Effect of polymer–clay interaction on solvent transport behavior of fluoroelastomer–clay nanocomposites and prediction of aspect ratio of nanoclay

Diffusion and sorption of methyl ethyl ketone and tetrahydrofuran through fluoroelastomer‐clay nanocomposites were investigated in the temperature range of 30–60°C by swelling experiments. Slightly non‐Fickian transport behavior was found for these nanocomposites, having variation of type of nanoclay and loading. Different transport parameters depend on the size and shape of the penetrant molecules. The results were used to study the effect of nanoclay on the solvent transport‐properties of nanocomposites and their interactions with solvents. The diffusion coefficient of methyl ethyl ketone at 30°C for neat rubber was 1.43 × 10^?8 cm² s^?1, while those of the unmodified and the modified clay filled samples at 4 phr loading were 0.24 × 10^?8 and 0.50 × 10^?8 cm² s^?1, respectively. At 8 and 16 phr loading of the unmodified clay, it was found to be 0.44 × 10^?8 and 0.64 × 10^?8 cm² s^?1, respectively. The samples were also reswelled after deswelling. Surprisingly, transport behavior became Fickian on reswelling. Interestingly, ratio of diffusion coefficients of the filled system to the neat system was found to be almost same for the first time swelling and reswelling experiments. The results showed that better polymer‐clay interaction in the case of the unmodified‐clay filled nanocomposites is responsible for enhanced solvent‐resistance property. From the permeation data, for the first time, aspect ratio of nanoclays in different composites was calculated and found to have good correlation with the morphology data obtained from transmission electron microscopy. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Quantification of clay dispersion in nanocomposites of styrenic polymers

Polymer‐clay nanocomposites are materials with many interesting structures, properties, and potential applications. Microstructural evaluation of a nanocomposite is not an easy task, as clay may form hierarchical structures which may look different when observed at various magnifications under a microscope, and also as the concepts of “intercalation” and “exfoliation” are not self‐sufficient to describe its morphology. In this work polymer‐clay nanocomposites of polystyrene and two styrene‐containing block copolymers (styrene‐butadiene‐styrene and styrene‐ethylene/butylene‐styrene) were prepared using three different techniques. Clay dispersion was evaluated by a recently developed microscopy image analysis procedure, combining the analysis of optical and transmission electron micrographs, and the characterization was complemented by X‐ray diffraction and rheological measurements. The results showed better clay dispersion for both block copolymers nanocomposites, mainly due to their molecular architectures. Moreover, the techniques which showed the best results involved mixing the materials in a solvent medium. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Preparation and characterization of anionically polymerized butadiene‐isoprene copolymer/clay nanocomposites

Butadiene‐isoprene copolymer/montmorillonite (BIR/MMT) nanocomposites were synthesized successfully via in situ anionic polymerization. The results of transmission electron microscopy and X‐ray diffractometer showed that the clay layers were exfoliated and high reaction temperature benefited the exfoliation of layers in BIR/MMT. The polymerization still exhibited “living” characteristics with the addition of organophilic montmorillonite (OMMT). However, the contents of 1,2‐polybutadiene and 3,4‐polyisoprene of the copolymer decreased with the addition of OMMT, because of its absorption effect on N,N,N′,N′‐tetramethylethanediamine as revealed by ¹H NMR. Moreover, it was observed that the glass‐transition temperature of the BIR/MMT nanocomposites also decreased when compared with the BIR copolymers. The thermal stability of the nanocomposites was improved, because of the barrier property of exfoliated clay layers. © 2006 Wiley Periodicals, Inc. J Appl PolymSci 102: 1167–1172, 2006     

Poly(3‐dodecyl thiophene)—Organically modified montmorillonite clay nanocomposites: Influence of chain regioregularity and preparation condition on physical,mechanical, optical,and conductivity properties

