Effect of surface modification of montmorillonite on the properties of aromatic polyamide/clay nanocomposites

The surface modification of montmorillonite clay was carried out through ion‐ exchange reaction using p‐phenylenediamine as a modifier. This modified clay was employed to prepare aromatic polyamide/organoclay nanocomposite materials. The dispersion behavior of clay was examined in the polyamide matrix. Polyamide chains were synthesized from 4‐aminophenyl sulfone and isophthaloyl chloride (IPC) in dimethylacetamide. These amide chains were suitably end‐capped with carbonyl chloride end groups to interact chemically with modified montmorillonite clay. The resulting nanocomposite films containing 2–20 wt% of organoclay were characterized by TEM, X‐ray diffraction (XRD), thin‐film tensile testing; thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and water absorption measurements. Mechanical testing revealed that modulus and strength improved up to 6 wt% organoclay loading while elongation and toughness of nanocomposites decreased with the addition of clay content in the matrix. Thermal decomposition temperatures of the nanocomposites were in the range 225–450 °C. These nanocomposites expressed increase in the glass‐transition temperature values relative to pure polyamide describing interfacial interactions among the phases. The percent water uptake of these composites reduced upon the addition of modified layered silicate depicting improved barrier properties. Copyright © 2008 John Wiley & Sons, Ltd.     

Preparation and properties of aramid/layered silicate nanocomposites by solution intercalation technique

Polymer—clay nanocomposites were synthesized from aromatic polyamide and organoclay using the solution intercalation technique. Polyamide chains were produced through the reaction of 4,4′‐oxydianiline (ODA) and isophthaloyl chloride (IPC) in N, N′‐dimethyl acetamide, using stoichiometry yielding chains with carbonyl chloride end groups. The intercalation of sodium montmorillonite (Na‐MMT) was carried out using p‐phenylene diamine as a swelling agent through an ion exchange reaction. Different concentrations of organoclay were blended with the polyamide solution for complete dispersion of clay throughout the matrix. The resulting composite films were characterized by X‐ray diffraction (XRD), transmission electron microscopy (TEM), mechanical testing, thermogravimetry (TGA), differential scanning calorimetry (DSC) and water absorption measurements. The XRD pattern and morphology of the nanocomposites revealed the formation of exfoliated and intercalated clay platelets in the matrix. The film containing a small amount of clay was semitransparent and had a tensile strength of the order of 70 MPa (relative to the 52 MPa of the pure aramid). Thermal decomposition temperatures were in the range of 300–450°C and the weight of the samples remaining after heating to 900°C was found to be roughly proportional to the clay loading. DSC showed a systematic increase in the glass transition temperature with increase in clay content. Water absorption of the pristine aramid film was rather high (5.7%), which reduced upon loading of organoclay. Copyright © 2008 John Wiley & Sons, Ltd.     

Influence of clay modification on the properties of aramid-layered silicate nanocomposites

Nanocomposites from organoclay and aromatic polyamide were prepared using solution intercalation method. Aramid chains were synthesised by reacting 4-aminophenylsulfone with isophthaloyl chloride in dimethylacetamide. Dodecylamine was used as a modifier to change the hydrophilic nature of montmorillonite into organophilic. Suitable quantities of organoclay were mixed in the aramid solution with high-speed stirring for homogeneous dispersion of the clay. Thin films cast from these materials after evaporating the solvent were characterised. The morphology of nanocomposites was determined by X-ray diffraction and TEM. Results revealed the formation of delaminated and disordered intercalated clay platelets in the aramid matrix. Mechanical data indicated improvement in the tensile strength and modulus with clay loading up to 6 wt.%. The glass transition temperature increased up to 20 wt.% organoclay, suggesting better cohesion between the two phases and thermal stability augmented with increasing clay loading. The water uptake reduced gradually as a function of organoclay showing decreased permeability.     

