Thermodynamics of interfacial interactions in composites based on nanodispersed NiO and methacrylic acid derivatives

Interfacial interactions in composites based on nanodispersed nickel oxide and methacrylate polymer matrices are studied via isothermal microcalorimetry. The thermochemical cycle is used to estimate the concentration dependences of the enthalpies of mixing of nickel oxide with, respectively, poly(methyl methacrylate), poly(butyl methacrylate), poly(acrylic acid), poly(methacrylic acid), and the butyl methacrylate copolymers containing 1 and 5 mol % methacrylic acid units. On the basis of these data, the maximum enthalpies of adhesion and the parameters of the glassy structure of the polymers are calculated. It is shown that the increase in the absolute values of the maximum enthalpy of adhesion is related to a gain in the fraction of carboxyl groups in the macromolecular chain. Strengthening of interfacial interactions for glassy polymers correlates with an increase in the fraction of metastable vacancies and in the thickness of the adhesion glassy layer.     

Thermal Degradation,Flame Retardance and Mechanical Properties of Thermoplastic Polyurethane Composites Based on AluminumHypophosphite简

Aluminum hypophosphite （AP） was used to prepare flame-retarded thermoplastic polyurethane （FR-TPU） composites, and their flame retardancy, thermal degradation and mechanical properties were investigated by limiting oxygen index （LOI）, vertical burning test （UL-94）, thermogravimetric analysis （TGA）, cone calorimeter （CC） test, Fourier transform infrared （FTIR） spectroscopy, scanning electron microscopy （SEM） and tensile test. TPU containing 30 wt% of AP could reach a V-0 rating in the UL-94 test, and its LOI value was 30.2. TGA tests revealed that AP enhanced the formation of residual chars at high temperatures, and slightly affected the thermal stability of TPU at high temperatures. The combustion tests indicated that AP affected the burning behavior of TPU. The peak of heat release rate （PHRR）, total heat release （THR） and mass loss rate （MLR） greatly reduced due to the incorporation of AP. The tensile test results showed that both the tensile strength and the elongation at break slightly decreased with the addition of AP. The digital photos and SEM micrographs vitrified that AP facilitated the formation of more compact intumescent char layer. Based on these results mentioned above, the flame-retarding mechanism of AP was discussed. Both the self-charring during the decomposing process of AP and its facilitation to the charring of TPU led to the great improvement in the flame retardancy of TPU.     

Thermal transformations of a polymeric composite consisting of poly(methyl methacrylate) and phosphorus-containing nanodispersed aluminum oxide

Thermal-oxidative properties of polymeric composites based on poly(methyl methacrylate), containing surface-modified nanosized aluminum oxide as filler, were examined. The possibility of chemical grafting to the Al₂O₃ surface of phosphorus-containing groups to decrease the combustibility of filled polymeric composites was examined by IR spectroscopy.     

Thermal behaviour of gypsum based composites

DTA/TG and X-ray investigations were carried out on different building composites in order to examine their relative hydration processes. The presence of lime, hemihydrate gypsum, ferosilicate, and some other wastes as leaner and hydrophobic additive in different proportions into composites provokes hydration reactions, leading to calcium silicate hydrate (CSH), ettringite and an intermediate phase formation with varying chemical composition of calcium, aluminum, silicon and sulfur. DTA curves indicate several transformations taking place between composites components, related to hydration of some phases. The content of ettringite component corresponds to the properties and it is used as an indicator for the possibility of industrial application. It is found out that gypsum based cementitious binders could be used as building material in the industry. The same time it is confirmed that the selected wastes could be considered as secondary raw materials.     

Thermal analysis of aged hdpe based composites

HDPE based composites were produced with 10-20-30 and 40% composite mass of wood fiber. The coupling agents were epolene and silane. The thermal behavior of composite samples was analyzed as a function of the coupling agent content, the exposure time and the wood fibers content by means of differential scanning calorimetry. Calorimetric curves of all samples of first and second heating shows a similar behavior. Some significant relation has been observed between the exposure time and the degree of crystallinity for the same percentage of fiber samples. A linear relation between the melting enthalpy average vs. content in cellulosic fibers is detected. Nevertheless, the fibers non-pretreated with coupling agent show a lower loss of crystallinity of the HDPE matrix at low wood fiber content (10%). A slight diminution of the melting peak temperature is detected as increasing the exposure time. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermal conductivity of ammonia borane complex and its composites with aluminum powder

The thermal conductivity of ammonia borane (AB) complex, in the temperature range of 300-420 K, was measured experimentally using ASTM method E 1225. At 300 K, the thermal conductivity of pure AB was found to be approximately 15 W/m-K. A composite pellet prepared by mixing 10 wt% aluminum powder with AB had a thermal conductivity that was a factor of 4 higher than that of pure AB complex. The extent of the pyrolytic weight loss for AB/Al composite and pure AB complex was 25.4% and 33.9%, respectively—indicating comparatively lower levels of volatile species evolved as impurities (e.g. monomeric aminoborane, borazine, diborane, etc.) in the product hydrogen.     

