Green composites made from cellulose nanofibers and bio-based epoxy: processing, performance, and applications
Bamdad Barari and Krishna M. Pillai
University of Wisconsin-Milwaukee, Milwaukee, WI, United States
In this chapter, the scalable cellulose nanocomposites made using a bio-based resin through an improvised version of the liquid composite molding (LCM) process are investigated. Two different types of nanocellulose preforms (one isotropic and the other anisotropic), created using the freeze-drying process, are considered for making the cellulose nanofiber (CNF) composite. LCM processes form a set of liquid molding technologies that are used quite commonly for making the conventional polymer composites. An improvised vacuum-driven LCM process is used to make the CNF-based nanocomposites from CNF preforms using a “green” epoxy resin with high bio-content. Application of cooling surfaces during the freeze-drying process can significantly alter the microskeleton of CNF preforms and render it either nonaligned/isotropic or aligned/anisotropic. The mechanical properties of the composites were studied experimentally and the causes of failure were discussed by analyzing the SEM micrographs of fractured surfaces. The silane treatment of CNF preform led to better wettability and consequently a better CNF/bio-epoxy interface, which resulted in superior mechanical properties in silylated CNF/bio-epoxy composites. The anisotropic CNF/bio-epoxy composites displayed mechanical properties that were superior to those of pure bio-epoxy, while the isotropic CNF/ bio-epoxy composites were found to be slightly inferior. Later the tribological properties of the composites were studied using the pin-on-rotating-disk test. It was observed that the coefficient of friction (COF) and volume loss were a strong function of CNF volume fraction over a range of speeds and normal loads. During the study of wear surfaces using SEM and stereoscope, the CNF/bio-epoxy composites displayed distinctly different surface properties, roughness, and wear mechanisms compared to the pure bio-epoxy samples.