Composites of polypropylene (PP) and multi‐walled carbon nanotubes (MWCNTs) were prepared via melt‐mixing utilizing Li‐salt of 6‐amino heaxanoic acid (Li‐AHA) modified MWCNTs in the presence of a compatibilizer (polypropylene‐g‐maleic anhydride; PP‐g‐MA). Improved interaction between the anhydride group of PP‐g‐MA and the amine functionality of Li‐AHA was confirmed via FTIR and Raman spectroscopic analysis. A higher glass transition temperature (Tg) of the PP phase has been observed in these composites as compared to pristine MWCNTs‐based composites. The crystallization temperature (Tc) of the PP phase was increased as a function of pristine MWCNTs concentration in PP/MWCNTs composites indicating hetero‐nucleating action of MWCNTs. However, Tc value was decreased in the presence of Li‐AHA modified MWCNTs indicating the adsorbed Li‐AHA on the MWCNTs surface. Moreover, Tc value was higher in the presence of Li‐AHA modified MWCNTs with PP‐g‐MA as compared to that of without PP‐g‐MA, suggesting the desorbed Li‐AHA from the MWCNTs surface due to melt‐interfacial reaction. Further, MWCNTs were extracted by hot vacuum filtration technique from PP/MWCNTs composites containing Li‐AHA and PP‐g‐MA. The isothermal crystallization kinetics showed a variation in crystallization behavior of the PP phase in the corresponding composites as compared to the “extracted MWCNTs.” POLYM. ENG. SCI., 57:183–196, 2017. © 2016 Society of Plastics Engineers

The isothermal crystallization behaviour of the polypropylene (PP) phase in PP/multi-walled carbon nanotubes (MWCNTs) composites has been investigated via differential scanning calorimetric analysis, which showed the influence of the varying dispersion level of MWCNTs in the respective PP matrix. PP/MWCNTs composites were prepared via melt-blending technique, wherein two different grades of MWCNTs of varying average "agglomerate" size and varying entanglements (N-MWCNTs and D-MWCNTs) were utilized. Furthermore, the influence of melt-viscosity of the PP phase was investigated on the crystallization kinetics of the PP/MWCNTs composites. Heterogeneous nucleation ability of MWCNTs has resulted in a decrease in half time of crystallization (t 1/2 ) from $14 min for pure PP to $6 min for PP/N-MWCNTs and $11 min for PP/ D-MWCNTs composites at 1 wt% of MWCNTs at 132 8C. Overall rate of crystallization (k) has significantly increased to 4.9 3 10 22 min 21 for PP/N-MWCNTs composite as compared with 6.2 3 10 23 min 21 for PP/D-MWCNTs composite at 0.5 wt% of MWCNTs at 132 8C. Moreover, the effect of a novel organic modifier, Li-salt of 6-amino hexanoic acid along with a compatibilizer (PP-g-MA) has also been investigated on the crystallization kinetics of the PP phase in PP/ MWCNTs composites.

Transmission electron microscopic image of separated MWCNTs (N51L15G5) showing the wrapped polymer chains on the MWCNTs surface, which corresponds to the α-phase of the PP.