Abi Santhosh Aprem

Recent Developments in Crosslinking of Elastomers

Abstract The recent developments in the vulcanization of elastomers, major types of crosslinking, and mechanism of crosslinking have been reviewed. Attention has been made to sum up the accelerated...

Studies on accelerated sulphur vulcanization of natural rubber using 1-phenyl-2, 4-dithiobiuret/tertiary butyl benzothiazole sulphenamide

Abstract The use of binary accelerators has gained tremendous importance since it increases the production rate of the article made of that elastomer. The authors have analyzed the performance of a novel binary accelerator system in the sulphur vulcanization of natural rubber (NR). The vulcanizates resulting from the binary accelerated process obtained good mechanical properties, ageing and swelling resistance. Network characterization of the mixes was done using swelling measurements, stress–strain analysis etc. The chain entanglement density was measured using dynamic mechanical analysis. However the performance is found to be dependent on the relative proportion of mono, di and polysulphidic linkages in the material. The result of the study points out that the proposed system can be active in NR regardless of the vulcanization recipe and temperature. The performance of the new binary system in filled vulcanizates is also studied. Based on the processing, mechanical and chemical characterization an optimum concentration is suggested for the new system.

Cure Characteristics and Mechanical Properties of Natural Rubber–Layered Clay Nanocomposites

The effect of interlayer distance of nanoclay on mechanical properties, cure characteristics, and swelling resistance of natural rubber (NR) in varying clay proportion were studied. X-ray diffraction results of nanocomposite with 10 phr of nanoclay showed the formation of an intercalated structure. The rate of vulcanization and maximum torque value of the nanocomposite are higher than the gum compound. Nanocomposites with clay having higher interlayer distance shows superior mechanical properties. Mechanical properties gradually increase with increase in clay loading up to 10 phr. A 50% increase in tensile strength and about 150% increase in modulus at 300% elongation were observed for the nanocomposite with 10 phr clay loading. Better barrier properties offered by the nanocomposites due to the presence of tortous path was confirmed by the Nielsons model.

Thermal and Barrier Properties of Organoclay-filled Polysulfone Nanocomposites

Organo-modified fluorohectorite (OFH) clay-filled polysulfone (PSf) nanocomposites were prepared by a solution casting method. The dispersion of OFH clay in PSf nanocomposites was investigated using X-ray diffraction (XRD), atomic force microscopy (AFM), and transmission electron microscopy (TEM). Thermal analysis revealed that incorporation of organoclay increased the thermal stability and glass transition temperature (Tg) of nanocomposites. The barrier properties of the nanocomposites studied were found to be significantly improved. It is worth mentioning that the improved thermal stability and barrier performance of these nanocomposites with the addition of organoclay in PSf matrix obviously offers immense potential in industrial and automobile applications.

Influence of hygrothermally degraded polyester-urethane on physical and mechanical properties of chloroprene rubber ☆

Abstract The influence of hygrothermally-degraded polyester urethane (HD-PUR) waste on chloroprene rubber (CR) has been studied giving special attention to curing behaviour, mechanical properties and dynamic mechanical behaviour. The presence of primary and secondary amines in HD-PUR, did not increase the cure rate of CR. The mechanical properties of chloroprene vulcanizates were improved upon HD-PUR addition. The strain-induced crystallisation of CR did not show any deviation upon the addition of HD-PUR. Crosslink densities calculated from swelling studies, stress–strain behaviour, and modulus measurements are found to increase upon HD-PUR addition and showed similar trend. The glass transition temperature (Tg) did not show any significant change, with the addition of HD-PUR. Scanning electron microscopic studies have been done in order to have an insight into fracture behaviour of the samples and to analyse the microstructure of the blends.

