Wide-angle X-ray Diffraction Studies Research Articles

Development of thermoplastic elastomers based on maleated ethylene propylene rubber (m-EPM) and polypropylene (PP) by dynamic vulcanization

Dicumyl peroxide (DCP)-cured thermoplastic vulcanizates (TPVs) based on blends of maleated ethylene propylene rubber (m-EPM) and polypropylene (PP) using maleated-PP as a compatibilizer have been developed. Physical properties of these TPVs change significantly with concentrations of DCP and rubber/plastic blend ratios. Important correlations were obtained from rheometer delta torque values with various physical properties of the TPVs like tension set and crosslink density etc. Wide angle X-ray diffraction study confirms that concentration of DCP has a strong influence on the crystallinity of PP, which might affect the final physical properties of TPVs. The recyclability and ageing characteristics of these TPVs are also found excellent.

Solid lipid nanodispersions containing mixed lipid core and a polar heterolipid: Characterization

This paper describes the characterization of solid lipid nanodispersions (SLN) prepared with a 1:1 mixture of theobroma oil and goat fat as the main lipid matrix and Phospholipon 90G ® (P90G) as a stabilizer heterolipid, using polysorbate 80 as the mobile surfactant, with a view to applying the SLN in drug delivery. The 1:1 lipid mixture and P90G constituting the lipid matrix was first homogeneously prepared by fusion. Thereafter, the SLN were formulated with a gradient of polysorbate 80 and constant lipid matrix concentration by melt-high pressure homogenisation. The SLN were characterized by time-resolved particle size analysis, zeta potential and osmotic pressure measurements, differential scanning calorimetry (DSC) and wide angle X-ray diffraction (WAXD). Transmission electron microscopy (TEM) and isothermal heat conduction microcalorimetry (IMC) which monitors the in situ crystallization were also carried out on the SLN containing P90G and 1.0 % w/w of polysorbate 80. The results obtained in these studies were compared with SLN prepared with theobroma oil with and without phospholipid. Particle size analysis of SLN indicated reduction in size with increase in concentration of mobile surfactant and was in the lower nanometer range after 3 months except SLN prepared without P90G or polysorbate 80. The lipid nanoparticles had negative potentials after 3 months. WAXD and DSC studies revealed low crystalline SLN after 3 months of storage except in WAXD of SLN formulated with 1.0 % w/w polysorbate 80. TEM micrograph of the SLN containing 1.0 % w/w polysorbate 80 revealed discrete particles whose sizes were in consonance with the static light scattering measurement. In situ crystallization studies in IMC revealed delayed crystallization of the SLN with 1.0 % w/w polysorbate 80. Results indicate lipid mixtures produced SLN with lower crystallinity and higher particle sizes compared with SLN prepared with theobroma oil alone with or without P90G, and would lead to higher drug incorporation efficiency when used in formulation of actives. Mixtures of theobroma oil and goat fat would be suitable for the preparation of nanostructured lipid carriers. SLN of theobroma oil containing phospholipid could prove to be a good ocular or parenteral drug delivery system considering the low particle size, particle size stability and in vivo tolerability of the component lipids. SLN prepared with lipid admixture, which had higher increase in d 90% on storage are suitable for preparation of topical and transdermal products.

Understanding the thermal, mechanical and electrical properties of epoxy nanocomposites

In the present work, the electrical, mechanical and thermal properties of epoxy nanocomposite materials were studied. The electrical insulation characteristics were analyzed through short time breakdown voltage test, accelerated electrical ageing test, and by tracking test. The breakdown voltage increases with increase in nano-clay content up to 5 wt%, under AC and DC voltages. The volume resistivity, permittivity and tan( δ) of the epoxy nanocomposites were measured. The Weibull studies indicate that addition of nanoclay upto 5 wt% enhances the characteristic life of epoxy nanocomposite insulation material. The tracking test results indicate that the tracking time is high with epoxy nanocomposites as compared to pure epoxy. Ageing studies were carried out to understand the surface characteristic variation through contact angle measurement. The hydrophobicity of the insulating material was analysed through contact angle measurement. The diffusion coefficients of the material with different percentage of clay in epoxy nanocomposites were calculated. The exfoliation characteristics in epoxy nanocomposites were analyzed through wide angle X-ray diffraction (WAXD) studies. The thermal behaviour of the epoxy nanocomposites was analyzed by carrying out thermo gravimetric-differential thermal analysis (TG-DTA) studies. Heat deflection temperature of the material was measured to understand the stability of the material for intermittent temperature variation. The dynamic mechanical analysis (DMA) results indicated that storage modulus of the material increases with small amount of clay in epoxy resin. The activation energy of the material was calculated from the DMA results.