The properties of regioregular(R) (98.5 mol % H‐T) and regioirregular(I) (80.5 mol % H‐T) poly(3‐dodecyl thiophene)(P3DDT)—organically modified montmorillonite (om‐MMT) clay nanocomposites obtained from solvent‐cast and melt‐cooled procedures are compared. The solvent‐cast P3DDTI nanocomposites showed partially exfoliated clay structure but P3DDTR nanocomposites showed multistack exfoliation. Type 1 crystalline polymorph was produced in solvent‐cast systems whereas melt‐cooled P3DDTI samples showed mesomorphic structure. Storage modulus of P3DDTI nanocomposites increased with clay concentration showing a maximum increase of 255%. The UV‐vis spectra showed blue shift of π–π* transition band and photoluminescence spectra indicated seven times increase of normalized intensity in solvent cast P3DDTI composites. DC conductivity and I–V characteristic curves showed increased insulating properties with om‐clay concentration. The physical, mechanical, and optical properties of P3DDTI nanocomposites are more improved than that of P3DDTR nanocomposites and from their pristine polymers. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of clay platelet dispersion as affected by the manufacturing techniques on thermal and mechanical properties of PMMA‐clay nanocomposites

In this work, the properties of Poly(methyl methacrylate) (PMMA)‐clay nanocomposites prepared by three different manufacturing techniques viz., solution mixing, melt mixing, and in‐situ bulk polymerization in presence of clay were studied. Morphological analysis revealed that the extent of intercalation and dispersion of the nanoclay were relatively higher in the in‐situ polymerized nanocomposites than those of solution and melt blended nanocomposites. Differential Scanning Calorimetric study indicated maximum increment in T_g of the PMMA in the in‐situ polymerized PMMA‐clay nanocomposites. Thermo gravimetric analysis showed improved thermal stability of PMMA in all the nanocomposites and the maximum improvement was for in‐situ polymerized nanocomposites. The storage moduli of all the nanocomposites were higher than the pure PMMA. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling kinetics of linseed oil‐based polymers

Kinetics of swelling and sorption behavior of copolymers (based on linseed oil, styrene, divinylbenzene, and acrylic acid via cationic and thermal polymerization) is studied in tetrahydrofuran (THF) at different temperatures. The values of n in the transport equation are found to be below 0.4, showing non‐Fickian or pseudo‐Fickian transport in the polymers. The dependence of diffusion coefficient on the composition and temperature has also been studied for the linseed oil‐based polymers. The diffusion coefficient in cationic samples decreases with an increase in the oil contents in the samples. In case of thermal samples, the diffusion coefficient first increases up to 30% oil contents and then decreases. The diffusion coefficient decreases with an increase in temperature for all of the linseed oil polymer samples. The sorption coefficient increases with an increase in the oil contents for all samples. The crosslink density (calculated from the THF swelling) ranges from 20.16 to 92.34 × 10⁶ mol/cm³ for cationic samples and 20.62 to 86.01 × 10⁶ mol/cm³ for thermal samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Water absorption and hygrothermal aging study on organomontmorillonite reinforced polyamide 6/polypropylene nanocomposites

The water absorption and hygrothermal aging behavior of organomontmorillonite (OMMT) reinforced polyamide 6/polypropylene (PA6/PP ratio = 70/30), with and without maleated PP (MAH‐g‐PP), was studied at three different temperatures (30, 60, and 90°C). The water absorption and hygrothermal aging response of the composites was studied and analyzed by tensile tests and morphology assessment (scanning electron microscopy and transmission electron microscopy), indicating the effect of the immersion temperature, OMMT, and MAH‐g‐PP compatibilizer. The mathematical treatment used in analyzing the data was the single free phase model of diffusion, which assumed Fickian diffusion and utilized Fick's second law of diffusion. The kinetics of water absorption of the PA6/PP nanocomposites conformed to Fickian law behavior, whereby the initial moisture absorption follows a linear relationship between the percentage gain at any time t and t^1/2 (the square root of time), followed by saturation. It was found that the equilibrium moisture content and the diffusion coefficient are dependent on the OMMT loading, MAH‐g‐PP concentration, and immersion temperatures. Both the tensile modulus and strength of the PA6/PP nanocomposites deteriorated after being exposed to hygrothermal aging. MAH‐g‐PP acted as a good compatibilizer for PA6/PP/OMMT nanocomposites, which was attributed to its higher retention ability in modulus and strength (in the wet and redried states), lower equilibrium moisture content, and reduced water diffusivity of the nanocomposites. Morphological sketches for both uncompatibilized and MAH‐g‐PP compatibilized PA6/PP/OMMT nanocomposites, toward water uptake are proposed. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 780–790, 2005     

