Two series of polypropylenes with different molecular weight distribution and tacticity characteristics were injection molded into flexural test specimens by varying cylinder temperature and the effects of the molecular weight distribution and tacticity on the structure and properties of the moldings were studied. Measured propertied were flexural modulus, flexural strength, heat distortion temperature, Izod impact strength, and mold shrinkage and structures studied were crystallinity, the thickness of skin layer, a*-axis-oriented component fraction and crystalline orientation functions. The relations between the structures and properties were also studied. It was found that the molecular weight distribution and tacticity characteristics affect the properties mainly through the molecular orientation and crystallinity, respectively.

Rheological properties of metallocene-catalyzed isotactic polypropylenes (MET-PP) were evaluated in comparison with those of Ziegler-Natta-catalyzed isotactic polypropylenes (ZN-PP) and MET-PP was generally characterized in a rheological aspect. Based on the characterization, various flow processibilities and their effect on the higher order structure and product properties of the processed article were estimated. The capillary flow properties at various temperatures, elongational flow properties, and dynamic viscoelasticities of MET-PPs and ZN-PPs with various melt flow indexes (MFIs) were measured. Furthermore, as an example of application of rheological analysis, the selection of proper raw resin and processing conditions in the sheetextrusion of MET-PP was studied. MET-PP shows the following rheological features due mainly to the narrow molecular weight distribution in comparison with ZN-PP with equivalent MFI to that of MET-PP: while the viscosities at low shear rates are lower, those at high shear rates are higher. Although there is little difference in the loss modulus GЉ (viscosity), the storage modulus GЈ (elasticity) is very (about one decade) lower. The die swell is much smaller. The entrance pressure loss and end correction coefficient are lower. The critical shear rate at which a melt fracture begins to occur is lower. The melt tension, elongational viscosity, and melt flow index ratio are lower. The flow activation energy is slightly lower. The zero-shear viscosity obeys the 3.4th-power law independent of catalyst.

ABSTRACT:The measurement of crystallization and melting behaviors under constant rates of cooling and heating and the Avrami's analysis of isothermal crystallization were carried out for various metallocene-(MET-PP) and Ziegler-Natta-catalyzed (ZN-PP) random polypropylene copolymers with various ethylene contents. Both the melting point T m and the crystallization temperature T c decrease with increasing ethylene content. Compared at the same ethylene content, both are lower for MET-PP because of the higher uniformities of stereoirregular bonds and copolymerization bonds. T m and T c show a linear correlation, and compared at the same T c , T m of MET-PP is lower than that of ZN-PP. This is because MET-PP has narrower distributions of isotactic sequence length and hence of lamellar thickness than ZN-PP. The heat of fusion and the latent heat of crystallization decrease with ethylene content. At the same ethylene content, both are lower for MET-PP, owing also to the higher uniformities of stereoirregular bonds and copolymerization bonds. From the Avrami's analysis, it is assumed that there is little difference in crystallization modes of both catalyst PPs.

ABSTRACT:Relationships between the rheological properties and the molecular weight distribution of two polypropylene series with different molecular weight distribution characteristics were studied. The end correction coefficient in capillary flow is determined by the molecular weight M w and the molecular weight distribution M w /M n , and is higher as both characteristic values are larger. The die swell ratio at a constant shear rate depends on M w , M w /M n , and M z /M w , and is higher as the three characteristic values are larger. The critical shear rate at which a melt fracture begins to occurs depends on the molecular weight M w and the molecular weight distribution M z /M w , and is proportional to M z /M w 2 in a log-log plot. The critical shear stress does not depend on the molecular weight, and is higher as M z /M w is higher. The zero-shear viscosity is determined by a molecular weight of slightly higher order than M w , and the characteristic relaxation time is determined by M z . The storage modulus at a constant loss modulus scarcely depends on the molecular weight, and is higher as the molecular weight distribution M w /M n is higher.

Maleic anhydride was grafted onto poly(propylene) (PP)-type thermoplastic elastomer PER by reactive processing with a screw extruder and a maleated PER (MPER) was prepared. With the intent of ionic crosslinking, metal compounds such as aluminum stearate (AlSt), magnesium stearate (MgSt), calcium stearate (CaSt), zinc stearate (ZnSt), potassium stearate (KSt), sodium stearate (NaSt), magnesium hydroxide (MH), zinc oxide (ZnO), and zinc sulfide (ZnS) were added to the MPER and meltmixed with the screw extruder, and crosslinked compounds were obtained. The degree of crosslinking estimated from the gel fraction was in the order AlSt, MgSt, CaSt, ZnSt Ͼ NaSt, KSt Ͼ MH Ͼ ZnO, ZnS Ͼ MPER. The rheological properties, such as capillary flow properties and dynamic viscoelasticities, of the compounds were measured and their melt processabilities were evaluated. The viscosity increased with increasing the content of the metal compounds and the increase was higher at the lower shear rate. The increasing effect of the viscosity at low shear rates was AlSt Ͼ MgSt Ͼ ZnSt Ͼ NaSt Ͼ KSt Ͼ MH Ͼ ZnO Ͼ ZnS Ͼ MPER. Namely, the viscosity increasing effect of the metal salt of stearic acid is the higher for the larger ionic charge and the viscosity increasing effects of other compounds are lower than those of the metal salts of stearic acid. Accordingly, by changing the kind and content of the metal compounds, the viscosity can be freely controlled. Considering also other rheological characteristics, these ionically crosslinked compounds are assumed to show ideal flow processabilities except for the extrudate appearance. To improve the appearance, it is necessary to dilute the compound with unmodified PER, PP, or fillers.