Dispersibility of clay and crystallization kinetics for in situ polymerized PET/pristine and modified montmorillonite nanocomposites

Nanocomposite materials composed of poly (ethylene terephthalate) (PET) and montmorillonite (MMT) clays were prepared by in situ polymerization. Samples consisted of PET blended with various quantities of either pristine (Na⁺‐MMT) or organically modified MMT (A10‐MMT). The morphology and thermal and mechanical properties were evaluated for each sample. TEM micrographs, acquired at a 20 nm resolution, provide direct evidence of exfoliation of the clay particles into the PET matrix and show the effect of the alkyl‐modifier on clay dispersibility. The dispersion of PET/A10‐MMT was greater than that observed for the PET/Na⁺‐MMT nanocomposites. The greatest degree of exfoliation occurred for PET/A10‐MMT 0.5 wt %. However, PET/Na⁺‐MMT exhibited higher crystallization temperatures and rates suggesting that Na⁺‐MMT is a more efficient nucleating agent. Both mechanically and thermally, PET/A10‐MMT nanocomposites exhibited superior properties over pure PET. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 1022–1035, 2008     

Preparation and characterization of rigid poly (vinyl chloride)/MMT nanocomposites

In this article, a Haake torque rheometer equipped with an internal mixer is used to study the influence of the amount of sodium montmorillonite (Na⁺‐MMT) and organically modified MMT (O‐MMT) on the characteristics of rigid poly (vinyl chloride) (PVC)/Na⁺‐MMT and PVC/O‐MMT nanocomposites, respectively. It is observed that the fusion time and temperature of the rigid PVC/Na⁺‐MMT nanocomposites are decreased with increasing the amount of Na⁺‐MMT. On the contrast, the fusion time and temperature of the rigid PVC/O‐MMT nanocomposites are increased with increasing the amount of O‐MMT. Results of X‐ray diffraction (XRD) and transmission electron microscope (TEM) indicate that MMT is partially encapsulated and intercalated in the rigid PVC/Na⁺‐MMT nanocomposites. However, results of XRD and TEM show MMT is partially intercalated and exfoliated in the rigid PVC/O‐MMT nanocomposites. Tensile strength, yield strength, and elongation at break of the rigid PVC/MMT (including PVC/Na⁺‐MMT and PVC/O‐MMT) nanocomposites were improved simultaneously with adding 1–3 wt % Na⁺‐MMT or O‐MMT with respect to those of pristine PVC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1465–1474, 2005     

Preparation and characterization of rigid poly(vinyl chloride)/MMT nanocomposites. II. XRD,morphological and mechanical characteristics

A Haake torque rheometer equipped with an internal mixer is used to study the influence of the amount of sodium montmorillonite (Na⁺‐MMT) and organically modified MMT (O‐MMT) on X‐ray diffraction (XRD), morphology, and mechanical characteristics of rigid poly (vinyl chloride) (PVC)/Na⁺‐MMT and PVC/O‐MMT nanocomposites, respectively. Results of XRD and transmission electron microscopy (TEM) indicate that MMT is partially encapsulated and intercalated in the rigid PVC/Na⁺‐MMT nanocomposites. However, results of XRD and TEM show MMT is partially intercalated and exfoliated in the rigid PVC/O‐MMT nanocomposites. Tensile strength, yield strength, and elongation at break of the rigid PVC/MMT nanocomposites were improved simultaneously with adding 1–3 wt % Na⁺‐MMT or O‐MMT with respect to that of pristine PVC. However, the addition of Na⁺‐MMT or O‐MMT should be kept as not more than 3 wt % to optimize the mechanical properties and the processing stability of the rigid PVC/MMT nanocomposites. SEM micrographs of the fractured surfaces of the rigid PVC/Na⁺‐MMT and PVC/O‐MMT nanocomposites both before and after tensile tests were also illustrated and compared. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 2145–2154, 2006     

Effects of organic modifications of clay on the ultraviolet‐curing behavior and structure of a polyester‐acrylate/clay nanocomposite system

