Mechanical and morphological investigations of UHMWPE/Fe composites

Ultra-high molecular weight polyethylene/iron composites were investigated. The specimens were obtained by pressing in a steel die and sintering at different temperatures. By means of porosimetry, microscopy, microhardness, density, and partial volumes of the components it is shown that there are no microcavities. The microhardness does not depend upon the weight % content of the metal in the composites. It also neither depends on the pressure nor the temperature of sintering. For low metal content within the composites, microhardness Mayer equations are linear. For high metal content the dependence is nonlinear. With the increasing of the iron content tensile strength weakly decreases. However, plane-strain compression, dimension steadiness, Vicat softening temperature, and tribometric characteristics of the composites are improved. It is shown that the polymer is a well-dispersive medium. The particles of the components have a good mechanical compatibility. The polymer wets the surface of the iron; this is probably connected with the surface oxidation of the metal particles.     

Thermal shrinkage of electrospun PVP nanofibers

This paper outlines the shrinkage of electrospun polyvinylpyrrolidone (PVP) fiber mats during thermal treatment. The thermal behavior and phase changes within the fibers were investigated by DSC and TGA/DTA. Five precursors with different PVP loading in ethanol were electrospun. The mats shrinkage as function of temperature was measured in the RT–200 °C range. Shrinkage rate drastically increased above the polymer glass transition point, T_g (150–180 °C), due to increase in polymer chain mobility. Mats shrinkage at 200 °C as function of PVP concentration showed a minimum at ∼10%wt. Below 10% PVP the mats morphology is non‐uniform, consisting of beads and fibers. Above 10% PVP, only flat and uniform fibers were observed. This paper outlines the dominant mechanism governing the mats shrinkage during heating. In addition, the effect of PVP concentration on the expansion of fibers diameter was investigated and found to be consistent with the linear shrinkage observing a minimum at ∼10% PVP. The effect of applied voltage on mat shrinkage was investigated, and showed a minimum at 12 kV. Understanding the interplay between fibers morphology and thermal shrinkage allows precursor composition and system optimization needed for minimizing shrinkage negative effects on the structure and properties of electrospun fiber mats. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 248–254     

Degradation of agar films in a humid tropical climate: Thermal, mechanical, morphological and structural changes

Agar films were subjected to natural weathering exposure in a humid tropical climate for 90 days to determine their biodegradation behavior and functionality. Exposed samples were taken at 15, 30, 45, 60 and 90 days. Mechanical, thermal, structural and morphological properties were determined using tensile test, differential scanning calorimetry (DSC), attenuated reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction and environmental scanning electron microscopy (ESEM). The photodegradation process and temperature-relative humidity fluctuations promoted a decrease in agar mechanical properties in early exposure stages (30-45 days) caused by a reduction in agar molecular size and a decrease in the number of sulfate groups. These changes alter agar crystallinity, causing contraction that leads to formation of micro-fractures and embrittlement, and promote microbial attack. Accelerated weathering exposure of agar films showed that outdoor climate parameters play an important role in their degradation. These results will aid in further research to determine the potential use of agar as an environmentally friendly solution to the problem of biodegradable composites disposal.     

Thermal,mechanical, and morphological properties of phenolic resin/silica hybrid ceramers

Phenolic resin/silica hybrid ceramers were prepared through sol–gel technology. Differential scanning calorimetry and thermogravimetric analysis methods were utilized to study the thermal properties of the fabricated hybrid ceramers. The results showed that the heat resistance of the ceramers was slightly higher than that of the phenolic resin. The hydrogen bonding occurring inside the hybrid ceramers was investigated by Fourier transform infrared. The results showed that the intermolecular hydrogen bonding between the phenolic resin and the silica was stronger than the intramolecular hydrogen bonding between the phenolic resin molecules themselves. Furthermore, the hybrid ceramers were utilized to fabricate carbon‐fiber‐reinforced composites. The fabricated ceramer composites possessed better flexural strength and flexural modulus than that fabricated from neat phenolic resin. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 1699–1706, 2000     

