Synthesis and characterization of bionanocomposites with tunable properties from poly(lactic acid) and acetylated microfibrillated cellulose.

In the present study, novel bionanocomposite materials with tunable properties were successfully prepared using a poly(lactic acid) (PLA) matrix and acetylated microfibrillated cellulose (MFC) as reinforcing agent. The acetylation of MFC was confirmed by FTIR and (13)C CP-MAS NMR spectroscopies. The grafting of acetyl moieties on the cellulose surface not only prevented MFC hornification upon drying but also dramatically improved redispersibility of the powdered nanofibers in chloroform, a PLA solvent of low polarity. Moreover, we demonstrate that the properties of the resulting PLA nanocomposites could be tailored by adjusting both the acetyl content (Ac%) and the amount of MFC. These nanomaterials showed improved filler dispersion, higher thermal stability, and reduced hygroscopicity with respect to those prepared with unmodified MFC. Dynamic mechanical analysis (DMA) highlighted the reinforcing potential of both the unmodified and the acetylated MFC on the viscoelastic properties of the neat PLA. But more interesting, an increase in the PLA glass transition temperature was detected when using the 8.5% acetylated MFC at 17 wt %, indicating an improved compatibility at the fiber-matrix interface. These findings suggest that the final properties of nanocomposite materials can be controlled by adjusting the %Ac of MFC.