Volume 34, Issue 9

In this study, styrene-(ethylene-butylene)-styrene (SEBS) samples with different viscosities were cured using 2,5-dimethyl-2,5-di(t-butylperoxy) hexane (DBPH) and dicumyl peroxide (DCP) separately in the presence of co-agents 2,4,6-tris-2-propenyloxy-1,3,5-triazin (TAC) or 1,3,5-trially-s-triazine-2,4,6,(1H,3H,5H)-trione (TAIC). Curing was carried out by means of a moving die rheometer device (MDR). Curing rate constants and energy of activation were obtained. Swelling and percent gelation values were evaluated by Sol-Gel analysis. Optimal curing conditions were determined to shed light on the curing characteristics of SEBS. It was shown that the rate of curing reaction of SEBS depended on the type of peroxides, co-agents and the viscosity of SEBS. Also it was shown that increased temperature enhanced the rate of curing.

Novel high thermally stable polyimide-chrysotile (PI-Chr) composites were synthesized. Firstly, Chrysotile (Chr) was modified with 3-aminopropyltriethoxysilane (APS). Poly(amic acid) solution was synthesized from pyromellitic dianhydride (PMDA) and 4,4′-diaminodiphenyl ether. Then, PI-Chr composites were prepared from poly(amic acid) solution and different ratios of modified Chr. Prepared PI-Chr composites were characterized by Fourier transform infrared (FTIR) spectroscopy, X-ray spectroscopy and thermal analysis techniques. Thermal analysis results showed that the PI-Chr composites have higher decomposition temperatures in comparison with the pure PIs. A 10% weight loss belonging to PI-Chr composites was observed between 489°C and 536°C in air atmosphere, but this value was 468°C in air for pure PIs. The glass transition temperatures (T g s) of the PI-Chr composites were 373°C–384°C, depending upon the amount of the Chr. PI-Chr composites exhibited improved thermal stability. The activation energies ( E a s) of the thermal degradation reaction were calculated using the Kissinger method for pure PI and composites. The E a s of the PI-Chr composites were found to be 77 and ∼117 kJ/mol. The fire retardant properties of Chr in the PI matrix were also tested by the total heat release test. The introduction of Chr in the composites leads to a slight increase in fire retardant properties thermal stability.

In this work, we investigated the effect of aluminum chloride hexahydrate as a flame retardant coating on the flammability of cellulosic and polyester (polyethylene terephthalate, PET) fibers. The samples were characterized by several techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FT-IR) spectroscopy, vertical flammability test, limiting oxygen index (LOI), thermogravimetric analysis (TGA)and differential thermogravimetric (DTG). Aluminum chloride hexahydrate <100 nm in size has been found to form continuous and dispersed particles coatings on the fibers surface which shows efficient flame retardant properties. The optimum loadings to impart flame retardant properties were about 8.73–9.93% for cellulosic fiber and 20.30–23.48% for polyester fiber. Flame retardant activity was tested by a vertical flammability tester and LOI. XRD results of ashes revealed that after combustion of the treated specimens, the existence of α-Al 2 O 3 nanoparticles was detected in the ashes of treated samples. TGA/DTG of pure, treated fibers and the salt was accomplished, and thermograms were compared and discussed. The results obtained are in favor of the free radical theory and also the dust or wall effect theory.

Polyblend films were prepared from high-density polyethylene (HDPE) and poly(l-lactic acid) (PLLA) up to 20% PLLA by the melt blending method in an extrusion mixer with post-extrusion blown film attachment. The 80/20 (HDPE/PLLA) blend was compatibilized with maleic anhydride grafted polyethylene (PE- g -MA) in varying ratios [up to 8 parts per hundred of resin (phr)]. Tensile properties of the films were evaluated to obtain optimized composition for packaging applications of both non-compatibilized and compatibilized blends. The compositions HDPE80 (80% HDPE and 20% PLLA) and HD80C4 (80% HDPE, 20% PLLA and 4 phr compatibilizer) were found to be optimum for packaging applications. However, better tensile strength (at yield) and elongation (at break) of 80/20 (HDPE/PLLA) blend were noticed in the presence of PE- g -MA. Further, thermal properties and morphologies of these blends were evaluated. Differential scanning calorimetry (DSC) study revealed that blending does not much affect the crystalline melting point of HDPE and PLLA, but heat of fusion of 80/20 (HDPE/PLLA) blend was decreased as compared to that of neat HDPE. Spectroscopy studies showed evidence of the introduction of some new groups in the blends and gaining compatibility in the presence of PE- g -MA. The compatibilizer influenced the morphology of the blends, as apparent from scanning electron microscopy (SEM) and supported by Fourier transform infrared (FTIR).

