The development of nanocellulose has attracted significant interest in the last few decades due to its unique and potentially useful features. Novel nanocelluloses boost the strongly expanding field of sustainable materials and nanocomposites. Their potential areas of application include reinforcing agents in nanocomposites, paper, biodegradable films, barriers for packaging, stabilizing agents in dispersions for technical films and membranes, additives in food, texturing agents in cosmetics, and medical devices such as wound dressings and bioactive implants. This review organizes current knowledge on the isolation of microfibrillated and nanofibrillated cellulose from plant sources. Details of the extraction of fibrils from cellulose are reviewed. In addition, the terms cellulose “microfiber” and cellulose “nanofiber” are formally defined and distinguished.

Keratin from wool fibers was extracted with different extraction methods, for example oxidation, reduction, sulfitolysis, and superheated water hydrolysis. Different samples of extracted keratin were characterized by molecular weight determination, FT-IR and NIR spectroscopy, amino acid analysis, and thermal behavior. While using oxidation, reduction, and sulfitolysis, only the cleavage of disulfide bonds takes place; keratin hydrolysis leads to the breaking of peptide bonds with the formation of low molecular weight proteins and peptides. In the FT-IR spectra of keratoses, the formation of cysteic acid appears, as well as the formation of Bunte salts (–S–SO₃–) after the cleavage of disulfide bonds by sulfitolysis. The amino acid composition confirms the transformation of amino acid cystine, which is totally converted into cysteic acid following oxidative extraction and almost completely destroyed during superheated water hydrolysis. Thermal behavior shows that keratoses, which are characterized by stronger ionic interaction and higher molecular weight, are the most temperature stable keratin, while hydrolyzed wool shows a poor thermal stability.

Wool fibers were submitted to “green hydrolysis” with superheated water in a microwave reactor, in view of the potential exploitation of keratin-based industrial and stock-farming wastes. The liquid fraction was separated by filtration from the solid fraction, which consists mainly of small fragments of wool fibers and other insoluble protein aggregates. The liquid fraction contains free amino acids, peptides and low molecular weight proteins, with a small amount of cystine and lanthionine, and has a different secondary structure when compared with keratins extracted from wool via reductive or oxidative methods. Cleavage of the cystine disulfide bonds without the use of harmful, often toxic, reductive or oxidative agents allows the extraction of protein material from keratin wastes, offering the possibility of larger exploitation and valorization.