Premamoy Ghosh

Characterization of poly(vinyl pyrrolidone) modified polyaniline prepared in stable aqueous medium

Abstract Polyaniline (PANI) of high stability and good processibility was prepared in acidic aqueous dispersion/solution, using the support of a water soluble polymer poly(vinyl pyrrolidone) (PVP). The high degree of dispersion and near solubility and storage stability of the PANI prepared, are explained on the basis of the synchronized establishment of hydrogen bonding, between segments of PANI being formed during the polymerization of aniline and the PVP present in the solution. Studies of the prepared dispersions/solutions of the PANI–PVP composites, by viscometry and UV-visible spectrophotometry, lend support to this view. Results of studies of the isolated PANI–PVP composites of different PANI loadings by FTIR spectroscopy, also support this view. The PANI–PVP composites were also thermally characterized, employing thermogravimetric analysis and differential scanning calorimetry (TGA and DSC, respectively). They were characterized microscopically, by transmission electron microscopy (TEM), for the prepared dispersion or solution of PANI in the presence of PVP, and by scanning electron microscopy (SEM) for selected isolated PANI–PVP composites.

Conducting carbon black filled EPDM vulcanizates: assessment of dependence of physical and mechanical properties and conducting character on variation of filler loading

Abstract The effects of incorporation of different extents of extra conducting carbon black as filler on some selected physical and mechanical properties, aging behavior and DC electrical conducting character of vulcanizates of ethylene-propylene diene monomer (EPDM) based compounds have been studied. Increasing carbon black loading caused a monotonic increase in density and hardness and in tensile strength with a leveling off trend for carbon black filler loading >40 phr. Elongation at break of the initial EPDM vulcanizates, however, passes through a maximum corresponding to 20 phr carbon black loading; the position of the maximum shifts to 30 phr carbon black loading on aging of the vulcanizates at 135°C for 7 days. DC electrical conductivity measurements of the filled EPDM vulcanizates indicate a percolation concentration range over 15–30 phr of conducting carbon black loading. Trends of change in voltage ( V ) developed with increase in the current ( I ) applied for the carbon black filled EPDM vulcanizates at different temperatures commonly indicate ohmic behavior for application of current up to a critical level. Beyond the critical current ( I C ), the developed voltage becomes practically insensitive to large enhancements in the applied current; the filled vulcanizates, thus, exhibit non-ohmic character for I > I C . An attempt has been made to analyze and interpret the observed effects. Electromagnetic interference (EMI) shielding effectiveness (SE) generally increases on increasing the carbon black loading. Vulcanization substantially contributes to enhancement in the EMI SE of the filled EPDM compounds.

Modification of low density polyethylene (LDPE) by graft copolymerization with some acrylic monomers

Abstract Graft copolymerization of low density polyethylene (PE) with acrylic acid (AA), ethyl acrylate (EA) and butyl acrylate (BA) using dicumyl peroxide (DCP) as the initiator was studied using differential scanning calorimetry (DSC) under the dynamic (non-isothermal) condition and in the shear mixer of a Brabender plasticorder at 170°C (443°K). DSC studies allowed measurements of the heat of reaction and the kinetics and energetics of the overall reaction during graft copolymerization. For each monomer system, the reaction was first order with respect to monomer concentration and the observed activation energy (150–170 kJ mole −1 ) followed the order AA > EA > BA. The grafting efficiency (%) was highest when using AA. The higher volatility of the EA monomer makes it less suitable for grafting on PE under a shearing action at 170°C (443°K). A low DCP dose (0.75 mmole per 100 g of PE) produced optimum conversion and grafting effects. Studies of melt rheology at 190°C (463°K) showed that 10–15% grafting of acrylic polymers on polyethylene resulted in a three- to five-fold increment in the melt viscosity of the polymer and substantial lowering in its melt flow index (MFI). Some cross-linking of PE during DCP-induced grafting unavoidably occured as a side reaction, particularly for grafting using the AA monomer and generally when using a high DCP dose ( > 1.0 mmole per 100 g of PE) for all the monomers. The nature and extent of changes in the mechanical properties of PE on acrylic grafting depended on the chemical nature of the monomer used and on the extent of grafting achieved.