Thermal analysis of composites based on crystalline polymers and metals

Differential scanning calorimetry (DSC), thermogravimetric analysis (TG) and infrared (IR) spectroscopy have been used to examine the chemical and physical changes (crystallinity, accumulation of oxygen-containing groups, etc.) during thermal oxidation of polyethylene, polypropylene and Penton contained in coatings and metalfilled films, taking into account the thickness of the polymer layer and catalytic activity of the metal.

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Zusammenfassung DSC, thermogravimetrische Analyse (TG) und infrarot (IR) Spektroskopie wurden zur Untersuchung der während der thermischen Oxidation von in Belägen und metallgefüllten Filmen enthaltenem Polyäthylen, Polypropylen und Penton stattfindenden chemischen und physikalischen Veränderungen (Kristallinität, Anhäufung stickstoffhaltiger Gruppen usw.) eingesetzt. Hierbei wurden die Stärke der Polymerschicht und die katalytische Aktivität des Metalls in Betracht genommen.

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Structure and texture of oxyhydroxides formed by oxidation of nanodispersed aluminum with water

Aluminum oxyhydroxides were prepared by oxidation with water (55°C) of nanodispersed aluminum powders obtained by electric explosion of conductors in argon, nitrogen, carbon dioxide, and their mixtures. The structure and texture of aluminum oxyhydroxides were studied using methods of thermal desorption of nitrogen, derivatography, electron microscopy, and X-ray phase analysis.     

On the fracture of composites based on ultrahigh-molecular-weight polyethylene and fine aluminum particles

Mechanical characteristics of polymerization filled composite materials based on ultrahigh-molecular-weight polyethylene and fine aluminum particles are studied. The prepared composites preserve their ability for high plastic deformations even when the volume filler content is φ = 0.57. For the tensile drawing of the composite material with randomly distributed particles, an equation describing the dependence of breaking stress on the volume filler content is derived. For the model of the composite with regularly ordered particles, the Nielsen equation is the approximation of the equation proposed in this work for a material with randomly distributed particles.     

Influence of nanodispersed boehmite on polypropylene photooxidation

Nanocomposites containing pure or organically modified nanoboehmites of different sizes were prepared by melt compounding with polypropylene. The samples were UV light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies. The presence of pristine nanoboehmites was shown to change the rate of oxidation of polypropylene by reducing the oxidation induction period due to the presence of residual processing antioxidant. The differences of the oxidation induction periods between the nanocomposites and the pristine polymer disappear after solvent extraction of the antioxidant. The inefficiency of traditional antioxidant in retarding the photooxidation of polypropylene containing nanodispersed boehmite is proved. Antioxidant migration to the boehmite surface induced by the preferential interaction with the polar filler is proposed as an explanation. The oxidative behaviour of the organically modified boehmites was shown to depend on the type of organic substituent. p-Toluenesulfonate reduces the adsorption of antioxidants while the presence of a long-chain alkyl benzensulfonate increased the oxidation rate by generation of radical initiators.     

Thermal degradation of epoxy composites based on thermally expanded graphite and multiwalled carbon nanotubes

Thermal degradation of epoxy composites filled with various carbon materials (thermally expanded graphite, multiwalled carbon nanotubes) was studied. The dynamics of the thermal degradation of epoxy composites was evaluated by thermogravimetric analysis in the temperature range of 55–700°С (heating rate 10 deg min^–1) in an oxidizing medium. Carbon fillers were studied by scanning electron microscopy, transmission electron microscopy, and low-temperature nitrogen adsorption. The influence of the composite preparation procedure on its thermal stability was determined. The type of filler significantly influences the thermal oxidative degradation of the composites.     

Effect of nanodispersed silica (Aerosil) on the thermal and chemical resistance of photocurable polyacrylate compounds

The effect of filling of a photopolymeric composite based on oligoacrylates (OKM-2, TGM-3) with highly dispersed silicas (Aerosils) was examined. Thermograms recorded in the range 20–900°C were analyzed in detail. A scheme of the effect of silica on the polymer structure, accounting for the filler effect on the thermal and chemical resistance of the composites, was suggested.     

Influence of nanodispersed hydrotalcite on polypropylene photooxidation

Nanocomposites containing hydrotalcite and prepared by melt compounding with polypropylene were UV-light irradiated in artificial accelerated conditions representative of solar irradiation (λ > 300 nm) at 60 °C in air. The chemical modifications resulting from photooxidation were followed by IR and UV-visible spectroscopies.The presence of hydrotalcite was shown to change the global rate of photooxidation of polypropylene by reducing the oxidation induction time and increasing the oxidation rate. The differences of the oxidation induction time disappeared after solvent extraction of the antioxidant. They were attributed to a quenching of the antioxidant activity resulting from a migration onto the filler surface induced by the preferential interaction with the polar hydrotalcite. Extracting the antioxidant did not change the oxidation rate at the permanent regime. The increase of the oxidation rate was attributed to transition metal ions, present as impurities in hydrotalcite, which can accelerate the oxidation of the polymer by various mechanisms including a catalysed decomposition of hydroperoxides.     

