Dispersion Of Silicate Layers Research Articles

Evaluation of polymethacrylic ionomer as compatibilizers for MCPA6/clay composites

AbstractThe compatibilization effects provided by polymethacrylic ionomer (PMMA ionomer) on monomer‐casting polyamide6 (MCPA6)/clay (pristine sodium montmorillonite) composites were studied in this work. The PMMA ionomer used in this study was sodium polymethacrylate ionomer (PMMA Na+‐ionomer), which is a copolymer of methyl methacrylate and sodium methacrylate, prepared using emulsion polymerization. MCPA6/clay/PMMA Na+‐ionomer composites were prepared by in situ anionic ring‐opening polymerization (AROP) of ε‐caprolactam (CLA). X‐ray diffraction (XRD) and transmission electron microscopy (TEM) plus rheological measurement were used to characterize those composites. The results indicated that PMMA Na+‐ionomer is a good compatibilizer for this system. With increasing PMMA Na+‐ionomer content, a better dispersion of clay layers was successfully achieved in the MCPA6 matrix. Furthermore, differential scanning calorimetry (DSC) and XRD results indicated that well dispersed silicate layers limit the mobility of the MCPA6 molecule chains to crystallize, reduce the degree crystalline, and favor the formation of the γ‐crystalline form of the MCPA6 matrix. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Influence of degree of intercalation on the crystal growth kinetics of poly[(butylene succinate)-co-adipate] nanocomposites

The influence of the degree of intercalation of polymer chains in the two dimensional silicate galleries on the crystallization behavior of poly[(butylene succinate)-co-adipate] (PBSA) is being reported on. The nanocomposites were prepared by melt-blending of PBSA and organically modified montmorillonite (OMMT) in a batch-mixer. Two different types of commercially available OMMTs, with different extents of miscibility of organic modifiers with PBSA, were used, leading to highly delaminated and stacked/intercalated nanocomposite structures as revealed by X-ray diffraction (XRD) patterns and transmission electron microscopy (TEM) observations. The non-isothermal crystallization behavior of PBSA and the nanocomposite samples were studied by differential scanning calorimetry (DSC). Crystal growth kinetics studies showed that when silicate layers are highly delaminated into the PBSA matrix, nucleation behaviors decreased significantly, relative to the stacked/intercalated silicate layers. These observations indicate that the overall crystal growth kinetics retard in delaminated nanocomposites, opposed to increasing in the case of stacked/intercalated nanocomposites. Polarized optical microscopy (POM) observations and light scattering studies indicate that PBSA spherulites are fairly large and more perfectly grown in the case of delaminated nanocomposites, relative to the pure PBSA matrix. The effect of high levels of dispersion of silicate layers in the PBSA matrix on cold crystallization behavior was also studied.

Modification of biodegradable polylactide by silica and wood flour through a sol–gel process

AbstractThe aim of this work is the production of new biodegradable nanocomposites from polylactide (PLA), tetraethoxysilane (TEOS), and wood flour (WF) by means of an in‐situ sol–gel process and a melt blending method. Characterizations of SiO2, PLA, and hybrids were performed by FTIR, 29Si solid‐state NMR, XRD, DSC, TGA, and SEM analyses. As the results, the SiO2 can be well dispersed into the acrylic acid grafted polylactide (PLA‐g‐AA) in nanoscale sizes since the TEOS is partially compatible with PLA‐g‐AA and allows PLA‐g‐AA chains intercalating into SiO2 layers. 29Si solid‐state NMR analysis showed that Si atoms coordinated around SiO4 units were predominantly Q3 and Q4. The PLA‐g‐AA/SiO2 hybrid demonstrates dramatic enhancement in thermal and mechanical properties of PLA; for example, 80°C and 20 MPa increases in IDT and TS with the addition of 10 wt % SiO2 due to the formation of SiOC bond, and the nanoscale dispersion of silicate layers in the polymer matrix. On the basis of the consideration of thermal and mechanical properties, it is also found that 10 wt % of SiO2 content is optimal for preparation of PLA‐g‐AA/SiO2 nanocomposites. The biodegradable nanocomposites produced from our laboratory can provide a plateau tensile strength at break when the WF content is up to 50 wt %. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Comparative studies for the effect of dual‐ and mono‐organic modifiers on the physical properties of polyimide‐clay nanocomposite membranes