Thermal stability of shear‐induced precursor structures in isotactic polypropylene by rheo‐X‐ray techniques with couette flow geometry

AbstractCombined in situ rheo‐SAXS (small‐angle X‐ray scattering) and ‐WAXD (wide‐angle X‐ray diffraction) studies using couette flow geometry were carried out to probe thermal stabilty of shear‐induced oriented precursor structure in isotactic polypropylene (iPP) at around its normal melting point (162 °C). Although SAXS results corroborated the emerging consensus about the formation of “long‐living” metastable mesomorphic precursor structures in sheared iPP melts, these are the first quantitative measures of the limiting temperature at which no oriented structures survive. At the applied shear, rate = 60 s−1 and duration ts = 5 s, the oriented iPP structures survived a temperature of 185 °C for 1 h after shear, while no stable structures were detected at and above 195 °C. Following Keller's concepts of chain orientation in flow, it is proposed that the chains with highly oriented high molecular weight fraction are primarily responsible for their stability at high temperatures. Furthermore, the effects of flow condition, specifically the shear temperature, on the distributions of oriented and unoriented crystals were determined from rheo‐WAXD results. As expected, at a constant flow intensity (i.e., rate = 30 s−1 and duration, ts = 5 s), the oriented crystal fraction decreased with the increase in temperature above 155 °C, below which the oriented fraction decreased with the decrease in temperature. As a result, a crystallinty “phase” diagram, i.e., temperature versus crystal fraction ratio, exhibited a peculiar “hourglass” shape, similar to that found in many two‐phase polymer–polymer blends. This can be explained by the competition between the oriented and unoriented crystals in the available crystallizable species. Below the shear temperature (155 °C), the unoriented crystals crystallized so rapidly that they overwhelmed the crystallization of the oriented crystals, thus depleting a major portion of the crystallizable species and increasing their contribution in the final total crystalline phase. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 3553–3570, 2006

Investigation of surface-modified solid lipid nanocontainers formulated with a heterolipid-templated homolipid

There is increasing interest in the search for improved drug delivery systems with greater versatility. Consequently, many drug delivery systems have been studied. In this study, surface-modified lipid nanocontainers were formulated with a homolipid from Capra hircus (goat fat) templated with a heterolipid (Phospholipon 90G ®) which was also the surface modifier. The solid lipid nanocontainers (SLN) were formulated by hot high pressure homogenisation using increasing concentrations of polysorbate 80 as the mobile surfactant. Prior to SLN preparation, the templated homolipid was formulated by fusion to obtain a homogeneous lipid matrix, which was characterized using differential scanning calorimetry (DSC), polarized light microscopy (PLM) and wide angle X-ray diffraction (WAXD) to obtain its thermal and crystal characteristics. Isothermal heat conduction microcalorimetry (IMC) and freeze-fracture transmission electron microscopy (FFTEM) studies were carried out on the templated homolipid and SLN containing 1.0% (w/w) of polysorbate 80 to study their in situ crystallization kinetics and morphology, respectively. The formulated SLN were also subjected to time-resolved DSC, WAXD and particle size analyses for one month. The thermal and crystal characteristics were compared with those of the bulk lipid matrix (templated homolipid). Result of the particle size analysis indicated that the particles size remained roughly within the lower nanometer range after one month. FFTEM micrograph of the lipid matrices revealed lamellar sheets for Phospholipon 90G ® and layered triglyceride structures for the homolipid and Phospholipon 90G ®-templated homolipid. FFTEM micrograph of SLN revealed anisometric structures. PLM of the templated homolipid did not show, but goat fat (homolipid) alone showed slight growth in crystals with time. WAXD and DSC studies revealed minor increase in crystallinity of the new lipid matrix after one month and DSC also detected templation of homolipid by the heterolipid noted by the disappearance of the lower melting peak of the homolipid. However, for the SLN, WAXD results showed low crystalline particles while DSC only showed a very little endothermic process after one month of storage at 20°C. The implication of this finding is that progression of the SLN to highly ordered particles over time would not occur. This will be favourable for any incorporated drug as drug expulsion, due to increase in crystallinity, will not occur. Result obtained from analysis of the isothermal crystallization exotherms indicated that the templated homolipid and SLN1 containing 1.0% polysorbate 80 possess similar nucleation mechanisms and growth dimensions different from the pure homolipid. The SLN containing 0.5 and 1.0% polysorbate 80 possessed good properties and could prove to be good delivery systems for drugs for parenteral or ocular administration. The result of this study also shows a method of improving natural lipids for use in particulate drug delivery systems.

