Polylactide (PLA) has a low heat deflection temperature (HDT) such that its mechanical properties fall off at temperatures greater than 55 - 60°C, significantly hampering its industrial implementation. However, PLA is a commercially produced bio-based thermoplastic with unique properties such as high strength, biocompatibility and biodegradability. This work evaluates the use of cellulose nanocrystals (CNCs) as a potential solution to mentioned problem. CNCs are derived from cellulose which is highly abundant in nature, non-toxic, biodegradable, and has a low density. CNCs possess many attractive features for use in nano-composites. The main problem of adding CNCs to reinforce hydrophobic matrixes is that they are very dissimilar, CNCs are hydrophilic and therefore phase separate leading to a decrease in mechanical properties. A one-step method based on both Fischer esterification and acid hydrolysis was used in this work to obtain functionalized and ready-to-use CNCs, with the aim to improve the filler dispersion into the polymeric matrix. The study assesses the reinforcing effect of CNCs on PLA-based materials. CNCs functionalized with acetate (AA-CNCs), lactic acid (LA-CNCs) and unfunctionalized CNCs were synthesized and blends of PLA and these CNCs were prepared by direct melt blending. The corresponding thermomechanical properties were investigated by DMTA. Blends with LA-CNCs possessed the highest storage modulus. Based on these results, blends with up to 20 % LA-CNCs were prepared by direct melt blending and an increase of up to 20 °C in the HDT resulted. A decrease in oxygen permeability also resulted from increasing the nano-filler content. This increase in materials properties can potentially expand the applications of PLA based materials.