Crystallisation behaviour of composites of HDPE and MWCNTs: The effect of nanotube dispersion, orientation and polymer deformation

Abstract

Multi-walled carbon nanotubes (MWCNTs) were readily dispersed and distributed in the high density polyethylene (HDPE) matrix and a very low (<0.3 wt%, 0.17 vol%) rheological percolation threshold obtained. The polymer is seen to coat the MWCNTs, which act as a nucleating agent and induce an oriented nanohybrid shish-kebab (NHSK) crystalline structure, in part an artefact of the injection moulding process. The elastic modulus and yield stress of HDPE increased on addition of MWCNTs, but the polymer strain at break increased sharply below percolation before decreasing again above percolation. Addition of MWCNTs, above the percolation threshold, hindered orientation of the polymer chains such that failure occurred before necking during tensile testing, the inclusion of MWCNTs altered the uniaxial deformation behaviour of HDPE. SAXS/WAXS studies on samples post uniaxial drawing revealed that the HDPE and composites of HDPE and MWCNTs developed a highly oriented sheared herringbone lamellar structure. The drawing process also caused surface cavitation and voiding in the composites.