Morphological and X‐ray diffraction studies of crystalline hydroxyapatite‐reinforced polycaprolactone

Morphological and mechanical properties of hydroxyapatite (HAP)-reinforced polycaprolactone (PCL) were studied. The objective was to examine how morphological features alter the bulk mechanical properties in our laboratory-synthesized HAP-reinforced PCL. HAP crystals were synthesized by hydrolysis of mixtures of calcium and phosphate salts in the laboratory with wet chemical methods. The properties of the commercially available hydroxyapatite (HAP(1)) are compared with that of laboratory-synthesized hydroxyapatite (HAP(2)). The HAP crystals and composition were characterized using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and Fourier transform infrared spectrometry (FTIR). The HAP(1) and HAP(2) crystals were dispersed into polymers to examine the mechanical behavior of bioactive composites, and the interfacial interactions between the polymer and HAP crystals are addressed. The FTIR results confirmed that the two forms of HAP crystals are consistent in terms of the functional chemical groups. The wide angle X-ray diffraction study was performed to determine the crystallinity of the bioactive composites. It was observed that the crystallinty of HAP-filled PCL steadily increased as the filler concentration increased. Generally, HAP(2) has a particle size considerably smaller than HAP(1) and the composite derived had higher modulus than conventional HAP-filled polymers. This increase in modulus is attributed to better interfacial interaction. Bioresorbability tests performed on HAP particles found that the synthesized HAP had higher resorption rates. It is clear that the mechanical properties are influenced by the particle size and therefore by the processing method used.

Further characterization of theobroma oil–beeswax admixtures as lipid matrices for improved drug delivery systems

There is an increasing interest in lipid based drug delivery systems due to factors such as better characterization of lipidic excipients and formulation versatility and the choice of different drug delivery systems. It is important to know the thermal characteristics, crystal habit, texture, and appearance of a new lipid matrix when determining its suitability for use in certain pharmaceutical application. It is line with this that this research was embarked upon to characterize mixtures of beeswax and theobroma oil with a view to applying their admixtures in drug delivery systems such as solid lipid nanoparticles and nanostructured lipid carriers. Admixtures of theobroma oil and beeswax were prepared to contain 25% w/w, 50% w/w, and 75% w/w of theobroma oil. The admixtures were analyzed by differential scanning calorimetry (DSC), small angle X-ray diffraction (SAXD), wide angle X-ray diffraction (WAXD), and isothermal heat conduction microcalorimetry (IMC). The melting behavior and microstructures of the lipid admixtures were monitored by polarized light microscopy (PLM). Transmission electron microscopy (TEM) was used to study the internal structures of the lipid bases. DSC traces indicated that the higher melting peaks were roughly constant for the different admixtures, but lower melting peaks significantly increased ( p < 0.05). The admixture containing 25% w/w of theobroma oil possessed highest crystallinity index of 95.6%. WAXD studies indicated different reflections for the different lipid matrices. However, new interferences were detected for all the lipid matrix admixtures between 2 θ = 22.0° and 2 θ = 25.0°. The lipid matrices containing 50% w/w and 25% w/w of theobroma oil showed absence of the weak reflection characteristic of pure theobroma oil, while there was disappearance of the strong intensity reflection of beeswax in all the lipid matrix admixtures at all stages of the study. PLM micrographs revealed differences with regard to the thermal and optical behaviors depending on the composition of the matrix. The lipid matrix consisting of 75% w/w of theobroma oil showed a spherulite texture after 4 weeks of isothermal storage. Crystallization exotherms of lipid matrices containing 50% w/w and 25% w/w of theobroma oil showed change in modification after 30 min with the latter having a greater time-dependent crystallization. Generally, low non-integral Avrami exponents and growth rate constants were obtained for all the lipid matrices, with the admixture containing 25% w/w theobroma oil having the lowest Avrami exponent and growth rate constant. Based on the results obtained, admixtures containing 50% w/w and 75% w/w of theobroma oil could be applied in the formulation of solid lipid nanoparticles and nanostructured lipid carriers as these lipid matrices possessed crystal characteristics that favour such drug delivery systems.

