The relationship between rheology, morphology and physical properties in heterogeneous blends

Abstract

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.

Cocontinuous morphologies in polystyrene/ethylene–vinyl acetate blends: The influence of the processing temperature

“…Several relationships have been proposed for estimating the phase‐inversion point based on the torque ratio6–8 or viscosity ratio of the blend components,9, 10 According to these theories and empirical relationships, when the viscosities of the blend components are unequal, the low‐viscosity component encapsulates the high‐viscosity component and becomes the continuous phase. All these theories predict that the cocontinuous morphology is reached at only one certain value of composition.…”

Manufacturing of Polymer Blends Using Polymeric and Low Molecular Weight Reactive Compatibilizers

“…In the range 40/60 to 60/40, there are usually co continuous phases. However, material variables such as the interfacial tension and viscosity ratio strongly influence the morphology of the blend [90][91][92][93][94]. Danesi and Porter [90], studying (polypropylene/ethylene propylene rubber) blends, found that finer dispersions were obtained when the minor phase had an equal or lower viscosity than the major phase.…”

“…This is a well-known phenomenon with a low-viscosity liquid such as combinations of oil in water or in salad dressings. There is a long history of investigations of coalescence in polymer melt blends, especially under quasi-quiescent conditions [60,92,[94][95][96][97]. The rate of coalescence of dispersed phases is increased by large interfacial tensions, small droplet size, anisotropic droplet shape, and quiescent low deformation rate conditions.…”

Reactive Compatibilization of NBR/EPDM Blends by the Combination of Mercapto and Oxazoline Groups

“…This procedure has been reported to be a good tool for determining the cocontinuous region and phase inversion in heterogeneous polymer blends. [40][41][42] A cocontinuous structure is assumed when the complete NBR phase can be extracted and the specimen still maintains its dimensional stability. The weight of the specimen after the extraction corresponds to the weight fraction of the EPDM component.…”

“…[40][41][42] The torque values of the EPDM and NBR components correspond to 27 Nm and 17 Nm, respectively. [39] From the torque ratio, one can estimate the phase inversion point at a NBR/EPDM ¼ 39:61 vol.-%.…”