorillonite showed the highest tensile, flexural, and thermal properties among all nanocomposites. This could be attributed to better exfoliated structure in the PA6/PP nanocomposite containing stearylamine modified montmorillonite. The storage modulus and HDT of PA6/PP blend were increased significantly with the incorporation of both Na‐MMT and OMMT. The highest value in both storage modulus and HDT was found in the PA6/PP nanocomposite containing stearylamine modified montmorillonite due to its better exfoliated structure. POLYM. COMPOS., 31:1156–1167, 2010. © 2009 Society of Plastics Engineers     

Synthesis of unsaturated polyester‐clay nanocomposites using reactive organoclays

Two polymerizable cationic surfactants, vinylbenzyl n‐alkyldimethyl (n = 12 or 18) ammonium chlorides, were used for functionalization of montmorillonite (MMT) and preparation of unsaturated polyester (UP)‐clay nanocomposites. Polymerizable organophilic clays were prepared by exchanging the sodium ions of MMT with vinylbenzyldodecyldimethyl ammonium chloride (VDAC) or vinylbenzyloctadecyldimethyl ammonium chloride (VOAC) in an aqueous medium. The dispersion of organoclays in UP led to gel formation. UP/VDAC‐MMT resulted in intercalated nanocomposites while UP/VOAC‐MMT formed partially exfoliated nanocomposites. The nanocomposites exhibited higher dynamic modulus than pristine UP.     

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     

Synthesis and evaluation of high‐performance ethylene–propylene–diene terpolymer/organoclay nanoscale composites

The main objective of this study was to synthesize and characterize the properties of ethylene–propylene–diene terpolymer (EPDM)/clay nanocomposites. Pristine clay, sodium montmorillonite (Na⁺–MMT), was intercalated with hexadecyl ammonium ion to form modified organoclay (16Me–MMT) and the effect of intercalation toward the change in interlayer spacing of the silicate layers was studied by X‐ray diffraction, which showed that the increase in interlayer spacing in Na⁺–MMT by 0.61 nm is attributed to the intercalation of hexadecyl ammonium ion within the clay layers. In the case of EPDM/16Me–MMT nanocomposites, the basal reflection peak was shifted toward a higher angle. However, gallery height remained more or less the same for different EPDM nanocomposites with organoclay content up to 8 wt %. The nanostructure of EPDM/clay composites was characterized by transmission electron microscopy, which established the coexistence of intercalated and exfoliated clay layers with an average layer thickness in the nanometer range within the EPDM matrix. The significant improvement in thermal stability and mechanical properties reflects the high‐performance nanocomposite formation. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 2429–2436, 2004     

Synthesis and properties of polystyrene–montmorillonite nanocomposites by suspension polymerization

Organophilic montmorillonite was prepared using ion‐exchange method between sodium ions in clay layers and stearyltrimethyl ammonium chloride in the various solvents, including deionized water, ethanol, acetone, and toluene. The montmorillonite has the largest d₀₀₁ spacing, as determined by X‐ray diffraction in toluene, than the other solvents considered. Ethanol can completely wash out the overexchanged stearyltrimethyl ammonium chloride among layers of montmorillonite. However, deionized water is the preferred ion‐exchange solvent. The thermal stability of organophilic montmorillonite was investigated by high‐resolution thermogravimetric analysis (TGA). Polystyrene–montmorillonite nanocomposites were obtained by suspension free radical polymerization of styrene in the dispersed organophilic montmorillonite. X‐ray diffraction (XRD) and transmission electron microscopy (TEM) revealed that montmorillonite had been exfoliated. 5.0 wt % of clay in the synthesized nanocomposite was found to be the optimum content that improved both thermal and mechanical properties over those of pure polystyrene under the experimental conditions applied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 101–109, 2004     

Effect of montmorillonite on properties of styrene–butadiene–styrene copolymer modified bitumen