Reactive melt processing of polyethylene: effect of peroxide action on polymer structure, melt rheology and relaxation behaviour

Abstract Reactive melt processing of polyethylene (PE) was accomplished at 170°C under the influence of two different doses (0.75 and 1.25 mmol per 100 g PE) of dicumyl peroxide (DCP). The effect of peroxide action on melt rheology of PE at 160, 180 and 190°C was studied by a constant shear rate plate and cone viscometer. Peroxide action led to establishment of a mild degree of crosslinkages in PE and hence to enhancement of its melt viscosity, the effect being higher for use of a higher DCP dose. The melts of PE and modified PE showed pseudoplastic flow behaviour. The pseudoplastic character, however was less pronounced at higher rates of shear and at a relatively low temperature. Use of a low dose of DCP (0.75 mmol per 100 g PE) modified the polymer marginally, causing little or only marginal changes in relaxation time and shear modulus, while a higher DCP dose (1.25 mmol per 100g PE) incorporated significant changes in the polymer structure due to establishment of more than a critical degree of peroxide induced crosslinkages, thereby causing a substantial enhancement in the shear modulus and a drop in relaxation time. Odd effects of temperature on viscoelastic character are also interpreted on the basis of total dissolution of residual crystalline orientations in PE melts at ≥ 170°C.

Dynamic mechanical analysis of FRP composites based on different fiber reinforcements and epoxy resin as the matrix material

Three-ply composite laminates prepared from E-glass or N-glass chopped strand mats (CSMs) and jute (J) fabrics as reinforcing agents and amine-cured epoxy resin as the matrix material were subjected to dynamic mechanical thermal analysis at a fixed frequency of 1 Hz over a temperature range of 30–180°C. The volume fraction of fibers ranged between 0.21 and 0.25. The reinforcing effect for the three fibers is in the order E-glass > N-glass ≫ jute. Glass-reinforced composites show a higher storage modulus (E′) than that of jute-reinforced composites. The E′ values of glass-jute hybrid composites lie between those of glass-reinforced and jute-reinforced composites. Odd trends in temperature variability of the loss modulus (E′) and the damping parameter, tan δ, and in the glass transition temperature (Tg) for the three different unitary and four different hybrid composites are interpreted and understood on the basis of odd differences in (1) the chemical nature and physical properties of the three different fibers (E-glass, N-glass, and jute), (2) the void content and distribution, (3) the thermal expansion coefficients of the main phases in the composites, (4) the degree of matrix stiffening at or near the fiber-matrix interface, and (5) the extents of matrix softening in the zone next to the interface.

Studies on stable aqueous polyaniline prepared with the use of polyacrylamide as the water soluble support polymer

Abstract Peroxodisulfate-induced polymerization of aniline in aqueous acidic (HCl) media using the support of a water soluble polymer polyacrylamide, PAAm produced polyaniline (PANI) in aqueous dispersion/solution having high stability and easy processability. PAAm support apparently allows limited grafting of PANI on it in addition to causing a template effect through hydrogen bonding between segments of the two polymers; this explains fairly uniform and high degree of dispersion or solubility of PANI with exceptional storage stability. Aqueous and isolated dry PANI–PAAm composites were characterized spectroscopically (UV-Vis and FTIR), thermally (TGA, DSC) and with respect to their electrical conductivity at different PANI loadings and temperatures. The morphology of the composites were studied by transmission electron microscopy (TEM) and scanning electron microscopy (SEM).

Photopolymerization of methyl methacrylate with the use of bromine as photoinitiator

Low concentrations of bromine (0.008–0.06M) were used to initiate photopolymerization of MMA in bulk and in diluted (near bulk) systems, the diluents or solvents used being benzene, toluene, dioxane, tetrahydrofuran, carbon tetrachloride, chloroform, methylene chloride, and methanol. Polymerization in bulk follows usual free-radical kinetics. Inert solvents (benzene, toluene) as well as the other solvents used enhance the rate of polymerization MMA even when used in the range of catalytic concentrations (0.04–0.4M). An initiation mechanism involving solvent molecules appears to be predominant in diluted systems.