Thermal conductive PS/graphite composites

Polystyrene (PS) was compounded with graphite that possesses high thermal conductivity and layer structures, and the PS/graphite thermal conductive nano‐composites were prepared. Thermal conductivity of PS improved remarkably in the presence of the graphite, and a much higher thermal conductivity of 1.95 W/m K can be achieved for the composite with 34 vol% of colloidal graphite. The Maxwell‐Eucken model and the Agari model were used to evaluate the thermal conductivity of the composites. For the purpose of improving the interfacial compatibility of PS/graphite, realizing the exfoliation and nano‐dispersion of graphite in the PS matrix, three intercalation methods, including rolling intercalation, solvent intercalation, and pan milling intercalation, were applied to prepare the composites, and the morphologies, thermal conductivities, and mechanical properties of the composites were investigated. It should be noted that the one prepared by pan milling intercalation not only had excellent thermal conductivity but also much higher mechanical properties, resulting from a high degree of layer exfoliation of the graphite, the formation of the chain structure agglomerates of the graphite, and the creation of more conductive paths under the strong shear stress of pan milling. Copyright © 2008 John Wiley & Sons, Ltd.     

Thermal characterization of polypropylene/vermiculite composites

Vermiculite clay (VMT) was organically modified with a quaternary organic salt and added to polypropylene (PP). The compounds were prepared by melt intercalation using a twin extruder. The morphology of the composites was investigated through wide-angle X-ray diffraction (WAXD). The WAXD results suggested that exfoliation phenomena were found for the composites with modified clay. The thermal properties of the obtained composites were studied by means differential scanning calorimetry (DSC) and thermogravimetry (TG) measurements. A variation in the crystallinity of PP was found. A significant increase of the thermal stability of PP was achieved in the presence of the modified VMT.     

Thermal,structural and electrical properties

The chloro compound of 3-hydroxy-2-quinoxalinecarboxylic acid with nickel(II) has been prepared in ethanolic solution from which a solid compound was isolated. Spectral and magnetic measurements show that the nickel ions are in an octahedral environment. Thermogravimetry, differential thermal analysis and electrical conductivity data are reported for 3-hydroxy-2-quinoxalinecarboxylic acid and its nickel complex. The conductivity measurements indicate that electron/hole traps are emptied during heating of the complex but repopulation occurs in about 24 h at room temperature.     

Natural rubber composites filled with zinc ferrite nanoparticles: focus on structural,morphological, curing,thermal and mechanical properties

Research on Chemical Intermediates - Metal oxide nanofillers are a special type of additives in rubber composites that impart special qualities such as thermal resistance, tensile strength,...     

Thermal degradation and decomposition of jute/vinylester composites

Thermal analysis of jute fibre reinforced vinylester resin with 30 vol% of fibre were performed by TG/DTG under dynamic conditions. The fibres were treated with alkaline solution at different temperatures and the final composition (cellulose, hemicellulose and lignin) of the fibre was determined by chemical analysis. Apparent activation energies were determined using a variety of conventional thermogravimetric methods. Two peaks were found in the composite differential curves: the first peak close to 327 and the second peak at 408°C. The apparent activation energy values for the second peak decreased when fibre were treated. The addition of the jute fibres produced a slightly decrease in the thermal stability of the composites.     

Thermal stability,decomposition and glass transition behavior of PANI/NiO composites

Journal of Thermal Analysis and Calorimetry - Polyaniline/NiO (PANI/NiO) composites were synthesized by in situ polymerization at the presence of HCl (as dopant). FTIR, TEM and XRD were...     

Effects of accelerated aging on mechanical,thermal and morphological behavior of polyurethane/epoxy/fiberglass composites

Wind blades, an important application of polymeric composite materials, are subject to natural weathering. This study aims to evaluate mechanical, thermal and morphological behavior during accelerated aging in three thicknesses of epoxy and fiberglass polyurethane-coated composite plates used in wind turbines, in addition to testing with two acoustic emission techniques. An accelerated aging chamber simulated natural weathering mechanisms for 45, 90, 135 and 180 days. This degradation primarily reduced the mechanical properties of the thinner composites, with some damaged specimens exhibiting fiber-matrix debonding. Thermal properties deteriorated. There were no morphological changes on the polyurethane–epoxy interface; however, degradation occurred in the fiber-matrix interface on the surface exposed to radiation. The degree of chalking indicated coating deterioration on the external surface of the polyurethane. The acoustic wave propagation speed and attenuation coefficient measured prior to mechanical testing indicated the presence of damage areas.     

