Microfibrillated cellulose (MFC) fibers were alkylated by propargyl bromide, allyl bromide and propyl bromide in an aqueous medium without any stirring. The chemical modifications were confirmed by Fourier transform infrared spectroscopy (FTIR), solid-state C-13 nuclear magnetic resonance spectroscopy (NMR) and X-ray photoelectron spectrometry (XPS). The alkylated MFC fibers were obtained with degrees of substitution (DS) ranging from 0.12 to 0.33. All the samples were combined with low-density polyethylene (LDPE), and then the morphology, mechanical properties and water absorption behavior of the ensuing composites were investigated. Study of the morphology of the composites by Scanning Electron Microscopy (SEM) shows a slight improvement of the MFC/LDPE interface after allylation and propargylation. Moreover, the mechanical properties of the composites were significantly improved and the moisture absorption was reduced compared to unmodified MFC fibers. (C) 2017 Elsevier Ltd. All rights reserved.