AbstractIn this study, a series of nanocomposite membranes consisted of organic polyimide and organo‐modified clay were successfully prepared by an in situ polymerization through thermal imidization reactions using a dual‐ (i.e., CTAB/melamine) and mono‐organic modifier as swelling agent of clay mineral. A sequential comparative study was performed to investigate the effect of various feeding ratios of dual‐ and mono‐organic modifiers on the physical properties of as‐prepared samples. The as‐synthesized nanocomposite membranes were subsequently characterized by WAXRD and TEM. It should be noted that all the nanocomposite membranes prepared from a dual‐organic modifier system exhibited a better dispersion of silicate layers in PI matrices as compared with that of mono‐organic modifier system. Comparative studies for the effect of various feeding ratios of dual‐ and mono‐organic modifiers on the thermal stability, mechanical strength, molecular barrier properties, and optical clarity of PI‐clay nanocomposite membranes were performed with measurements of TGA, DSC, DMA, GPA, VPA, and UV–visible transmission spectroscopy, respectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Nonisothermal crystallization behavior of exfoliated poly(ethylene terephthalate)‐layered silicate nanocomposites in the presence and absence of organic modifier

AbstractExfoliated poly(ethylene terephthalate) (PET)‐layered silicate nanocomposites (PetLSNs) excluding (PetLSNeom) and including (PetLSNiom) organic modifiers were obtained by solution methods with and without solvent‐nonsolvent system, respectively. From wide angle X‐ray diffraction and high resolution transmission electron microscopy, both PetLSNs were found to have exfoliated structure attributed to sufficient dispersion of silicate in prepared solvents, regardless of sample preparation method. However, organic modifier in PetLSNeom was confirmed to be well removed by elemental analysis, whereas organic modifier was still remained in PetLSNiom. Thus, the effect of the presence and absence of organic modifiers in PetLSNs on the nonisothermal crystallization behavior was investigated by differential scanning calorimetry (DSC) on the basis of a modified Avrami analysis and polarized optical microscopy (POM). From DSC results, it was found that both PetLSNs had higher degrees of crystallinity and shorter crystallization half‐times than neat PET, because of the dispersed silicate layers acted as nucleating agents in both PetLSNs. However, PetLSNiom exhibited a lower degree of crystallinity and longer half‐time of crystallization than PetLSNeom. Difference of crystallization behavior between PetLSNeom and PetLSNiom was ascribed to organic modifier in PetLSNiom, which may act as crystallization inhibitors. POM measurements also revealed the results which were in good agreement with crystallization behavior observed from DSC measurement. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 989–999, 2008

Characterization of EVA/Clay Nanocomposite Membranes and Its Pervaporation Performance

Pervaporation separation of chlorinated hydrocarbon/acetone mixtures has been investigated using nanoclay modified poly(ethylene-co-vinyl acetate) films. The results have been compared with the unfilled poly(ethylene-co-vinyl acetate) films. The nanoclay modified membranes were characterized by X-ray diffraction technique. The dispersion of layered silicates in the polymer matrix was analyzed using transmission electron microscopy. The nanoclay showed excellent dispersion in the polymer matrix. The effect of free volume on the pervaporation performance was investigated by positron annihilation lifetime spectroscopy. Poly(ethylene-co-vinyl acetate) nanocomposite membrane showed high selectivity because of the plateletlike morphology and high aspect ratio of layered silicates. The nano clay content and the swelling effects on pervaporation performance of nano composite membranes have been investigated in detail.

