Green Composites Prepared from Cellulose Nanoparticles

Abstract

Nanoparticles were prepared from bacterial cellulose. The particles were topochemically modified with poly(caprolactone), (PCL), via a ring-opening polymerization on the surface hydroxyl groups. The reaction is a facile, solvent-free system, containing only cellulose as the initiator, an organic acid as the catalyst, and ε-caprolactone as the monomer. Graft weight % was calculated by gravimetric methods and confirmed with NMR, while chemical attachment of PCL was confirmed by spectroscopic methods including Fourier Transform Infrared (FTIR), and 13C Cross Polarization Magic-Angle Spinning NMR (CP-MAS). The grafting reaction was performed as a route to improve compatibility between the cellulose nanoparticles and a PCL matrix in thermoplastic composites. Nanocomposites were formed by extensive mixing of the continuous and filler phases in a twin-screw extruder to create good particle dispersions. The thermal and viscoelastic properties of the composites were investigated by differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Thermal analysis data does not indicate a significant enhancement in composite particle-matrix interactions with surface grafting. The tensile modulus of the PCL matrix was improved by reinforcement with all filler types. The grafted cellulose-PCL filled composites offered only marginal improvements in tensile modulus relative to unmodified cellulose nanoparticle filled composites. All cellulose nanoparticle based composites closely matched the mechanical properties of similarly prepared nanoclay composites.