A single polymer pair (BR and EPDM) was used to confirm experimentally rheology-morphology relationships that have been previously gleaned from comparison of a variety of blend systems. The relative importance of the primary factors which govern blend morphology (composition and relative mixing viscosity of the components) was determined over the range of practical interest. In addition, correlation of mixing rheology with more accurate and complete shear modulus data allowed (a) molecular interpretation of rheological behavior in terms of network parameters, such as physical entanglements, and (b) estimation of the elastic and loss components of the shear modulus during mixing. An attempt was made at explaining the dependence of blend morphology on the viscoelastic properties of the components in terms of a fracture or tearing mechanism.

The morphology of heterogeneous blends of polybutadiene (PBD) and EPDM was selectively varied by a change of either the rheology of the blend components during mixing or of the blend composition. Under a given set of mixing conditions, the blend system approaches a "steady state morphology", which was found to be relatively independent of sample history. However, during subsequent compression molding, the morphology of the sample may be altered substantially with phase inversion occurring in some cases. A mechanism is proposed for the observed rheology-morphology behavior.The strain moduli of the vulcanizates prepared by irradiation of the elastomer blends were similar to those predicted using the parallel Takayanagi models. A positive synergism with respect to energy to break and stress at break was noted particularly in cases where the blend components showed a significantly different mechanical response. The sensitivity of the stress-strain response of these blends to changes in morphology was less than anticipated. This is attributed to restrictions imposed on the movement of the softer phase by the hard phase component of the blend. ZUSAMMENFASSUNG:Die Morphologie heterogener Polymermischungen aus Polybutadien (PBD) und Athylen-Propylen-Dien-Terpolymeren (EPDM) wurde selektiv variiert, indem entweder die Rheologie der Mischungskomponenten wahrend der Mischung oder die Zusammensetzung der Mischung geandert wurden. Bei gegebenen Mischungsbedingungen nahert sich das Mischungssystem einer ,,Steady-State-Morphologie", die sich als relativ unabhangig * Paper presented at the joint meeting of the GDCh-Fachgruppe "Makromolekulare Chemie" and the FachausschuR "Physik der Hochpolymeren" of the Deutsche Physikalische Gesellschaft on "Multiphase Polymer Systems" in Bad Nauheim (Germany) on March 30th 1976. jedoch die Morphologie wesentlich andern, wobei in einigen Fallen Phasenumwandlung eintritt. Fur das rheologisch-morphologische Verhalten wird ein Mechanismus vorgeschlagen.Die Dehnungsmoduln der durch Bestrahlung der Elastomermischungen hergestellten Vulkanisate glichen denjenigen, die durch die Takayanagi-Modelle vorausgesagt wurden. Ein positiver Synergismus hinsichtlich der Bruchenergie und der Zugspannung beim Bruch wurde speziell in den Fallen beobachtet, in denen die Mischungskoponenten ein ausgesprochen unterschiedliches mechanisches Verhalten zeigten. Die Empfindlichkeit des Zug-Dehnungsverhaltens dieser Mischungen bezuglich der hderungen in der Morphologie erwies sich geringer als vorher angenommen. Dies wird auf Einschrankungen in der Bewegungsmoglichkeit der weicheren durch die harte Phase in der Mischung zuruckgefuhrt.

Fundamentals of composite material technology are applied to the investigation of multi-ply cord-reinforced rubber systems as used in pneumatic tires. The stiffness parameters of such multi-ply systems are determined through the use of the elastic properties of the constituent cord and rubber components. The effects of coupling between the bending and stretching modes of deformation are discussed along with the limitations of present composite material technology as applied to soft rubbery systems. The predicted stiffness parameters are related to tread wear, obstacle envelopment, vibration, and stress analysis of tires.

The nuclear quadrupole coupling constant provides an example of a property which is sensitive to the form of the electronic wavefunction in the region of the quadrupolar nucleus. A method is discussed in which the wavefunction is separated into a core and a portion surrounding the quadrupolar nucleus. This latter portion of the wavefunction is determined by means of a single-center expansion. Calculations of the electric field gradient at the deuteron in LiD are presented. The dependence of the calculations on the core and on the position of the expansion center is studied. The results are in good agreement with experiment and more elaborate calculations.

Tensile properties of two-phase elastomer-elastomer vulcanizates were measured and evaluated in terms of the initial number average molecular weight (Mn), the crosslink density (veff) and the glass temperatures (Tg's) of the composite. Interpretations of the tensile behavior of elastomers with a single Tg are reasonably clear. Such interpretations are much more complex for heterogenous blends of two materials having dissimilar viscoelastic properties. Heterogeneous blends of either an EPDM (−60° Tg) with a BR (−60° Tg) or with an EPDM (−60° Tg) with a BR (−5° Tg) were prepared with differing composition, morphology and two levels of radiation crosslinking. The morphology of the samples used in this study has been described in Part 1.[1] The rupture energies of the blends having −60°/05° Tg's were usually greater than a weight averaged value of the components and for equivalent compositions were higher than that obtained for blends having equal (−60°/−60°) Tg's. This favorable synergism persisted after the data were put into a form which takes into account the large effects of Mn.Veff and Tg. The effect of domain size in the experimental range of 0.2 to 10 micrometres on rupture energy was small. There is some evidence for a maximum in rupture energy at the 1 micrometre level. At a given Mooney–Rivlin 2C1 modulus, a higher rupture energy was observed for vulcanizates from the higher Mn blends. Such higher Mn vulcanizates have a higher ratio of physical entanglements to chemical crosslinks and a lower proportion of free ends in the network.