Thermal stability and oxygen resistance of polypropylene composites with fullerene/montmorillonite hybrid fillers

Journal of Thermal Analysis and Calorimetry - Silane coupling agent (KH-550) was used to connect fullerene (C60) with montmorillonite (MMT) to prepare C60-decorated MMT hybrid (C60-Si-MMT), and the...     

Thermal and chemorheological modelling of the processing of advanced epoxy based composites

A general model for the prediction of the rheological behavior of epoxy resins during the processing of epoxy based laminates is presented. The model is able to predict the temperature and the extent of reaction across the laminate thickness during processing. The model leads the computation of the viscosity inside the composite where experimental measurements are not possible. Thermal characterization of the reacting systems gives the input data necessary for the mathematical modelling. The numerical simulation has confirmed the necessity of a controlled temperature ramp in order to obtain a more homogeneous laminated structure. Moreover, the numerical results indicated that the process variables may present anomalous behavior which may affect the physical properties and durability of the final product.     

Electrodes based on nanodispersed titanium and tungsten oxides for a sensor of dissolved oxygen

It is suggested to use films of nanodispersed Ti and W oxides as electrodes in a sensor for dissolved oxygen. It is shown that films of this kind have stable characteristics in electroreduction of O₂ in saline.     

Thermal analysis of light-curing composites

The aim of this study has been to evaluate light-curing composites polymerization quality (monomer/polymer) with an halogen and diode lamp through the thermal analysis (TG-DTA). Samples have been polymerized at 20, 40 and 50 s through a constant and a soft start polymerization and, subsequently, analyzed by TG-DTA. The TG/DTA analysis shows that different light-curing times affect the degree of conversion of the composite, since by increasing the curing time the quantity of the monomer that has not reacted (residual) decreases. The halogen lamp, compared to the diode lamp, produces a lower mass loss at 20 s, while for 40 and 50 s the results are overlapping. The soft start polymerization (20 s) initially produces a higher mass loss, if compared to the constant intensity, but, by performing a polymerization for at least 40 s, the results can be overlapped.     

Thermal characterization of rubberwood-polymer composites

The thermal properties of five types of radiation-induced wood-polymer composites based on a tropical hardwood, rubberwood (Hevea braziliensis), was studied by oxygen index measurement, differential thermal analysis (DTA) and thermogravimetry (TG). The DTA and TG curves of composites were different from those of rubberwood, which can be attributed to the presence of the incorporated polymers. Of the five composites, the one impregnated with bis(2-chloroethyl)vinyl phosphonate reduced the initial temperature of decomposition, increased the peak temperatures of exothermic reactions, and increased the char yield. Comparison with physical blends of rubberwood and the corresponding polymer provided some evidence of chemical interaction of wood and polymer in some of the composites.     

Thermophysical properties of polypropylene/aluminum composites

This article is dedicated to the study of the thermal parameters of composite materials. A nonlinear least‐squares criterion is used on experimental transfer functions to identify the thermal conductivity and the diffusivity of aluminum‐polymer composite materials. The density measurements were achieved to deduce the specific heat and thereafter they were compared to values given by differential scanning calorimetry measurement. The thermal parameters of the composite material polypropylene/aluminum were investigated for the two different types of aluminum filler sizes. The experimental data were compared with several theoretical thermal conductivity prediction models. It was found that both the Agari and Bruggeman models provide a good estimation for thermal conductivity. The experimental values of both thermal conductivity and diffusivity have shown a better heat transport for the composite filled with large particles. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 722–732, 2004     

Preparation of high performance composites based on aluminum nitride/poly(ether-ether-ketone) and their properties

Novel high performance aluminum nitride (AlN)/poly(ether-ether-ketone) (PEEK) composites containing 0-50 wt.% fractions of AlN were prepared by solution blending method followed by hot pressing to evaluate their density, melting temperature, crystallization, thermal stability, morphological behavior and Vickers hardness by using different characterization techniques. Differential scanning calorimetry results indicated that the AlN particles are very effective nucleating agent, which results in increase in melting point, hot crystallization temperature and crystallinity of composites as the AlN content increases. Thermogravimetric analysis showed enhanced thermal stability of the composites with respect to PEEK. Density and X-ray diffraction techniques showed that crystallinity of the composites increases as the wt.% of AlN content increases in polymer matrix. Scanning electron microscopy revealed that AlN particles were well dispersed with no porosity in composites. Vickers hardness of the samples increased from 24 kg/mm² for the pure PEEK to 35 kg/mm² for AlN/PEEK composites.