Flame retardancy and thermal stability of polyhedral oligomeric silsesquioxane nanocomposites

The flame retardancy and thermal stability of polyhedral oligomeric silsesquioxane (POSS) nanocomposites are reviewed. Results are summarized and compared on the basis of structure–property relationships. Because of the variability of groups attached on POSS, they exhibit different performance in polymer nanocomposites: metal‐containing POSS show good catalytic charring ability; vinyl‐containing and phenyl‐containing POSS promote the strength of char. Improvements in the cone calorimeter (such as reduced peak heat release rate) are advantages of POSS as preceramics for fire retardancy compared with traditional flame retardants, and it will pave the way to the design of inorganic–organic hybrid polymer nanocomposites with enhanced flame retardancy and thermal stability. Copyright © 2011 John Wiley & Sons, Ltd.     

Layered clay/epoxy nanocomposites: Thermomechanical,flame retardancy,and optical properties

In this study, layered clay/polymer nanocomposites were developed based on epoxy resins and montmorillonite as the nanoplatelet reinforcement. Clay particles were treated with hexadecyltrimethylammonium chloride (HTCA) through an ion exchange reaction. In this way, Na⁺ interlayer cations of the clay is exchanged with onium cation of the surfactant that turns the hydrophilic clays (MMT) to organophilic (OMMT) characteristics. Thermal analysis results revealed that the glass transition temperature (T_g) and the dynamic mechanical properties including the storage and loss modulus of the neat epoxy resin increases by the incorporation of clay particles. It was also found that flame resistance of the polymer is improved by the addition of the clay particles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Enhancement of radiation‐resistant effect in ethylene–vinyl acetate copolymers by the formation of ethylene–vinyl acetate copolymers/clay nanocomposites

Ethylene–vinyl acetate (EVA) copolymers/clay nanocomposites, prepared by using nonreactive organophilic clay and reactive organophilic clay, were characterized by X‐ray diffraction and by high‐resolution transmission electron microscopy. The influence of gamma irradiation on the structure and properties of the pure EVA and EVA/clay nanocomposites was systematically investigated. In the presence of gamma radiation, the clay can effectively restrain the increase of the storage modulus of EVA/clay nanocomposites, which was supported by dynamical mechanical analysis. Gamma irradiation had almost no effect on the thermal properties of EVA/clay nanocomposites by using nonreactive organophilic clay, but it obviously improved the thermal stability of EVA/clay nanocomposites by using reactive organophilic clay. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 2532–2538, 2005     

Flame retardancy and char microstructure of nylon‐6/layered silicate nanocomposites

We investigated the effect of organically modified clay alone and in combination with zinc borate on the thermal/flammability behavior of nylon‐6 nanocomposites. Differential thermogravimetric analysis indicated that the peak decomposition temperature was not affected by the addition of clay, but the rate of weight loss decreased with increase in clay concentration. Nanocomposite films of approximately 0.5 mm thickness with 2.5 and 5 wt % clay burned for almost the same duration as neat nylon‐6 but with reduced dripping in horizontal flame test. The 10 wt % clay nanocomposite sample burned without any dripping and the flame spread rate was reduced by 25–30%. Zinc borate/clay containing nanocomposite developed into a very good intumescent system in cone calorimeter test, swelling about 10–13 mm height prior to ignition forming a cellular char structure. This was found to be an effective composition in reducing the heat release and mass loss rate of nylon‐6 by about 65% and at par with 10 wt % clay nanocomposite. Flame retardant behavior could be attributed to distinct char morphologies observed through scanning electron microscopy. Fourier transform infrared spectroscopy of the 10 wt % clay nanocomposite char showed the presence of amides, indicating possible residual polymer within the shielded char. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 1540–1550, 2007     

