Synthesis of polylactide/clay composites using structurally different kaolinites and kaolinite nanotubes

Polymer/clay nanocomposites receive much attention due to their interesting mechanical and thermal properties. Currently, the vast majority of plastics are made from petroleum-based synthetic polymers that do not degrade in a natural environment and their disposal poses a serious problem. An environmentally-conscious alternative is to design polymer nanocomposites that are biodegradable.In the present work the synthesis and properties of novel polymer/clay nanocomposites based on biodegradable polymer-polylactide (PLA) were investigated. Kaolinite nanotubes obtained by an intercalation/deintercalation method as well as platey kaolinites of different structural orders were used as fillers. Mechanical properties of composites (tensile strength (S_U) and Young's modulus (E)) were measured. The surface of the formed polymer derivatives was examined by AFM (Atomic Force Microscopy). The structural characterization was carried out using infrared spectroscopy (IR). Composites surface wettability was studied by measuring the water contact angle.The mechanical tests revealed that both S_U and E values increased significantly after addition of the nano-filler in comparison to the pure PLA. Regardless of the filler content the increase of S_U and E values was higher in the case of the nanotubular kaolinite. In particular, a threefold increase of the E value was noticed. For the most homogeneous kaolinite nanotubes/PLA nanocomposite S_U increased from ~ 29 MPa (pure PLA) to ~ 43 MPa, while E increased from ~ 0.7 GPa (pure PLA) to ~ 2.3 GPa. These mechanical parameters were comparable with the ones measured for polypropylene (S_U = 40 MPa; E = 1.5–2.0 GPa) and polystyrene (S_U = 40 MPa; E = 3.0–3.5 GPa). Differential IR spectra of the nanocomposites indicated an interaction of kaolinites inner surface hydroxyls with PLA which was confirmed by an intensity decrease of a band at ~ 3690 cm^? 1. The presence of highly dispersed nanotubular kaolinite particles in the polymer matrix which contributed to the improvement of PLA mechanical properties was observed using AFM. The contact angle measurements showed that the addition of kaolinites led to changes of wettability, yet the synthesized materials still possessed hydrophilic surfaces.     

Characterization,degradation and biocompatibility of PBAT based nanocomposites

The characterization, biocompatibility and hydrolytic degradation of poly(butylene adipate-co-terephthalate) (PBAT) and its nanocomposites based on 10 wt.% of an unmodified sepiolite and unmodified and modified montmorillonites and fluorohectorites were studied. All nanocomposites were prepared by melt blending using an internal mixer at 140 °C, showing a good level of clay distribution and dispersion into the PBAT matrix, especially those systems based on modified clays and sepiolite. The compression tests of all nanocomposites showed significant increases in the mechanical properties of PBAT matrix, associated to a reinforcement effect of nanoclays. An effective hydrolytic degradation of PBAT and nanocomposites in a phosphate buffered solution of pH 7.0 at 37 °C was also obtained. The addition of nanoparticles tended to delay slightly the hydrolysis of the polymer matrix in the early degradation stages; afterwards the presence of nanoparticles did not affect significantly the degradation trend of the polymer. Cytotoxicity tests, protein absorption analyses and complete blood count tests indicated that nanocomposites showed good biological safety: non-cytotoxicity, higher in vitro hemocompatibility than neat PBAT and non-negative hemostatic effects after contacting with blood. In general, these results showed that all the studied PBAT based nanocomposites could be very attractive for various tissue engineering applications, particularly to bone defects.     