Clay/styrene–butadiene–styrene (SBS) modified bitumen composites were prepared by melt blending with different contents of sodium montmorillonite (Na‐MMT) and organophilic montmorillonite (OMMT). The structures of clay/SBS modified bitumen composites were characterized by XRD. The XRD results showed that Na‐MMT/SBS modified bitumen composites may form an intercalated structure, whereas the OMMT/SBS modified bitumen composites may form an exfoliated structure. Effects of MMT on physical properties, dynamic rheological behaviors, and aging properties of SBS modified bitumen were investigated. The addition of Na‐MMT and OMMT increases both the softening point and viscosity of SBS modified bitumens and the clay/SBS modified bitumens exhibited higher complex modulus, lower phase angle. The high‐temperature storage stability can also be improved by clay with a proper amount added. Furthermore, clay/SBS modified bitumen composites showed better resistance to aging than SBS modified bitumen, which was ascribed to barrier of the intercalated or exfoliated structure to oxygen, reducing efficiently the oxidation of bitumen, and the degradation of SBS. POLYM. ENG. SCI., 47:1289–1295, 2007. © 2007 Society of Plastics Engineers     

A study of the effect of surfactants on the properties of polystyrene‐montmorillonite nanocomposites

Polystyrene‐Organo Montmorillonite (PS‐MMT) nanocomposites were prepared by suspension free radical polymerization of styrene in the dispersed organophilic montmorillonite. The results of X‐ray diffraction (XRD) and Transmission Electron Microscopy (TEM) indicated that exfoliated nanocomposites were achieved. The effect of organic modifiers (surfactants) on the properties of the synthesized nanocomposites was studied. It is found that polystyrene‐MMT nanocomposite with 5.0 wt% of organo‐MMT gave the greatest improvement in thermal stability, and polystyrene‐MMT nanocomposites with 7.5 wt% of organo‐MMT showed the greatest improvement in mechanical properties, compared with that of pure polystyrene (PS) in our experimental conditions. The alkyl chain length of surfactant used in fabricating organo‐MMT affects the synthesized PS nanocomposites: the longer the alkyl chain length that the surfactant possesses, the higher the glass transition temperature of the PS nanocomposite, However, the organoclay in the nanocomposites seems to play a dual role: (a) as nanofiller leading to the increase of storage modulus and (b) as plasticizer leading to the decrease of storage modulus. This results in a lower storage modulus of PS‐TMOMMT and PS‐TMTMMT nanocomposites than that of PS‐TMDMMT and PS‐TMCMMT nanocomposites. Further study is needed to confirm the above hypothesis.     

Synthesis and dielectric properties of polystyrene‐clay nanocomposite materials

Polystyrene‐clay nanocomposite (PsCN) materials were synthesized and their properties of crystallinity, thermal behavior, and dielectric characteristics were investigated. A polymerizable cationic surfactant, [2‐(dimethylamino)ethyl]triphenylphonium bromide, was used for the intercalation of montmorillonite (MMT). The organophilic MMT was prepared by Na⁺‐exchanged MMT and ammonium cations of a cationic surfactant in an aqueous medium. Organophilic styrene monomers were intercalated into the interlayer regions of organophilic clay hosts followed by a free‐radical polymerization. Exfoliation to 2 wt % MMT in the polystyrene (PS) matrix was achieved as revealed by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Thermal properties by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were also studied. The dielectric properties of PsCNs in the form of film with clay loading from 1.0 to 5.0 wt % were measured under frequencies of 100 Hz–1 MHz at 25–70°C. A decreased dielectric constant and low dielectric loss were observed for PsCN materials. The dielectric response at low frequency that originated from dipole orientation was suppressed due to the intercalation of clay materials. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1368–1373, 2004     

Preparation of exfoliated high‐impact polystyrene/MMT nanocomposites via in situ polymerization under controlling viscosity of the reaction medium

Exfoliated high‐impact polystyrene (HIPS)/montmorillonite (MMT) nanocomposites were prepared via in situ polymerization of styrene in the presence of polybutadiene, using an intercalated cationic radical initiator‐MMT hybrid (organoclay). In the solution polymerization in toluene, the silicate layers of the clay were well exfoliated, due to the low extra‐gallery viscosity that can facilitate the diffusion of styrene monomers into the clay layers during the polymerization. The exfoliated HIPS/MMT nanocomposites were also successfully prepared by controlling the viscosity of the reaction medium with prolong swelling of the organoclay in styrene, prior to bulk polymerization. The HIPS/MMT nanocomposites, obtained from bulk polymerization, exhibited a significant improvement in thermal stability, compared to those obtained from solution polymerization as well as the pure polymer counterparts. POLYM. COMPOS., 2008. © 2007 Society of Plastics Engineers     

Solid‐state graft polymerization of styrene in spherical polypropylene particles in the presence of montmorillonite

