Nanostructured thin lignin-derived carbon sheets as excellent reinforcement fillers in polypropylene

In this article, natural alkali lignin was freeze-dried and then annealed at different temperatures to achieve lignin-derived carbons (LCs) with mesh-shape or sheet-like morphology, which were incorporated into polypropylene (PP) matrix by melt compounding. Owing to the significantly increased interfacial area and improved dispersion of the carbons in the polymer matrices, with the addition of only 2 wt% relatively low temperature annealed freeze-dried lignin-derived carbon (FD-LC), the obtained PP/LC composites show notably enhanced tensile mechanical properties, including markedly improved Young's modulus and remarkably increased elongation at break compared with those of neat PP. The enhancements brought by the nano-structured thin FD-LC sheets are far more impressive than that with the same loading of particulate as-received lignin-derived carbon (AR-LC). The FD-LC filled PP composites also have rough fractured surfaces with fiber pull-out near the interface, revealing the non-negligible toughening effect of the LC. In addition, the higher temperature annealed FD-LC filler induces the further reinforcement of the composites. For the FD-LC annealed at 900 °C, the corresponding composite possesses the highest Young's modulus of 668 MPa.