Chemical Engineering

A mixture of epoxy with liquid nitrile rubber, carboxyl-terminated (butadiene-co-acrylonitrile) (CTBN) was cured under various temperatures. The cured resin was a two-phase system, where spherical rubber domains were dispersed in the matrix of epoxy. The morphology development during cure was investigated by scanning electron microscope (SEM). There was slight reduction in the glass transition temperature of the epoxy matrix (Tg) on the addition of CTBN. It was observed that, for a particular CTBN content, Tg was found to be unaffected by the cure temperature. Bimodal distribution of particles was noted by SEM analysis. The increase in the size of rubber domains with CTBN content is due probably to the coalescence of the rubber particles. The mechanical properties of the cured resin were thoroughly investigated. Although there was a slight reduction in tensile strength and young's modulus, appreciable improvements in impact strength, fracture energy, and fracture toughness were observed. Addition of nitrile rubber above 20 parts per hundred parts of resin (phr) made the epoxy network more flexible. The volume fraction of dispersed rubbery phase and interfacial area were increased with the addition of more CTBN. A two-phase morphology was further established by dynamic mechanical analysis (DMA). © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2531–2544, 2004

Sisal fibers were subjected to various chemical and physical modifications such as mercerization, heating at 100 °C, permanganate treatment, benzoylation and silanization to improve the interfacial bonding with matrix. Composites were prepared by these fibers as reinforcement, using resin transfer molding (RTM). The mechanical properties such as tensile, flexural and impact strength were examined. Mercerized fiber-reinforced composites showed 36% of increase in tensile strength and 53% in Young’s modulus while the permanganate treated fiber-reinforced composites performed 25% increase in flexural strength. However, in the case of impact strength, the treatment has been found to cause a reduction. The water absorption study of these composites at different temperature revealed that it is less for the treated fiber-reinforced composites at all temperatures compared to the untreated one. SEM studies have been used to complement the results emanated from the evaluation of mechanical properties.

Hybrid composites prepared by the incorporation of two or more different types of fibres into a single polymer matrix deserve much attention. This method of hybridisation of composites offers a profitable procedure for the fabrication of products while the resulting materials are noted for their high specific strength, modulus and thermal stability. The influence of the relative composition of short sisal/glass fibres, their length and distribution on the tensile properties of short sisal/glass intimately mixed polyethylene composites (SGRP) was examined. Different compositions of sisal and glass such as 70/30, 50/50 and 30/70 have been prepared with varying fibre lengths in the range of 1–10 mm. Emphasis has also been given to the variation of fibre–matrix adhesion with several fibre chemical modifications. Chemical surface modifications such as alkali, acetic anhydride, stearic acid, permanganate, maleic anhydride, silane and peroxides given to the fibres and matrix were found to be successful in improving the interfacial adhesion and compatibility between the fibre and matrix. The nature and extent of chemical modifications were analysed by infrared spectroscopy while improvement in fibre–matrix adhesion was checked by studying the fractography of composite samples using a scanning electron microscope. Assessment of water retention values has been found to be a successful tool to characterize the surface of the stearic acid modified fibres. It was found that the extent of improvement in tensile properties of SGRP varied with respect to the nature of chemical modifications between fibre and matrix. Improved mechanical anchoring and physical and chemical bonding between fibre and polyethylene matrix are supposed to be the reasons for superior tensile strength and Young's modulus in treated composites. Several secondary reasons such as high degree of fibre dispersion and reduced hydrophilicity in chemically modified fibres also are believed to play a role. Among the various chemical modifications, the best tensile strength and modulus was exhibited by the SGRP with benzoyl peroxide treated fibres. This is attributed to the peroxide-initiated grafting of polyethylene on to the fibres. Copyright © 2004 Society of Chemical Industry

Calcium phosphate nanoparticles were prepared by the matrix mediated synthesis and were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. The particle size was found to be around 10 nm. Nanocomposites of polystyrene with calcium phosphate were prepared by melt mixing technique. Dynamic mechanical analysis and differential scanning calorimetric studies of the composites were performed. The storage modulus increased with respect to the filler loading and the glass transition temperature showed a positive shift indicating good reinforcement. The specific heat capacity measurements showed a drastic reduction, which indicated good filler matrix interaction.