Preparation and conductive properties of polycaprolactone‐grafted carbon black nanocomposites

Polycaprolactone‐grafted carbon black (CB‐g‐PCL) nanocomposites were prepared by surface‐initiated ring‐opening polymerization of ε‐caprolactone on the surface of CB. Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), atomic force microscope (AFM), X‐ray diffraction (XRD), and polarizing optical microscope (POM) method were employed to characterize the resultant CB‐g‐PCL. The effect of temperature on resistivity of polycaprolactone‐grafted CB (CB‐g‐PCL) nanocomposites was investigated and compared with that of mixture of CB and PCL. It was found that CB‐g‐PCL nanocomposites exhibited positive temperature coefficient (PTC) phenomena between 48 and 51°C, and negative temperature coefficient (NTC) phenomena and between 51 and 54°C. The prepared CB‐g‐PCL nanocomposites have the potential to be temperature‐dependent switch materials. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Phosphonium‐based layered silicate—Poly(ethylene terephthalate) nanocomposites: Stability,thermal and mechanical properties

PET‐clay nanocomposites were prepared using alkyl quaternary ammonium and phosphonium modified clays by melt‐mixing at 280°C using a micro twin screw extruder. The latter clays were prepared by synthesizing phosphonium surfactants using a simple one‐step method followed by a cation exchange reaction. The onset temperature of decomposition (T_onset) for phosphonium clays (>300°C) was found to be significantly higher than that of ammonium clays (around 240°C). The clay modified with a lower concentration (0.8 meq) of phosphonium surfactant showed a higher T_onset as compared to the clay modified with a higher concentration (1.5 meq) of surfactants. Nanocomposites prepared with octadecyltriphenyl phosphonium (C18P) modified clay showed a higher extent of polymer intercalation as compared with benzyltriphenylphosphonium (BTP) and dodecyltriphenylphosphonium (C12P) modified clays. The nanocomposites prepared with ammonium clays showed a significant decrease in the molecular weight of PET during processing due to thermal degradation of ammonium surfactants. This resulted in a substantial decrease in the mechanical properties. The molecular weight of PET was not considerably reduced during processing upon addition of phosphonium clay. The nanocomposites prepared using phosphonium clays showed an improvement in thermal properties as compared with ammonium clay‐based nanocomposites. T_onset increased significantly in the phosphonium clay‐based nanocomposites and was higher for nanocomposites which contained clay modified with lower amount of surfactant. The tensile strength decreased slightly; however, the modulus showed a significant improvement upon addition of phosphonium clays, as compared with PET. Elongation at break decreased sharply with clay. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Influence of clay and predispersion method on the structure and properties of polystyrene (PS)‐clay nanocomposites

To prepare the polystyrene (PS)‐clay nanocomposites via an in situ emulsion polymerization, a clay predispersion method, i.e. dispersing the organic clay in the emulsifier solution by the assistance of ultrasonic, was proposed in this study. The conventional method, predispersing the organic clay into the monomer, was also presented for the comparison. The morphology analysis based on the X‐ray Deflection (XRD) and Transmission Electronic Microscopy (TEM) results suggested that the more uniform clay dispersion in the final nanocomposites could be achieved through the new method. The inorganic clay (Na‐MMT) and two organic clays (C₁₈‐MMT and VC₁₈‐MMT) synthesized by exchanging inorganic cations with the trimethyloctadecyl ammonium chloride (OTAC) and the vinylbenzyldimethyloctadecyl ammoniun chloride (VOAC) were chosen to investigate the influence of the clay surface modification on the properties of nanocomposites. The Dynamic Mechanical Analysis (DMA) results showed the storage modulus G′s of the nanocomposites had different enhancements over that of the pure PS, especially when the temperature approached the glass transition temperature (T_g). The T_gs of the nanocomposites, however, varied with the microstructure and the interactions between the polymer and the clay layers. The Na‐MMT and VC₁₈‐MMT increased the T_g, while the T_gs of PS/C₁₈‐MMT nanocomposites were slightly lower than that of the pure PS. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Optimization of processing parameters for the synthesis of low‐density polyethylene/organically modified montmorillonite nanocomposites using X‐ray diffraction with experimental design