Morphology and transport characteristics of poly(ethylene- co-vinyl acetate)/clay nanocomposites

Poly(ethylene- co-vinyl acetate)/clay nanocomposite membranes were prepared with different clay loadings. The morphology of the nanocomposites was investigated using X-ray diffraction technique and transmission electron microscopy. The dispersion of layered silicates decreased with increasing filler loading. Samples with low filler content showed excellent dispersion of layered silicates resulting in a partially exfoliated structure. The transport characteristics of aromatic hydrocarbons through the nanocomposite membranes were studied by the simple sorption gravimetric analysis in the temperature range 28–70 °C and the results were compared with unfilled membranes. The solvent uptake nature of the nanoclay filled polymer samples was found to be much reduced. The solvent uptake was minimum for composites with 3 wt% of filler and increased with increasing filler content, which is presumably due to aggregation of clay filler at higher loading. The influence of free volume on the transport properties of the membranes was studied using positron annihilation lifetime spectroscopy. The transport phenomenon was found to follow an anomalous mode. Activation parameters were estimated and the molar mass between crosslinks was calculated using Flory–Rehner Theory. The experimental data were compared with theoretical predictions.

Thermal degradation kinetics of epoxy/organically modified montmorillonite nanocomposites

AbstractNanocomposites based on a commercial epoxy resin and organically modified montmorillonites (OMMTs), containing 5 and 10 phr OMMT, were prepared and characterized. Poly(oxypropylene) diamine (Jeffamine D400) and octadecylamine were used as organic modifiers. Another poly(oxypropylene) diamine (Jeffamine D230) was used as a curing agent. The thermal degradation kinetics of the neat resin system and nanocomposites were investigated by thermogravimetric analysis. The dispersion of silicate layers within the crosslinked epoxy matrix was verified by transmission electron microscopy. The activation energy of degradation for the investigated systems was determined by the isoconversional Kissinger–Akahira–Sunose method. The thermal behavior of the neat resin systems and nanocomposites was modeled with an empirical kinetic model. The influence of organic modifiers and the OMMT loading on the thermal stability of the nanocomposites was discussed. © 2007 Wiley Periodicals, Inc. JAppl Polym Sci, 2008

Preparation and characterization of poly(propylene carbonate)/montmorillonite nanocomposites by solution intercalation

Poly(propylene carbonate) (PPC) is a new biodegradable aliphatic polycarbonate. However, the poor thermal stability and low glass transition temperatures ( T g) have limited its applications. To improve the thermal properties of PPC, organophilic montmorillonite (OMMT) was mixed with PPC by a solution intercalation method to produce nanocomposites. An intercalated-and-flocculated structure of PPC/OMMT nanocomposites was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The thermal and mechanical properties of PPC/OMMT nanocomposites were investigated by thermal gravimetric analysis (TGA), differential scanning calorimetric (DSC), and electronic tensile tester. Due to the nanometer-sized dispersion of layered silicate in polymer matrix, PPC/OMMT nanocomposites exhibit improved thermal and mechanical properties than pure PPC. When the OMMT content is 4 wt%, the PPC/OMMT nanocomposite shows the best thermal and mechanical properties. These results indicate that nanocomposition is an efficient and convenient method to improve the properties of PPC.

Nonlinear optical polyimide/montmorillonite nanocomposites consisting of azobenzene dyes

A reactive organoclay was formed using trifunctional 1,1,1-tris[4-(4-amino-2-trifluoromethylphenoxy)phenyl] as a swelling agent for the silicate layers of montmorillonite. One of the functional groups of the swelling agents formed an ionic bond with the negatively charged silicates, whereas the remaining functional groups were available for further reaction with poly(amic acid) end capped with anhydride groups. Subsequently, the hydroxyl groups of the ensuing polyimide could be further reacted with isocyanate-containing dyes to form nonlinear optical polyimides with high T gs. X-ray diffraction and transmission electron microscopy revealed that the dispersion of silicate layers in the polyimide created an exfoliated structure as a result of using the trifunctional groups of the swelling agent. This particular structure of the nanocomposite resulted in enhanced thermal properties and excellent optical transparency. Using in situ contact poling, r 33 coefficients ranging from 4.6 to 7.6 pm/V were obtained for the organic/inorganic NLO materials; excellent temporal stability at 100 °C was obtained.