Thermal and oxidative degradation of PE-EPDM blends vulcanized differently using sulfur accelerator systems

Abstract Blends of low density polyethylene (PE) of density 915 kg m− 3 and ethylene propylene diene rubber (EPDM) of density 860 kg m− 3 were vulcanized using two different sulfur accelerator curative systems: (A) a conventional curative system based on a combination of TMTD, MBTS and S; and (B) a silane curative system based on a combination of TMTD, Si69 and S. For each curative system, torque rheometric and morphological studies indicated development of a co-continuous phase morphology (involving hard PE and soft EPDM phases) for 30 70 PE/EPDM blend composition, particularly under dynamic curing conditions. Thermal degradation studies employing DSC and TGA indicated that sulfur vulcanization made the PE/EPDM blends thermally more stable. Between the two curative systems used, the conventional curative system imparted somewhat higher stability to the blend vulcanizate. Dynamic curing rendered the vulcanizates slightly more thermally stable than static curing under comparable conditions. Thermal degradation of the blend vulcanizates took place much faster at a relatively low temperature in air than in nitrogen. Studies of air oven aging of the blend vulcanizates enabled prediction of their life time in insulated cable applications at different temperatures. The predicted life time of 30 70 PE/EPDM blend vulcanizates at 70 °C (343 K) ranges between 10 and 15 yr.

Thermoplastic elastomers from blends of polyethylene and ethylene-propylene-diene rubber: influence of vulcanization technique on phase morphology and vulcanizate properties

Abstract Comparative studies on the dynamic and static vulcanization of blends of polyethylene (PE) and ethylene-propylene-diene monomer rubber (EPDM) are reported. The studies were made using a PE/EPDM blend ratio range of 40 60 to 20 80 , over which the occurrence of phase inversion was indicated from torque rheometric studies. The state and rate of sulfur cure were varied by use of different appropriate doses of (a) tetramethylthiuram disulfide-mercaptobenzthiazyl disulfide-sulfur (TMTD-MBTS-S) combination as a conventional curative and (b) TMTD-Si69-S combination as a silane curative system. Of the two curative systems, the conventional system imparted measurably higher cure rates. For a particular blend ratio and for a given crosslink density level established in each case, the tensile strength and elongation at break measured at 298 K were higher for vulcanizates obtained statically compared to those obtained dynamically, while the corresponding modulus values followed the opposite trend. High-temperature tensile properties (at 403 K) and hot elongation and hot set values (at 523 K) for the vulcanizates were also evaluated. The property differences for vulcanizates from static and dynamic curing have been explained in the light of differences in the morphology developed.

Modification of cotton by acrylic acid (AA) in the presence of NaH2PO4 and K2S2O8 as catalysts under thermal treatment

Abstract Cotton fabric was modified using acrylic acid (AA) as the finishing agent in the presence of K2S2O8 and NaH2PO4 catalysts separately or in selected combinations, employing a pad-dry-cure technique. Treatment with 8% AA at 30°C and at pH 7 produced optimum effects: a batching time of 30–45 min at 30°C followed by drying of the batched fabric at 95°C for 5 min and curing of the dried fabric at 140°C for 5 min produced most balanced improvements in the textile related properties. NaH2PO4 catalyst allowed esterification of AA with the cellulosic constituent of cotton, and K2S2O8 catalyst allowed radical polymerization of free-AA or cotton bound AA moieties, ultimately leading to some degree of crosslinking of the chain polymers of cotton. Examination of the surface morphology of untreated and treated cotton fabrics by scanning electron microscopy revealed a good degree of masking of the convolutions of the cellulosic fibres and surface crack by a cohesive film of poly(acrylic acid) or its salt, particularly when K2S2O8 was used either alone or in combination with NaH2PO4 as catalyst.