Porous Cellulose Nanofibril–Natural Rubber Latex Composite Foams for Oil and Organic Solvent Absorption

Nanocellulose-based foams are widely used as absorbents due to their highly porous networks and large surface areas. However, their inherent hydrophilicity and poor wet resilience limit their applications in water remediation for the removal of hydrophobic components (e.g., oil and organic solvent spills). A straightforward process combining biomass-derived materials, cellulose nanofibrils (CNFs), and natural rubber (NR) latex, in the absence of any organic solvent, is herein elucidated to design eco-friendly hydrophobic foams. NR acts as an anchoring filler within the CNF three-dimensional (3D) network, tailoring the production of CNF foams with tunable morphologies, interconnected walls, specific surface areas (∼226 m2·g–1), and higher porosities (more than 92%). Aqueous NR and CNF dispersion exhibited great colloidal stability (ζ-potential above −30 mV), a desirable characteristic to obtain controlled structures. The spherical shape of NR (diameter of ca. 500 nm) and the fibrous morphology of CNF, both by themselves and when mixed, were evidenced by cryogenic transmission electron microscopy. The porous architecture built up through ice templating was corroborated by scanning electron microscopy and 3D X-ray microtomography (μCT). The CNF 3D network and NR promoted rigid and robust foams with elevated compressive modulus (∼600 kPa, for NR20/CNF80). In situ four-dimensional (4D) μCT revealed an impressive increase in oil uptake—from 44 ± 5 to 90 ± 7%—by foam pores upon NR addition. NR was demonstrated by pore segmentation to be evenly distributed throughout the CNF surface, awarding great hydrophobicity (apparent contact angle of around 100°), excellent and quick oil/organic solvent absorption (above 50 g·g–1 in 3 s), and excellent reusability (20 cycles) for organic solvents and oils. This green material exhibits great capacity of soaking nonpolar molecules, standing out as an environmentally friendly, cost-effective, and promising alternative for water cleanup.