Effect of Organoclay on the Morphology and Properties of Poly(propylene)/Poly[(butylene succinate)‐co‐adipate] Blends

AbstractThe effect of organically modified clay on the morphology and properties of poly(propylene) (PP) and poly[(butylene succinate)‐co‐adipate] (PBSA) blends is studied. Virgin and organoclay modified blends were prepared by melt‐mixing of PP, PBSA and organoclay in a batch‐mixer at 190 °C. Scanning electron microscopy studies revealed a significant change in morphology of PP/PBSA blend in the presence of organoclay. The state of dispersion of silicate layers in the blend matrix was characterized by X‐ray diffraction and transmission electron microscopic observations. Dynamic mechanical analysis showed substantial improvement in flexural storage modulus of organoclay‐modified blends with respect to the neat polymer matrices or unmodified blends. Tensile properties of virgin blends also improved in the presence of organoclay. Thermal stability of virgin blends in air atmosphere dramatically improved after modification with organoclay. The effect of organoclay on the melt‐state liner viscoelastic properties of virgin blends was also studied. The non‐isothermal crystallization behavior of homopolymers, virgin, and organoclay‐modified blends were studied by differential scanning calorimeter. The effect of incorporation of organoclay on the cold crystallization behavior of PP/PBSA blends is also reported.magnified image

Rheological behavior of polypropylene/layered silicate nanocomposites prepared by melt compounding in shear and elongational flows

AbstractMelt rheology and processability of exfoliated polypropylene (PP)/layered silicate nanocomposites were investigated. The nanocomposites were prepared by melt compounding process in the presence or absence of a PP‐based maleic anhydride compatibilizer. PP/layered silicate nanocomposites showed typical rheological properties of exfoliated nanocomposites such as nonterminal solid‐like plateau behavior at low frequency region in oscillatory shear flow, higher steady shear viscosity at low shear rate region, and outstanding strain hardening behavior in uniaxial elongational flow. The melt processability of exfoliated PP/layered silicate nanocomposites was significantly improved due to good dispersion of layered silicates and increased molecular interaction between the PP matrix and the layered silicate organoclay. Small‐angle X‐ray scattering and transmission electron microscopy results revealed that the layered silicate organoclay was exfoliated and good interaction between PP matrix and organoclay was achieved by using the PP‐g‐MAH compatibilizer. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3506–3515, 2007

On the use of TEM in the characterization of nanocomposites

Both an organically modified commercial clay of montmorillonite type (MMT) and its nanocomposites, based either on polyamide 6 (PA6) or an epoxy resin, as matrix polymer, have been characterized by transmission electron microscopy (TEM). Sample micrographs, taken at increasing exposure times ( t e), have shown the gradual disappearance of clay layers, because of an amorphisation of the MMT crystalline structures caused by prolonged sample exposure to electron beam. Indeed, the above phenomenon, which is mostly evident in the case of intercalated nanocomposites, makes the detection of the layered silicate dispersion in the polymer matrix rather difficult and compels to perform TEM measurements using very short exposure times. Moreover, the microscopy accelerating voltage has turned out to affect sample stability; namely, when decreasing the above parameter, the disappearance of clay structure occurs at lower exposure times.

