Rheological Properties of Olefinic Thermoplastic Elastomers

Abstract

Rheological properties of olefinic thermoplastic elastomers (TPO), which contain fully crosslinked rubber particles in a continuous matrix of polyolefin (especially polypropylene, PP), were studied.Samples employed are a commercial TPO (Santoprene®, A. E. S. Japan) and a series of new TPOs produced from PP and acrylate rubber using a unique method, called “dynamic valcunization”.Even above melting point of matrix (PP), the TPOs behave as normal cross-linked rubber materials in the linear viscoelastic region.However, the TPOs show plastic flow due to a mutual displacement of the rubber particles. The stress σC needed for the displacement of the particles is almost independent from angular velocity or shear rate. The value of σC, however, depends strongly on a kind of oil contained in TPOs. The mechanism on this dependence is not clear, but it was confirmed that plasticizing or swelling of the matrix due to transferring oil from rubbers to matrix are not main reasons for this dependence, i. e., change the stress value σC.