Effects of epoxidized natural rubber as a compatibilizer in melt compounded natural rubber-organoclay nanocomposites

Nanocomposites containing natural rubber (NR) as matrix, epoxidized natural rubber (ENR) as compatibilizer and organophilic layered clay (organoclay) as filler were produced in an internal mixer and cured using a conventional sulphuric system. The effects of ENR with 25 (ENR 25) and 50 mol% epoxidation (ENR 50), respectively, were compared at 5 and 10 parts per hundred rubber (phr) concentrations. The organoclay content was fixed at 2 phr. Cure characteristics, clay dispersion, (thermo)mechanical properties of the nanocomposites were determined and discussed. Incorporation of ENR and organoclay strongly affected the parameters which could be derived from Monsanto MDR measurements. Faster cure and increased crosslink density were attributed to changes in the activation/crosslinking pathway which was, however, not studied in detail. The organoclay was mostly intercalated according to X-ray diffraction (XRD) and transmission electron microscopic (TEM) results. The best clay dispersion was achieved by adding ENR 50. This was reflected in the stiffness of the nanocomposites derived from both dynamic mechanical thermal analysis (DMTA) and tensile tests. The tensile and tear strengths of the ENR 50 containing nanocomposites were also superior to the ENR 25 compatibilized and uncompatibilized stocks.     

Influence concentration of modifying agent on properties of natural rubber/organoclay nanocomposites

Sodium-montmorillonite (Na-MMT) nanoclay was modified with different concentrations of octadecylamine organic modifying agent at 0.5, 1.0 and 1.5 times the CEC of Na-MMT. Influence of concentration of modifying agent on properties of the organoclays and natural rubber/organoclay nanocomposites was investigated. It was found that the optimum concentration of modifying agent was 1.5 times the CEC of Na-MMT. That is, at this concentration, larger d-spacing of organoclay particles and higher degree of clay dispersion in natural rubber matrix were observed. Larger interlayer d-spacing also caused enhancement of the mechanical properties of the NR/organoclay nanocomposites. Additionally, the NR/organoclay nanocomposites with higher concentration of modifying agent exhibited faster curing reaction with higher crosslink density. Furthermore, the organoclays with larger d-spacing and higher degree of dispersion in the natural rubber matrix exhibited enhancement of the mechanical and dynamic properties and thermal stability of natural rubber/organoclay nanocomposites.     

Thermal and mechanical properties of syndiotactic polystyrene/organoclay nanocomposites with different microstructures

The fabrication of syndiotactic polystyrene (sPS)/organoclay nanocomposite was conducted via a stepwise mixing process with poly(styrene‐co‐vinyloxazolin) (OPS), that is, melt intercalation of OPS into organoclay followed by blending with sPS. The microstructure of nanocomposite mainly depended on the arrangement type of the organic modifier in clay gallery. When organoclays that have a lateral bilayer arrangement were used, an exfoliated structure was obtained, whereas an intercalated structure was obtained when organoclay with a paraffinic monolayer arrangement were used. The thermal and mechanical properties of sPS nanocomposites were investigated in relation to their microstructures. From the thermograms of nonisothermal crystallization and melting, nanocomposites exhibited an enhanced overall crystallization rate but had less reduced crystallinity than a matrix polymer. Clay layers dispersed in a matrix polymer may serve as a nucleating agent and hinder the crystal growth of polymer chains. As a comparison of the two nanocomposites with different microstructures, because of the high degree of dispersion of its clay layer the exfoliated nanocomposite exhibited a faster crystallization rate and a lower degree of crystallinity than the intercalated one. Nanocomposites exhibited higher mechanical properties, such as strength and stiffness, than the matrix polymer as observed in the dynamic mechanical analysis and tensile tests. Exfoliated nanocomposites showed more enhanced mechanical properties than intercalated ones because of the uniformly dispersed clay layers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 1685–1693, 2004     

PREPARATION AND CHARACTERIZATION OF POLYAMIDE 11/CLAY NANOCOMPOSITES

INTRODUCTIONIn recent years, polymer/clay nanocomposites have attracted great interest from researchers since they frequentlyexhibit unexpected hybrid properties synergistically derived from the two components. Compared to their microcounterparts and the pristine polymer matrix, polymer/clay nanocomposites exhibit improved tensile strength andmodulus, decreased thermal expansion coefficient, decreased gas permeability, increased swelling resistance,enhanced ion conductivity, and reduced fl…     

Investigating the structure–property relationship of aromatic–aliphatic polyamide/layered silicate hybrid films

