Poly(lactic acid)–multi-wall carbon nanotube conductive biopolymer nanocomposite vapour sensors

Conductive biopolymer nanocomposites (CPC) have been prepared by dispersing multi-wall carbon nanotubes (CNT) “guest conducting filler” in biopolymer, poly(lactic acid) (PLA) “host matrix” via solution mixing to develop volatile organic compounds (VOC) sensors. CPC transducers were fabricated by spray layer by layer (sLbL) technique and the derived sensors chemo-resistive properties have been investigated by exposition to a set of organic vapours (chloroform, methanol, toluene and water) exhibiting different physical properties such as solubility, polarity and molecular size. The influence of both vapour nature and CNT content has been elucidated and explained on the basis of solubility parameters and percolation theory. The selectivity of PLA/CNT CPC towards vapours, was found to be well correlated to solubility parameters. Among all, chloroform was the vapour that led to the highest response of sensors. To determine the influence of crystallization on conductive network architecture and thus on chemo-resistive characteristics of PLA/CNT, a comparative study has been carried out before and after annealing of sensors. The modification induced by this thermal treatment on both surface morphology and bulk crystallinity of PLA/CNT CPC, has clearly evidenced by atomic force microscopy (AFM) and differential scanning calorimetry (DSC) are found to be responsible for important changes in vapour sensing behaviour.