Rubber/LDH nanocomposites by solution blending

The rubber nanocomposites containing ethylene vinyl acetate (EVA) having 60 wt % of vinyl acetate content and organomodified layered double hydroxide (DS‐LDH) as nanofiller have been prepared by solution intercalation method and characterized. The XRD and TEM analysis demonstrate the formation of completely exfoliated EVA/DS‐LDH nanocomposites for 1 wt % filler loading followed by partially exfoliated structure for 5–8 wt % of DS‐LDH content. EVA/DS‐LDH nanocomposites show improved mechanical properties such as tensile strength (TS) and elongation at break (EB) in comparison with neat EVA. The maximum value of TS (5.1 MPa) is noted for 3 wt % of DS‐LDH content with respect to TS value of pure EVA (2.6 MPa). The data from thermogravimetric analysis show the improvement in thermal stability of the nanocomposites by ≈15°C with respect to neat EVA. Limiting oxygen index measurements show that the nanocomposites act as good flame retardant materials. Swelling property analysis shows improved solvent resistance behavior of the nanocomposites (1, 3, and 5 wt % DS‐LDH content) compared with neat EVA‐60. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Flame retardancy and mechanical properties of EVA nanocomposites based on magnesium hydroxide nanoparticles/microcapsulated red phosphorus

The flame retardancy and mechanical properties of ethylene vinyl acetate (EVA) polymer nanocomposite based on magnesium hydroxide (MH) nanoparticles with lamellar‐shape morphological structures and synergistic agent microcapsulated red phosphorus (MRP) have been studied by limiting oxygen index (LOI), cone calorimeter test (CCT), UL‐94 test, tensile strength (TS), and elongation at break (EB). Results showed that LOI values of lamellar‐like nanosized MH (50 × 350 nm²) samples were 1–7 vol. % higher than those of the common micrometer grade MH (1–2 μm) in all additive levels. When 1–3 phr MRP substituted for nanosized MH filler, LOI value increased greatly from original 37 to 55, and met the V‐0 rating in the UL‐94 test. The values of TS for MH nanoparticles composites increased from 10.4 to 17.0 MPa as additive loading levels increased from 80 to 150 phr, respectively, while the corresponding values for common micrometer MH composites decreased steadily from 9.7 to 7.1 MPa. Thermogravimetric analysis (TGA) and dynamic Fourier‐transform infrared spectroscopy (FTIR) results revealed two‐step flame‐retardant mechanism. First, MH particles decompose endothermically with the release of 30.1% hydration water in the 320–370°C temperature range. Second, MRP promote the formation of compact charred layers slowly in the condensed phase in the 450–550°C temperature range. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

粘土橡胶纳米复合材料研究进展

简要概述了粘土的有机改性机理、橡胶/粘土纳米复合材料的制备方法、结构与表征和橡胶/粘土纳米复合材料的研究进展.     

无机阻燃剂的应用进展

介绍了无机类阻燃剂的种类及其阻燃机理、特点,分析了各自存在的问题,以及无机阻燃剂在国内外的应用研究现状,对今后无机阻燃剂的研究与应用方向提出了建议。涉及的阻燃剂包括氢氧化铝、氢氧化镁、无机磷系、锑系、硼酸盐、氮系、无机硅系和钼类化合物。     

Effect of organic peroxides on the morphology and properties of EVA/Cloisite 15A nanocomposites

This article describes the effect of the presence of organic peroxides on the morphology and properties of ethylene vinyl acetate copolymer (EVA)/Cloisite 15A nanocomposites. The results show that the presence of dicumyl peroxide (DCP) or dibenzoyl peroxide (DBP) during the preparation of EVA/Cloisite 15A clay nanocomposites gives rise to intercalated, exfoliated, or mixed morphologies, which are not normally observed for samples prepared in the absence of organic peroxides. In the absence of clay, both DCP and DBP initiate de‐acetylation and chain scission of EVA chains, but the influence of DBP is more pronounced. The presence of clay inhibits the initiation of EVA degradation by DCP free radicals, which can be observed in the higher tensile strength values for DCP treated samples, as well as in the de‐acetylation step in the TGA curves. DBP has a more significant influence on the polymer degradation, and this gives rise to reduced thermal stability and mechanical properties. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Silicate layer dispersion in copolymer/clay nanocomposites

