Effect of some molecular parameters on the flexural properties of injection‐molded polypropylene

Structure and properties of injection‐molded polypropylenes with different molecular weight distribution and tacticity characteristics

“…The relations between the flexural (tensile) modulus and the skin thickness are studied by the authors for homo PPs2, 13–15, 43, 49 (the effects of molecular weight distribution and tacticity are not studied), PP copolymers with ethylene,16, 17 particulate‐filled PPs,5, 10 and GF‐filled PPs,20 and by other researchers,22, 26 and similar results are obtained. Phillips et al26 separated the effect of crystallinity on the flexural modulus from the effect of the skin thickness and corrected the flexural modulus by the crystallinity.…”

“…The relation between the flexural strength and the skin thickness can be similarly discussed to the case of flexural modulus. The relations between the flexural (tensile) strength and the skin thickness are studied by the authors for homo PPs2, 13–15, 43, 49 (the effects of molecular weight distribution and tacticity are not studied), PP copolymers with ethylene,16, 17 particulate‐filled PPs,5, 10 and GF‐filled PPs,20 and by Kantz et al21 for a homo PP and a copolymer, and similar results are obtained.…”

“…The fact that the skin thickness of injection‐molded PP decreases with increasing cylinder temperature is already reported by the authors for homo PPs,2, 8, 11, 13–15, 33, 43, 44 PP copolymers with ethylene,11, 16, 17, 44 β‐crystal nucleator‐added PPs,18, 19 particulate‐filled PPs,5, 9–11 and GF‐filled PPs,20 and by other researchers,21, 26, 32, 38, 45–48 and is considered to be common knowledge. The fact that the skin thickness decreases with increasing the MFI or with decreasing the molecular weight is reported by the authors2, 8, 11, 13–15, 33, 43, 44, 49 and by other researchers 26, 48. The fact that the skin layer is thicker as the molecular weight distribution is broader is shown by the authors33, 49 and by other researchers26, 30, 31, 45, 50, 51 mainly by use of controlled rheology PPs.…”

“…The fact that the skin thickness decreases with increasing the MFI or with decreasing the molecular weight is reported by the authors2, 8, 11, 13–15, 33, 43, 44, 49 and by other researchers 26, 48. The fact that the skin layer is thicker as the molecular weight distribution is broader is shown by the authors33, 49 and by other researchers26, 30, 31, 45, 50, 51 mainly by use of controlled rheology PPs. As for the effect of tacticity, Phillips et al26 showed that it scarcely affects the skin thickness as in the case of the present study.…”

Effects of montmorillonite on structures and properties of injection‐molded polypropylene

“…The morphology and crystallinity in different layers differ from each other, which leads to various properties. Fujiyama investigated the orientation of PP crystallites in an injection‐molded specimen with wide‐angle X‐ray diffraction (WAXD) and small‐angle X‐ray scattering and found that the c ‐axis and a *‐axis were oriented to flow direction (FD), while the b ‐axis was oriented parallel to the thickness direction. In presence of fillers, especially if they have a high aspect ratio, the orientation behavior of polymer matrix may be changed and becomes more complicated.…”