Vapor sensing performance as a diagnosis probe to estimate the distribution of multi-walled carbon nanotubes in poly(lactic acid)/polypropylene conductive composites

Multi-walled carbon nanotubes (MWCNT)/poly (lactic acid) (PLA)/polypropylene (PP) with different polymer blend ratios were fabricated by melt processing method. When fixed the MWCNT content at 1.0 wt.%, A6P4 (PLA/PP 60w/40w) showed the lowest resistivity, which is attributed to the formation of a co-continuous structure. According to the thermodynamics prediction, MWCNT is estimated to be selectively distributed in PLA phase. To further investigate the MWCNT localization behavior in polymer blend, a two-step compounding sequence approach was utilized to fabricate Pre-PLA (i.e., MWCNT were firstly mixed with PLA) and Pre-PP composites. Morphology observation and rheology tests were then carried out to demonstrate the MWCNT distribution in the composites. Vapor sensing behaviors of CPCs towards organic vapors with different polarity were investigated in detail. CPCs with higher PLA content showed a higher responsivity to dichloromethane, a 'good solvent' to PLA. CPCs containing higher PP content exhibited a higher responsivity towards xylene due to the strong interaction between PP and the xylene vapor. While for cyclohexane, a 'poor solvent' to PLA and PP, all the CPCs demonstrate a low responsivity. Interestingly, the vapor sensing feature can be used to testify the MWCNT localization in the polymer blend as a diagnosis probe.