γ-Radiation Induced Changes in the Physical and Chemical Properties of Lignocellulose

gamma-radiation induced effects on the physical and chemical properties of natural lignocellulose (jute) polymer were investigated. Samples were irradiated to required total doses at a particular dose rate. The changes in the parameters such as the tensile strength, elongation at break, and work done at rupture for the lignocellulose samples on irradiation with the gamma-rays from a cobalt-60 source were measured. The mechanical properties were found to have nonlinear relations with the radiation doses. The chemical stability of irradiated fibers was found to degrade progressively with the increase of radiation dose. Additionally, other chemical changes of the samples due to exposure to high-energy radiation were also investigated using fluorescence and infrared spectroscopic analysis. Differential scanning calorimetry and thermogravimetric studies showed a significant reduction in thermal stability. The wide-angle X-ray diffraction study showed that structural changes of cellulose appeared due to the radiation-induced chemical reaction of lignocellulose.

Investigation of Spectral Properties, Thermal Stability, and Morphology in Polyaniline Doped with Chlorocarboxylic Acids

The morphology of polyaniline (PANI), granular or tubular, depends on the acidity conditions during the reaction rather than on the chemical nature of the acid. In reference to acetic acid in which media nanotubes had been observed, dichloroacetic acid (DCA) and trichloroacetic acid (TCA) were used to synthesize polyaniline by the oxidative polymerization technique. Characterization by Fourier-transform infrared (FTIR), UV-visible, and electron paramagnetic (EPR) spectroscopy techniques indicated that the polymers are in the protonated emeraldine form and suggest that the protonation of PANI in media containing such acids was achieved with the help of sulfuric acid produced during the reaction from ammonium peroxydisulfate. The conductivity of polyaniline prepared in DCA was 0.04 S cm−1 and 0.5 S cm−1 in TCA. The thermal stability of polyaniline salts was tested by thermogravimetric analysis and a three-step decomposition pattern was observed. Wide-angle X-ray diffraction (WAXD) study showed enhanced crystallinity in polyaniline prepared in TCA. The morphology is discussed in relation to the formation of polyaniline nanotubes reported in the literature.

Propylene-ethylene Copolymer Filled Nanocomposites: Influence of Zn-ion Coating upon Nano-SiO2 on Structural, Thermal, and Dynamic Mechanical Properties

Propylene-ethylene copolymer (EP) nanocomposites based on nano-SiO2 with and without Zn-ion coating were developed by conventional melt blending technique in a sigma internal mixer. Two composites each with 2.5 wt% filler were developed. The first composite was made by melt blending EP with nano-SiO2 in a co-rotating sigma internal mixer. The second one was obtained by melt blending the same EP, but with Zn-ion coated nano-SiO2. In case of Zn-ion coated nano-SiO2 filled EP, wide-angle X-ray diffraction study (WAXD) showed a decrease in interplanar distance and lamellar polymer crystal size when compared to nano-SiO2 filled EP. Differential scanning calorimetric (DSC) results showed Zn-ion coated nano-SiO2 acting more as an effective nucleating agent than that of the nano-SiO2. Thermogravimetric analysis (TGA) results showed improved thermal stability for EP in the presence of both the nanofillers. However, the thermal stability of Zn-ion coated nano-SiO2 filled EP is higher than that of the nano-SiO2 filled EP. Scanning electron microscope (SEM) study reveals that the Zn-ion coated nano-SiO2 homogeneously distributed in the matrix, whereas nano-SiO2 forms chainlike aggregates in the matrix phase. Dynamic mechanical analysis (DMA) study indicates that both the fillers increase storage modulus, E′; this increment is more prominent in nano-SiO2 filled EP due to the formation of chain-type aggregates of nano-SiO2.

