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Butyl rubber (polyisobutylene‐co‐isoprene) mixed with polyisobutylene was crosslinked to yield elastomeric macromolecular networks containing dissolved linear macromolecules. Adhesion of these materials to themselves (self‐adhesion) and to an inert substrate was investigated over a wide range of peel rates and test temperatures. Greatly enhanced self‐adhesion was found when linear polyisobutylene molecules of high molecular weight were present, but the strength of adhesion to a rigid inert substrate was hardly affected. The enhancement of self‐adhesion is attributed to interdiffusion of polyisobutylene molecules. It was greatest at intermediate peel rates and temperatures, becoming insignificant at extremely low rates, probably because the diffusing species can then migrate readily, and at high effective rates of peel when the polymer approaches the glassy state and the strength of adhesion is high in all cases. A transition to somewhat lower levels of adhesion at relatively high rates of peel is tentatively ascribed to the onset of molecular fracture in place of pullout. The presence of large amounts of low‐molecular‐weight polyisobutylene (M̄v = 50,000 g/mol) increased the level of self‐adhesion and of adhesion to an inert substrate to a similar degree, over a broad range of peel rates. This effect is attributed primarily to enhanced viscous losses in the elastomeric layer during separation. Application of these results to crack and weld‐line healing in glassy plastics is discussed.

Ethylene‐propylene‐diene‐terpolymer (EPDM) and polypropylene (PP)‐based uncross‐linked and dynamically cross‐linked blends were prepared both in an internal mixer and in a corotating twin‐screw extruder. The effects of composition, plasticization and mixing equipment on the morphology development and the final viscoelastic properties were studied. In the uncross‐linked blends, the plasticization resulted in a coarser morphology. Furthermore, it was shown that the majority of the plasticizer resided in the EPDM phase, enabling its deformation in the flow direction. In addition, the intensive mixing conditions inside the twin‐screw extruder resulted in a finer morphology. In the dynamically cross‐linked blends, the twin‐screw extrusion process resulted in a higher level of gel content with larger EPDM domains. The plasticization showed again a coarsening effect, resulting in interconnected cross‐linked EPDM domains. An interesting interfacial phenomenon was observed especially in the plasticized vulcanized blends where nanometer size occluded PP domains were stripped off and eroded into the EPDM phase. With the exception of the nonplasticized uncross‐linked blends, the viscoelastic properties of all other blending systems were found to be directly affected by the morphology, gel content (in the case of cross‐linked blends), and the presence of the plasticizer. POLYM. ENG. SCI., 2012. © 2011 Society of Plastics Engineers

Semi-crystalline polyolefins, e.g., polypropylene in its isotactic and syndiotactic forms, become brittle at low temperature due to their inherent crystallinity and relatively high Tg. It has been discovered that certain “non-polar” aliphatic esters, in particular monomeric tallates and sebacates can effect a large depression in Tg of the polypropylene amorphous component which is in line with free volume considerations. The melting point of the crystalline fraction was also depressed albeit to a much smaller extent. This successful plasticization of polypropylene was applied to heterophase systems with the elastomer crosslinked in situ during melt blending with polypropylene and in the presence of a plasticizer. The plasticizer was distributed in both polymer components of the blend. Therefore the glass transition temperatures of both the polypropylene and the elastomer phases could be greatly depressed through simultaneous plasticization of both polymer phases resulting in a supertough material at −40°C and below. Since only the amorphous component of polypropylene is plasticized, the crystalline fraction is not much affected and the upper service temperature range is maintained. The resulting TPEs have an excellent balance of engineering properties to −125°C and are much more elastic than unplasticized TPEs due to the suppression of yielding behavior.

ABSTRACT:The high rate shear flow behavior and the morphology of five different oil-extended polypropylene (PP)/ethylene-propylene-diene monomer (EPDM) thermoplastic vulcanizate blends were investigated with the melt flow rate (MFR) of the PP varying from 0.7 to 20. The ratio of rubber to PP is 70 : 30 in three of the thermoplastic vulcanizates (TPVs) and 50 : 50 in the other two TPVs. The distribution of the high-temperature oil between the PP melt and the rubber is a key parameter because this will affect the viscosity of the PP/oil medium. The object of this study was to estimate the matrix composition in each of the TPVs at processing temperatures and to compare the shear viscosity of the effective matrix with that of the TPV. To this end, several PP/oil mixtures were prepared and their viscosity curves were correlated with the neat PP melt viscosity curves by means of shift factors varying with oil concentration. The oil distribution between the PP and rubber phases was estimated from TEM micrographs of the TPV blends. The results show that the PPs are mixed with oil to different proportions in the different TPVs and the viscosity curves of these mixtures exhibit the same trends in magnitude as the corresponding TPV viscosity curves. Hence, the shear flow of TPVs can be understood more readily in terms of the effective PP/oil medium flow behavior than in terms of the neat PP melt flow.