Strategies Leading to Novel Nanomaterials & Performance Industrial Products, 2013

 

Project Leader

You-Lo Hsieh, professor of fiber and polymer science, Division of Textiles and Clothing, UC Davis

This project is developing strategies to isolate major rice-straw components and convert them into new nanomaterials and value-added industrial products. Several processes that involve minimal chemical input, water use, thermal input, and wastes have been evaluated and optimized to separate the major rice-straw components—cellulose, hemicellulose, silica, and lignin.

Specific research objectives in 2013 were to:

   • Examine new processes to isolate cellulose, hemicellulose, lignin, and silica and new processes for “defibrillating” nanocellulose.

   • Optimize self-assembled carbon nanocrystals and nanofibers with novel functional properties.

   • Develop functional carbon-based products from hemicellulose, lignin, and silica.

New processes examined

An organic solvent process used in biofuel production has the potential for large-scale isolation of pure cellulose from rice straw. This process isolates lignin with the least structural alteration and has been successfully applied mainly to wood pulp. Clean rice straw was processed with this method at the University of Tennessee. The processed rice-straw pulp appeared light brown when wet and yellowish when dried. Additional hemicellulose may be removed by alkaline bleaching to yield white cellulose.

A new technique that applies high pressure to mechanically defibrillate cellulose in aqueous suspensions has the potential to achieve total conversion of rice-straw cellulose. Samples of pure rice-straw cellulose were processed at Kyushu University in Japan. This process resulted in nanocellulose that could be separated into differently sized fibrils—from coarse-branched microfibrils to nanofibrils.

These new processes have shown to be highly effective in isolating major rice straw components and in producing nanocellulose, but in varied qualities than the chemical processes developed previously.

Cellulose nanofibrils have been developed into products with novel functional properties

Optimizing nanoproducts

A coupled chemical-oxidation and mechanical-blending process was optimized to generate cellulose nanofibrils (CNFs) from rice straw cellulose, yielding as high as 97%. These CNFs ranged from 1.5 to 2.8 nanometers (nm) in width and 1 to several micrometers in length. These rice straw CNFs could self-assemble into either ultrafine fibers 125 to 500 nm wide and several hundred micrometers long or into highly porous aerogels by rapid freezing from dilute or higher concentrations of aqueous suspensions. These highly crystalline and ultrafine fibers are more crystalline than any cellulose in nature and have great potential to be strong reinforcing fibers.

These rice-straw nanocellulose aerogels are the lightest aerogels among all from organic polymers, natural or synthetic. Furthermore, these rice straw CNF aerogels were super-absorbent of both water and oils. The ability to rapidly and completely absorb hydrocarbon solvents and oils from water demonstrates the excellent oil removal capability of the modified CNF aerogels for oil-spill clean up and refined organic-aqueous separation.

Developing carbon-based and silica products

An efficient three-step process has been developed for isolating pure cellulose from rice straw while generating two filtrates as activated carbon and silica particle precursors. These particles, along with nanocellulose, are advanced materials that utilize all major components in rice straw. This approach has potential as a feasible alternative to current, costly technologies for highly porous activated carbon and silica manufacturing used in chemical, metal, and gas absorbents and purification; in food and pharmaceutical applications; and in precursors for numerous functional materials.

Super-hydrophilic hydrogels and super-absorbing and ultralight aerogels studied in this work are excellent candidates for applications in filtration, separation, sensing, and chemical-oil-water separation. Nanoparticles are expected to exhibit antimicrobial, catalytic, magnetic, photo- and electro-active, sensing, and color properties.