The blending of lignin as a component in a thermoplastic blend poses a challenge in the form of dispersion and compatibility. Polyesters such as poly(lactic acid) and poly(butylene adipate-co-terephthalate) offer the best opportunity of compatibility in melt blending with lignin due to their ability to form hydrogen bonds. The fractionation of lignin into more homogeneous fractions offers better dispersion and more consistent properties, retaining the toughness of the original polymer in addition to bridging stress transfer between PLA and PBAT. Functionalization of lignin was done by lactic acid grafting. The resulting blend of PLA/PBAT/modified fractionated lignin showed improved interaction between lignin and PLA, but reduced compatibility between lignin and PBAT. This thesis provides a deeper understanding on the effect of lignin heterogeneity, its fractions, and the functionalization of lignin on lignin and bioplastic blends to further the use of a largely produced industrial by-product in high value applications. / Natural Sciences and Engineering Research Council (NSERC) – Lignoworks Biomaterials and Chemicals Strategic Research Network, Canadian Foundation for Innovation (CFI), Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)