Abstract
A high content of magnesium hydroxide was filled into a polypropylene-type resin containing maleated polypropylene-type elastomer PER (MPER) and an ionically crosslinked compound was prepared. The rheological properties of the ionically crosslinked compound were measured and compared with those of a compound without MPER, MPER, PER, and a flexible polyvinyl chloride (PVC) resin. The temperature dependence of the viscosity of MPER is stronger than that of PER and the viscosity of MPER tends to rise at low shear rates, which suggests the existence of light crosslinking in MPER. The viscosity of the ionically crosslinked compound continues to increase linearly even at low shear rates. Therefore, it shows a very high value at the low shear rates encountered during drawdown of shaped molten articles. However, it scarcely differs from those of usual resins at the high shear rates of extrusion and injection molding. Although the change of viscosity with shear rate is large, the change with temperature is very small. The die swell ratio is nearly unity and the extrudate scarcely swells after leaving a die. The change of die swell ratio with temperature and shear rate is very small and the extrudate is stable at disturbances. The ionically crosslinked compound does not generate a melt fracture until high shear rates. The elongational viscosity is about one decade higher than those of other samples. The dynamic viscoelasticity shows a rubbery plateau modulus of 3×104Pa. These rheological properties come from the synergy between the ionic crosslinking and the filling effect of magnesium hydroxide. From these experimental results, it may be assumed that the ionically crosslinked compound is a kind of thermoplastic elastomer and is suitable for contour extrusion, vacuum/pressure molding, big blow molding and foam molding. Flexible PVC shows similar rheological behaviors to the ionically crosslinked compound and has good processability. However, it has a very high activation energy for flow (the temperature dependence of viscosity and other rheological properties) of 3-5 times that of the ionically crosslinked compound. It also shows a large die swell ratio of 1.1-1.3 in comparison with 1.0 for the ionically crosslinked compound. It shows a considerably lower viscosity at low shear rates than that of the ionically crosslinked compound at around 190°C which is a suitable Processing temperature for flexible PVC. It also has the drawback of easy generation of melt fracture. Accordingly it may be said that the ionically crosslinked compound in this study has better processability than flexible PVC.
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