Melt‐mixing was employed to prepare multiwall carbon nanotubes (MWCNTs) based polypropylene (PP) composites, wherein MWCNTs vary in “agglomerate” size and also in terms of “agglomerate” structure. Morphological analysis revealed MWCNTs‐D type exhibits bigger “agglomerate” size with compact “agglomerate” structure with respect to MWCNTs‐N type, that show smaller “agglomerate” size with porous “agglomerate” structure in the corresponding PP/MWCNTs composites. Melt‐rheological analysis showed a rheological percolation threshold of 2 to 3 wt% in PP/MWCNTs‐N composites, whereas PP/MWCNTs‐D composites exhibited a rheological percolation of 3 to 4 wt% of MWCNTs. AC electrical conductivity measurements exhibited an electrical percolation threshold of 0.5 to 1 wt% of MWCNTs‐N, whereas MWCNTs‐D type depicts an electrical percolation threshold of 2 to 3 wt% of MWCNTs in the respective composites. Further, an unique dispersant; Li salt of 6‐aminohexanoic acid (Li‐AHA) was utilized to “deagglomerate” MWCNTs. Moreover, PP‐g‐MA was also utilized in combination with Li‐AHA encapsulated MWCNTs in the corresponding composites. An extensive morphological, rheological, and electrical conductivity measurements suggested the influence of Li‐AHA encapsulated MWCNTs and PP‐g‐MA on the transformation of MWCNTs “agglomerate” into “individualized” and smaller MWCNTs “agglomerate” in PP/MWCNTs composites.
Silicone core dendrimers bearing terminal dialkoxy and trialkoxy silane groups were prepared in a three-step synthesis. Initially, the Si-H terminated multifunctional silicone dendrimer, i.e. tetrakis(dimethylsiloxy)silane, was prepared by the reaction of tetraethoxysilane and dimethylethoxysilane. Tetrakis(dimethylsiloxy)silane on reaction with allylglycidylether in the presence of Speier's catalyst under pressure (100 psi) yielded epoxy-terminated dendrimer in very high yield (95%). The epoxy-terminated dendrimer was reacted with aminopropylalkoxysilanes to yield the next-generation dendrimer bearing dialkoxy and trialkoxy silane groups. The dendrimers were characterized by the usual physico-chemical techniques, i.e. elemental analysis, FT-IR, 1 H, 13 C and 29 Si NMR. Thermal studies (Thermogravimetric analysis and Thermomechanical analysis) of the alkoxy terminated dendrimers and its cured products were also carried out.
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.
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