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Adhesion between two unvulcanized rubber surfaces of the same material is termed autohesive tack. Interdiffusion of polymer chains that takes place across the interface and their bulk properties controls the strength of the interface. In this work, for the first time, we have studied the influence of sepiolite nanoclay on the autohesive tack strength of brominated isobutylene-co-p-methylstyrene (BIMS) rubber. The tack strength of BIMS rubber dramatically increases with nanoclay concentration. For example, the tack strength of 8 phr of nanoclay loaded sample is nearly 300% higher than the tack strength of neat BIMS rubber. Various tack governing factors such as green strength, creep compliance, entanglement molecular weight, relaxation times, self-diffusion coefficient, average penetration depth of rubber chains, and monomer friction coefficient have been analyzed. The addition of nanoclay reduces the extent of molecular diffusion across the interface by reducing the chain mobility; however, the diffusion level is still sufficient to form entanglements on either side of the interface. The entanglements arising from the diffused chains of the nanocomposite samples show greater resistance to separation due to an increase in cohesive strength, onset of transition zone relaxation time, and monomer friction coefficient value of the BIMS rubber matrix by the nanoclay reinforcement. On the other hand, the diffused chains of the unfilled sample exhibit facile chain separation due to the less cohesive strength of the BIMS rubber matrix.

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Polypropylene (PP) is one of the most useful general purpose plastics. However, the poor transparency and brittleness of PP restricts its applications in the field of medical and personal care where silicone and polyvinyl chloride (PVC) are presently used. This work concentrates on developing highly transparent elastomeric PP blends and also thermoplastic elastomer by blending isotactic polypropylene (I‐PP) with styrene/ethylene‐butylene/styrene (SEBS) triblock copolymer. PP/SEBS blend derived from high melt flow index (MFI) PP and high MFI SEBS exhibit remarkable transparency (haze value as low as 6%) along with good percentage of elongation and processability. The reduction in difference of refractive index (RI) between PP and SEBS has been observed by blending SEBS with PP. The wide angle X‐ray diffraction studies show that there is significant reduction in the percentage crystallinity of PP by the addition of SEBS block copolymer. Temperature‐dependent polarized light microscopy studies reveal the reduction in spherulites size by the addition of SEBS block copolymer. Transmission electron micrographs show that the SEBS polymer forms a fine lamellar structure throughout the PP matrix with phase inversion at higher SEBS concentration. Development of phase morphology, crystalline morphology, and crystallinity in different blends has been analyzed and microstructure‐haze correlations have been developed. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers

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Distinct melt viscoelastic properties of novel polyamide 6 (PA6)/fluoroelastomer (FKM) thermoplastic elastomeric blends have been reported with special reference to the micro‐ and nano‐structures. In the entire frequency regime (0.0628–628 rad/s), nanostructured blend (the average dimension of the dispersed rubber phase, D ~ 90 nm) exhibited higher complex viscosity than the microstructured blend (D ~ 0.35 µm). The values of various interfacial parameters such as specific interfacial area per unit volume, interfacial tension, interaction parameter, interfacial thickness and infrared spectroscopic analysis confirmed the existence of more contact surface area between the blend components in nanostructured blend which increased intermolecular interaction. Due to the existence of greater restriction of mobility of the polymer chains, the relaxation time for the nanostructured blend was higher than that of the microstructured blend. The etched extrudate surface morphology was studied using field emission scanning electron microscopy and correlated with viscoelastic response of the blends.

The effects of change in surface energy and bulk viscoelastic properties on the autohesive tack strength of brominated isobutylene‐co‐p‐methylstyrene (BIMS) rubber have been investigated by the addition of hydrocarbon resin (HCR) tackifier and maleated hydrocarbon resin (MA‐g‐HCR) tackifier. The addition of compatible HCR tackifier results in a reasonable increment in the tack strength of BIMS rubber by modifying only the bulk viscoelastic properties (compliance, entanglement molecular weight, relaxation time, self‐diffusion, and monomer friction coefficient values) of BIMS rubber to perform better during the course of bonding and debonding steps of the peel test. Incorporation of MA‐g‐HCR tackifier (containing 5–20 wt % of grafted maleic anhydride) steadily increases the tack strength of BIMS rubber further by precisely modifying both the surface energy and bulk viscoelastic properties to perform much better in the bonding and debonding steps. However, beyond 20 wt % of grafted maleic anhydride in the HCR tackifier, the tack strength starts decreasing due to the incompatibility between the blend components, and hence, the bulk viscoelastic properties required for bond formation are severely retarded by the interrelated reinforcing effect and the phase separation effect of the brittle MA‐g‐HCR tackifier in the BIMS rubber. Hence, the polar groups in a tackifier will contribute to significant enhancement of autohesive tack strength only if the bulk viscoelastic property of the rubber‐tackifier blend is favorable for bond formation and bond separation. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 972–982, 2010

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