Surface treated montmorillonite was used to prepare nanocomposites with aromatic–aliphatic polyamide by solution intercalation technique. The polyamide chains were produced through polycondensation of 4-aminophenyl sulfone with sebacoyl chloride in dimethyl acetamide. Compatibility between the polymer and organoclay was achieved through carbonyl chloride end-capped amide chains prepared by adding extra sebacoyl chloride near the end of polymerization reaction. The nanocomposites morphology and clay dispersion were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Delaminated and intercalated morphologies were observed for different loading of organoclay. Tensile strength and modulus improved for nanocomposites with optimum organoclay content (10-wt.%). Thermal stability and glass transition temperature of nanocomposites increased relative to pristine polyamide with augmenting organoclay content. Water uptake of these materials decreased as compared to the neat polyamide indicating reduced permeability.     

Thermal properties from membrane of polyamide 6/montmorillonite clay nanocomposites obtained by immersion precipitation method

The aim of this work was to obtain membranes from polyamide 6/montmorillonite clay nanocomposites through the phase inversion technique. The nanocomposites and membranes from polyamide 6/montmorillonite clay were characterized by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Thermogravimetry (TG) and Differential Scanning Calorimetry (DSC). Microporous and asymmetric membranes were successfully obtained from nanocomposites and the results showed that the salts were incorporated by intercalation between the organoclay layers and, apparently that the nanocomposites and membranes were thermally more stable than the pure polyamide.     

Effect of dendrimer modified montmorillonite on structure and properties of EPDM nanocomposites

The purpose of this work was to study the effect of dendrimer modified clay minerals on the structure and properties of ethylene-propylene-diene monomer (EPDM) nanocomposites.Flame-retardant and dendrimer modified organic montmorillonite (FR-DOMt) was successfully prepared by Na⁺-montmorillonite, tetrahydroxymethyl phosphonium chloride (THPC), N, N-dihydroxyl-3-aminomethyl propionate, and boric acid. This dendritic type of organoclay (OC) was used in preparation of EPDM/FR-DOMt nanocomposites. The properties of these nanocomposites were studied. The dispersion status of the layered silicates in EPDM was revealed by X-ray diffractometer (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD and TEM results showed that FR-DOMt was exfoliated in the EPDM matrix when 10 phr of FR-DOMt was incorporated. The mechanical behavior, thermal stability, and flame retardance of the samples were examined. The experimental data demonstrated that the EPDM hybrids owned an improved tensile strength and elongation at break. In addition, the nanocomposites exhibited higher thermal stability and flame retardance than that of unfilled EPDM matrix.     

Microstructure and fracture behavior of semicrystalline polymer–clay nanocomposites

The relationships between the microstructure and the fracture behavior of three polymer/clay nanocomposites were studied. Two different polymer matrices were chosen, namely polyamide‐6 and polyethylene (compatibilized with PE‐g‐MA or PE‐g‐PEo), to reach very different clay dispersion states. The microstructure was characterized in terms of polymer crystallinity, orientation of the polymer crystalline lamellae, clay dispersion state, and orientation of the clay tactoids. The mechanical behavior was characterized by tensile tests. The essential work of fracture (EWF) concept was used to determine the fracture behavior of the nanocomposites. Both tensile and EWF tests were performed in two perpendicular directions, namely longitudinal and transversal. It is shown that the fracture behaviors of the matrices mainly depend on the polymer crystalline lamellae orientation. For the nanocomposites, the relationships between the matrix orientation, the clay dispersion states, the values of the EWF parameters (w_e and βw_p), and their anisotropy are discussed. The results show that the lower the average clay tactoid thickness, the lower is the decrease of fracture performance for the nanocomposite and the more consumed energy as longer the path of the crack. Besides, a linear dependence of the anisotropy of the EWF parameters of the nanocomposites on the average clay aspect ratio is found. The more exfoliated the structure is, the less pronounced the anisotropy of the EWF parameters. Interestingly, it is thought that the average clay aspect ratio is the parameter representing the clay dispersion state that governs the fracture anisotropy of the nanocomposites (as the elastic properties determined by tensile tests). © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1820–1836, 2008     

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     

XRD,SAXS, and PALS investigations of three different polymers reinforced with tetraoctylammonium exchanged montmorillonite

Three different polymer nanocomposites were prepared using clay modified with tetraoctylammonium (4C8) surfactant. The dispersion of clay silicate layers was studied using X-ray diffraction and small-angle scattering. Free-volume cavity sizes were studied with positron annihilation lifetime spectroscopy. Scattering methods confirmed disruption of all polymer lamellae organization upon organoclay addition and the creation of partially intercalated systems for polyamide and polycaprolactone. The presence of organoclay in the polymers enlarges the lower value of average positronium lifetime τ₃ of polyamide and reduces the higher value of τ₃ for polycaprolactone and polyethylene.     

