Modification of nano-fibrillated cellulose has been investigated through a sequence of xanthation and alkylation steps, resulting in alkylated nanocellulose materials with a relatively low degree of substitution (DS<0.03). Long alkyl chains with an average chain length of up to C66 have been employed, which are initially prepared as long-chain alkyl iodides through an iron-catalysed chain growth procedure. The alkylation of nanocellulose has been confirmed by NMR and IR spectroscopy, thermal analysis and X-ray powder diffraction. The long-chain alkylated cellulosic materials have been incorporated into low density polyethylene (LDPE) up to 1.5 wt% loading using melt extrusion. This has provided LDPE/cellulose composite materials, which have been characterised by IR spectroscopy, calorimetry, contact angle and Young’s modulus measurements. The use of long-chain alkylation at relatively low levels of substitution has allowed the incorporation of cellulose into LDPE with excellent dispersion, improved surface polarity and retention of the mechanical properties of the composite material.