Study on superabsorbent composites. IX: Synthesis,characterization and swelling behaviors of polyacrylamide/clay composites based on various clays

A series of clay-based superabsorbent composite from acrylamide (AM) and various clays, such as attapulgite, kaolinite, mica, vermiculate and Na⁺-montmorillonite, was prepared by free-radical aqueous polymerization, using N,N′-methylenebisacrylamide (MBA) as a crosslinker and ammonium persulfate (APS) as an initiator, and then saponified with sodium hydroxide solution. In this paper, the reaction mechanism and thermal stability of the superabsorbent composites incorporated with various clays were characterized by FTIR, XRD and TGA, respectively. The effects of clay kind and clay content on equilibrium water absorbency of these composites were also investigated and compared. In addition, the influences of clay kind on comprehensive swelling behaviors of the PAM/clay superabsorbent composites were studied. The results indicated that the introduced clays could influence physicochemical properties of obtained superabsorbent composites. Mica could improve thermal stability of corresponding superabsorbent composites to the highest degree comparing with the other clays. The PAM/clay superabsorbent composites incorporated with 10 wt% clay of various kinds were all endowed with equilibrium water absorbency of more than 1300 g g⁻¹. The equilibrium water absorbency decreases with increasing clay content and correlates with the kind of clay. Attapulgite-based superabsorbent composite was endowed with higher water absorbency in univalent cationic saline solution, however, the vermiculite- and the kaolinite-based ones acquired the highest water absorbency in CaCl₂ and FeCl₃ aqueous solution, respectively. Moreover, the superabsorbent composites incorporated with Na⁺-montmorillonite have higher swelling rate and that of doped with mica was endowed with higher reswelling capability.     

Rheological properties of montmorillonitic clay suspensions: Effect of firing and interlayer cations

The effect of a prior firing of three montmorillonite clays, exhibiting different nature of interlayer cations, on the rheological behaviour of related aqueous suspensions (5 and 10 mass% of solid content) was examined. Calcinations were performed at 150 °C, 250 °C, 300 °C or 450 °C for 30 min. The rheological properties were characterized at 25 °C in the flow mode using the Herschel–Bulkley model.The alkaline interlayer cation (Na) tended to increase the yield stress of montmorillonite suspensions in comparison with earth-alkaline ones (Ca, Mg). As expected, increasing solid content led to increasing yield stress.For calcinations until 200 °C, the relevant suspensions exhibited an increasing yield stress due to a gel-like behaviour in relation with a card-house-like structure. Furthermore, calcination above 300 °C favoured the decrease of the corresponding yield stress. This behaviour seemed to be related to the modification of the surface properties of the clay platelets, more precisely to the beginning of clay dehydroxylation.     

Organomontmorillonite/poly(methyl methacrylate) nanocomposites prepared by in situ photopolymerization. Effect of the organoclay on the photooxidative degradation

Montmorillonite/PMMA nanocomposites were obtained by in situ photopolymerization. Methyl methacrylate was photopolymerized in the presence of modified clay minerals using thioxanthone (TX) and ethyl 4-(dimethylamino) benzoate (EDB) as photoinitiating system. The organomontmorillonites (SWy-1-C8-Mt and SWy-1-C16-Mt) were prepared by ion exchange of SW-1 Mt with octyltrimethylammonium bromide (C8) and hexyltrimethylammonium bromide (C16), respectively. X-ray diffraction indicated that clay/PMMA nanocomposites can have intercalated or exfoliated structures, or even a mixture of exfoliated and partially intercalated structure layers. The structure of each particular clay polymer nanocomposite (CPN) depends on the clay mineral loading and the solvent used for the preparation. The molecular weights of the SWy-1-C8/PMMA and SWy-1-C16/PMMA (1.0, 3.0 and 5.0%) obtained by photopolymerization in ethanol, were in the range of 1,000,000 to 3,000,000 D, and in acetonitrile the M_w values varied from 220,000 to 270,000 D. Photooxidative degradation of clay/PMMA nanocomposites has been investigated using size exclusion chromatography (SEC). Evidence was found that PMMA and CPN degrade by random chain scissions. The polydispersity increases after irradiation and the degradation rate coefficient for pure PMMA is up to 6 times larger than that for CPN. The effects of the clay mineral content, clay mineral type (clay mineral modified by surfactants with different lengths of alkyl chains) and solvent used for dispersion of organoclay on the photodegradation rate coefficients were also studied. The influence of these parameters on the photodegradation process was statistically evaluated using a two-level factorial design. The importance of the parameters was proved to follow the order: clay mineral content > clay mineral type > solvent. CPN with higher clay mineral loadings showed slower rates of oxidation. The clay mineral stabilizes the polymer against UV irradiation. SWy-1 clay mineral scatters and absorbs the incident light, decreasing the degradation rate of polymer present in the CPN.     