Preparation and Characteristics of a Novel Silicone Rubber Nanocomposite Based on Organophilic Montmorillonite

Novel room-temperature-vulcanized silicone rubber (RTV-SR)/organic montmorillonite (OMMT) nanocomposites were prepared by a solution intercalation process. Di(2-oxyethyl)-12 alkane- 3 methyl-amine chloride was used as the intercalation agent to treat Na°-montmorillonite and form a new kind of OMMT. Four types of RTV-SR/OMMT composites were synthesized with different amounts of OMMT. Properties such as tensile strength, differential scanning calorimeter (DSC) and thermogravimetric analysis (TGA) were measured and compared. A combination of Fourier transform infrared spectroscopy (FT-IR), wide angle X-ray diffraction (WAXD) and transmission electronic microscopy (TEM) studies showed that RTV-SR/OMMT composites were on the nanometer scale and the presence of OMMT interfered with the segmented structure of RTV-SR, due to the reaction between the monomer and the intercalation agent. Results showed that the RTV-SR system with 10 phr OMMT has the best physical and mechanical properties due to the exfoliation of OMMT and the resultant nano-effect on the system

High pressure crystallization of random propylene–ethylene copolymers: α–γ Phase diagram

Two random propylene copolymers with low ethylene content synthesized by Ziegler–Natta catalysts were used is this study to investigate the formation of γ-crystal phase during isothermal crystallization at high pressures. At atmospheric pressure these copolymers crystallize in a mixture of α- and γ-crystals. The content of the γ-phase in the copolymer crystals increased with increasing defect content, crystallization temperature and pressure. Wide-angle X-ray diffraction studies showed that crystallization of these copolymers at pressures above 88MPa and temperature above 142°C leads to formation of pure γ-phase. The equilibrium melting temperature of the γ-phase has been determined as a function of defect content and crystallization pressure. Temperature–pressure-composition α–γ phase diagram of isotactic polypropylene was constructed based on the Gibbs free energy approach. This diagram enabled the extrapolation of the equilibrium melting temperatures of both phases for defect free isotactic polypropylene. They were found to be 186.9°C for the α-phase and 189.9°C for the γ-phase.

Poly(ɛ-caprolactone)- block-polystyrene metallopolymers via sequential ROP and ATRP condition with in situ generated ruthenium catalyst

Poly(ɛ-caprolactone)- b-polystyrene with vacant bipyridine coordinating sites and metallated AB type diblock with well-defined metal loci in the polymer chain were synthesized and characterized. Solution atom transfer radical polymerization (ATRP) of styrene where a poly(ɛ-caprolactone) macromonomer acted as initiator and derivative complex of [Ru( p-cymene)Cl 2] 2 as catalyst is reported. ATRP reaction conditions with respect to polymer molecular weights and polydispersity indices (PDI) of the target bifunctional polymers were examined. Electronic absorption and emission spectra of the resultant functional polymers provided evidence of the ruthenium metal chromophores in the diblock copolymer. The thermal properties of all polymers were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA), and indicated that they possess a high thermal stability and are miscible in the molten state. The semicrystalline nature of the PCL macroligand and the morphology of thin films of the metal free diblocks were also elucidated by combination of atomic force microscopy (AFM), scanning electron microscopy (SEM) and wide angle X-ray diffraction (WAXD) studies.