Biobased epoxy/carbon fiber composites: Effect on mechanical,thermo-mechanical and morphological properties

Biobased epoxy was synthesized from diglycidyl ether of bisphenol A (DGEBA) and epoxidized castor oil (ECO) at a ratio of 80:20. Carbon fiber (CF) was used as a reinforcing agent to fabricate composites using biobased epoxy as matrix. Mechanical, Thermal and morphological properties of neat epoxy and biobased epoxy composites were investigated. Mechanical test results revealed that the composites prepared using five plies were higher than those with three plies and one ply respectively. This phenomenon revealed the effective reinforcing effect of carbon fiber due to its higher strength and higher crosslinking density. The composites also demonstrate high damping behavior as compared with neat epoxy and biobased epoxy blend. With increasing number of plies the composites thermal properties also shows an improvement. The SEM micrographs of the composites depicted that the biobased epoxy was fully adhered to the carbon fiber, thus representing a strong interface between CF/epoxy matrix.     

Thermal and morphological characteristics of solution blended epoxy/NBR compound

Systematic study about the effect of acrylonitrile–butadiene rubber (NBR) concentration on the fracture toughness and thermal behavior of epoxy resin is conducted in this study. NBR is solved in an aromatic hydrocarbon solvent and is added to epoxy resin. We used diethylene-teriamin as the curing agent for epoxy resin. Tensile test results, performed followed by molding procedure, show that the toughness is improved owing to the increase of rubber content. Scanning electron microscopy (SEM) and atomic force microscopy besides thermogravimetric analysis (TG) are used to investigate the epoxy/rubber interface and chemical decomposition of the resultant mixture. The thermal behavior of cured epoxy resin was analyzed via TG instrument at different heating rates. Thermogravimetry curves showed that the thermal decomposition of epoxy system was occurred in only one stage regardless of the rubber content. The apparent activation energies of the rubber/epoxy systems containing 0, 5, and 10 phr of rubber were determined by Flynn–Wall–Ozawa, Kissinger–Akahira–Sunose, and Friedman methods. The results prove that the thermal stability of epoxy resin was decreased with enhancing the rubber content. However, the trend of changing activation energy versus conversions is totally different followed by adding the elastomer to the system compared to neat epoxy resin. Moreover, the results obtained via our proposed facile solution blending method are compared to those of resins modified with nano-powdered elastomer.     

Electrical and structural analysis of conductive polyaniline/polyacrylonitrile composites

Conducting composites of polyacrylonitrile (PAN) copolymer containing 10% mass ratio methylacrylate and dodecylbenzene sulfonic acid doped polyaniline (PANI-DBSA) were prepared by solution blending. Electrical properties of the blends were characterized by means of electrical conductivity measurements and the phase structures were investigated via scanning electron microscopy (SEM), X-ray diffraction (XRD), FT-IR spectroscopy, differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA). It was found that the electrical conductivity of the composites increased with the increase of PANI-DBSA content and the percolation threshold lay around 3.2 wt%. DSC and DMA measurements showed that there was only one T_g for each blend and the values of T_g varied with the PANI-DBSA content, implying that the PANI-DBSA/PAN blend was at least partially compatible. The formation of the hydrogen bonding between the carbonyl groups in PAN copolymer and the imine groups in PANI-DBSA was identified by the FT-IR spectra. XRD demonstrated that the intrinsic layered arrangement of PANI-DBSA was disaggregated in the blends. Nanosize network structure of PANI-DBSA dispersing in PAN matrix and the so-called phase reverse occurring in the skin layer of the film samples at low PANI-DBSA loading were observed by SEM.     