Effect of ultrasound on HDPE/clay nanocomposites: Rheology,structure and properties

High density polyethylene (HDPE)/organoclay nanocomposites of varying concentrations of clay were prepared by a single screw compounding extruder with the attached ultrasound die operating at various amplitudes. The die pressure and power consumption due to ultrasound were measured at different feed rates of nanocomposites of various clay concentrations. The structure and morphology of nanocomposites were studied by X-ray diffraction (XRD), transmission electron microscopy (TEM) and infrared spectroscopy. It was found that ultrasonic treatment enhanced the intercalation of HDPE into lattice layers of clay by increasing d-spacing up to 50%. Mechanical and rheological properties of these nanocomposites were investigated as a function of clay concentration and ultrasonic amplitude. Complex viscosity, storage and loss moduli of nanocomposites were increased after ultrasonic treatment. Mechanical properties such as the elongation at break, yield stress, toughness and impact strength of ultrasonically treated nanocomposites increased in comparison with the untreated nanocomposites. A reduction in oxygen permeability of nanocomposites was observed after ultrasonic treatment at an amplitude of 10 μm with the highest reduction by 20% at 2.5% clay concentration and a residence time of 21 s. This reduction in permeability was achieved even though results indicate that the crystallinity of ultrasonically treated nanocomposites was reduced.     

Chemical and thermal properties of organoclays derived from highly stable bentonite in sulfuric acid

Generally, acid activation modified the physico-chemical properties of the raw clay minerals. The extent of these modifications depended on the type, origin of the clay minerals and the conditions of the acid activation. In this study, a bentonite exhibited a strong stability toward the acid treatment at 90 °C and at higher acid/clay mineral ratios, with slight depletion of Mg^2 +, Fe^3 + and Al^3 + cations (about 5%). The resulting organo-acid activated clays prepared after a reaction with cetyltrimethylammonium (C16TMA) hydroxide solution, exhibited uptaken amounts of surfactants between 0.80 mmol and 0.7 mmol/g with interlayer spacings of 2.20 nm and 1.80 nm, independently of the initial concentrations of the organic molecules. These organoclays were stable in acidic and basic solutions. However, after heating at 200 °C, the interlayer spacing shrunk due to the degradation of the organic surfactants as indicated by thermogravimetric analysis. The rehydration of the calcined organoclays at temperatures below 200 °C, did not lead to the increase of the basal spacings, due to change in configuration of the C16TMA cations.     

Effects of montmorillonite on the chemical degradation kinetics of metsulfuron methyl in aqueous media

The degradation kinetics of the sulfonylurea herbicide metsulfuron methyl (MM) has been studied in batch experiments by UV–VIS spectroscopy, and the effects of pH and the presence of a clay mineral (Na-montmorillonite) are reported. The proposed UV–VIS method gives kinetic results that are comparable to those obtained with chromatographic methods. In aqueous solutions, the chemical degradation of MM is undetectable at pH 6.5–9.5, but increases about 500 times by decreasing the pH from 6 to 2, and 300 times by increasing pH from 9.5 to 11.5. For example, the half-life of MM is shorter than 1 d at pH 2 and 11.5, but longer than a year at pH 6. Na-montmorillonite has an inhibitory effect on MM degradation. A combination of adsorption–desorption studies and degradation kinetic measurements demonstrates that in the presence of Na-montmorillonite only MM that remains in solution is subject to degradation; adsorbed MM is protected by the clay from being degraded. However, since adsorption only occurs at low pH (around 3) it can be envisaged that montmorillonite and supposedly other phyllosilicate clays do not affect significantly the chemical degradation rate of MM in soils and other natural systems.     