The magnetic Ni 0.3 Zn 0.7 Fe 2 O 4 nanoparticles were expected to have wide applications in bionanoscience and electronic devices technology. In this work, Ni 0.3 Zn 0.7 Fe 2 O 4 nanoparticles were synthesized successfully by a redox chemical reaction in an aqueous solution of nickel chloride, zinc chloride and ferric chloride. Fourier transform infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the shape, structure and size of the synthesized magnetic nanoparticles. The magnetic properties of Ni 0.3 Zn 0.7 Fe 2 O 4 nanoparticles were studied using a vibrating sample magnetometer (VSM). The XRD patterns of the synthesized nanoparticles revealed the formation of the single phase spinel structure of the synthesized materials. The synthesized Ni 0.3 Zn 0.7 Fe 2 O 4 nanoparticles were used for the preparation of Ni 0.3 Zn 0.7 Fe 2 O 4 /polyvinyl acetate (PVAC) nanocomposites by an in situ emulsion polymerization method. The synthesized Ni 0.3 Zn 0.7 Fe 2 O 4 nanoparticles exhibited superparamagnetic behavior at the room temperature under an applied magnetic field. Magnetization measurements indicated that the saturation magnetization of synthesized Ni 0.3 Zn 0.7 Fe 2 O 4 /PVAc nanocomposites was markedly less than that of Ni 0.3 Zn 0.7 Fe 2 O 4 magnetic nanoparticles.

Bis(cyclopentadienyl) zirconium (IV) dichloride of empirical formula C 10 H 10 Cl 2 Zr was used as a catalyst. Doped titania with iron (TiO 2 /Fe) nanofillers were used to study the effect of nanofillers on ethylene homopolymer and ethylene/propylene copolymer properties. Using titanium dioxide doped with iron (TiO 2 /Fe) resulted in the increase in the molecular weight ( M w ) of polyethylene and ethylene/propylene copolymer nanocomposites of up to 80% when compared to the neat polymer. The catalyst activity was increased by using TiO 2 /Fe nanofiller for both ethylene polymerization and ethylene/propylene copolymerization. Besides the investigation of the catalyst activity and the molecular weight ( M w ) of the obtained polymer, molecular weight distribution, copolymer composition, crystallinity and thermal characteristics of polyethylene and polyethylene/polypropylene nanocomposites were also studied. Non-isothermal crystallization kinetics of polyethylene and polyethylene/polypropylene nanocomposites fits well with the Avrami-Erofeev model.

The mechanical properties of Christmas palm-reinforced polyester composite were improved by chemical modification of Christmas palm fibers through alkali treatment. An attempt was made in this investigation to identify the possibility of using potassium hydroxide as alkali solution. The fibers treated with potassium hydroxide aqueous solution at varying solution concentrations and soaking times were reinforced in a polyester matrix and tested for their mechanical properties. The physicochemical interaction between the treated Christmas palm fiber and polyester matrix was characterized using scanning electron microscopy and X-ray diffraction. The surface modification of fibers improved the compatibility of fibers with polyester matrix, which, in turn, resulted in better mechanical properties. A nonlinear regression model was developed to predict the mechanical properties of the composites using response surface methodology. The better treatment conditions for optimum mechanical properties were determined using a heuristic optimization method called particle swarm optimization (PSO). The optimized value obtained using the PSO technique was validated through a confirmation test, and the result was found to be significant.

This study deals with the effect of hybridization on the natural frequency of woven laminated hybrid composite beams with and without cutouts under the clamped-free boundary condition. Woven carbon, Kevlar and S-glass fibers with epoxy were used for the production of hybrid composites. Natural frequencies of the hybrid composite beams were experimentally determined for [(0/90) 3 ] S stacking sequence. Numerical analyses were performed to investigate the influences of fiber orientation angles, circular and rectangular cutouts, cutout size ratios and positions on natural frequency. Good agreement between experimental and numerical results was found from a comparison of natural frequencies. The results shows that the fiber type used in the layers, cutout size and position on the beam strongly effects the natural frequency.

A novel solid polymer electrolyte based on poly vinyl alcohol (PVA) with oxalic acid was prepared by the solution caste technique. X-ray diffraction (XRD) and differential scanning calorimetry (DSC) measurements carried out on the samples clearly revealed the modification of the PVA structure; the PVA crystallinity was reduced with increasing oxalic acid content and became more amorphous. The surface morphology of these complexed polymer electrolytes was analyzed by scanning electron microscopy (SEM). Fourier transform infrared spectroscopy (FTIR) spectral studies of the samples suggested that the interaction between H + ions of oxalic acid and oxygen of the hydroxyl group (OH) of PVA plays a major role in proton conductivity. The optical absorption studies were performed on these samples in a range of wave numbers from 200 nm to 600 nm and the optical band gap values were evaluated. Direct current (DC) conductivity was measured and temperature dependence in the range 27–273°C was studied. It was observed that the conductivity at temperatures beyond the glass transition temperature (T g ) showed a Vogel-Tamman-Fulcher (VTF) type behavior. The electrical conductivity studies on PVA with oxalic acid, in a 70:30 proportion by wt%, demonstrated that the polymer composite is a promising electrolyte for applications in electrochemical cells.