Thermal and mechanical characteristics of polyurethane/curaua fiber composites

Polyurethane composites reinforced with curaua fiber at 5, 10 and 20% mass/mass proportions were prepared by using the conventional melt-mixing method. The influence of curaua fibers on the thermal behavior and polymer cohesiveness in polyurethane matrix was evaluated by dynamic mechanical thermal analysis (DMTA) and by differential scanning calorimetry (DSC). This specific interaction between the fibers and the hard segment domain was influenced by the behavior of the storage modulus E′ and the loss modulus E″ curves. The polyurethane PU80 is much stiffer and resistant than the other composites at low temperatures up to 70°C. All samples were thermoplastic and presented a rubbery plateau over a wide temperature range above the glass transition temperature and a thermoplastic flow around 170°C.     

Thermal conductivity and properties of cyanate Ester/nanodiamond composites

The aim of this study was to improve thermal conductivity, thermal stability, and mechanical properties of bisphenol A dicyanate ester with the addition of nanodiamond. Cyanate ester/nanodiamond composites containing various ratios of nanodiamond were prepared. Thermal stability and thermal conductivity of the samples were evaluated by thermogravimetric analysis, differential scanning calorimetry, and laser flash method, respectively. The samples were characterized with the analysis such as gel content, water absorption capacity, and stress–strain test. Hydrophobicity of the samples was determined by contact angle measurements. Moreover, the surface morphology of the samples was investigated by a scanning electron microscopy. The obtained results prove that the cyanate ester/nanodiamond composites have good thermal and mechanical properties and can be used in many applications such as the electronic devices, materials engineering, and other emergent. Copyright © 2014 John Wiley & Sons, Ltd.     

Thermal analysis of PMMA/gel silica glass composites

Thermal analysis of poly-methylmethacrylate (PMMA) impregnated porous gel silica glasses confirms that the PMMA chains form hydrogen bonds with the pore surface silanol groups. The adopted conditions for the insitu polymerisation result in about 4% of residual monomers trapped in the polymer, most of them in the amorphous structure. The polymer and monomer mixture takes up the whole of the free pore volume. Most of the residual monomer polymerises during the DSC scans above the glass transition temperature providing an excellent probe for the weak glass transition. Polymerisation in the gel silica glass medium affects the glass transition temperature, the length of polymer chains, and the degree of polymerisation.     

MISCIBILITY, THERMAL STABILITY AND RETENTION OF PVP FOR CROSSLINKED PVA/PVP BLENDS

The thermal behavior, miscibility, crystallite conformation and thermal stability ofcrosslinked(CL-) PVA/PVP blends were studied by DSC and TG methods, respectively. DSCresults showed that in the blend, the crystallinity,T_m and T_c of PVA were obviously lower thanthose of pure PVA; the crystal growth changed from three dimensional to two dimensional andonly a single T_g was detected. These facts demonstrated that this crystalline and amorphousblend have good miscibility. TG curves showed that providing the quantity of K_2S_2O_8 added ismore than 3 wt%,in the blends PVA will form a stable CL-network, whose thermal degradationtemperature was near to that of PVP. But crosslinking reaction will not take place for PVP. Theprocesses of thermal degradation of CL-blends are based on combining both the thermaldegradation of PVP and that of PVA crosslinked with corresponding quantity of K_2S_2O_8 CL-agent, respectively. The UV measurements showed that 75 wt% of PVP may be remained in CL-blend hydrogelscrosslinked by adding (3--5 wt% )K_2S_2O_8. This is mainly due to the stable CL-network formed and the good compatibility and properentanglement between the composites in the CL-blends.     

Thermal degradation kinetics of polystyrene/cadmium sulfide composites

The thermal degradation kinetics of polystyrene/CdS composites were studied by thermogravimetry. The samples were heated in nitrogen, with three different heating rates: 5, 20 and 40 °C min⁻¹. We calculated kinetic parameters using KAS isoconversion method. The results showed that the maximum activation energy of thermal degradation is achieved for PS/CdS composite with about 10% of the CdS filler. Higher concentration of CdS in the composite (20%) induced acceleration of the thermal degradation, approaching the rate of degradation of the pure polystyrene matrix.