Producing well-dispersed cellulose nanocrystals (CNCs) in poly(lactic acid) (PLA)

Abstract Bionanocomposites from renewable sources that can replace petroleum-based plastics at comparable cost represent a significant current challenge. In this context, the authors proposed using coconut oil (CO) as a spacer for cellulose nanocrystals (CNC). This method aims to hinder hornification during CNC drying and improve its redispersion in poly(lactic acid) (PLA). With this goal, an oven-dried CNC masterbatch dispersed in coconut oil (CNC/xCO)m, free of water and residual organic solvents, was prepared by solvent exchange to ethyl alcohol (CNCa). This mixture is ready for use in any PLA/CNC nanocomposite processing route at lower cost than CNC powder produced by freeze-drying. Films of neat PLA; PLA with 3 phr of never-dried CNCs, prepared by solvent exchange to chloroform (PLA/3CNCc); PLA with 3 phr (PLA/3CO) and 12 phr of CO (PLA/12CO); and PLA/(3CNC/xCO)m at 1:1 and 1:4 ratios were prepared by solvent casting. Afterwards, these films were characterized by Fourier-transform infrared spectroscopy (FTIR), light transmittance, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), field-emission scanning electron microscopy (FESEM), contact angle, and tensile testing. FESEM images showed that PLA/(3CNC/xCO)m achieved better CNC dispersion than PLA/3CNCc. However, the droplet-shaped morphology of CO produced a discontinuous PLA matrix. As a result, PLA/(3CNC/xCO)m had lower mechanical performance than PLA/3CNCc. The attempt to inhibit hornification of CNCs during drying by using CO as spacers was hindered by the effects of CO’s droplet morphology in the brittle polymer matrix. Regardless of that, this new route produced a CNC masterbatch free of moisture, and ready for redispersion by any polymer processing method. This study is a step forward in developing a competitive, clean technology for producing CNC nanocomposites in hydrophobic matrices.