Polyimides are a sophisticated family of materials, which cover an exhaustive range of high performance polymers and find applications from aerospace to microelectronics. Microelectronic applications demand low dielectric constant and high performance. Aromatic terpolyimides were synthesized by reacting 3,3′,4,4′-biphenyl tetracarboxylic dianhydride (BPDA), 3,3′,4,4′-benzophenone tetracarboxylic dianhydride (BTDA) and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride (6FDA) with 4,4′-oxydianiline (ODA) by thermal imidization with the view to decrease their dielectric constant without compromising thermal properties and mechanical properties compared to their homo and copolyimides. They were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Their FTIR spectra established formation of polyimide by the characteristic vibrations at 1375 cm -1 (C-N stretch) and 1113 cm -1 (imide ring deformation). The TGA results showed decomposition of imides at about 515°C. The glass transition temperature (T g ) of the polymers varied from 261°C to 281°C. The XRD spectrum of BPDA/BTDA/6FDA-ODA, which contained 50% of 6FDA, showed a broadened envelope with a peak at 16.8° (2θ), illustrating a semicrystalline nature. Incorporation of 6FDA, with a bulky bridging group into the backbone of BPDA/6FDA-ODA and BPDA/BTDA/6FDA-ODA (0.25:0.25:0.5::1) caused a decrease in the dielectric constant (2.13 and 2.38, respectively). Such polyimides can find application in microelectronics such as flexible printed circuits and tape automated bonding applications.

Natural composites of high filler content, such as nacre, a composite comprised of 95–99% w/w aragonite layers, have been of interest due to their hardness, strength and toughness. High filler content composites have been prepared synthetically, although due to viscosity and processing requirements, the filler content was limited compared with natural systems. In this paper we describe hybrid high filler content composites prepared to be biomimetic of nacre. Development of processing conditions increased the filler content from 50% w/w using a laboratory stirrer to obtain hybrid composites with 77–86% w/w filler content, prepared by centrifugal deposition and hot compression molding techniques. Both methods were very different from natural formation from layer-by-layer (LBL) construction, however, the composites formed were of high filler content approaching the level in nature. The composites exhibited high modulus and strength, although deformation at break was low, consistent with highly filled materials. Glass transition of the resin phase was increased slightly, while damping was decreased by filler content. Surface morphology of the fractured composite showed a layered structure of well dispersed fillers with minute voids scattered evenly, indicating that the composite was effectively compacted.

Graphene nanoplatelets (xGnP-C) with specific surface areas varying from 300 to 750 m 2 /g were investigated as novel reinforcing fillers for carboxylated acrylonitrile- butadiene rubber (XNBR). The effects of graphene nanoflakes loadings up to 15 parts per hundred rubber (phr) on the rheometric characteristics, stress-strain behavior, crosslink density ( ν ), resistance to UV radiation and thermo-oxidative aging of the XNBR/ZnO/graphene xGnP-C composites were investigated. Substantial improvement in the mechanical properties of XNBR with increased contents of xGnP-C filler was achieved. It was found that the addition of 5 phr of graphene significantly increased UV stability, tensile strength (TS) and modulus at 100%, 200% and 300% elongation of rubber material. The effect was more pronounced for composites containing graphene with the highest specific surface area 750 m 2 /g. The chemical information on the functional groups on the xGnP-C surface was obtained by X-ray photoelectron spectroscopy (XPS) method. In this case, the reinforcing effect of graphene xGnP-C may result from an additional chemical bonding which is possible between the -COOH groups of the rubber and the reactive, oxygen-containing groups on the filler surface.

Poly(lactic acid) (PLA)-hemp-nanosilica (PHS) composites were prepared by impregnation of hemp woven fabric with PLA solution. Nanosilica was dispersed in the PLA solution to introduce a matrix reinforcing nanophase within the composite. The melting behavior of PLA composites was obtained by using differential scanning calorimetry (DSC) and modulated-temperature DSC (mT-DSC). Multiple melting which appeared in the non-isothermal heating curve showed that the temperature of a low melting peak increased when using a slower scanning rate. The incorporation of nanosilica in PLA composites affected the melting temperature ( T m ) and sufficiently formed nucleation sites that promoted the growth of PLA crystals. Composites analyzed by a temperature-modulated program showed a broad exothermic peak before the melting peak in the non-reversing heat capacity and endothermic melting in the reversing heat capacity curve. This behavior was explained by a process of partial melting, recrystallization and remelting (mrr). The mT-DSC resolved that hemp fiber induced recrystallization and nanosilica acted as an effective nucleating agent, which promoted small and imperfect crystals that changed successively into more stable crystals through a melt-recrystallization process.