The influence of the processing parameters on the synthesis of low‐density polyethylene (LDPE)/organically modified montmorillonite (OMM) nanocomposite films was studied using experimental design. Intercalation in the nanocomposites was analysed using X‐ray diffraction and verified using atomic force microscopy. Four direct melt processing parameters were studied to obtain surface maps of intercalation in the nanocomposites: concentration of OMM (clay‐%), concentration of Polybond^® 3149 (compatibilizer‐%), mixing temperature (T_mix) and mixing time. An ANOVA validated the polynomial function, and intercalation maps from response surface methodology (RSM) were obtained. The clay‐% parameter had the most significant effect, and T_mix showed no significant effect on intercalation (p < 0.05). A strong synergic interaction between clay‐% and compatibilizer‐% was observed, which is not possible to detect using univariate experiments. RSM provides a powerful tool for choosing the best processing conditions that lead to formulations with the highest intercalations by considering the main factors and their interactions. © 2013 Society of Chemical Industry     

Synthesis and characterization of epoxy based nanocomposites

Epoxy‐clay nanocomposites were synthesized to examine the effects of the content and type of different clays on the structure and mechanical properties of the nanocomposites. Diglycidyl ether of bisphenol‐A (epoxy) was reinforced by 0.5–11 wt % natural (Cloisite Na⁺) and organically modified (Cloisite 30B) types of montmorillonite. SEM results showed that as the clay content increased, larger agglomerates of clay were present. Nanocomposites with Cloisite 30B exhibited better dispersion and a lower degree of agglomeration than nanocomposites with Cloisite Na⁺. X‐ray results indicated that in nanocomposites with 3 wt % Cloisite 30B, d‐spacing expanded from 18.4 Å (the initial value of the pure clay) to 38.2 Å. The glass transition temperature increased from 73°C, in the unfilled epoxy resin, to 83.5°C in the nanocomposite with 9 wt % Cloisite 30B. The tensile strength exhibited a maximum at 1 wt % modified clay loading. Addition of 0.5 wt % organically modified clay improved the impact strength of the epoxy resin by 137%; in contrast, addition of 0.5 wt % unmodified clay improved the impact strength by 72%. Tensile modulus increased with increasing clay loading in both types of nanocomposites. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1081–1086, 2005     

Synthesis,structure, and thermal stability of poly(methyl methacrylate)‐co‐ poly(3‐tri(methoxysilyil)propyl methacrylate)/ montmorillonite nanocomposites

The structure and the thermodegradation behavior of both poly(methyl methacrylate)‐co‐poly(3‐tri(methoxysilyil)propyl methacrylate) polymer modified with silyl groups and of intercalated poly(methyl methacrylate)‐co‐poly(3‐tri(methoxysilyil)propyl methacrylate)/Cloisite 15A? nanocomposite have been in situ probed. The structural feature were comparatively studied by Fourier transform infrared spectroscopy (FTIR), ¹³C and ²⁹Si nuclear magnetic resonance (NMR), and small angle X‐ray scattering (SAXS) measurements. The intercalation of polymer in the interlayer galleries was evidenced by the increment of the basal distance from 31 to 45 Å. The variation of this interlayer distance as function of temperature was followed by in situ SAXS. Pristine polymer decomposition pathway depends on the atmosphere, presenting two steps under air and three under N₂. The nanocomposites are more stable than polymer, and this thermal improvement is proportional to the clay loading. The experimental results indicate that clay nanoparticles play several different roles in polymer stabilization, among them, diffusion barrier, charring, and suppression of degradation steps by chemical reactions between polymer and clay. Charring is atmosphere dependent, occurring more pronounced under air. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Catalytic activity during the preparation of PE/clay nanocomposites by in situ polymerization with metallocene catalysts

