The morphology and properties of high modulus polypropylenes (PP) are characterized over a wide range of material variables. These variables include the tacticity, room temperature xylene solubles (XSRT), molecular weight, melt flow rate (MFR), and polydispersity index (PI). Flexural modulus in quench‐cooled compression moldings of propylene homopolymer can be correlated to the volume fraction crystallinity, ϕc, by an empirical logarithmic dependence. The quantitative zero orientation results for the quench‐cooled compression moldings provide an approximate crystallinity normalization for oriented moldings. WAXS analyses of crystalline orientation were determined over a range of melt temperatures and mold locations and correlated to the skin area fraction by optical microscopy. WAXS analysis of the balance of orientations for the crystallographic axes suggest that the orientation balance is primarily determined by the “melt orientability” of the resin type. An empirical description of flexural modulus in injection molded PP is developed for the range of material variables and molding conditions studied. This description is represented as a function of crystallinity‐normalized modulus vs. the frozen‐in crystalline orientation.

The nucleation and growth behavior of a poly(1‐butene) melt has been measured as a function of undercooling and shear rate. Experiments were conducted using a parallel‐plate rotary shearing device with polarized light microscopy as the measuring technique. An exponential increase of nuclei with time at constant undercooling and shear rate was found. Growth rates of the crystalline bodies showed no significant change in a shear field. Nucleation and growth rate data were analyzed using expressions of the form I = I0 exp [‐ΔE/RT ‐ UTm/TΔT] G = G0 exp [‐ΔE/RT ‐ UTm/TΔT] where ΔT is the undercooling, Tm is the equilibrium melting temperature, and U contains lateral s̀ and end‐surface s̀e free energies. The value of s̀s̀e calculated from U for crystallization under shear differed from that calculated for the quiescent case by a factor of two. This difference is tentatively explained in terms of an entropy loss in the sheared system.

This paper reports an investigation of asynchronous flow marks on the surface of injection molded parts and short shots made from two different blends of polypropylene and ethylene-propylene random copolymer elastomers. Flow marks were observed on the surface with both blends; the spatial frequency of flow marks on the surface was greater in the blend B1, which also exhibited a greater contrast between the surface regions. The same blend was distinctly faster in the linear viscoelastic tests of shear creep recovery and shear viscosity growth. The degree of contrast between the flow-mark regions and the out-offlow-mark regions was examined with a detailed analysis of SEM micrographs of the surface regions as well as the near wall regions from short shots. This revealed that the dispersed phase was highly stretched to cylindrical strands in the glossy surface regions of both blends and retracted in the dull regions to different extents in the two cases. A comparison of the particle size distributions and aspect ratio distributions in different regions established that rapid retraction of the suspended elastomer phase was the dominant cause of changes in particle shape between surface regions. Nonlinear shear creep and creep recovery curves of the two elastomer components showed that at a time of 1 s, the fractional strain recovery of the elastomer in B1 was much higher than that of the elastomer in B2. Hence, the nonlinear elastic recovery of the elastomer phase at short times is an important factor in flow mark formation with blends of polypropylene and olefinic elastomers.

A high speed puncture impact apparatus was used to measure impact loss in thermally aged ABS (acrylonitrilebutadiene-styrene) as a function of time and temperature. Impact energy values decreased to a low level and degraded surface layer thickness increased as a function of aging time at three aging temperatures. Systematic removal of surface layers from thermally aged samples progressively increased impact energy values to control levels. Infrared spectroscopy, differential scanning calorimetry and molecular weight data indicate that degradation occurs in the rubber, graft and rigid phases at different times during the thermal aging period. Microscopy results show a critical degraded layer thickness which causes brittle failure of the entire sample.