Melt rheology analysis through experimental and constitutional mechanical models of exfoliated graphene based polylactic acid (PLA) nanocomposites

Effect of incorporation of exfoliated graphene (GR) on the structural and flow nature of the melt processed polylactic acid (PLA) was investigated by melt rheology and solution viscosity measurements. Pristine polymer (PLA-M) and its composites (PLA-M-0.05GR and PLA-M-0.2GR) showed shear thinning behaviour. Excellent dispersion of GR and the single phase nature of the composites were noticed by studying Han plot and Cole-Cole plot and Van Grup-Palmen's plot. Viscosity average molecular weight (M-v) was found to be increased in case of the GR loaded composites as compared to PLA-M. Hydrodynamic radius being proportional to M-v(0.59) indicated homopolymeric PLA system. Melt rheology and solution viscosity investigations revealed good compatibility, uniform GR dispersion in the PLA matrix and the higher flowabilty was in case of PLA-M-0.05GR composite. Mechanical model fitting study implies Hershel-Bulkley model as more suitable mechanical model for the nanocomposite system with r-square 0.98 and rheology index 0.6. Inclusion of GR into PLA matrix has reduced the yield stress and viscosity for the nanocomposites.