One-step modification and nanofibrillation of microfibrillated cellulose for simultaneously reinforcing and toughening of poly(ε-caprolactone)

Extensive efforts have been devoted to utilize cellulose fibers as reinforcement for poly(ε-caprolactone) (PCL) to prepare fully biodegradable composites with enhanced mechanical properties, but unfortunately the improvement of strength is always at the sacrifice of toughness. In the current work, we have developed an efficient way to prepare poly(ε-caprolactone)/functionalized cellulose nanofibers (PCL/f-NFC) nanocomposite, which is both strong and ductile. Large scale f-NFC was produced from microfibrillated cellulose (MFC) in one step through the synergy of mechanical and chemical actions derived from ball milling. The f-NFC with nanosized scale and tailored hydrophobicity is compatible with PCL, which leads to strong interfacial interaction between f-NFC and PCL and good dispersion of f-NFC in PCL. The tensile strength of this bionanocomposite undergoes a remarkable enhancement nearly 100% and elongation-at-break increases by 68% with extremely low f-NFC content as 0.1 wt%. Since both surface property and fiber size affect the performance of composites, original MFC, functionalized MFC (f-MFC) and cellulose nanofibers (NFC) without hydrophobic modification are also incorporated into PCL to make a systematic comparative study to identify the dominating factor influencing the performance. The overall results suggest that surface modification plays a dominant role at low fiber content, while nano-sized scale is much more beneficial at high fiber content. Most importantly, the synergistic effect of surface modification and nano-sized scale leads to significantly improved tensile properties across a wide range of fiber content.