Sulphur Vulcanisation of Styrene Butadiene Rubber using New Binary Accelerator Systems

The influence of the newly developed binary accelerator 1-phenyl-2,4-dithiobiuret (DTB) in combination with sulphenamides like DCBS, MBS, TBBS on the cure characteristics, mechanical properties, viscoelastic behaviour and network characteristics of styrene butadiene rubber (SBR) is studied. Kinetics of vulcanisation is followed at three different temperatures. Mechanical properties are found to be improved upon DTB addition. Attempts have been made to correlate the observed properties with extent of crosslinking of DTB. Effect of aging on tensile properties of the vulcanisates was also done. The extent of crosslinking was also improved with DTB cured vulcanisates. Dynamic mechanical analysis has been done and the influence of the new accelerator systems on the modulus, glass transition and entanglement densities of the vulcanisates was investigated. The effect of fillers like carbon black and silica on DTB on technological properties of SBR vulcanisates and the extent of reinforcement caused by the fillers were also studied.

Permeation of Oxygen and Nitrogen Gases through Poly(ethylene-co-vinyl acetate) Membranes

The transport of oxygen and nitrogen gases through uncrosslinked and crosslinked poly(ethylene-co-vinyl acetate) membranes has been analyzed. Poly(ethylene-co-vinyl acetate) was crosslinked by dicumyl peroxide and benzoyl peroxide. Neat sample showed a lower permeation coefficient due to the crystalline nature. The crystalline nature was supported by X-ray diffraction analysis. The difference in the permeation behavior of the two crosslinked samples was correlated with crosslink density. Crosslink density was calculated using equilibrium sorption method. Differential scanning calorimetry analysis also supports the different permeation behavior of the crosslinked samples. The O2/N2 selectivity of the membranes was estimated. The influence of the crosslink density and size of penetrants on permeation were analyzed. The effect of free volume on the gas barrier properties was investigated by positron annihilation lifetime spectroscopy.

Sorption and diffusion of acrylonitrile monomer through crosslinked nitrile rubber

As the first step for the preparation of interpenetrating polymer networks from nitrile rubber and polyacrylonitrile, the sorption and diffusion of acrylonitrile monomer through nitrile rubber crosslinked by three different vulcanization systems—conventional (CV), dicumyl peroxide (DCP), and a mixture consisting of sulfur and peroxide (mixed)—were studied in the temperature interval of 30–70°C. Kinetic curves have been generated for these systems to compute diffusion and sorption coefficients. The equilibrium sorption is found to be maximum for the CV system. The molar mass between crosslinks (Mc) has estimated and compared with affine and phantom models. It was found that the Mc values follow the affine model. The diffusion coefficient values are highest for DCP and lowest for CV. It was observed that the kinetics of liquid sorption followed an anomalous behavior. The temperature dependence of the transport parameters was followed by an Arrhenius relationship, from which the activation energy for diffusion, permeation, and sorption were calculated. It is found that temperature activates diffusion in all cases. The polymer–solvent interaction parameter was determined. The amount of polysulfidic linkages in the rubber network was also estimated. The experimental results were compared with theoretical predictions.

Effect of 1-phenyl-2,4-dithiobiuret as secondary accelerator on cure characteristics and vulcanisate properties of natural rubber-styrene/butadiene rubber blends

Abstract Blends of natural rubber and styrene/butadiene rubber have been cured using a new binary accelerator system containing 1-phenyl-2,4-dithobiuret (DTB). This new accelerator was synthesised and used in combination with sulphenamides such as dicyclohexyl benzothiazyl sulphenamide, tertiary butyl benzothiazole sulphenamide and morpholinothio benzothiazole sulphenamide. A significant reduction in cure time was observed with the addition of DTB. Network characterisation of the vulcanisates was carried out by the estimation of cross-link density and relative proportions of crosslinks. The mechanical properties of the vulcanisates improved upon addition of DTB. Dynamic mechanical analysis was carried out to study the effect of the new accelerator on entanglement density and modulus. Based on the processing behaviour, mechanical properties and chemical characterisation it was found that DTB could be effectively used as a secondary accelerator in the curing of NR-SBR blends.