Influence of cellulose nanofiber content on the expansion of polystyrene nanocomposites expanded by supercritical CO₂

Nanotechnology applied to polymer foams is an emerging field. The possibility to add nanofillers to polymers and to expand them by supercritical carbon dioxide represents an important development in polymer foam production, tailoring the foams' properties. In this study, polystyrene (PS) composites with cellulose nanofibers (CNF) were obtained by producing PS/CNF nanocomposites and subsequently expanding them with supercritical CO₂. The viscosity, mechanical and dynamic-mechanical properties of non-expanded composites were obtained. The morphology and compressive strength of the expanded composites were evaluated. The non-expanded composites' mechanical properties remained unchanged, and the viscosity increased with the addition of CNF. PS/CNF non-expanded composites displayed higher storage modulus in the rubbery region with increasing CNF content. The expanded foams displayed smaller cell size as CNF is introduced, which increased the compressive strength and decreased the deformation at 5 wt% CNF. This allows the tailoring of the mechanical properties and cell size with varying CNF content to better suit a wide range of applications.