A pristine clay (Na⁺‐montmorillonite (MMT) and three different organoclays (20A‐MMT, vinylbenzyl dimethyldodecyl ammonium (VDA)‐MMT, and siloxane diamine ammonium (SDA)‐MMT) that originated from the pristine clay were used to prepare polyester‐acrylate (PEA)/clay nanocomposites by in situ ultraviolet (UV)‐curing. Except for the commercial organoclay (20A‐MMT), VDA‐MMT, and SDA‐MMT were prepared in this study by ion exchange method. The effects of organic modifications of the pristine clay on the UV‐curing behavior and structure of the nanocomposite system were investigated. The organic modifications of the clay affected considerably the UV‐curing behavior and structure of the nanocomposite system. Copyright © 2008 John Wiley & Sons, Ltd.     

Structure and properties of poly(ethylene terephthalate)/Na+‐montmorillonite nanocomposites prepared by solid state shear milling (S3M) method

This article reported a novel technology, solid state shear milling (S³M), to prepare poly(ethylene terephthalate)/Na⁺‐montmorillonite nanocomposites using the pristine Na⁺‐MMT without organic modification so as to avoid the problem that the organic modifiers, used for MMT treatment will decompose at high processing temperature of PET, and the structure and properties of the obtained samples were investigated. XRD and TEM analyses showed that Na⁺‐MMT layers were partially delaminated and intercalated, and uniformly dispersed in the PET matrix when suffering from the strong three dimensional shearing forces of pan‐milling. DSC analysis showed that Na⁺‐MMT serves as a nucleating agent, increasing the crystallization rate as well as the crystallization temperature of PET. The properties such as thermal stability and tensile strength of the PET/Na⁺‐MMT nanocomposites prepared by S³M got remarkably improved. Solid state shear milling (S³M) method was a simple and efficient method to get polymer/Na⁺‐MMT nanocomposites with pretty good performances without organic modification of pristine Na⁺‐MMT. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 807–817, 2008     

Preparation and properties of organo‐modifier free PET/MMT nanocomposites via monomer intercalation and in situ polymerization

In order to prevent the properties, especially transparency, color and health security, of PET/clay nanocomposites from being deteriorated due to the thermal degradation of clay organo‐modifer, we had directly modified sodium montmorillonite (Na⁺‐MMT) with PET's monomer, bis (hydroxyethyl) terephthalate (BHET) which had a degradation temperature higher than 400°C, and successfully prepared the hybrids via in situ polymerization. Nanodispersion of clay and the intercalated morphology were determined, and compared with PET/Na⁺‐MMT hybirds in which Na⁺‐MMT was directly added without any treatment. Improved mechanical properties and T_g were observed for the prepared PET/ BHET‐modified clay composites. More importantly, the film produced from the composites had the same transparency as that of pure PET even when 2 wt% of clay was added. Non‐isothermal and isothermal crystallization experiments showed a very good neculation capability of the nano‐dispersed clay, particularly at higher crystallization temperatures. Copyright © 2009 John Wiley & Sons, Ltd.     

Thermotropic liquid crystalline polyester nanocomposites via in situ intercalation polycondensation

A thermotropic liquid crystalline polyester (TLCP)/organoclay nanocomposite was synthesized via in situ intercalation polycondensation of diethyl‐2,5‐dihexyloxyterephthalic acid and 4,4′‐biphenol in the presence of organically modified montmorillonite (MMT). The organoclay, C18‐MMT, was prepared by the ion exchange of Na⁺‐MMT with octadecylamine chloride (C18‐Cl^?). TLCP/C18‐MMT nanocomposites were prepared to examine the variations of the thermal properties, morphology, and liquid crystalline phases of the nanocomposites with clay content in the range of 0–7 wt%. It was found that the addition of only a small amount of organoclay was sufficient to improve the thermal behavior of the TLCP hybrids, with maximum enhancement being observed at 1 wt% C18‐MMT. Copyright © 2008 John Wiley & Sons, Ltd.     