Catalytic activity during the formation of polyethylene (PE)/clay nanocomposites by in situ polymerization with metallocenes was studied. Ethylene polymerization was carried out with the homogeneous metallocene in the presence of the clay particles and using the clay‐supported metallocene catalyst. It was found that the catalytic activity of the homogeneous metallocene does not decrease in the presence of the clay particles and only a slight decrease of activity occurs using the clay‐supported catalyst. The modification of the clay with MAO cocatalyst as well as its intercalation with ODA surfactant were found to play an important role during the in situ formation of the PE/clay nanocomposite. ODA‐intercalated clay apparently facilitates the activation and monomer insertion processes on zirconocene centers located in internal sites of the clay structure. Although metallocene supported on MAO‐treated clay exhibited somewhat lower catalytic activity than that supported directly on the ODA‐intercalated clay, both systems favored the production of PE nanocomposites containing highly exfoliated clay particles. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Study on effect of duration of the ultrasonication process on solvent‐free polyurethane/organoclay nanocomposite coatings: Structural characteristics and barrier performance analysis

In this study, effect of duration of ultrasonication process on structural characteristics and barrier properties of solvent‐free castor oil‐based polyurethane (PU)/organically modified montmorillonite (OMMT) nanocomposites was investigated. A series of PU/OMMT composites were synthesized by in situ polymerization technique through an ultrasonication‐assisted process at various processing durations. Effect of ultrasonication duration on de‐agglomeration of clay stacks in castor oil dispersions was evaluated by optical microscopy, sedimentation test, and viscosity measurement. Wide angle X‐ray diffraction and Fourier‐transform infrared spectroscopy were employed to investigate the effect of processing time on degree of delamination of clay platelets and interfacial strength between clay layers and PU matrix. Also, surface morphology of the nanocomposites was analyzed by atomic force microscopy. The results showed that by increasing the ultrasonication time up to 60 min, the size of clay agglomerates decreased and the interlayer spacing of clay platelets increased. To evaluate the effect of ultrasonication duration on transport properties of the PU/OMMT composites, diffusion coefficient and permeability were determined through water uptake test. Electrochemical impedance spectroscopy was carried out to analyze the barrier properties and to evaluate the corrosion performance of these composite coatings on carbon steel panels. It was found that by increasing sonication time, the barrier property of nanocomposites against diffusion of water molecules improved, which is due to further separation of clay platelets, enhancement of the traveling pathways for water molecules and improvement of interactions between the two components. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of poly(styrene‐b‐butadiene‐b‐styrene)/montmorillonite nanocomposites

With some polymerizable small molecules grafting onto the montmorillonite surface, we disposed the clay through in‐situ emulsion polymerization, and the structure of the modified montmorillonites were studied through Fourier transform infrared spectroscopy (FTIR) and X‐ray diffraction (XRD). The nanocomposites of poly(styrene‐b‐butadiene‐b‐styrene) (SBS)/montmorillonite with excellent mechanical properties were prepared by mixing SBS and the modified montmorillonite on the double rollers at 150°C. The exfoliation of the layered silicates was confirmed by XRD analysis and transmission electron microscopy (TEM) observation. After mechanical kneading of the molten nanocomposites, the exfoliation structure of the silicates is still stable for polystyrene macromolecules grafting onto the silicates. Upon the addition of the modified montmorillonite, the tensile strength, elongation at break and tear strength of the nanocomposites increased from 22.6 MPa to 31.1 MPa, from 608% to 948%, from 45.32 N/mm to 55.27 N/mm, respectively. The low‐temperature point of glass‐transition temperature (T_g) of the products was about −77°C, almost constant, but the high‐temperature point increased from 97°C to 106°C. In addition, the nanocomposites of SBS and modified montmorillonites showed good resistance to thermal oxidation and aging. POLYM. COMPOS., 2009. © 2008 Society of Plastics Engineers     

