Percolation phenomena in bionanocomposites composed of the bioplastic polylactide and surface decorated supramolecular multiwalled carbon nanotubes (MWCNTs) are investigated. MWCNTs with three distinct surface chemistries-a native surface, a hydroxyl functionalized surface, and a short hydrocarbon functionalized surface-are prepared and studied. Two experimental methods are used to determine percolation thresholds; melt rheology provides a measure of the mechanical percolation threshold and electrical impedance spectroscopy provides values of the electrical percolation threshold. The MWCNT-loading level required to obtain mechanical percolation is systematically found to be lower than the loading level needed to achieve electrical percolation. Hydroxylated MWCNTs have the highest percolation thresholds of 1.8 (mechanical) and 6.7 wt % (electrical), which is attributed to aggregation caused by hydrogen bonding. Alkane-grafted MWCNTs have lower percolation thresholds of 0.76 (mechanical) and 2.8 wt % ( electrical). However, untreated MWCNTs have the lowest thresholds of 0.16 (mechanical) and 1.5 wt % (electrical). The reduced percolation threshold observed upon conversion of the hydroxylated surface to the alkylated surface is attributed to morphological differences-functionalization disrupts hydrogen bonding and leads to better nanotube dispersion. The combination of higher inherent conductivity and more favorable nanotube-polylactide interactions implies that unmodified MWCNTs are preferred to produce electrically conductive bionanocomposites. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 122: 2563-2572, 2011