Melt-processing and properties of thermoplastic composites based on ethylene-acrylic acid copolymer reinforced with wood nanocellulose

Abstract: Composites reinforced with cellulose nanofibers (CNF), both modified and unmodified cellulose nanocrystals (CNC) and pulp fibers have been prepared through small-scale and large-scale methods. The composites were produced by water-assisted dispersion mixing, drying and compression moulding on the laboratory scale and by extrusion and injection moulding for the large-scale production. The compression-moulded composites were stiffer and stronger by a factor of more than 10 for the CNF or pulp-based samples (>50 wt%) and by a factor of 3 for the CNC-based composites (at 10 wt%). The addition of a lubricant to pulp-based fibers resulted in a behaviour similar to that of a compatibilizer at low concentrations and to that of both compatibilizer and lubricant at higher concentrations. However, when the processing was scaled up, the improvement in properties was much less for the CNF-based and CNC-based composites after being melt-processed via extrusion and injection moulding, despite the fact that they showed a percolated cellulose network. Although the scale-up was successful, aggregates were observed. These aggregates could be reduced to some extent by changing the process design and parameters. Water-assisted extrusion was also used to reduce the aggregation but there was little improvement in properties. It is suggested that the extent of melt flow in the processing method influences the final properties of the composites, despite the nanoscale reinforcement.