Utilization of recycled paper processing residues and clay of different sources for the production of porous anorthite ceramics

Production of porous anorthite ceramics from mixtures of paper processing residues and three different clays are investigated. Suitability of three different clays such as enriched clay, commercial clay and fireclay for manufacturing of anorthite based lightweight refractory bricks was studied. Porous character to the ceramic was provided by addition of paper processing residues (PPR). Samples with 30–40 wt% PPR fired at 1200–1400 °C contained anorthite (CaO·Al₂O₃·2SiO₂) as major phase and some minor secondary phases such as mullite (3Al₂O₃·2SiO₂) or gehlenite (2CaO·Al₂O₃·SiO₂), depending on the calcite to clay ratio. Anorthite formation for all clay types was quite successful in samples with 30–40 wt% of paper residues fired at 1300 °C. A higher firing temperature of 1400 °C was needed for the fireclay added samples to produce a well sintered product with large pores. Gehlenite phase occurred mostly at lower temperatures and in samples containing higher amount of calcium (50 wt% PPR). Compressive strength of compacted and fired pellets consisting of mainly anorthite ranged from 8 to 43 MPa.     

Effects of cationic and anionic clays on the hydrolytic degradation of polylactides

Polylactide (PLA)/montmorillonite (MMT) cationic clay and PLA/hydrotalcite (HT) anionic clay composites at 5wt% clay were melt compounded and characterized for morphology before and after hydrolytic degradation. Semicrystalline and amorphous polymers were used as well as noncalcined and calcined clays. The addition of cationic clays led to the formation of microcomposites, whereas the addition of anionic clays produced a much finer dispersion and enhanced polymer intercalation corresponding to that found in nanocomposites. Hydrolytic degradation rate constants of cationic microcomposites and, particularly, of anionic nanocomposites are lower than those of the unfilled polymers, possibly due to the reduction of the carboxylic group catalytic effect through neutralization with the hydrophilic alkaline filler. Comparison of calcined MMT and HT clays vs. their noncalcined counterparts suggest that calcination can further reduce hydrolytic degradation rates, particularly for semicrystalline PLA. Based on the calculated activation energies, the degradation kinetics did not differ significantly above and below the assumed T_g of 58–60°C. The results of this work would be applicable to controlled release pharmaceutical formulations containing clay/drug combinations produced by melt compounding with a biodegradable polymer matrix. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Role of vermiculite and zirconium–vermiculite on the formation of zircon–cordierite nanocomposites

The Zr^4 +–vermiculites were studied in their new role of the zircon precursor in the clay minerals mixtures which were prepared for firing of the zircon–cordierite nanocomposites. Currently there is a lack of data available about the structure of Zr^4 +–vermiculites, on which this study was performed. The modeling of the arrangement of interlayer material in the Zr^4 +–vermiculite led to new findings that water molecules are attracted more strongly by Mg^2 + cations than by Zr-tetrameric cations, and that both the tetrameric cations [Zr₄(OH)₁₄(H₂O)₁₀]^2 + and [Zr₄(OH)₈(H₂O)₁₆]^8 + may be present in the interlayer space of the Zr^4 +–vermiculites. Vermiculites from two different localities Czech Republic (Verm1) and from Brazil (Verm2) were intercalated using the zirconyl chloride (ZrOCl₂–30% solution in HCl) and the prepared Zr^4 +–vermiculites were designated as Zr^4 +–Verm1 and Zr^4 +–Verm2, respectively. Influence of the Zr^4 +–Verm1 and Zr^4 +–Verm2 in the mixtures of clay minerals on the properties of zircon–cordierite nanocomposites were investigated by their comparison with the properties of the zircon–cordierite nanocomposites, which were prepared using saturation of the clay minerals mixtures containing Verm1 and Verm2 with the zirconyl chloride (ZrOCl₂–30% solution in HCl). The zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Zr^4 +–Verm1 and Zr^4 +–Verm2 showed a maximum porosity of P = 58 and 60%, skeletal density SD = 3.2 and 3.6, and the smallest pores with a median pores diameter MDP = 18 and 15 μm, respectively, in comparison with the zircon–cordierite nanocomposites fired from the clay mineral mixtures containing Verm1 and Verm2 and saturated with zirconyl chloride solution. The type of vermiculite Verm1 or Verm2 in the clay mineral mixtures did not affect the contents of the crystalline mineral phases in cordierite and zircon–cordierite nanocomposites.     