Preferential Association of Segment Blocks in Polyurethane Nanocomposites

Controlling the level of dispersion of silicate layers in polymer matrices through intermolecular interactions and exploiting these interactions to enhance thermomechanical behavior are key challenges in the field of polymer nanocomposites. In this investigation, unmodified Laponite platelets are dispersed in a segmented polyurethane containing a polar, hydrophilic soft segment and a hydrophobic hard segment using a novel solvent exchange method and compared to polyurethane nanocomposites containing more hydrophobic hard and soft domains. It was determined that the silicate layers were preferentially, but not exclusively, attracted to the hydrophilic, polar soft domains. An apparent microphase-segregated morphology was observed in transmission electron microscopy for this system, revealing regions of exfoliation and intercalation. According to polarizing optical microscopy, strain-induced alignment is inhibited for this polyurethane nanocomposite, which is reflected in dramatic reductions in tensile strength and ultimate extensibility. In comparison, the Laponite disks appear to be preferentially, but not exclusively, embedded within the hard domains in the segmented polyurethanes containing more hydrophobic hard and soft domains. Exfoliation of the clay platelets leads to enhanced modulus and toughness without a reduction in extensibility. This study provides clues for exploiting silicate-polymer interactions to tune material properties without chemical modification.

Effect of rotational speed of twin screw extruder on the microstructure and rheological and mechanical properties of nanoclay‐reinforced polypropylene nanocomposites

AbstractThe morphology and rheological and mechanical properties of nanoclay‐reinforced polypropylene nanocomposites were investigated with aid of transmission electron microscopy (TEM), thermo gravimetric analysis, rheometry, and mechanical tests. The organically modified silicate (montmorillonite) was used as a reinforcing material and maleic anhydride‐grafted polypropylene oligomer as a compatibilizer to improve the clay dispersion and adhesion. The object of the study was to examine the effect of screw speed of the co‐rotating twin‐screw extruder on the clay exfoliation and nanocomposite properties. Also, the effect of compatibilizing agent was taken into account. The main result of the study was that nanocomposites showed both intercalated and exfoliated structures depending on the screw speeds of extruder. TEM images revealed that the dispersion of silicate layers was greatly influenced by the screw speed. However, even when the silicate layers were highly exfoliated, there was no remarkable effect on mechanical properties of the nanocomposite. POLYM. ENG. SCI. 46:995–1000, 2006. © 2006 Society of Plastics Engineers.

Gas transport through nano and micro composites of natural rubber (NR) and their blends with carboxylated styrene butadiene rubber (XSBR) latex membranes

The gas permeability coefficient of nano and micro composites of natural rubber, carboxylated styrene butadiene rubber and 70:30 natural rubber/carboxylated styrene butadiene rubber blend membranes has been investigated with special reference to type of filler, gases, filler loading and pressure. The layered silicates such as sodium bentonite and sodium fluorohectorite were the nanofillers used and the conventional micro fillers were clay and silica. Latex nanocomposites were characterized by X-ray diffraction technique. The dispersion of layered silicates in the polymer matrix was analysed using transmission electron microscopy. The fluorohectorite silicate showed excellent dispersion in natural rubber matrix. The effect of free volume on the gas barrier properties was investigated by positron annihilation lifetime spectroscopy. It was observed that due to the platelet like morphology and high aspect ratio of layered silicates, the gas barrier properties of nano filled latex membranes were very high. The crosslink density values and extent of reinforcement were estimated in order to correlate with the gas barrier properties. The oxygen/nitrogen selectivity of these membranes were investigated. The diffusion of gas molecules through the polymer was determined by time-lag method and diffusion selectivity of the membranes was computed.

