Competition effect of shear‐induced nuclei and multiwalled carbon nanotubes (MWCNT) on β‐isotactic polypropylene (iPP) formation in preshear injection‐molded iPP/MWCNT nanocomposites

In this study, the influence of multiwalled carbon nanotubes (MWCNT) on β‐isotactic polypropylene (iPP) formation in preshear injection‐molded iPP/MWCNT nanocomposites is investigated layer by layer by wide angle X‐ray diffraction (WAXD). WAXD results suggest that in preshear injection‐molded pure iPP, β‐iPP exists in not only the shear region, but also the core region as a result of preshear‐induced nucleation. The addition of MWCNT can inhibit the β‐iPP formation. As the depth away from the specimen surface is decreased, the inhibiting effect is decreased. The reason responsible for that is given as follows: (1) with the addition of MWCNT, extra nuclei are induced during preshear. Both MWCNT and extra nuclei serve as α‐iPP nucleation point. Therefore, the formation of β‐iPP is restricted; (2) the cooling rate gradient is widely accepted to exist in the injection molded sample. A larger cooling rate at a smaller depth will give rise to a lower α‐iPP crystallization onset temperature and a lower nucleation efficiency of MWCNT. Since that β‐iPP grows only in the temperature range of 105°C‐140°C, the inhibiting effect of MWCNT on β‐iPP becomes weaker as the depth is decreased. POLYM. COMPOS., 39:E1149–E1158, 2018. © 2017 Society of Plastics Engineers