Melt‐compounded natural rubber nanocomposites with pristine and organophilic layered silicates of natural and synthetic origin

Composites based on natural rubber (NR) and containing organophilic and pristine layered silicates of natural and synthetic origin were produced by melt compounding and sulfur curing. The curing, thermomechanical, and mechanical properties of the mixes, which contained 10 phr (parts per hundred parts of rubber) silicates, were determined. The dispersion of the silicates was studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). Organophilic clays accelerated the sulfur curing of NR, which was believed to occur because of a complexation reaction in which the amine groups of the clay intercalants participated. The property improvements caused by the fillers were ranked as follows: organophilic clays > pristine synthetic layered silicate (sodium fluorohectorite) > pristine natural clay (purified sodium bentonite) > precipitated nonlayered silica (used as a reference). This was attributed to partial intercalation of the organophilic clay by NR on the basis of XRD and TEM results and to the high aspect ratio of the fluorohectorite. Apart from intercalation, severe confinement (i.e., the collapse of the interlayer distance) of the organoclays was observed. This peculiar feature was traced to the formation of a zinc coordination complex, which extracted the amine intercalant of the organoclays, thus causing the collapse of the layers. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 813–819, 2004     

Rubber–clay nanocomposite by solution blending

Ethylene vinyl acetate rubber (45% vinyl acetate content, EVA‐45) and organomodified clay (12Me‐MMT) composites were prepared by solution blending of the rubber and the clay. A combination of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy studies showed that the composites obtained are on the nanometer scale. The measurements of the dynamic mechanical properties for different compositions over a temperature range (?100 to +100°C) showed that the storage moduli of these rubber–clay nanocomposites are higher above the glass to rubber transition temperature compared to the neat rubber. The tensile strength of the nanocomposites is about 1.6 times higher than that of the EVA‐45. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2216–2220, 2003     

Crystallization behavior and mechanical properties of polypropylene copolymer by in situ copolymerization with a nucleating agent and/or nano‐calcium carbonate

The crystallization behavior of polypropylene (PP) copolymer obtained by in situ reactor copolymerization with or without a nucleating agent and/or nano‐CaCO₃ particles was investigated both by thermal analysis and by polarized light microscopy. The Avrami model is successfully used to describe the crystallization kinetics of the studied copolymer. The results of the investigation show that a dramatic decrease of the half‐time of crystallization t_1/2, as well as a significant increase of the overall crystallization rate, are observed in the presence of the nucleating agent. These effects are further promoted in the presence of the nano‐CaCO₃ particles. The incorporation of the nucleating agent and nano‐CaCO₃ particles into PP copolymer remarkably improved the mechanical properties and heat distortion temperature. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 431–438, 2004     

Characterization of poly(vinyl pyrrolidone‐co‐isobutylstyryl polyhedral oligomeric silsesquioxane) nanocomposites

Poly(vinyl pyrrolidone‐co‐isobutyl styryl polyhedral oligomeric silsesquioxane)s (PVP–POSS) were synthesized by one‐step polymerization and characterized using FTIR, high‐resolution ¹H‐NMR, solid‐state ¹³C‐NMR, ²⁹Si‐NMR, GPC, and DSC. The POSS content can be controlled by varying the POSS feed ratio. The T_g of the PVP–POSS hybrid is influenced by three main factors: (1) a diluent role of the POSS in reducing the self‐association of the PVP; (2) a strong interaction between the POSS siloxane and the PVP carbonyl, and (3) physical aggregation of nanosized POSS. At a relatively low POSS content, the role as diluent dominates, resulting in a decrease in T_g. At a relatively high POSS content, the last two factors dominate and result in T_g increase of the PVP–POSS hybrid. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2208–2215, 2004     

Preparation and properties of (BATB–ODPA) polyimide–clay nanocomposite materials

A series of polymer–clay nanocomposite (PCN) materials consisting of 1,4‐bis(4‐aminophenoxy)‐2‐tert‐butylbenzene–4,4′‐oxydiphthalic anhydride (BATB–ODPA) polyimide (PI) and layered montmorillonite (MMT) clay were successfully prepared by an in situ polymerization reaction through thermal imidization up to 300°C. The synthesized PCN materials were subsequently characterized by Fourier‐Transform infrared (FTIR) spectroscopy, wide‐angle powder X‐ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of material composition on thermal stability, mechanical strength, molecular permeability and optical clarity of bulk PI and PCN materials in the form of membranes were studied by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), dynamic mechanical analysis (DMA), molecular permeability analysis (GPA) and ultraviolet‐visible (UV/VIS) transmission spectra, respectively. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 1072–1079, 2004     

Morphology,crystallinity, and electrochemical properties of in situ formed poly(ethylene oxide)/TiO2 nanocomposite polymer electrolytes

A method to produce nanocomposite polymer electrolytes consisting of poly(ethylene oxide) (PEO) as the polymer matrix, lithium tetrafluoroborate (LiBF₄) as the lithium salt, and TiO₂ as the inert ceramic filler is described. The ceramic filler, TiO₂, was synthesized in situ by a sol–gel process. The morphology and crystallinity of the nanocomposite polymer electrolytes were examined by scanning electron microscopy and differential scanning calorimetry, respectively. The electrochemical properties of interest to battery applications, such as ionic conductivity, Li⁺ transference number, and stability window were investigated. The room‐temperature ionic conductivity of these polymer electrolytes was an order of magnitude higher than that of the TiO₂ free sample. A high Li⁺ transference number of 0.51 was recorded, and the nanocomposite electrolyte was found to be electrochemically stable up to 4.5 V versus Li⁺/Li. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2815–2822, 2003     

