Plasticisation and compatibilisation of poly(propylene) with poly(lauryl acrylate) surface modified MWCNTs

Abstract

Poly(lauryl acrylate) P[LA] synthesised using Cu(0)-mediated polymerisation was used to non-covalently functionalise multi-walled carbon nanotubes (MWCNTs) achieved via combined CH-π interactions and physical wrapping. The inclusion of P[LA] competed with the attractive van der Waals forces between MWCNTs altering interfacial interactions between neighbouring CNTs and, assisted their dispersion and distribution in a poly(propylene) (PP) matrix, confirmed from SEM/HR-TEM imaging and oscillatory rheology measurements. A rheological percolation threshold measured for composites of unmodified MWCNTs and PP at ∼0.5 wt% was shifted to lower MWCNT concentrations (∼0.25 wt%) for P[LA] functionalised MWCNTs. Addition of P[LA] also reduced the nucleating effect of MWCNTs for PP as a coating of P[LA] on the nanotube surfaces hindered trans-crystallisation of the PP. Evidence from static and dynamic mechanical measurements confirmed the P[LA] plasticised PP as both an increase in ductility and a decrease in the glass transition temperature (Tg) of PP of up to 25 °C was obtained. Addition of unmodified MWCNTs to PP resulted in an increase in the DC electrical conductivity of PP of 15 orders of magnitude, from 10−14 S/m to 101 S/m for a MWCNT loading of 5 wt%. Non-covalent functionalisation of MWCNTs utilising P[LA] only degraded electrical conductivity by about 2 orders of magnitude across the composition range.