The effects of blend ratio, compatibilization and vulcanization on the permeability of O2 and N2 gas through HDPE/EVA blends were analyzed. As the volume fraction of EVA in the blend increases the permeability increases. The variation in permeability is correlated with the phase morphology. Oxygen exhibits a higher permeability than nitrogen because the “kinetic diameter” of N2 is greater than that of O2. The O2/N2 selectivity of HDPE is higher than that of EVA and as a result the selectivity decreases with increase in EVA content in the system. The O2 and N2 permeabilities decrease and O2/N2 selectivity increase upon compatibilization and dynamic vulcanization. The experimental gas permeabilities in HDPE/EVA blends are compared with several theoretical models of permeation.

Polyamide 12 (PA12)/styrene–ethylene/butylene–styrene (SEBS) and PA12/maleic anhydride grafted SEBS (SEBS-g-MA) blends were prepared in a twin-screw extruder followed by injection moulding. Thermal and crystallisation behaviours of these blends were evaluated. Thermal properties and morphology of the blends were estimated using thermo gravimetric analysis (TGA) and scanning electron microscopy (SEM), respectively. The phase structure of the blends was interpreted by dynamic mechanical thermal analyser (DMTA). In terms of temperature at maximum rate of degradation (Tmax) and integral procedural decomposition temperature (IPDT), it was found that PA12/SEBS-g-MA (PM) blends possessed greater thermal stability than PA12/SEBS (PS) blends. The kinetics of degradation process of PA12 and its blends were studied using Coats–Redfern (CR) method. It was found that there is no appreciable change in the thermal stability of PA12 in the presence of small amount of rubber phase. A good correlation was observed between the thermal properties and phase morphology of the blends. Melting and crystallisation behaviours of the blends were analysed by differential scanning calorimetry (DSC). These results showed that the melting and crystallisation behaviours of PA12 were not significantly affected by blending with rubbers. It was also observed that the functional group present in the rubber phase has little effect on the melting and crystallisation behaviours of PA12.

Composites of isotactic polystyrene with different loading of titanium dioxide were prepared by melt mixing in a Brabender Plasticorder at a rotor speed of 60 rpm at 180 °C. Mechanical properties of the composites were measured by various techniques and most of the properties were found to be increasing with filler loading. Tapping mode atomic force microscopy was used to study the surface characteristics of the composites. Various AFM analytical parameters like power spectral density, roughness analysis and section analysis were measured. The mechanical properties of the composites were correlated with analytical data obtained from the AFM studies. The focused ion beam technique was also used to characterize the dispersion of the filler in the polymer matrix.

The properties of diglycidyl ether of bisphenol-A epoxy resin toughened with poly(ether sulfone ether ketone) (PESEK) and poly(ether sulfone) (PES) polymers were investigated. PESEK was synthesised by the nucleophilic substitution reaction of 4,4’-difluorobenzophenone with dihydroxydiphenylsulfone using sulfolane as solvent and potassium carbonate as catalyst at 230 °C. The T g–composition behaviour of the homogeneous epoxy resin/PESEK blend was modelled using Fox, Gordon–Taylor and Kelley–Bueche equations. A single relaxation near the glass transition of epoxy resin was observed in all the blend systems. From dynamic mechanical analysis, the crosslink density of the blends was found to decrease with increase in the thermoplastic concentration. The storage modulus of the epoxy/PESEK blends was lower than that of neat resin, whilst it is higher for epoxy/PES blends up to glass transition temperature, thereafter it decreases. Scanning electron microscopic studies of the blends revealed a homogeneous morphology. The homogeneity of the blends was attributed to the similarity in chemical structure of the modifier and the cured epoxy network and due to the H-bonding interactions between the blend components. The fracture toughness of epoxy resin increased on blending with PESEK and PES. The increase in fracture toughness was due to the increase in ductility of the matrix. The thermal stability of the blends was comparable to that of neat epoxy resin.