Crystallization and melting behavior of biodegradable poly(butylene succinate‐co‐butylene carbonate)

AbstractAs a new biodegradable poly(ester carbonate), poly(butylene succinate‐co‐butylene carbonate) (PEC) is a random copolymer, which is composed of butylene succinate unit and butylene carbonate unit. The crystal structure, melting behavior, and morphology of PEC have been investigated by means of wide angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), temperature modulated DSC (TMDSC), and optical microscopy (OM) in this manuscript. The crystal structure of PEC was found to be the same as that of poly(butylene succinate) (PBSU) through WAXD study, indicating that the butylene carbonate unit did not crystallize in the copolymer. Double melting behavior or one major melting endotherm with a shoulder was found on crystallizing PEC at various temperatures based on DSC study, which was explained by the melt‐recrystallization mechanism. The TMDSC experiment gave a direct proof for the melt‐recrystallization mechanism. The spherulitic growth of PEC was studied with OM at various crystallization temperatures. The spherulitic growth rates of PEC were analyzed by the Lauritzen‐Hoffman equation. The thermal parameters of PEC were compared with those of PBSU. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 1556–1561, 2006

In situ WAXD study of structure changes during uniaxial deformation of ethylene-based semicrystalline ethylene–propylene copolymer

In situ strain-induced structure changes during uniaxial deformation of an ethylene–propylene copolymer, containing 78 wt% (or 85 mol%) of ethylene moiety, were studied by synchrotron wide-angle X-ray diffraction (WAXD). The chosen sample could crystallize into orthorhombic, pseudo hexagonal or a mixed form, depending on the annealing conditions. Crystallization at high temperatures (e.g. 50 °C) favored the formation of orthorhombic form, while crystallization at low temperatures (e.g. 20 °C) favored the formation of pseudo hexagonal form. Under deformation, the transition from orthorhombic to pseudo hexagonal form was observed at relatively low strains (e.g. 0.12). At higher strains, WAXD data indicated the occurrence of direction-dependent crystal destruction at strains <0.25 and subsequent re-crystallization with extended-chain conformation at high strains (>1.0) all of the pseudo hexagonal form. The drastic changes in the crystalline structures (orthorhombic to pseudo hexagonal) and phase transitions (crystal destruction and re-crystallization) at modest strains can be attributed to the high mobility of the amorphous ethylene–propylene segments at room temperature.

Polarized Light Scattering and Synchrotron Radiation Wide-Angle X-ray Diffraction Studies on Smectic Liquid Crystal Formation of Main-Chain Polyester

Polarized Light Scattering and Synchrotron Radiation Wide-Angle X-ray Diffraction Studies on Smectic Liquid Crystal Formation of Main-Chain Polyester

Preparation and properties of a novel elastomeric polyurethane/organic montmorillonite nanocomposite

AbstractA novel elastomeric polyurethane (EPU)/organic montmorillonite (OMMT) nanocomposite has been synthesized. 18 Alkane‐3 methyl‐amine chloride and dihydroxethyl‐12 alkane‐3 methyl‐amine chloride were used as intercalation agents to treat Na+‐montmorillonite and for forming two kinds of OMMTs. The better OMMT was chosen according to fourier transform infrared spectroscopy (FTIR) and wide angle X‐ray diffraction (WAXD). Three types of EPU/OMMT nanocomposites were synthesized by in situ polymerization of EPU, with different amounts of OMMT. A combination of FTIR, WAXD, and transmission electronic microscopy (TEM) studies showed that EPU/OMMT composites were on the nanometer scale and the segmented structure of EPU was hindered by the presence of the OMMT, due to the reaction between toluene diisocyanate (TDI) and the intercalation agents. Properties such as tensile property, differential scanning calorimeter (DSC), and thermogravimetric analysis (TGA) were researched and compared. Results showed that the EPU/3% OMMT had the best physical and mechanical properties because of its uniform dispersion of the organic silicate layers. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 99: 3578–3585, 2006

Understanding the Performance of Epoxy Nano Composites-A Physico-Chemical Approach

