Lignin-PLA biopolymer composite for 3D printing

Lignin is renewable and the second most abundant polymer in nature. In contrast to carbohydrates’ plant polymers this aromatic substance has not got its proper position in the material science yet and its practical importance still needs to be explored.Using the new BLN process, it is possible to obtain near natural and sulfur-free biodegradable lignin from spruce wood. This BLN spruce lignin has a low negative impact factor on the environment. It is a very promising constituent in different polymeric blends, for instance those with polylactic acid (PLA). It has been found that lignin/PLA blend is suitable for hot-melting extrusion (HME) to obtain even filaments. Prior to the extrusion lignin and PLA were mixed on the molecular level in different proportions using the solutions-blending method. Those lignin/PLA filaments then were successfully used for 3D printing based on the Fused Deposition Modeling (FDM) technique. Based on the surface analysis, thermal and mechanical studies of the lignin/PLA blends, extruded filaments and 3D printed objects it can be concluded that lignin can a substitute part of expensive PLA in polymeric blends without substantial change of their main physic-chemical properties. For instance, even without plasticisers in the biocomposite containing up to 30% of lignin the final 3D objects exhibited physic-mechanical properties similar to those from pure PLA.Solid-state NMR and FT-IR spectroscopy methods revealed, that HME did not initiate chemical reactions between lignin and PLA. On the other hand, HP-GPC showed that PLA in blends as well as pure PLA is not very stable under elevated temperature used for HME and it undergoes molecular chain cleavage.   Since both lignin and PLA are biodegradable substances, corresponding 3D printed products will also be biodegradable in contrast to the ones based on petroleum chemistry.