The Dynamic Rheological Characterization Of Structure Development And Phase Morphology For Impact Polypropylene Copolymer Melt

The Rheological functions can sensitively reflect the structure change of polymers, so the dynamic rheological tests are believed to be an effective method for obtaining the information on structure change related to thermo-stability and the evolution of morphology.Impact polypropylene copolymer (IPC) is the blend of isotactic polypropylene (iPP), ethylene-propylene random copolymer (EPR), and ethylene-propylene crystalline copolymer (E-b-P). Here, the development of melt structure for IPC and its phase-separated morphology was probed by means of dynamic rheological tests.Development of melt structure for IPC was studied through examining the influence of temperature and additive antioxidant-B215 on dynamic rheological functions. The rheological functions of IPC vary with the increase of temperature, and the second plateau appears in the lg G'～lgω curves, in low ω range, which is related to the network formation of the blends. But the incorporation of antioxidant B215 into IPC makes this second plateau disappear below 230℃ in a certain time period. Moreover, G' rise rapidly after first descends while time goes on. The decrease of G' is caused by the degradation of EPR, and the increase of G' is attributed to the change of structure in IPC resulted from the oxidation-induced crosslinking. The incorporation of antioxidant B215 into IPC inhibits both the oxidation-induced crosslinking and degradation, but mainly inhibits the crosslinking at high temperature, because that the increase of temperature accelerates the thermal degradation rather than oxidation-induced degradation.The peaks of T_g for both EPR and iPP are present in the curves of the plot lg G' ～ lg ω, revealing that the blends are heterogeneous. The SEM and PCM micrographs lead to the same conclusion. It is believed that the phase morphology with good dispersion and compatibility is the reason of the good toughness for IPC. But the dispersed phase size of IPC is too small to be detected by dynamic rheological tests, so the second plateau doesn't appear in low ω range, and the Cole-Cole versu issmooth within whole frequencies, exhibiting characteristics of a homogenous blend. All these results indicates that in the temperature range from 170 to 230℃, the IPC melt shows no further phase separation and maintains the stability.