Highly Biodegradable and Tough Polylactic Acid-Cellulose Nanocrystal Composite

Poly(L-lactide) cellulose nanocrystals-filled nanocomposites were fabricated by blending of cellulose nanocrystalsg-rubber-g-poly(D-lactide) (CNC-rD-PDLA) and commercial PLLA, in which CNC-g-rubber was synthesized by ring opening polymerization (ROP) of D-lactide and a epsilon-caprolactone mixture to obtain CNC-P(CL-DLA), followed by further polymerization of D-lactide to obtain CNC-rD-PDLA. X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and solubility tests confirmed successful grafting of the rubber segment and the PDLA segment onto CNC. Stereocomplexation between CNC-rDPDLA nanofillers and PLLA matrix was confirmed by FT-IR, XRD, and differential scanning calorimetry (DSC) characterization. The PLLA/CNC-rD-PDLA nanocomposites exhibited greatly improved tensile toughness. With 2.5% CNC-rD-PDLA loading, strain at break of PLLA/CNC-rD-PDLA was increased 20-fold, and the composite shows potential to replace poly(ethylene terephthalate). SEM and small-angle X-ray scattering (SAXS) investigations revealed that fibrillation and crazing during deformation of PLLA/CNC-rD-PDLA nanocomposites were the major toughening mechanisms in this system. The highly biodegradable and tough cellulose nanocrystals-filled PLLA nanocomposites could tremendously widen the range of industrial applications of PLA.