Single-source-precursor synthesis of soft magnetic Fe3Si- and Fe5Si3-containing SiOC ceramic nanocomposites

We present here the single-source-precursor synthesis of Fe₃Si and Fe₅Si₃-containing SiOC ceramic nanocomposites and investigation of their magnetic properties. The materials were prepared upon chemical modification of a hydroxy- and ethoxy-substituted polymethylsilsesquioxane with iron (III) acetylacetonate (Fe(acac)₃) in different amounts (5, 15, 30 and 50 wt%), followed by cross-linking at 180 °C and pyrolysis in argon at temperatures ranging from 1000 °C to 1500 °C. The polymer-to-ceramic transformation of the iron-modified polysilsesquioxane and the evolution at high temperatures of the synthesized SiFeOC-based nanocomposite were studied by means of thermogravimetric analysis (TGA) coupled with evolved gas analysis (EGA) as well as X-ray diffraction (XRD). Upon pyrolysis at 1100 °C, the non-modified polysilsesquioxane converts into an amorphous SiOC ceramic; whereas the iron-modified precursors lead to Fe₃Si/SiOC nanocomposites. Annealing of Fe₃Si/SiOC at temperatures exceeding 1300 °C induced the crystallization of Fe₅Si₃ and β-SiC. The crystallization of the different iron-containing phases at different temperatures is considered to be a consequence of the in situ generation of a Fe–C–Si alloy within the materials during pyrolysis. Depending on the Fe and Si content in the alloy, either Fe₃Si and graphitic carbon (at 1000–1200 °C) or Fe₅Si₃ and β-SiC (at T > 1300 °C) crystallize. All SiFeOC-based ceramic samples were found to exhibit soft magnetic properties. Magnetization versus applied field measurements of the samples show a saturation magnetization up to 26.0 emu/g, depending on the Fe content within the SiFeOC-based samples as well as on the crystalline iron silicide phases formed during pyrolysis.     

Nonlinear optical,poly(amide-imide)–clay nanocomposites comprising an azobenzene moiety synthesised via sequential self-repetitive reaction

Poly(N-acylurea)–clay nanocomposites consisting of a modified montmorillonite and poly(N-acylurea) were prepared from which poly(amide-imide)–clay nanocomposites were subsequently obtained via the sequential self-repetitive reaction of poly(N-acylurea). The moderate T_g of poly(N-acylurea) allows the nonlinear optically active polymer to exhibit high poling efficiency; in situ poling and curing increased the T_gs of poly(amide-imide)–clay nanocomposites. Electro-optical coefficients, r₃₃ of ～17–20 pm/V (830 nm), were achieved; high temporal stability (120 °C) and waveguide optical losses of 3.4–3.9 dB/cm at 1310 nm were also obtained for poly(amide-imide)–clay nanocomposites.     