In this work, cetyltrimethyl ammonium bromide and methacryloyloxyethyhrimethyl ammonium chloride were used to prepare organophilic montmorillonite (O‐MMT). Then, polypropylene (PP)–clay nanocomposites were prepared by the in situ grafting polymerization of styrene (St)‐containing O‐MMT onto PP with tert‐butyl perbenzoate as an initiator in the solid state. Fourier transform infrared spectroscopy, gel permeation chromatography, transmission electron microscopy, and X‐ray diffraction were applied to study the structure of the layered silicate and modified PP. The surfaces of the composites and, thus, the distribution of the clay in the PP matrix were characterized by scanning electron microscopy. The rheology and mechanical properties were studied and are discussed. According to the characterization results, OMMT and St were already grafted onto the PP main chain. Also, the intercalated structure of montmorillonite could be stabilized, and a stable exfoliated structure could be attained. Namely, intercalated PP/OMMT nanocomposites were obtained. The rheological results clearly show that these PP/OMMT nanocomposites had long‐chain‐branched structures. The peroxide modification of PP had minor effects on the tensile and bending strengths of the modified PP; however, this modification resulted in a significant reduction in the impact strength. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Nanocomposite Formation in Hydrogenated Nitrile Rubber (HNBR)/Organo‐Montmorillonite as a Function of the Intercalant Type

Summary: Hydrogenated acrylonitrile butadiene rubber (HNBR) was melt compounded with montmorillonite (MMT) and organophilic modified MMTs prior to sulfur curing. In contrast to the micro‐composite formation resulting from the compounding of the HNBR and pristine MMT, the modified MMTs (i.e., octadecylamine: MMT‐ODA, octadecyltrimethylamine: MMT‐ODTMA, methyltallow‐bis(2‐hydroxyethyl) quaternary ammonium: MMT‐MTH intercalants) produced nanocomposites. It was found that the organoclay with primary amine intercalant (cf. MMT‐ODA) gave confined structures along with the exfoliated/intercalated structures. This was traced to its reactivity with the curatives. By contrast, the organoclays containing less reactive quaternary ammonium compounds (cf. MMT‐ODTMA, MMT‐MTH) were exfoliated and intercalated based on X‐ray diffraction (XRD) and transmission electron microscopy (TEM) results. The hydroxyl functional groups of the MMT‐MTH supported the clay dispersion. The better adhesion between MMT‐MTH and HNBR was explained by hydrogen bonding between the hydroxyl groups of the intercalant and the acrylonitrile group of the HNBR matrix. This HNBR/MMT‐MTH nanocomposite showed the best mechanical properties as verified by tensile mechanical tests and dynamic mechanical thermal analysis (DMTA). The high tensile strength along with the high elongation at break for the rubber nanocomposites were attributed to the ability of the ‘clay network’ to dissipate the input energy upon uniaxial loading.

Scheme of failure development in rubber/organoclay mixes with poor (a) and good (b) dispersion of the clay layers.     

Influence of clay content on the melting behavior and crystal structure of nonisothermal crystallized poly(L‐lactic acid)/nanocomposites

To study the effect of organophilic clay concentration on nonisothermal crystallization, poly(L ‐lactic acid) (PLLA)/montmorillonite (MMT) nanocomposites were prepared by mixing various amounts of commercial MMT (Cloisite^® 30B) and PLLA. The effect of MMT content on melting behavior and crystal structure of nonisothermal crystallized PLLA/MMT nanocomposites was investigated by differential scanning calorimetry (DSC), small‐angle X‐ray scattering, and wide‐angle X‐ray diffraction (XRD) analyses. The study was focused on the effect of the filler concentration on thermal and structural properties of the nonisothermally crystallized nanocomposite PLLA/MMT. The results obtained have shown that at filler loadings higher than 3 wt %, intercalation of the clay is observed. At lower clay concentrations (1–3 wt %), exfoliation predominates. DSC and XRD analysis data show that the crystallinity of PLLA/MMT composites increases drastically at high clay loadings (5–9 wt %). In these nanocomposites, PLLA crystallizes nonisothermally in an orthorhombic crystal structure, assigned to the α form of PLLA. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characteristics of nitrile rubber (NBR) nanocomposites based on organophilic layered clay