Ball milling: An effective technique for the preparation of exfoliated clay filled unsaturated polyester toughened epoxy nanocomposite

This paper investigates the possibility of improving the mechanical and thermal properties of epoxy and unsaturated polyester toughened epoxy resins through the dispersion of octadecyl ammonium ion-exchanged montmorillonite (organoclay) through exfoliated mechanism. The nanocomposites prepared are characterized for their structural change and studied for their crystallite size, mechanical, thermal and water absorption (hydrophilicity) properties. The mechanical data indicates significant improvement in the flexural and tensile properties over the neat epoxy and UP-epoxy matrix according to the percentage content of organoclay. The thermal behavior too shows noticeable enhancement in glass transition temperature T _g and high thermal stability. Hydrophilicity of all the composites decreases irrespective of the concentration of organoclay on the epoxy and UP-epoxy matrices. The homogeneous morphology of epoxy and UP toughened epoxy nanocomposite hybrid systems is ascertained using scanning electron microscope (SEM). X-ray results point out that the cetyl ammonium modified clay filled composites exhibited the exfoliated structure.     

Clay dispersibility and mechanical property of the epoxy/clay nanocomposites prepared by different treatment methods

The bisphenol‐A type epoxy resin was combined with layered clays. Three types of epoxy/clay nanocomposites were prepared by different clay pretreatment methods, that is, the slurry (clay swelling with polar solvent), organo, and solubilization (organoclay swelling with polar solvent) methods. The organo and solubilization systems showed good dispersibility. The basal spacing of the layered clays in the obtained nanocomposites was evaluated by XRD and TEM observations. The basal spacing of the nanoclay in the solubilization system drastically increased. The mechanical properties were improved with the increase in the clay dispersion. A high modulus and fracture toughness were obtained by improvement of the clay dispersion into the matrix. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1753–1761, 2009     

Synthesis,rheology, and morphology of nylon‐11/layered silicate nanocomposite

Exfoliated nylon‐11/layered silicate nanocomposites were prepared via in situ polymerization by dispersing organoclay in 11‐aminoundecanoic acid monomer. The original clay was modified by a novel method with 11‐aminoundecanoic acid. In situ Fourier transform infrared spectroscopy results show that stronger hydrogen bonds exist between nylon‐11 and organoclay than that of between nylon‐11 and original clay. The linear dynamic viscoelasticity of organoclay nanocomposites was investigated. Before taking rheological measurements, the exfoliated and intercalating structures and the thermal properties were characterized using X‐ray diffraction, transmission electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The results show that the clay was uniformly distributed in nylon‐11 matrix during in situ polymerization of clay with 4 wt % or less. The presence of clay in nylon‐11 matrix increased the crystallization temperature and the thermal stability of nanocomposites prepared. Rheological properties such as storage modulus, loss modulus, and relative viscosity have close relationship with the dispersion favorably compatible with the organically modified clay. Comparing with neat nylon‐11, the nanocomposites show much higher dynamic modulus and stronger shear thinning behavior. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2161–2172, 2006     

Crystallization behavior and thermal stability of poly(trimethylene terephthalate)/clay nanocomposites