Microsphere pressure sensitive adhesives—acrylic polymer/montmorillonite clay nanocomposite materials

In this study, the synthesis and characterization of acrylic polymer/montmorillonite (MMT) clay nanocomposite pressure sensitive adhesives (PSA) are presented. Different types and amounts of modified and unmodified montmorillonite clays were dispersed in ethyl acrylate (EA)/2-ethylhexyl acrylate (2-EHA) monomer mixture, which was then polymerized using a suspension polymerization technique. Polymerization was monitored in-line using attenuated total reflectance-fourier transform infrared (ATR-FTIR) spectroscopy. The adhesion properties of the synthesized nanocomposite materials were determined using standard measurements of tack, peel and shear strength. Viscoelastic properties of dried adhesive films were analyzed using dynamic mechanical analysis (DMA). The results showed that the kinetics of suspension polymerization was independent of the addition of MMT clays. On the other hand, adhesive properties were strongly influenced by the type and the amount of MMT clay added. While peel strength and tack gradually decreased with higher amount of modified MMT clay, a substantial increase in shear strength was determined with a maximal value at 1 wt% of added MMT clay. Moderate influence on tack, peel and shear strength was observed when the unmodified type of MMT clay was used. DMA analysis showed an increase in storage modulus (G′) for adhesives synthesized with MMT clay addition, but no significant differences were determined between particular types of MMT clays. A decrease in tan δ value for adhesives with 1 wt% of added MMT clay was observed, which also concurs with higher shear strength and implies to the improved cohesion of adhesive.     

Texturation of model clay materials using tape casting and freezing

The present work aimed to investigate the processing of textural clay based materials using tape casting together with freezing. Two model raw materials were used, namely: BIP kaolin from France and ABM montmorillonite from Mediterranean region. The mixtures of both clays were studied, whereby, the amount of montmorillonite was 0, 5, 10, 20 or 50 mass%. After tape casting, the as-obtained green bands were frozen into liquid nitrogen, lyophilized and then fired at 1050 °C or 1200 °C.The amount of montmorillonite appeared as a critical parameter that controls the cohesion of the dry products. For montmorillonite content ≥20 mass%, the products exhibited multiple cracks after lyophilisation. With lower montmorillonite content, the cohesion of the dry products was satisfactorily and a macroscopic cross-linked surface texturation was observed. After calcination at 1050 °C or 1200 °C, the texturation appeared well defined. Moreover, calcination at 1200 °C increased the densification of products and the occurrence of a glassy phase was noted.The combination of both tape casting and freezing (freeze tape casting) is a promising way to develop various clay-based and composites materials exhibiting unique microstructure organization and characteristics with potential application in the field sustainable and environmentally friendly filtration, adsorption or catalysis.     

Development of a new rapid,relevant and reliable (R3) test method to evaluate the pozzolanic reactivity of calcined kaolinitic clays

The present paper introduces a new rapid, relevant and reliable (R³) test to predict the pozzolanic activity of calcined clays with kaolinite contents ranging from 0 to 95%. The test is based on the correlation between the chemical reactivity of calcined clays in a simplified system and the compressive strength of blends in standard mortar. The simplified system consists of calcined clay portlandite and limestone pastes with sulfate and alkali levels adjusted to reproduce the reaction environment of hydrating blended cements. The pastes were hydrated for 6 days at 20 °C or for 1 day at 40 °C. The chemical reactivity of the calcined clay can be obtained first by measurement of the heat release during reaction using isothermal calorimetry and second by bound water determination in a heating step between 110 °C and 400 °C.Very good correlations were found between the mortar compressive strength and both measures of chemical reactivity.     