Determination of the infinite dilution diffusion and activity coefficients of alkanes in polypropylene by inverse gas chromatography

Infinite dilution diffusion and activity coefficients of n‐hexane, n‐heptane, and n‐decane in polypropylene were measured from 373.15 to 393.15 K by inverse gas chromatography. The influences of small molecule solvent and temperature on the infinite dilution diffusion and activity coefficients were investigated. The results showed that the infinite dilution diffusion coefficient decreased but the infinite dilution activity coefficient increased with an increasing number of CH₂ group in the aliphatic solvents. The temperature increase resulted in the increase in the infinite dilution diffusion coefficient and the decrease in the infinite dilution activity coefficient. The graphs plotted according to the results of the infinite dilution diffusion coefficient versus temperature were in agreement with the Arrhenius equation. Diffusion constant and activation energy were obtained from the Arrhenius equation. Also, the interdependence on the infinite dilute activity coefficient and temperature accorded with Gibbs‐Helmholtz equation. From the temperature dependence of the limiting activity coefficients partial molar excess enthalpy at infinite dilution H^E,∞ was obtained. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 1925–1930, 2006     

Temperature dependence of oxygen diffusion into clay‐doped PS films

Fluorescence technique was employed for the measurement of the diffusion coefficient of oxygen into polystyrene (PS) latex/modified Na‐activated bentonite (MNaLB) clay composite films. Three different MNaLB content (0, 5, and 20 wt%) composite films were prepared from PS/MNaLB mixtures by annealing them at 200°C, above the glass transition temperature of PS for 10 min. To determine the diffusivity of oxygen in PS/MNaLB composite films, diffusion measurements were performed over the temperature range from 25 to 70°C. Pyrene (P) was used as the fluorescent agent. The diffusion coefficients (D) of oxygen were determined by combining the fluorescence quenching method with Fickian transport model, and were found as a function of temperature for each MNaLB content film. The results showed that D values are strongly dependent on both temperature and clay content in composite film. It was also observed that D coefficients obey Arrhenius behavior, from where diffusion activation energies were measured. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Experimental study of diffusivity of hexane in bitumen-saturated porous media under high temperature/pressure conditions

Solvent mass transfer plays a key role in a thermal gravity drainage process involving solvent. The diffusion coefficients of solvent in such a process are not well studied. This article presents the effective diffusion coefficients of solvent in bitumen-saturated sands under high temperature/pressure conditions measured using a CT scanning technique. Experimental results show that the effective diffusion coefficient of n-hexane in bitumen-saturated sands varied with the solvent concentration or with the viscosity of solvent–bitumen mixture (i.e., D_e ∝ c^0.4 or D_e ∝ μ_m^−0.46). The solvent concentration weighted diffusion coefficient of n-hexane in the bitumen under the condition 160–170°C/1,900 kPa had an order of magnitude of about 10⁻⁵ cm²/s for solvent volume concentration less than 0.2. The penetration distance of n-hexane in bitumen-saturated sands depended on the nonlinearity of diffusion and had a value of −2 cm after 1-day diffusion. The stronger the nonlinearity of diffusion, the shorter the penetration distance.     

Polypropylene‐organoclay nanocomposite: Preparation,microstructure, and mechanical properties

A series of polypropylene (PP) nanocomposites containing 2, 4, and 6 wt % of an organophilic montmorillonite clay was prepared via direct melt mixing in the presence of maleic anhydride grafted polypropylene (PP‐g‐MAH) as compatibilizing agent. Microstructure characterization was performed by X‐ray diffraction analysis. Nanocomposites exhibited a 15 and 22% enhancement in tensile modulus and impact strength, respectively. The heat deflection temperature of PP nanocomposites was 36°C greater than for pure PP. Thermal and mechanical properties of nanocomposites were compared to properties of traditional PP‐talc and PP‐glass fiber composites. The results showed that the properties of nanocomposites improved compared to ordinary polypropylene composites. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009