Factors 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     

Morphology and mechanical properties of polypropylene/organoclay nanocomposites

Polypropylene (PP) nanocomposites were prepared by melt intercalation in an intermeshing corotating twin‐screw extruder. The effect of molecular weight of PP‐MA (maleic anhydride‐ modified polypropylene) on clay dispersion and mechanical properties of nanocomposites was investigated. After injection molding, the tensile properties and impact strength were measured. The best overall mechanical properties were found for composites containing PP‐MA having the highest molecular weight. The basal spacing of clay in the composites was measured by X‐ray diffraction (XRD). Nanoscale morphology of the samples was observed by transmission electron microscopy (TEM). The crystallization kinetics was measured by differential scanning calorimetry (DSC) and optical microscopy at a fixed crystallization temperature. Increasing the clay content in PP‐ MA330k/clay, a well‐dispersed two‐component system, caused the impact strength to decrease while the crystallization kinetics and the spherulite size remained almost the same. On the other hand, PP/PP‐MA330k/clay, an intercalated three‐component system containing some dispersed clay as well as the clay tactoids, showed a much smaller size of spherulites and a slight increase in impact strength with increasing the clay content. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1562–1570, 2002     

尼龙6/粘土纳米复合材料的性能

对尼龙6/粘土纳米复合材料(PA6CN)的力学性能、结晶性能、流变性能、热稳定性、阻隔性能、阻燃性能、各向异性和可纺性进行了综述。加入粘土后,基体尼龙6的晶型变为γ型,改善了尼龙6的力学性能,提高了热变形温度,降低了吸水率,改善了气体阻隔性和材料的阻燃性,拓宽了复合材料的应用范围。     

Mechanical properties and structures of dicyanate–clay nanocomposites

Dicyanate–clay nanocomposites comprising a dicyanate resin and a type of organically modified clay were prepared and characterized, and their thermomechanical properties were investigated. The organically modified clay had silicate layers of nanometer size intercalated with an organic modifier, which improved the compatibility between the clay and organic materials, such as dicyanate resins. Dynamic mechanical analysis was performed to investigate the thermomechanical properties of the dicyanate–clay nanocomposites containing various amounts of the clay. The storage modulus of the nanocomposites below their glass‐transition temperatures slightly increased with increasing clay content. The glass‐transition temperature of the dicyanate–clay nanocomposites increased with increasing clay content. The nanostructures of the dicyanate–clay nanocomposites were characterized by transmission electron microscopy and X‐ray diffraction analysis. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 2629–2633, 2003     

Fracture behavior of thermoplastic polyolefin/clay nanocomposites

A thermoplastic polyolefin (TPO) containing 70 wt % styrene–ethylene–butadiene‐styrene‐g‐maleic anhydride and 30 wt % polypropylene and its nanocomposites reinforced with 0.3–1.5 wt % organoclay were prepared by melt mixing followed by injection molding. The mechanical and fracture behaviors of the TPO/clay nanocomposites were investigated. The essential work of fracture (EWF) approach was used to evaluate the tensile fracture behavior of the nanocomposites toughened with elastomer. Tensile tests showed that the stiffness and tensile strength of TPO was enhanced by the addition of low loading levels of organically modified montmorillonite. EWF measurements revealed that the fracture toughness of the TPO/clay nanocomposites increased with increasing clay content. The organoclay toughened the TPO matrix of the nanocomposites effectively. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crystallization behavior of poly(L‐lactic acid)/montmorillonite nanocomposites

In this study, we modified montmorillonite (MMT) with dilauryl dimethyl ammonium bromide (DDAB) and then exfoliated the structures in a poly(L ‐lactic acid) (PLLA) matrix. We used polar optical microscopy and X‐ray diffraction (XRD) to examine the morphologies of the resulting composites, differential scanning calorimetry to study the melting and crystallization behavior, and Fourier transform infrared (FTIR) and Raman spectroscopy to measure the influence of the intermolecular interactions between PLLA and MMT on the isothermal crystallization temperature. We found that the DDAB‐modified MMT was distributed uniformly in the PLLA matrix. At temperatures ranging from 130 to 140°C, the crystalline morphology resembled smaller Maltese cross‐patterned crystallites; at temperatures from 150 to 170°C, however, the number of crystallites decreased, their sizes increased, and they possessed ringed spherulite structures. In the XRD spectra, the intensity of the diffraction peaks of the 200/110 and 203 facets of the PLLA/MMT nanocomposites decreased as the crystallization temperature increased. In the FTIR spectra, the absorption peak of the C?O groups split into two signals at 1748 and 1755 cm^?1 when the isothermal crystallization temperature was higher than 140°C. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Synthesis and properties of polystyrene–clay nanocomposites via in situ intercalative polymerization