The relationship between microstructure,fracture and abrasive wear in Al2O3/SiC nanocomposites and microcomposites containing 5 and 10% SiC

Alumina/SiC nanocomposites are much more resistant to severe wear than monolithic alumina. In order to clarify the mechanisms responsible for these improvements, alumina and alumina/SiC nanocomposites with 5 and 10 vol.% SiC and various alumina grain sizes were fabricated. For comparison, a 10 vol.% SiC “microcomposite” was also fabricated using 3 μm SiC particles. The extent of cracking beneath hardness indentations was examined and the specimens were tested in abrasive wear. Quantitative surface fractography of the worn surfaces was carried out. The wear properties depended strongly on the grain size in pure alumina, but were independent of the alumina grain size in the nanocomposites. This is consistent with the idea that much of the improvement in wear resistance when SiC is added to alumina stems from a reduction in the size of the individual pullouts owing to the accompanying change in fracture mode. In addition, crack initiation by plastic deformation during abrasion and indentation was found to be strongly inhibited when 10 vol.% nanosized SiC was added to alumina. The addition of 3 μm “micro-sized” SiC did not have the same effect. The ability of fine SiC particles to suppress cracking is attributed to the blocking of twins and dislocation pileups by intragranular SiC nanoparticles. This reduces the length of the twins or pileups and hence their ability to nucleate microcracks.     

Development of fireclay aluminosilicate refractory from lithomargic clay deposits

Lithomargic clay until now has not been utilised to produce refractory bodies due to its low plasticity. In this work, the development and evaluation of fireclay refractory material produced from lithomargic clay deposit has been studied by addition of clay binder. Three formulations were prepared by mixing, semi-dry moulding, drying and firing at temperatures ranging from 1200 to 1400 °C. The fired samples were investigated to determine their physical properties such as bulk density, apparent porosity, linear firing shrinkage, and cold crushing strength. The chemical and mineralogical compositions were also determined. The results show that the linear firing shrinkage values were within limits acceptable for refractory clays. The cold crushing strength increases as temperature increased to 1400 °C. Cold crushing strength increased with increasing binder content. The increase of the highly refractory phases (cristobalite and mullite) and the densification of the bricks due to the presence of fluxing agents were responsible for the high cold crushing strength values. The investigated properties indicate that lithomargic clay underlying bauxite deposits could be used to produce fire clay aluminosilicate refractories.     

Characterization and AC conductivity of polyaniline–montmorillonite nanocomposites synthesized by mechanical/chemical reaction

Polyaniline–clay nanocomposites were prepared by solid state polymerization of aniline chloride in the interlayer of montmorillonite through the use of persulfate of ammonium as oxidant. The proportion of aniline to clay and the molar ratio of oxidant to aniline are being varied. The analyse of UV visible and FTIR spectroscopy demonstrated that aniline has been polymerized to polyaniline (PANI) in its conducting emeraldine form. The conformation adopted by PANI chains in the clay interlayer depended on the molar ratio of aniline to montmorillonite. Thermogravimetric analysis of the nanocomposites suggested that polyaniline chains are more thermally stable than those of free polyaniline prepared by solid–solid reaction. The AC conductivity data of different synthesized nanocomposites were analyzed as a function of frequency. Low frequency conductivities of polyaniline/montmorillonite nanocomposites materials ranges from 0.18 to 5.6 × 10^?3 S/cm. All characterization data were compared to those of free polyaniline that was synthesized using a solid–solid reaction.     

The preparation of nano-clay/polypropylene composite materials with improved properties using supercritical carbon dioxide and a sequential mixing technique

A semi-continuous process using scCO₂ is reported for processing polymer–clay composites with high clay loading (i.e. 10 wt %) by reducing the collapse of the exfoliated clays. Two major modifications are involved in the new procedure: exfoliating the nano-clay directly into the hopper filed with pellets followed by processing the composite immediately and sequentially mixing the clay into the melt. This latter approach helped to minimize the clay collapse when processing the composites with high clay loadings. Transmission electron microscopy (TEM) and wide angle X-ray diffraction (WAXD) results are provided to investigate the effect of sequential mixing on reducing the clay collapse in the nanocomposite. Surface modified montmorillonite (MMT) nano-clay/polypropylene (PP) composite at 10 wt % nano-clay with improved clay dispersion was obtained with increased modulus and tensile strength of 63 % and 16%, respectively, compared to the pure PP matrix.