Three dimensional (3D) printing, or additive manufacturing, is a popular processing technique due to its versatility, cost efficiency and flexibility. This technique is used in industries ranging from automotive manufacturing to medical fields [1]. Fused deposition modelling (FDM) is one of the most common 3D printing techniques and is based on the extrusion of a thermoplastic material. One of the most used FDM printing materials is the renewable thermoplastic polylactic acid (PLA). Although having advantages such as good mechanical properties (high tensile strength, high Young’s modulus and good flexural strength) and biodegradability, PLA has shortcomings limiting its usage [2]. One major shortcoming is the costly production of PLA and one way to tackle this is to introduce a filler material. 
An attractive alternative is the abundant natural polymer lignin. Lignin has a high number of carbon content, aromatic rings and occurrence of functional groups such as hydroxyl and carbonyl groups making it a versatile material [3]. However, currently lignin is mainly considered an industrial by-product and not used to its full potential. We can change this by utilizing lignin in PLA composites. To improve the compatibility between lignin and PLA, lignin can be modified. More specifically, we ethylated and acetylated the lignin to evaluate how different modified lignins behaved. To maximize the compatibility, we prepared the composites by a solvent-casting technique, followed by extrusion into filaments. As the 3D printing of a material requires increased processing temperature, the thermal properties and melt rheology of the lignin-PLA filaments are studied. Prior to the FDM printing, the extruded filaments are processed by a pultrusion-technique to ensure even filaments with desired thickness. Lastly, the printability of the composites is optically evaluated as well as by SEM imaging.