Development of cellulose nanocrystal-reinforced polylactide: A comparative study on different preparation methods

A masterbatch of polylactide (PLA) containing cellulose nanocrystals (CNCs) prepared via a solution-cast method was further diluted with neat PLA in the melt state using either a twin-screw extruder or an internal batch mixer to reach a final CNC content of 4wt%. For the sake of comparison, a direct melt mixing method was employed to prepare PLA-CNC composites. Then, the efficiency of the preparation methods was assessed by comparing the morphological, rheological and thermomechanical properties of the compounded samples. Scanning electron microscopy showed the disappearance of large agglomerates when using the PLA-CNC masterbatch. Transmission electron microscopy revealed the existence of well-dispersed CNCs within the PLA matrix at a nanoscale for masterbatch-based nanocomposites. The rheological properties of the nanocomposites containing the PLA-CNC masterbatch were significantly increased for both steady and small-amplitude oscillatory shear flow fields, compared to the composites prepared via direct melt mixing. In addition, the masterbatch-based nanocomposites exhibited pronounced overshoots in the transient start-up viscosity. The crystalline content of the PLA in the nanocomposites and the crystallization temperature increased when the CNCs were well dispersed, which showed the nucleating effect of the CNCs. In dynamic mechanical thermal analysis, the storage modulus of the nanocomposites increased up to 41 and 128% in the glassy and rubbery regions, respectively. These results show that hydrophilic CNCs can be well dispersed and reinforce PLA using efficient preparation methods. POLYM. COMPOS., 40:E342-E349, 2019. (c) 2017 Society of Plastics Engineers