You-Lo Hsiah, professor, Division of Textiles and Clothing, UC Davis

The goal of this research is to develop efficient processes to isolate rice straw components and to convert them into new nanomaterials and advanced functional products. To date, four provisional patents related to this research have been filed. A diverse array of nanocelluloses have been fabricated from rice straw cellulose.

These nanocelluloses have been tested successfully as dispersants, antimicrobial agents, microbial coagulants, and synthesis templates for nanoparticles. In addition, they can be used as building blocks to fabricate nanofibers, films, coatings, hydrogels, and aerogels—each category with wide-ranging potential applications.

The goals for 2018 research were to continue the development of scalable processes and to expand functional applications of nanocelluloses and porous carbon products. Specific objectives were:

Diverse nanocelluloses

New rice straw nanocelluloses—both cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs)—have been generated by two-step oxidation with sodium periodate and sodium chlorite, followed by mechanical blending. This approach has produced a wide range of rod-like CNCs and ultra-thin CNFs in dimensions and surface charges that can be simply tuned by reaction conditions.

New green process

Researchers tested and validated a new “green” process utilizing a recyclable, multifunctional reagent, solvent, and acid precursor to produce more organic solvent compatible and hydrophobic nanocelluloses. This process is an efficient way to synthesize stable ethers with minimal environmental impact.

The cellulose nanofibrils generated are narrower than those previously produced but are far more thermally stable—a significant advantage. They are more compatible with polymers and plastics. Nanofibrils produced with this process will be further investigated as reinforcement composites for a wide range of applications such as sustainable packaging and building materials.

This breakthrough innovation is the only “one-pot” process known to date for producing more hydrophobic nanocelluloses. A provisional patent for this novel approach was filed in 2017.

Novel nanocellulose aerogels

Nanocellulose aerogels are the most developed rice straw-based products in this project. These rice straw nanocellulose aerogels are super-absorbent of aqueous, as well as organic liquids, and are far more versatile than hydrophilic silica aerogels and hydrophobic carbon nanotube or graphene aerogels. The unique amphiphilicity of rice straw nanocellulose aerogels can be fine-tuned to selectively absorb and remove organic solvents and oils from water. Research has led to the development of more thermally stable CNF-silica aerogels and electrically conductive nanocellulose aerogels.

Graphene Nanopaper A highly promising new applicaiton for rice straw cekkukise nanofibrils as a multifunctional agent for graphene has been discovered and validated. Graphene is a two-dimensional nanomateial with excellent electrical conductivity and thermnal properties, but it cannot be mass produced effectively and sustainably. Research from this project showed that rice straw CNF's om cp,bination with shear force can exfoliate graphite into high quality graphene in high yields and concentrations. Aqueous graphene suspensions stabilized by CNF's were easily filtered into a "foldable nanopaper" that exhibits a moisture responsive deformation behavior. This graphene-CNF nanopaper has potential applications as biological sensors and actuators. Two new provisional patents based on nanocellulose-based conducting aerogels and graphene materials were filed in 2018.

Nanocellulose-silica aerogels

Rice straw CNFs were combined with silica to produce CNF-silica aerogels. This approach takes advantage of their complementary properties and also more fully utilizes the major rice straw components, cellulose and silica. These aerogels showed much higher mechanical strength, modulus, and structural flexibility than silica aerogels and displayed greater thermal stability than CNF aerogels.

Electrically conductive aerogels

Electrically conductive aerogels are a new frontier in this work. Researchers invented a method to incorporate nanocellulose with conducting materials through protonation of a conducting polymer. These conductive composite aerogels may be used as strain sensors for potential applications such as health monitoring and diagnosis.