Synthesis and characterization of organosoluble,thermoplastic elastomer/clay nanocomposites

We synthesized organosoluble, thermoplastic elastomer/clay nanocomposites by making a jelly like solution of ethylene vinyl acetate containing 28% vinyl acetate (EVA‐28) and blending it with organomodified montmorillonite. Sodium montmorillonite (Na⁺‐MMT) was made organophilic by the intercalation of dodecyl ammonium ions. X‐ray diffraction patterns of Na⁺‐MMT and its corresponding organomodified dodecyl ammonium ion intercalated montmorillonite (12Me‐MMT) showed an increase in the interlayer spacing from 11.94 to 15.78 Å. However, X‐ray diffraction patterns of the thermoplastic elastomer and its hybrids with organomodified clay contents up to 6 wt % exhibited the disappearance of basal reflection peaks within an angle range of 3–10°, supporting the formation of a delaminated configuration. A hybrid containing 8 wt % 12Me‐MMT revealed a small hump within an angle range of 5–6° because of the aggregation of silicate layers in the EVA‐28 matrix. A transmission electron microscopy image of the same hybrid showed 3–5‐nm 12Me‐MMT particles dispersed in the thermoplastic elastomer matrix; that is, it led to the formation of nanocomposites or molecular‐level composites with a delaminated configuration. The formation of nanocomposites was reflected through the unexpected improvement of thermal and mechanical properties; for example, the tensile strength of a nanocomposite containing only 4 wt % organophilic clay was doubled in comparison with that of pure EVA‐28, and the thermal stability of the same nanocomposite was higher by about 34 °C. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 2065–2072, 2002     

Expansion distribution of basal spacing of the silicate layers in polyaniline/Na+‐montmorillonite nanocomposites monitored with X‐ray diffraction

Polyaniline/Na⁺‐montmorillonite (Na⁺‐MMT) nanocomposites synthesized by in‐situ intercalative polymerization of aniline into Na⁺‐MMT are reported. The expansion distribution of basal spacing of the silicate layers upon the increase of the amount of aniline relative to Na⁺‐MMT is, for the first time, estimated from the square of the full‐width at half‐maximum (FWHM²) of XRD patterns. According to the FT‐IR frequency shift of the C‐N stretching vibration, the change in the basal spacing of the silicate layers is closely related to the degree of hydrogen bonding between polyaniline and the silicate basal surface in a confined geometry.     

Effect of process variables on mechanical properties of polyurethane/clay nanocomposites

This paper addresses the effects of operating variables on mechanical properties of polyurethane/clay nanocomposites including tensile strength, abrasion resistance, and hardness. The variables were prepolymer type, clay cation, clay content, and prepolymer–clay mixing time. The experiments were carried out based on the design of experiments using Taguchi methods. The nanocomposites were synthesized via in situ polymerization starting from two different types of prepolymers (polyether‐ and polyester‐types of polyol reacted with toluene diisocyanate), and methylene‐bis‐ortho‐chloroanilline (MOCA) as a chain extender/hardener. Montmorillonite with three types of cation (Na⁺, alkyl ammonium ion, and MOCA) were examined. Among the parameters studied, prepolymer type and clay cation have the most significant effects on mechanical properties. Polyester nanocomposites showed larger improvements in mechanical properties compared to polyether materials due to higher shear forces exerted by polymer matrix on clay aggregates during polymer–clay mixing. The original MMT with Na⁺ cation results in weak improvements in mechanical properties compared to organoclays. It is observed that the stress and elongation at break, and abrasion resistance of the nanocomposite samples can be optimized with 1.5% of clay loading. The morphology and chemical structure of the optimum sample were examined by X‐ray diffraction and FT‐IR spectroscopy, respectively. Copyright © 2009 John Wiley & Sons, Ltd.     