Enhanced thermal Properties and Gas Barrier Property of PMMA Nanocomposites with Layered Silicate via Soap-Free Emulsion Polymerization

ABSTRACTPolymer/SWN nanocomposites were synthesized in the soap-free emulsion polymerization of methyl methacrylate (MMA) using 2-hydroxylethyl methacrylate (HEMA). The SWN in the polymer/SWN nanocomposites was individually dispersed in water, and these are adsorbed on the surface of monomer droplets. Polymer/SWN nanocomposites were obtained by adding an aqueous dispersion of layered silicate to the polymer emulsion. X-ray diffraction (XRD) and FT-IR spectra were utilized to characterize the structures of the nanocomposites. The degree of dispersion of these nanocomposites was investigated by transmission electron microscopy (TEM). Furthermore, the thermal and mechanical properties of polymer/SWN nanocomposites were determined using thermogravimetric analysis (TGA), differential scanning calorimeter (DSC) and dynamic mechanical analysis (DMA). The increased tanδ of the obtained nanocomposites is caused by the fine dispersion of SWN particles into the polymer matri

Dispersion of organically modified clays within n-alcohols

A method for formation of polymer–clay nanocomposites involves dispersion of the nanometer silicate layers of clays into a solvent, followed by dispersion into polymers. The dispersion of layered silicates within solvents affects the structure and properties of the nanocomposites. We report the dispersion of organically modified clays, used for formation of nanocomposites with organic polymers, within a range of alcohol solvents. Experiments involved stirring a mixture containing approximately 1 wt% of alkylammonium-modified clays in n-alcohols with general molecular structure R n OH, where n represents the number of carbons of alkyl chains, varying from 2 to 8. The clays precipitated from the dispersion when R n OH solvents with n < 5 were used, however, they formed gels for solvents with n ⩾ 5 . The increased dispersion was related to the decrease of polarity and hydrogen bonding force within solvents. X-ray diffraction for the dispersed clays indicated that the interlayer spaces (1.8 nm), formed by regular stacking of the silicate layers, expanded to a maximum of 3.0 nm after treatment with R n OH with n ⩾ 5 . The interlayer expansion was due to the intercalation of n-alcohol molecules within the interlayer spaces. It is suggested that the alkyl chains of n-alcohols remain parallel to the silicate surface in the intercalate. Preliminary experiments on the influence of these alcohol solvents on the intercalation of polyol (polyether) are also reported.

Crystallization behavior of polymer/montmorillonite nanocomposites. Part III. Polyamide-6/montmorillonite nanocomposites, influence of matrix molecular weight, and of montmorillonite type and concentration

Several series of polyamide-6 (PA-6) nanocomposites, differing in montmorillonite (MMT) type and content and PA-6 matrix molecular weight, were prepared by melt-extrusion and the associated PA-6 crystallization behavior and morphology was evaluated using (synchrotron) X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. The nucleating ability of silicate layers is poor in PA-6 nanocomposites made by melt-extrusion because highly active, stable PA-6 crystallization precursors are generated during melt-extrusion. In most of the studied PA-6/MMT nanocomposites the dispersed silicate layers act as impurities and decrease rather than increase the overall crystallization kinetics of PA-6, especially at high MMT contents. Furthermore, at a given MMT concentration, the crystal growth retardation inflates with increasing degree of exfoliation, which dependents on the MMT type and which increases with increasing PA-6 molecular weight. One of the considered MMT types leads to a poorly exfoliated nanomorphology and as a result no retardation of crystal growth is observed. Furthermore, the disturbed crystal growth does not alter the PA-6 semicrystalline stack morphology. Moderate nucleation effects due to the presence of MMT can be observed when the particle load is low (low amount of MMT and/or poor degree of exfoliation) and provided the supercooling is sufficiently large.

Silicate layer dispersion in copolymer/clay nanocomposites

AbstractFactors of silicate layer dispersions in polymers have been studied with copolymers. The influence of the copolymerization ratio of copolymers and the alkyl chain lengths of organomodified reagents of organophilic clay has been examined. The dispersion of silicate layers in copolymers is dependent on the copolymerization ratios of the functional groups, that is, the polarity of the polymer matrix. The alkyl chain lengths of organomodified reagents also have an important influence on silicate layer dispersions. From a comprehensive viewpoint, the polarity matching between polymers and organophilic clay is an important factor for silicate layer dispersions in polymers. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1554–1557, 2005