Abstract. In this study, the surface characteristics of blends and composites of epoxy resin were investigated. Poly (styreneco-acylonitrile)(SAN) was used to modify diglycidyl ether of bisphenol-A (DGEBA) type epoxy resin cured with diamino diphenyl sulfone (DDS) and the modified epoxy resin was used as the matrix for fibre reinforced composites (FRP's). E-glass fibre was used as the fibre reinforcement. The scanning electron micrographs of the fractured surfaces of the blends and composites were analyzed.

Abstract This paper reports the results of studies on the effect of phenol functionalization of carbon nanotubes (CNTs) on the mechanical and dynamic mechanical properties of natural rubber (NR) composites. Fourier transform infrared spectrometry (FTIR) indicates characteristic peaks for ether and aromatic rings in the case of phenol functionalized CNT.

Abstract. Polystyrene (PS) based nanocomposites were prepared by melt mixing in a Brabender Plasticoder with calcium phosphate as the nanofiller. These nanocomposites showed improvement in almost all physical properties. Contact angle measurements of the composites with water and methylene iodide were carried out. Various contact angle parameters such as total solid surface free energy, work of adhesion, interfacial free energy and spreading coefficient were analysed.

In this work, multiwall carbon nanotubes (CNT) were functionalized by acid treatment and characterized using Fourier Transform Infrared Spectroscopy (FTIR) and thermogravimetric analysis (TGA). Polystyrene/CNT composites of both the untreated and acid treated carbon nanotubes were prepared by thermal bulk polymerization without any initiator at different loadings of CNT. The tensile tests showed that the addition of 0.5 wt.% of acid treated CNT results in 22% increase in Young’s modulus. The DSC measurements showed a decrease in glass transition temperature (Tg) of PS in the composites. The rheological studies at 190 °C showed that the addition of untreated CNT increases the viscoelastic behavior of the PS matrix, while the acid treated CNT acts as plasticizer. Thermogravimetric analysis indicated that the incorporation of CNT into PS enhanced the thermal properties of the matrix polymer.

Microcrystalline powders of yttrium barium copper oxide [YBa2Cu3O7] have been prepared by conventional ceramic preparation technique. The powder belong to orthorhombic symmetry with unit cell dimensions ‘a’=3.8214 Å, ‘b’=3.8877 Å and ‘c’=11.693 Å. XRD and SEM studies revealed that its particle size is in the micrometer range. Micro composites of polystyrene with different loading of yttrium barium copper oxide fillers were prepared by melt mixing in a brabender plasticorder at a rotor speed of 60 rpm. The lattice parameters of the constituent phases are the same in all the composites. Mechanical properties such as stress–strain behavior, Young's modulus, and tensile strength were studied as a function of filler loading. Addition of filler enhances the Young's modulus of the polymer. Because of the poor filler-matrix adhesion, tensile strength and strain at break decreases with filler loading. To explore more carefully the degree of interfacial adhesion between the two phases, the results were analyzed by using models featuring an adhesion parameter. Finally experimental results were compared with theoretical predictions. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Morphology, mechanical properties, thermal stability and gas transport behaviour of interpenetrating polymer networks (IPNs) based on PI/PMMA have been investigated using various techniques. Crosslinking level of both phases and concentration of PMMA were found to have noticeable effects on the compatibility of immiscible components during IPN formation. Effect of crosslinking was studied by preparing IPNs with varying amount of crosslinker concentration in each phase. Crosslinking of both phases facilitated deeper interpenetrations between both networks, and certain degree of compatibility is attained during IPN formation. Nanometre-sized domains were observed for highly crosslinked IPN. Lower concentration of PMMA was found to favour phase mixing more effectively than others. DSC curve of 65/35 IPN showed a broad transition arising from the α and β-relaxations of PMMA due to the higher flexibility attained by mixing with the highly mobile PI chains. The mechanical properties of the IPNs were correlated to the morphology of the system and 50/50 composition showed maximum mechanical properties among the studied compositions. Mode of mechanical failure, thermal stability and gas transport behaviour were also analysed. IPNs having nanometre-sized domains showed least gas permeability among the studied samples.