In the present work, the electrical and mechanical properties of epoxy nanocomposite materials were studied. The hydrophobicity of the insulating material was analyzed through contact angle measurement. The diffusion coefficients of the material with different percentage of clay in epoxy nanocomposites were calculated. The exfoliation characteristics in epoxy nanocomposites were analyzed through Wide Angle X-ray Diffraction (WAXD) studies. The thermal behaviour of the epoxy nanocomposites was analyzed by carrying out Thermo gravimetric Differential Thermal Analysis (TG-DTA) studies. The tensile test, flexural test, impact test were carried out to understand the mechanical characteristics of the material with different percentage of clay. Heat deflection temperature of the material was measured to understand the stability of the material for intermittent temperature variation. The Dynamic Mechanical Analysis (DMA) results indicated that storage modulus of the material increases with small amount of clay in epoxy resin. The activation energy of the material was calculated from the DMA results. The short time insulation breakdown studies of nanocomposite material indicate that the breakdown voltage increases with small percentage of nano clay in epoxy resin. Also, it was shown that the positive DC breakdown voltage is higher than the negative DC voltage, irrespective of the percentage of nano clay in epoxy resin.

A study on melt processing and thermal properties of fluoroelastomer nanocomposites

Fluoroelastomer (FKM)/layered clay nanocomposites were prepared by melt mixing and their clay dispersion, morphological, rheological and thermal properties were characterized. Wide angle X-ray diffraction (XRD) and transmission electron microscopic (TEM) studies revealed the presence of intercalated/exfoliated clay layers with good dispersion at lower levels of filler loading. Both the pure FKM and FKM/clay nanocomposites showed shear thinning behavior and temperature dependency on shear stress. The apparent shear viscosity of the FKM/organo clay (O-MMT) nanocomposites was lower than that of the pure polymer at all shear rates and temperatures. The activation energy of the melt flow process decreased with increasing shear rate for all of the systems studied. However, the FKM/O-MMT hybrids exhibited higher activation energy compared to other filled systems. The nanocomposites exhibited reduced equilibrium die-swell with a smooth extrudate appearance. A comparison of the flow properties of the nanocomposites with the conventional composites revealed that the nanocomposites exhibited improved processability. The addition of layered clay increased the glass transition temperature of FKM. Although, the addition of untreated clay improved the thermal stability of FKM, organo clay reduced degradation initiation temperature due to the decomposition of organic component of modified clay.

Nucleation Mechanism of α-Cyclodextrin-Enhanced Crystallization of Some Semicrystalline Aliphatic Polymers

The nucleation effects of α-cyclodextrin (α-CD) and its inclusion complexes (ICs) with poly(ε-caprolactone) (PCL), poly(ethylene glycol) (PEG), and poly(butylene succinate) (PBS) on the crystallization of PCL, PEG, and PBS were investigated by differential scanning calorimetry (DSC) and polarized optical microscopy. The formations of ICs of α-CD with PCL, PEG, and PBS were characterized by DSC, Fourier transform infrared spectroscopy, wide-angle X-ray diffraction (WAXD), and solution 1H NMR. The WAXD studies showed that all of the α-CD-ICs adopt a channel structure. Both DSC and 1H NMR results suggested that the polymer chains were partially complexed by α-CDs. Thus, the polymer chains in the bulk phase can contact not only the exterior of the α-CD macrocycle but also the end parts of polymer chains protruding from the α-CD cavity and/or the free chain segments uncovered by α-CD, when the α-CD-IC as a nucleating agent is added into the polymers. Therefore, the difference in the interfacial interaction between bulk polymers and the nucleating agents should be responsible for the difference in the nucleation effects. α-CD-PCL-IC particles have little nuclear formation effect on the crystallization of bulk PBS; however, they can greatly accelerate the nucleation and crystallization of the bulk PCL. The same results are also observed during the crystallization of PBS and PEG; that is, PBS-IC and PEG-IC particles can greatly accelerate the nucleation and crystallization of PBS and PEG, respectively. It seemed that IC of a given polymer could greatly enhance the nucleation and crystallization of the polymer itself. This result may be attributable to the limited mobility of the uncovered part of the polymer segments constrained by its interior part resided in the α-CD cavity, leading to the nucleation of polymer crystallization. The effect of fine talc powder was also examined. The experimental results suggested that the nucleation ability of α-CD on the crystallization of the polymer is comparable to that of the talc.