Properties of Nylon‐6/Na+‐Montmorillonite Nanocomposites Obtained by Hydrolyzed Ring‐Opening Polymerization

Summary: Nylon‐6/Na⁺‐montmorillonite (MMT) nanocomposites (NNNs) are synthesized by a hydrolyzed ring‐opening polymerization. At a loading of only 2 wt.‐% MMT, the tensile modulus, the flexural modulus, and the heat distortion temperature of the NNNs exhibit increases of nearly 20%, 60%, and 63 °C, respectively. Compared with that of neat nylon‐6, the temperature of the main α‐relaxation (T_α) of the NNNs is shifted 3.6 °C toward higher temperatures and two β‐relaxation peaks are observed. Another interesting phenomenon is that there is a new melting peak (at about 206 °C) for the NNNs.

DSC second heating curves of neat nylon‐6 (N6), nylon‐6/Na⁺‐MMT nanocomposites with highly swollen Na⁺‐MMT (NHM), and nylon‐6/Na⁺‐MMT nanocomposites with slightly swollen Na⁺‐MMT (NSM) with various amounts of Na⁺‐MMT.     

Characterization of poly(vinylidene fluoride)/Na+‐MMT composites: An investigation into the β‐crystalline nucleation effect of Na+‐MMT

Poly(vinylidene fluoride)(PVDF)/Na⁺‐MMT composites have been successfully prepared utilizing sodium montmorillonite (Na⁺‐MMT) via N,N‐dimethylformamide (DMF) solution mixing. The dispersion of Na⁺‐MMT layers in composites were investigated by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). The effect of adding Na⁺‐MMT on crystallization behavior of PVDF was specifically studied. The β‐crystalline nucleation effect of Na⁺‐MMT was investigated and confirmed by differential scanning calorimetry (DSC), XRD, and Fourier transform infrared (FTIR) results. The interaction between PVDF and the surface of Na⁺‐MMT layers in DMF solution was confirmed by UV‐Vis absorbency. The effect of adding Na⁺‐MMT on rheological and electrical properties of PVDF/Na⁺‐MMT composites were also determined. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 903–911, 2009     

Gelatin/montmorillonite biohybrid films prepared via a novel photocrosslinking method: structure–properties investigations

Gelatin/sodium montmorillonite (Na⁺MMT) hybrid nanocomposite films were prepared by a new photocrosslinking method using 4-(2-hydroxyethoxy)phenyl-(2-hydroxy-2-propyl)ketone (Irgacure 2959) as a photoactive radical initiator and N,N′-Methylenebisacrylamide (MBA) as a crosslinking agent. The prepared samples were characterized by X-ray diffraction (XRD), differential scanning calorimetry, stress–strain measurements and UV–Vis spectrophotometry. XRD patterns showed the formation of exfoliation structure resulting in considerable improves in mechanical properties of the nanocomposite. Retaining of transparency also suggested that Na⁺MMT nanosheets were uniformly distributed in the gelatin matrix. The tensile strength and Elastic’s modulus of nanocomposites were also improved notably by enhancing amount of Na⁺MMT. Furthermore, gelatin/Na⁺MMT nanocomposites showed a second T _g at a higher temperature in presence of Na⁺MMT.     

Layered silicate/epoxy nanocomposites: synthesis,characterization and properties

Novel epoxy‐clay nanocomposites have been prepared by epoxy and organoclays. Polyoxypropylene triamine (Jeffamine T‐403), primary polyethertriamine (Jeffamine T‐5000) and three types of polyoxypropylene diamine (Jeffamine D‐230, D‐400, D‐2000) with different molecular weight were used to treat Na‐montmorillonite (MMT) to form organoclays. The preparation involves the ion exchange of Na⁺ in MMT with the organic ammonium group in Jeffamine compounds. X‐ray diffraction (XRD) confirms the intercalation of these organic moieties to form Jeffamine‐MMT intercalates. Jeffamine D‐230 was used as a swelling agent for the organoclay and curing agent. It was established that the d₀₀₁ spacing of MMT in epoxy‐clay nanocomposites depends on the silicate modification. Although XRD data did not show any apparent order of the clay layers in the T5000‐MMT/epoxy nanocomposite, transmission electron microscopy (TEM) revealed the presence of multiplets with an average size of 5 nm and the average spacing between multiplets falls in the range of 100 Å. The multiplets clustered into mineral rich domains with an average size of 140 nm. Scanning electron microscopy (SEM) reveals the absence of mineral aggregate. Nanocomposites exhibit significant increase in thermal stability in comparison to the original epoxy. The effect of the organoclay on the hardness and toughness properties of crosslinked polymer matrix was studied. The hardness of all the resulting materials was enhanced with the inclusion of organoclay. A three‐fold increase in the energy required for breaking the test specimen was found for T5000‐MMT/epoxy containing 7 wt% of organoclay as compared to that of pure epoxy. Copyright © 2004 John Wiley & Sons, Ltd.     

