Influence of noncovalent modification on dispersion state of multiwalled carbon nanotubes in melt-mixed immiscible polymer blends.

Multiwalled carbon nanotubes (MWNTs) were melt-mixed with polyamide6 (PA6) and acrylonitrile butadiene styrene copolymer (ABS) to obtain electrically conducting composites. MWNTs were noncovalently modified with sodium salt of 6-aminocaproic acid (MWNTs-m1) and 3-pyrenealdehyde (MWNTs-m2) to 'deagglomerate' MWNTs. Raman spectroscopic analysis indicated a G-band shift from ∼1581.9 cm(-1) for pristine MWNTs to ∼1590.2 cm(-1) for MWNTs-m1 and ∼1588.8 cm(-1) for MWNTs-m2, indicating the interaction between MWNTs and the respective modifier molecules. Blends showed 'co-continuous' morphology on the addition of MWNTs. TEM observations showed that a higher population of pristine MWNTs exhibited a 'nanoagglomerated' state in PA6 and ABS phases in the case of a 40/60 PA6/ABS blend, unlike a 60/40 blend, which depicted a higher population of 'individualized' MWNTs. Further, the corresponding blends with MWNTs-m1 and MWNTs-m2 showed 'nanoagglomerated' and 'individualized' MWNTs. Blends with pristine MWNTs showed an increase in DC electrical conductivity with an increase in PA6 concentration in the blend. Moreover, the corresponding blends with MWNTs-m1 and MWNTs-m2 exhibited an increased DC electrical conductivity value as compared to the corresponding blend with pristine MWNTs. Ratio of the intensity (H1/H2) of the crystallization peak at lower temperature (H1) to the intensity of the crystallization peak at higher temperature (H2) depicted lower values for blends with pristine MWNTs as compared to the corresponding blends with MWNTs-m1 and MWNTs-m2. TGA studies indicated the formation of a thicker 'interphase' involving MWNTs and the interacting polymer chains.