University of California, Davis,
Keywords: nanocellulose, amphiphilicity, super absorbents, nanofibers, porous membranes
Summary:Nanocellulose derived from waste streams, such as crop residues and food/beverage processing waste and post consumer products, is among the least exploited and yet the most abundantly available biologically derived nanomaterials and renewable nanobuilding blocks. Developing nanocellulose feedstock and applications is therefore key to many sustainable solutions for a biobased economy as it provides non-fossil fuel alternatives, reduces environmental impact of the food supply chain as well as generates new domestic economic opportunities. This paper presents the multi-faceted characteristics of nanocellulose derived from various agricultural and processing waste streams via a range of chemical, mechanical and coupled defibrillation processes. The unique nanocellulose attributes linked to source and/or process will be presented. Based on the geometries and surface functionalities, these nanocellulose may be regulated to exhibit chemical functions such as reducing, coupling and chelating agents and affinities to various liquids and can be assembled into diverse range of structures of nanofibers, porous template, hydrogels, aerogels, films and coatings. Cellulose isolated from cotton linter, grape skin, tomato pomance, almond shell and hull, as well as rice straw have been defibrillated into nanocellulose in the forms of nanoparticles, nanocrystals (CNCs)/nanowhiskers and nanofibrils (CNFs) in wide ranging lateral dimensions, lengths and aspect ratios, as well as levels of surface chemistries and charges, permitting dispersing in not only aqueous but also polar and non-polar organic media, including ethanol and DMF. While most CNCs are rod-like with assymetric cross-sections, those from grape skins are mainly ca. 5 nm nanospheres. Upon drying, CNCs from these different sources self-assemble into significantly different forms that depend on not only the above mentioned attributes, but also the environment and drying means. Cellulose nanofibrils (CNFs) defibrillated by chemical, mechanical shear and blending are far finer, but also much longer. The dispersion and viscoelastic behaviors of these CNFs depend on defibrillation methods as well as cellulose sources. Intriguingly, amphiphilicity and unique properties of various self-assembled solids including nano-fibers, macro-fibers, ultra-thin films, aerogels and porous monolithic films will also be highlighted. Self-assembly and potential driving forces for such structural formation will be discussed from the perspective nanocellulose structures, hydrophobic-hydrophilic balance and surface charge nature as well as the environment. The opportunities of sources and the manner in which these nanocellulose self-assemble may be regulated and the diverse material structures generated open up opportunities for future advance sustainable materials. Material structures from nanocellulose including nanofibers, porous membranes, hydrogels, aerogels, thin films, coatings and nanocomposites will be presented. High performance products such as super-absorbents (super-hydrophilic, amphiphilic and super-hydrophobic), molecular sensors, membranes for oil-water separation, toxicant collection, chemical recovery, etc. and catalysis will be given. Acknowledgement: Research findings were generated by experiments conducted by Feng Jiang, Ping Lu, Jin Gu, Juri Fukuda, Gabriel Patterson, Teresa Lopez and Ying Shen. Funding support from USDA NIFA (2011-67021-20034), California Rice Research Board (RU-9), Chevron, NSF (DBIO722538) and (NIH RR11978) is appreciated.