Encapsulated clay particles in polystyrene by RAFT mediated miniemulsion polymerization

RAFT grafted montmorillonite (MMT) clays [i.e., N,N‐dimethyl‐N‐(4‐(((phenylcarbonothioyl)thio)methyl)benzyl)ethanammonium‐MMT (PCDBAB‐MMT) and N‐(4‐((((dodecylthio)carbonothioyl)thio)methyl)benzyl)‐N,N‐dimethylethanammo‐nium‐MMT (DCTBAB‐MMT)] of various loadings were dispersed in styrene (S) monomer and the resultant mixtures emulsified and sonicated in the presence of a hydrophobe (hexadecane) into miniemulsions. The stable miniemulsions thus obtained were polymerized to yield encapsulated polystyrene‐clay nanocomposites (PS‐CNs). The molar mass and polydispersity index (PDI) of the PS‐CNs depended on the amount of RAFT agent in the system, in accordance with the features of the RAFT process. The morphology of the PS‐CNs ranged from partially exfoliated to an intercalated morphology, depending on the percentage clay loading. The thermomechanical properties of the PS‐CNs were better than those of the neat PS polymer, and were dependent on the molar mass, PS‐CN morphology and clay loading. The similarities and differences of the PS‐CNs prepared here by miniemulsion polymerization were compared to those prepared using the same RAFT agents and polymer system by bulk polymerization (as reported by us in a previous article). © Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7114–7126, 2008     

Natural rubber/clay nanocomposites: Influence of poly(ethylene glycol) on the silicate dispersion and local chain order of rubber network

A novel preparation of natural rubber (NR)/Na⁺-montmorillonite (MMT) nanocomposites in only one step by using poly(ethylene glycol) (PEG) has been investigated. PEG behaves as dispersing agent favouring the intercalation of rubber chains into the silicate galleries and providing substantially improved clay dispersion. Intercalated/exfoliated miscible hybrids were observed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The influence of PEG on the network structure has also been evaluated by static proton double-quantum nuclear magnetic resonance spectroscopy (¹H DQ NMR) at low-field. Silicate nanoparticles with a high aspect ratio (clay tactoids) and a more crosslinked rubber network have been obtained for an optimum PEG/MMT ratio. Both effects were responsible of the enhancement on mechanical properties.     

Flame retarding polyamide 6 with melamine cyanurate and layered silicates

The flammability behavior of the system polyamide 6 (PA 6) + melamine cyanurate (MC) with or without organically modified layered montmorillonite (OMMT) or sodium montmorillonite (Na⁺MMT) was studied. The high degree of flame retardancy (FR) obtained with 13 wt% MC is maintained upon adding up to 0.2 wt% OMMT or Na⁺MMT. Increase mass % of OMMT is antagonistic to the MC effect. The rate of dripping decreases while the size and mass of drops in the UL‐94 tests increases with increasing wt% OMMT indicating increase in viscosity of the melt and decrease in the rate of sublimation of melamine. Addition of poly vinyl pyrrolidone (PVP) decreases the viscosity and partially restores the FR rating. Na⁺MMT does not increase the viscosity and the FR ratings are partially preserved. The peak of heat release rate (PHRR) in the cone calorimeter decreases with increased loading of OMMT. Addition of Na⁺MMT or PVP has little influence on the PHRR. The time of ignition decreases with increase in OMMT, but is not affected when Na⁺MMT is used. This is explained by the low thermal conductivity of the clay containing surface layer of samples during pyrolysis and combustion. Mechanistic considerations are presented. Copyright © 2008 John Wiley & Sons, Ltd.     