The effect of clay modification on organo‐montmorillonite/NBR nanocomposites has been studied. Organo‐montmorillonite/NBR nanocomposites were prepared through a melt intercalation process. NBR nanocomposites were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), dynamic mechanical thermal analysis (DMTA) and a universal testing machine (UTM). XRD showed that the basal spacing in the clay increased, which means that the NBR matrix was intercalated in the clay layer galleries. On TEM images, organo‐montmorillonite (MMT) particles were clearly observed, having been exfoliated into nanoscale layers of about 10–20 nm thickness from their original 40 µm particle size. These layers were uniformly dispersed in the NBR matrix. The DMTA test showed that for these nanocomposites the plateau modulus and glass transition temperature (T_g) increased with respect to the corresponding values of pure NBR (without clay). UTM test showed that the nanocomposites had superior mechanical properties, ie strength and modulus. These improved properties are due to the nanoscale effects and strong interactions between the NBR matrix and the clay interface. Copyright © 2003 Society of Chemical Industry     

Syndiotactic Polystyrene/Organoclay Nanocomposites: Synthesis via In Situ Coordination‐Insertion Polymerization and Preliminary Characterization

Summary: Syndiotactic polystyrene (sPS)/organophilic clay nanocomposites were obtained by in situ coordination‐insertion polymerization of styrene. Two cationic surfactants (alkylammonium and alkylphosphonium) were used for the intercalation of montmorillonite (MMT). For each organically modified clay, three protocols were performed using an MAO‐activated hemi‐metallocene catalyst, in order to compare the influence of experimental conditions on the composite microstructure and on its thermal stability. The microstructures of nanocomposites were investigated by wide angle X‐ray scattering and DSC. Partially exfoliated or intercalated materials were obtained in all cases and a decrease of crystallinity is observed. Thermal properties were also studied by DSC and thermogravimetric analysis. The presence of clay does not have a strong influence on the sPS thermal transitions but the thermal decomposition process of the material was slowed down in the presence of few organoclay percents, particularly in the degradation beginning. The influence of these two organically modified clays on the thermal stability of the material is discussed.

Gel and suspension formed from the combination of cloisite with toluene (left) and styrene (right), respectively.     

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     

Nanocomposite structure depending on the degree of surface treatment of layered silicate

Nanocomposite structures depending on the degree of surface modification of montmorillonite (MMT) were studied. To change the degree of surface modification, MMT was treated with a controlled amount of stearylamine. The structures of MMTs and nanocomposites were investigated by X‐ray diffraction. To confirm the extent of surface coverage of the stearylamine as a organophilic modifier, TGA and elemental analysis experiments were performed. Different structures (intercalated or exfoliated) of a polymer/clay nanocomposite were obtained according to the interfacial characteristics between the polymer chains and the clay by controlling the degree of surface coverage. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2143–2147, 2002     

Synthesis and thermal properties of polystyrene/montmorillonite nanocomposites by γ‐ray radiation polymerization

Polystyrene/montmorillonite nanocomposites were prepared by γ‐ray radiation polymerization. X‐ray diffraction and high‐resolution transmission electron microscopy confirmed that polystyrene (PS) could be easily inserted between the sheets of montmorillonite (MMT) to form intercalated nanocomposites. In these PS/MMT nanocomposites, the distance between the sheets of MMT was barely influenced by varying the content of the MMT. Thermal stabilities of the samples were studied by thermal gravimetric analysis and differential scanning calorimetry. The glass‐transition temperature of PS/MMT nanocomposites was obviously higher than that of the pure PS. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1692–1696, 2003     

Synthesis of effective poly(4‐vinylpyridine) nanocomposites: in situ polymerization from edges/surfaces and interlayer galleries of clay

Poly(4‐vinylpyridine) (P4VP) nanocomposites have been prepared by using an in situ polymerization method in the presence of organically modified montmorillonite (MMT) clays with a quarternary salt of cocoamine containing a vinyl group, as well as trimethoxy vinyl silane. The nanocomposites were characterized by X‐ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The desired exfoliated nanocomposite structure was achieved when the MMT modification was conducted in the presence of both modifiers, whereas individual modifications all resulted in intercalated structures. This resultant exfoliated nanocomposite was found to have better thermal stability and dynamic mechanical performance when compared to the other nanocomposites, even with 2 % clay loading. Copyright © 2005 Society of Chemical Industry