The Study on the Rheological Properties of Polymer Matrix for MIF (Molded-In Foaming) Process

In order to select polymer matrix for MIF (Molded-In Foaming) process, in this study, we investigated rheological properties of commercial polymers, SBC (Styrene-Butadiene Copolymers, K-resin KK38) and SBS (StyreneButadiene-Styrene, KTR 101 and KTR 301). In time sweep test, the rheological properties (G', G", eta*) of SBS at 155 and 170 degrees C display almost constant value as a function of time from 0 s to 1800 s. On contrast, the rheological properties of SBS at 185 and 200 degrees C exponentially increase as a function of time. It could be due to gelation of SBS at high temperature conditions. These increment of rheological properties are not observed in SBC. From LAOS (large amplitude oscillatory shear) test, the nonlinear rheological properties of SBS at 155 and 200 degrees C after 1800 s are compared. The nonlinear rheological properties at 155 degrees C show simple strain thinning behavior such as linear homopolymer, however, the nonlinear rheological properties at 200 oC show 2 times strain thinning behavior (Payne effect). It well match with the gelation of SBS at 200 oC. From rheological studies, it is confirmed that the proper polymer matrix for MIF process (low rheological properties at initial time and high rheological properties after process) is SBS KTR 301.