Optimization of toughening of Polylactic Acid Nanocomposites/ Nanofibrillated Cellulose

Structure-property relation is of vital importance in developing advanced polymer nanocomposites as well as enhancing their ultimate properties. In this research study, toughening of polylactic acid (PLA) with nanofibrillated cellulose (NFC) was studied and comparison was made between thermal and mechanical properties of systems containing pristine and modified NFC. NFC was modified through two different methods; acetylation of hydroxyl groups and grafting of polyethylene glycol (PEG) onto cellulose chains. Fourier transform infrared spectroscopy , X-ray diffraction , and differential scanning calorimetry were employed to probe into the surface characteristics, thermal properties and crystallinity of NFC/modified NFC, respectively; moreover, SEM imaging was utilized for surface morphology of samples. Subsequently, PLA with modified and unmodified NFC was prepared to evaluate the filler addition effect on toughness. Acetylated NFC has changed the PLA crystallinity degree and rate, which affected the modulus of PLA, as signaled by the changed NFC surface. Particularly, mechanical and toughening behavior of the prepared nanocomposites were analyzed based on tensile measurements which showed an eight-fold rise in toughening along with 18% decrease in modulus of the samples comprising 1 wt.% of acetylated NFC compared to the blank PLA. In the light of the obtained results, it can be inferred that brittle PLA can be toughened by the surface modified NFC. This research study can illuminate the way for future works on the modifications of nano-scale fillers/additives to achieve improved mechanical and thermal properties of PLA.