Nonisothermal shear-induced crystallization of polypropylene-based composite materials with montmorillonite
Résumé
A combined effect of organo-modified montmorillonite (o-MMT) and shear flow on nonisothermal crystallization and emerging structure of isotactic polypropylene (iPP) was studied. Composite materials of iPP with 3 wt.% of o-MMT, nanocomposite compatibilized with maleic anhydride grafted iPP and non-compatibilized composite, blend of iPP with the compatibilizer and neat iPP were sheared for 10 s at a rate ranging from 1 to 40 s−1 during cooling at 10 °C min−1, beginning at different temperatures: 143, 153 and 163 °C. The crystallization behavior of all the materials studied did not differ under quiescent conditions. However, the effects of flow, that is an increase of crystallization temperature, enhancement of nucleation and decrease of grain size, and also orientation of crystals, although dependent on shear temperature and rate, were amplified by the presence of o-MMT. The strongest effects were observed for the compatibilized nanocomposite with exfoliated clay. In the nanocomposite sheared at 143 °C crystallization temperature increased by 16 °C, more than 12 °C achieved for the blend and the non-compatibilized composite. However, even in the latter case the increase was larger than 7 °C measured for neat iPP. The sheared nanocomposite exhibited the orientation of α-phase crystals with (0 4 0) crystallographic planes parallel to the shearing direction and (1 1 0) planes bimodally oriented, parallel and normal to the shearing direction.