Wet compounding of cellulose nanocrystals into polylactic acid for packaging applications

Cellulose nanomaterials have been demonstrated to improve the mechanical and barrier properties of various polymers, but numerous challenges, such as drying, remain to viably produce polymeric cellulose nanocomposites for packaging applications. In this paper we describe a method for drying and blending cellulose nanocrystals into polylactic acid (PLA) using a single process referred to as wet compounding. Aqueous suspensions of CNCs were directly compounded with PLA in a thermokinetic mixer in which viscous heating creates sufficient temperature to evaporate water and melt polymers during mixing. Here, CNCs with and without lignin were compounded with PLA followed by cast extrusion to produce films, which were evaluated for their mechanical and barrier properties. Composite films with de-lignified CNCs produced through wet compounding were found to have improved mechanical and barrier properties compared to neat PLA, whereas lignin-containing CNCs did not improve the barrier properties of PLA. The process of rapid wet compounding was not found to detrimentally affect the properties of PLA controls. In addition, using a discharge temperature setpoint well below the melting point of polymer resulted in the most favorable composite properties, indicating that further optimization and investigation of wet compounding is needed. The use of novel processing, such as wet compounding, has tremendous promise for advancing the viability of cellulose nanocomposites.