The morphological, mechanical, and thermal stability of Nitrile rubber nanocomposites reinforced with fillers such as layered silicate (LS), calcium phosphate (CP) and titanium dioxide (TO) having different particle size and chemical nature were analyzed. The results revealed that the filler geometry played an important role on the mechanical and thermal stability of the composites. Calcium phosphate and titanium dioxide filled systems showed comparatively better mechanical and thermal stability compared to neat rubber. The activation energy needed for the thermal degradation was found to be higher for layered silicate filled system. DSC (Differential Scanning Calorimetry) analysis revealed a change in the Tg values as a result of the addition of fillers. This was more prominent with the case of layered silicate filler addition in comparison with calcium phosphate and titanium dioxide. The heat capacity values of the nanocomposites were carefully evaluated. The (∆Cp) with values obtained for different nanocomposites were correlated with the degree of reinforcement. It can be assumed that more polymer chains are attached on to the surface of the filler and there exists an immobilized layer around the filler surface and the layers do not take part in the relaxation process. The FTIR spectrum of the different samples highlighted the possible filler matrix interaction. The filler dispersion and aggregation in the polymer matrix were analyzed using X-ray diffraction studies (XRD), transmission electron microscopy (TEM), and atomic force microscopy (AFM).

Poly(ethylene-co-vinyl acetate) (EVA) based nanocomposites were prepared by melt mixing in an internal mixer with nanoparticles of calcium phosphate. Contact angle measurements of the composites with water and methylene iodide were measured. Parameters such as total solid surface free energy, work of adhesion, interfacial free energy and spreading coefficient were calculated. The interaction parameter between the polymer and the liquid has been calculated using Girifalco-Good’s equation. Water diffusion studies of the composites were done at two different temperatures, 27 °C and 50 °C to know the solvent uptake behaviour. Water diffusion showed remarkable reduction with respect to the filler content. Gas permeability studies with oxygen and nitrogen also showed improvement in barrier properties for the composites.

Poly(styrene-co-acylonitrile) was used to modify diglycedyl ether of bisphenol-A type epoxy resin cured with diamino diphenyl sulfone and the modified epoxy resin was used as the matrix for fiber-reinforced composites (FRPs) to get improved mechanical properties. E-glass fiber was used as fiber reinforcement. The tensile, flexural, and impact properties of the blends and composites were investigated. The blends exhibited considerable improvement in mechanical properties. The scanning electron micrographs of the fractured surfaces of the blends and tensile fractured surfaces of the composites were also analyzed. The micrographs showed the influence of morphology on the properties of blends. Results showed that the mechanical properties of glass FRPs increased gradually upon fiber loading. Predictive models were applied using various equations to compare the mechanical data obtained theoretically and experimentally. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Organo-modified fluorohectorite (OFH) clay filled polysulfone (PSf) nanocomposite films were prepared by solution casting method. The morphology of the nanocomposites was investigated using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The surface properties assessed by contact angle measurements showed significant increase in hydrophobicity of the nanocomposites relative to the virgin polymer. The relationship between contact angle, surface roughness, and surface chemistry was discussed. From the measured contact angle values, various surface parameters such as total surface free energy, interfacial free energy, work of adhesion, spreading coefficient, and Girifalco-Good's interaction parameter were calculated. The mechanical properties like tensile strength and elongation at break were increased considerably upon increasing the organoclay content to 3 wt%. But further increase in the clay content decreased the properties to some extent. The dielectric investigation carried out in room temperature indicated that dielectric constant of PSf/OFH clay nanocomposite films decreases with the increase of the clay content. This work describes the preparation of PSf nanocomposite with desired hydrophobic, dielectric, and mechanical properties for water repellent and electronic applications.