Gas barrier of polystyrene montmorillonite clay nanocomposites: Effect of mineral layer aggregation

Three polystyrene (PS)/clay hybrid systems have been prepared via in situ polymerization of styrene in the presence of unmodified sodium montmorillonite (Na‐MMT) clay, MMT modified with zwitterionic cationic surfactant octadecyldimethyl betaine (C18DMB) and MMT modified with polymerizable cationic surfactant vinylbenzyldimethyldodecylammonium chloride (VDAC). X‐ray diffraction and TEM were used to probe mineral layer organization and to expose the morphology of these systems. The PS/Na‐MMT composite was found to exhibit a conventional composite structure consisting of unintercalated micro and nanoclay particles homogeneously dispersed in the PS matrix. The PS/C18DMB‐MMT system exhibited an intercalated layered silicate nanocomposite structure consisting of intercalated tactoids dispersed in the PS matrix. Finally, the PS/VDAC‐MMT system exhibited features of both intercalated and exfoliated nanocomposites. Systematic statistical analysis of aggregate orientation, characteristic width, length, aspect ratio, and number of layers using multiple TEM micrographs enabled the development of representative morphological models for each of the nanocomposite structures. Oxygen barrier properties of all three PS/clay hybrid systems were measured as a function of mineral composition and analyzed in terms of traditional Nielsen and Cussler approaches. A modification of the Nielsen model has been proposed, which considers the effect of layer aggregation (layer stacking) on gas barrier. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1733–1753, 2007     

Preparation of Poly(ε‐caprolactone)/Clay Nanocomposites by Microwave‐Assisted In Situ Ring‐Opening Polymerization

PCL/clay nanocomposites were prepared by microwave‐assisted in situ ROP of ε‐caprolactone in the presence of either unmodified clay (Cloisite® Na⁺) or clay modified by quaternary ammonium cations containing hydroxyl groups (Cloisite 30B). This PCL showed significantly improved monomer conversion and molecular weight compared with that produced by conventional heating. An intercalated structure was observed for the PCL/Cloisite Na⁺ nanocomposites, while a predominantly exfoliated structure was observed for the PCL/Cloisite 30B nanocomposites. Microwave irradiation proved to be an effective and efficient method for the preparation of PCL/clay nanocomposites.

     

Impact of the clay organic modifier on the morphology of polymer–clay nanocomposites prepared by in situ free‐radical polymerization in emulsion

Poly(styrene‐co‐butyl acrylate) copolymers were prepared by free‐radical random copolymerization of styrene and butyl acrylate in emulsion in the presence of 10% of surface‐modified sodium montmorillonite (Na‐MMT). The objective of this work was to evaluate the impact of the clay organic modifier in terms of its chemical structure, its degree of interaction within the clay galleries surface, and its ability to copolymerize with monomers, on the morphology and properties of the final nanocomposite prepared. Na‐MMT was modified using different organic modifiers, namely: sodium 1‐allyloxy‐2‐hydroxypropyl (Cops), 2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS), N‐isopropylacrylamide (NIPA), and sodium 11‐methacryloyloxy‐undecan‐1‐yl sulfate (MET), respectively. The morphology and properties of the nanocomposites obtained were found to be dependant on the clay organic modifier. X‐ray diffraction (XRD) and transmission electron microscopy indicated that, nanocomposites at 10% clay loading with Cops‐, NIPA‐, and MET‐modified clays, yielded intercalated to partially exfoliated structures, whereas AMPS‐modified clay gave a nanocomposite with a fully exfoliated structure. All polymer–clay nanocomposites were found to be more thermally stable than neat poly(S‐co‐BA) as were determined by TGA. However, nanocomposites with intercalated structures exhibited greater thermal stability relative to fully exfoliated ones. Furthermore, nanocomposites with exfoliated structures exhibited higher storage moduli (G^I) than partially exfoliated once, whereas intercalated structure showed the lowest G^I values. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3619–3628, 2008