Poly(trimethylene terephthalate) (PTT)/montmorillonite (MMT) nanocomposites were prepared by the solution intercalation method. Two different kinds of clay were organomodified with an intercalation agent of cetyltrimetylammonium chloride (CMC). X‐ray diffraction (XRD) indicated that the layers of MMT were intercalated by CMC, and interlayer spacing was a function of the cationic exchange capacity of clay. The XRD studies demonstrated that the interlayer spacing of organoclay in the nanocomposites depends on the amount of organoclay. From the results of differential scanning calorimetric analysis, it was found that clay behaves as a nucleating agent and enhances the crystallization rate of PTT. The maximum enhancement of the crystallization rate for the nanocomposites was observed in nanocomposites containing about 1 wt % organoclay with a range of 1–15 wt %. From thermogravimetric analysis, we found that the thermal stability of the nanocomposites was enhanced by the addition of 1–10 wt % organoclay. According to transmission electron microscopy, the organoclay particle was highly dispersed in the PTT matrix without a large agglomeration of particles for a low organoclay content (5 wt %). However, an agglomerated structure did form in the PTT matrix at a 15 wt % organoclay content. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2902–2910, 2003     

Barrier and Mechanical Properties of Poly(caprolactone)/organoclay Nanocomposites

In this study, biodegradable poly(caprolactone) (PCL) hybrids with two types of organoclays: Cloisite 30B (30B) and Cloisite 93A (93A) have been prepared by melt mixing and their barrier performance to air permeation and mechanical properties were investigated. The hybrids of PCL/30B were found to be nanocomposites resulted from the strong interaction between organic modifier of 30B and PCL and those of PCL/93A were microcomposites. The barrier performance of PCL/30B nanocomposite film to air permeation was much more improved than pure PCL and PCL/93A microcomposites at low organoclay concentration. With the increase of organoclay content the permeability coefficient was also increased that could attributed to the extra tortuous pathway for gas permeation caused by organoclay exfoliation. The barrier behaviour of PCL/30B nanocomposites could be approximately described by a theoretical model developed for composites. The mechanical properties measurements showed that the reinforcement of organoclay 30B in nanocomposites is more significant than 93A in microcomposites. Both tensile modulus and tensile strength were increased in PCL/30B nanocomposites even at at low amount of organoclay without much loss of strain at break as compared to pure PCL. The significant improvements in both barrier and mechanical properties in PCL nanocomposites could be attributed to the fine dispersion state of organoclay 30B platelets in PCL matrix and the strong interaction between organic modifier of 30B and matrix molecules.     

Preparation, structure, and properties of styrene-ethylene-butylene-styrene block copolymer/clay nanocomposites: Part II fracture behaviors

Styrene-ethylene-butylene-styrene block copolymer (SEBS)/clay nanocomposites were prepared via a melt mixing technique. Various amounts of two types of maleated compatibilizers, styrene-ethylene-butylene-styrene block copolymer grafted maleic anhydride (SEBS-g-MA) and polypropylene grafted maleic anhydride (PP-g-MA), were incorporated to improve the dispersion of commercial organoclay (denoted as 20A), respectively. PP-g-MA compatibilized system conferred higher tensile strength and tear strength (initiation condition) than SEBS-g-MA compatibilized system. At a fixed content of compatibilizers, the above mechanical properties were improved with increasing clay content as well. By relating tensile strength to tear strength (arrest condition), the average depth of flaw was in the range of 33.8 ± 3.4 μm, which successfully confirmed the extension of Rivlin and Thomas’s theory for conventional elastomers to thermoplastic elastomer/clay nanocomposites for the first time. Cutting strength of SEBS/clay nanocomposites gave an intermediate value when compared with crystalline plastics and conventional amorphous elastomers, which further signified the importance of micro-yielding of styrene domains, crystalline yielding of compatibilizer, and filler reinforcement even in the nano-fracture zone of deformation.     

New clay-reinforced polyamide nanocomposite based on 4-phenylenediacrylic acid: Synthesis and properties

New type of aromatic polyamide/montmorillonite nanocomposites were produced using solution intercalation technique in N-methyl-2-pyrrolidone. High-molecular-weight amide chains were synthesized from 4,4′-diaminodiphenyl ether and 4-phenylenediacrylic acid in N-methyl-2-pyrrolidone. The resulting nanocomposite films containing 5–20 wt.% of organoclay (Cloisite® 20A) were characterized for FT-IR, scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), optical transparency and water absorption measurements. The distribution of organoclay and nanostructure of the composites were investigated by (XRD) and SEM analyses. Thermogravimetric analysis indicated an increase in thermal stability of nanocomposites as compared to pristine polyamide. The percentage optical transparency and water absorption of these hybrids was found to be much reduced upon the addition of modified layered silicate indicating decreased permeability.