Effect of selective distribution of MWCNTs on the solid-state rheological and dielectric properties of blends of PMMA and LDPE

The effects of adding multi-walled carbon nanotubes (MWCNTs) on the solid-state rheological and dielectric properties of blends of poly(methyl methacrylate) (PMMA) and low-density polyethylene (LDPE) were studied as a function of varying polymer ratio. Dynamic mechanical thermal analysis (DMTA) was performed in torsion mode, on the blends and their composites with MWCNTs. For a PMMA/LDPE blend with a ratio of 80:20, the evolution of the loss tangent with temperature showed a single thermal event, associated with the glass transition (Tg) of PMMA, confirming that co-continuity has not been achieved. Upon loading with 2 wt.% MWCNTs, a decrease in the magnitude of this peak is observed. Even though the MWCNTs preferentially locate in the polymer phase first to melt, i.e., LDPE, selective solvent extraction on this sample demonstrated that some of the MWCNTs are trapped in the major phase, PMMA. Moreover, DMTA measurements also revealed the formation of a “rheological” percolated network at ~ 3.5 wt.% MWCNTs in PMMA/LDPE blends with polymer ratios of 50:50 and 20:80, but not in 80:20. In contrast, for the same MWCNT concentration, a 80:20 blend displayed a well-developed AC conductivity plateau at low frequencies and highly enhanced dielectric properties, as a consequence of the high concentration of micro-capacitors formed by polymer films sandwiched by nanotubes within the LDPE phase, as proven from atomic force microscopy observations.