Poly(trimethylene terephthalate) nanocomposite fibers comprising different organoclays: Thermomechanical properties and morphology

Poly(trimethylene terephthalate) (PTT) nano composites were synthesized by in situ polymerization at high temperature with two thermally stable organoclays: 1,2‐dimethylhexadecylimidazolium‐montmorillonite (IMD‐MMT) and dodecyltriphenyl phosphonium‐MMT (C₁₂PPh‐MMT). PTT hybrid fibers with various organoclay contents were melt‐spun at various draw ratios (DRs) to produce monofilaments. The thermomechanical properties and morphologies of the PTT hybrid fibers were characterized using differential scanning calorimetry, thermogravimetric analysis, wide‐angle X‐ray diffraction, electron microscopy, and mechanical tensile properties analysis. The nanostructure of the hybrid fibers was observed by both scanning and transmission electron microscopy, which showed that the clay layers were well dispersed into the matrix polymer, although some clusters or agglomerated particles were also detected. Unlike the hybrids containing IMD‐MMT, the clay layers of the C₁₂PPh‐MMT hybrid fiber were more dispersed into the matrix polymer. The thermal stability and tensile properties of the hybrid fibers increased with increasing clay content for DR = 1. However, as DR increased from 1 to 9 the ultimate strength and initial modulus of the hybrid fibers with IMD‐MMT increased slightly whereas those of C₁₂PPh‐MMT hybrid fibers decreased slightly. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4535–4545, 2006     

Crystalline morphology and isothermal crystallization kinetics of poly(ethylene terephthalate)/clay nanocomposites

A poly(ethylene terephthalate) (PET)/montmorillonite clay nanocomposite was synthesized via in situ polymerization. Microscopic studies revealed that in an isothermal crystallization process, some crystallites in the nanocomposite initially were rod‐shaped and later exhibited three‐dimensional growth. The crystallites in the nanocomposite were irregularly shaped, rather than spherulitic, being interlocked together without clear boundaries, and they were much smaller than those of neat PET. With Avrami analysis, the isothermal crystallization kinetic parameters (the Avrami exponent and constant) were obtained. The rate constants for the nanocomposite demonstrated that clay could greatly increase the crystallization rate of PET. The results for the Avrami exponent were consistent with the observation of the rodlike crystallites in the PET/clay nanocomposite during the initial stage. Wide‐angle X‐ray scattering and Fourier transform infrared studies showed that, in comparison with neat PET, the crystal lattice parameters and crystallinity of the nanocomposite did not change significantly, whereas more defects may have been present in the crystalline regions of the nanocomposite because of the presence of the clay. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1381–1388, 2004     

Preparation and electrical conductivity of polyethers/WS2 layered nanocomposites

Utilizing the solvothermal synthesis technique, lithium intercalated tungsten disulfide Li_xWS₂ with x > 1 was obtained, which was allowed to react with water to the formation of single-molecule-layer suspension of tungsten disulfide. The layered nanocomposites PEG, PEO/WS₂, intercalating poly(ethylene glycol) (PEG, MW ≈ 1 × 10³, 6 × 10³, 1 × 10⁴) and poly(ethylene oxide) (PEO, MW ≈ 3 × 10⁵) into the tungsten disulfide host galleries, were prepared using the improved exfoliation-adsorption technique. It was revealed that the intercalated polymers within the host galleries are in a double-layer arrangement with an interlayer expansion of about 9 Å. Despite high conductivity of the host material, those of the PEG, PEO/WS₂ nanocomposites were found to be high in the order of 1 × 10⁻² to 10⁻³ S cm⁻¹ at ambient temperature, resulted from the guest-host charge transfers.     

剥离型酚醛树脂/蒙脱土纳米复合材料研究

用十六烷基三甲基溴化铵(CTAB)对蒙脱土进行了有机化处理,使蒙脱土由亲水性变成亲油性。采用XRD、FTIR及TEM研究了有机蒙脱土及其在酚醛树脂中的剥离行为,制备了酚醛树脂/蒙脱土纳米复合材料并测试了其层间剪切性能和烧蚀性能。实验结果表明,经CTAB处理的蒙脱土与酚醛树脂具有良好的相容性,且CTAB的含量较多时所制得的有机蒙脱土的结构较好,根据Bragg方程计算,CTAB用量超过蒙脱土量50%时,蒙脱土的片层间距由原来的1.48 nm增加到2.33 nm;有机蒙脱土用量小于5%时生成完全剥离型酚醛树脂/蒙脱土纳米复合材料;与碳布增强酚醛树脂复合材料相比,碳布增强酚醛树脂/蒙脱土纳米复合材料的力学性能和烧蚀性能均有一定的提高和改善,层间剪切强度随蒙脱土含量的增多而增大,蒙脱土用量为15%时,层间剪切强度提高了27.1%,线烧蚀率在用量为3%时降低了48.5%,质量烧蚀率变化不明显。