Organophilic montmorillonite (MMT) was prepared by ion exchange between Na⁺ ions in the clay and twin benzyldimethyloctadecylammonium bromine cations in an aqueous medium. The organophilic MMT particles were easily dispersed and swollen in styrene monomer. Polystyrene–MMT nanocomposites were prepared by the free‐radical polymerization of styrene containing dispersed clay. The intercalation spacing in the nanocomposites and the degree of dispersion of these composites were investigated with X‐ray diffraction and transmission electron microscopy, respectively. The nanocomposites had higher weight‐average molecular weights, lower glass‐transition temperatures, and better thermal stability (the decomposition temperature was improved by ca. 70°C) than the virgin polystyrene. The rheological behavior of the polystyrene–MMT nanocomposites was also studied. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 201–207, 2005     

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     

Microwave‐assisted preparation of polylactide/organomontmorillonite nanocomposites via in situ polymerization

Microwave technology was introduced to assist the synthesis of polylactide (PLA)/organomontmorillonite (OMMT) nanocomposites in bulk by the in situ ring‐opening polymerization of D,L ‐lactide. Factors that influenced the polymerizing effects, such as the microwave power, irradiation time, and dosages of the catalyst and OMMT, were studied in terms of tensile strength. The polymerization time was decreased dramatically to 10 min under 90 W of microwave irradiation, and the mechanical and thermal properties of the PLA/OMMT nanocomposites were significantly improved. The composite with the highest mechanical properties was obtained when the dosages of the OMMT and the catalyst were 1.0 and 0.6 wt % of the lactide, respectively. The initial decomposition temperature of the PLA/OMMT(1.0 wt % OMMT) nanocomposite was heightened 11.5°C compared with that of pure PLA. The results of scanning electron microscopy confirmed an improvement in the toughness with the addition of OMMT. The transmission electron microscopy and X‐ray diffraction results indicate that an exfoliated and intercalated nanocomposite was successfully prepared. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Compounding of nanocomposites by thermokinetic mixing

Nanocomposites have been prepared by melt mixing poly(propylene) (PP) and different levels of a premixed montmorillonite‐organoclay masterbatch (PP/clay concentrate). Melt mixing was achieved using a Gelimat, a high‐speed thermokinetic mixer. The Gelimat system is designed to handle difficult compounding and dispersion applications and can achieve mixing, heating, and compounding of products within a minute. Therefore, the thermal history of the compounded polymer is short, which limits degradation. The structure and properties of the nanocomposites prepared with a Gelimat were compared to ones prepared with a twin‐screw extruder. The structure and properties of PP/clay nanocomposites were compared by TEM, X‐ray diffraction, mechanical testing, and rheological analysis. Results indicate that a better dispersion of the clay can be achieved by thermokinetic mixing when compared to extrusion, resulting in better mechanical properties. Calculations, based on simplifying assumptions, showed that the shear rates generated in a Gelimat are at least one order higher than those generally generated in an extruder. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1557–1563, 2005     

New method for the synthesis of clay/epoxy nanocomposites

A new liquid–liquid method for the synthesis of epoxy nanocomposites was developed. This new method improved the dispersion and exfoliation of the organoclay in the polymer matrix, thus improving the end‐use properties. The microstructure and physical properties of the clay/epoxy nanocomposite synthesized by the new method were studied. Rheological tests of the uncured epoxy–organoclay system demonstrated that this method resulted in a great increase in viscosity, much more than the most commonly used direct‐mixing method. The Krieger–Dougherty model successfully described the dispersion of the clay layers in the uncured epoxy. In the 5 wt % organoclay nanocomposite, compressive tests on the cured samples showed that there was a 45% increase in the maximum strength, a 10% increase in the yield strength, and a 26% increase in the modulus over the pure epoxy–amine cured system. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4286–4296, 2006