Chapter 6 - Morphology-correlated mechanical properties of ionic liquid-modified multiwalled carbon nanotubes/poly(vinyl chloride) nanocomposites

Abstract

Herein investigate the morphology-correlated studies on microstructure, mechanical, and thermal properties of ionic liquid modified multiwalled carbon nanotube (MWCNT)/poly vinyl chloride (PVC) nanocomposites. The influence of ionic liquid modification of MWCNT on the microfracture morphology, mechanical, and thermal properties of nanocomposites was focused in detail. Mechanical studies elucidated the fact that, once the percolation threshold limit is crossed, the MWCNT-MWCNT interactions dominated over the MWCNT-matrix interactions. From the microstructure and mechanical behavior of nanocomposites, it is clear that, both the cation-π interactions and hydrogen bonding interactions are driving forces for the exfoliated or intercalated state of MWCNT in polymer matrices. At lower loading, exfoliated state of carbon nanotubes (CNTs) plays a key role in improving the mechanical properties of nanocomposites. But at higher loading, exfoliation and intercalation mechanism is competing, as a result of interconnection of CNTs. In case of type 1 nanocomposites [ionic liquid modified MWCNT-based PVC nanocomposites with MWCNT and IL in 1:2 ratio (CNx (12))], the mechanical percolation limit reaches a value of 1%, and further decreases. But in case of type 2 nanocomposites [ionic liquid modified MWCNT based PVC nanocomposites with MWCNT and IL in 1:6 ratio (CNx (16))], percolation limit reaches beyond 0.1%. This variation in mechanical percolation limit for ionic liquid modified nanocomposites is as a result of plasticizing action of ionic liquid. With increase in concentration of ionic liquid used for modifying MWCNT, plasticizing action increases. Thus it is concluded that, at higher (3%) MWCNT loading, as a result of enhanced MWCNT-MWCNT interactions dominating over polymer–MWCNT interactions, there is a slight decrease in mechanical properties. In ionic liquid modified MWCNT nanocomposites, the plasticizing action of ionic liquid is also another factor for decrease in mechanical properties at higher MWCNT concentrations. This is supported by the ductile features exhibited by the nanocomposites which are confirmed from the necking behavior. Thermal stability was improved for all the nanocomposites. Ionic liquid has a positive role in preventing the liberation of HCl and enhancing the thermal stability of nanocomposites.