MORPHOLOGY AND RHEOLOGY OF NONREACTIVE AND REACTIVE EPDM/PP BLENDS IN TRANSIENT SHEAR FLOW: PLASTICIZED VERSUS NONPLASTICIZED BLENDS

Abstract

Abstract Both nonplasticized and plasticized ethylene-propylene-diene-terpolymer/polypropylene (EPDM/PP) based thermoplastic elastomers (TPEs) were prepared in the presence and absence of a curing system (i.e., reactive vs nonreactive TPEs). The nonlinear viscoelastic behavior and morphology evolution of these blends were investigated through single and multiple start-up transient experiments to find out the effects of composition, plasticizer, and the presence of the curing system in a homogeneous shear flow field. Due to the highly elastic nature of the elastomeric component, the shear rate was set to 0.1 s−1 and in the case of multiple start-up experiments a 10 min rest time was set between consecutive shearing cycles. The specific interfacial area (Q) of the TPEs was analyzed prior and after shearing and subsequently correlated to the corresponding rheological response of these blends. The magnitude and the width of the stress overshoot were correlated to the morphology of the blends, elastomer content, the presence of plasticizer and curing system. The presence of a plasticizer (paraffinic oil) drastically decreased the viscosity and elasticity of both neat polymers and consequently the resulting TPEs; and it further reduced the initial curing rate of the elastomeric component at the early shearing stage of the reactive TPEs. Moreover, the plasticization promoted swelling and coalescence, enlarging the size of the polymeric domains, and decreasing the specific interfacial area. Furthermore, the in situ curing reaction in the reactive TPE blends resulted in less elongated polymeric domains with an irregular and larger interface compared to the nonreactive blends. A phase inverted morphology has also been observed for nonplasticized high elastomer content reactive TPEs sheared for long periods. The obtained experimental morphology data of the nonreactive blends subjected to multiple start-up experiments was fairly well predicted using a phenomenological model proposed by Lee and Park [J. Rheo. 38(5), 1994].