Novel Nanomaterials and Performance Industrial Products, 2017

 

Project Leader

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

This project is developing efficient processes to isolate rice straw components and convert them into new nanomaterials and advanced functional products.

To date a diverse array of nanocelluloses have been fabricated from rice straw cellulose. These nanocelluloses have been demonstrated as dispersants, antimicrobial agents, microbial coagulants, and synthesis templates for nanoparticles, as well as building blocks to fabricate nanofibers, films, coatings, hydrogels, and aerogels—each category with wide-ranging potential applications. For instance, rice straw derived nanocellulose aerogels have been demonstrated for aqueous–organic separation, water purification, oil clean up, and other uses.

The overall goal for 2017 research was to continue the development of scalable processes and to expand functional applications of nanocelluloses and porous carbon products. Specific research objectives were:

  • Diversify nanocellulose structures using sodium periodate oxidation and mechanical shear.
  • Establish the simultaneous isolation and utilization of cellulose and silica from rice straw.
  • Optimize aerogel properties and processes into scalable industrial and consumer products.
  • Develop a new “green” process to generate hydrophobic cellulose nanofibrils.

Diverse nanocelluloses

New rice straw nanocelluloses, both cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs), have been efficiently generated by two-step oxidation followed by mechanical blending.

The dimensions, yields and surface charges on these nanocelluloses can be optimized and varied by simply tuning the primary and secondary oxidation reaction conditions. A wide range of CNCs and CNFs with potentially more highly decorated carboxyl surface groups than the 2,2,6,6-tetramethylpyperidine-1-oxyl (TEMPO) method can be produced.

The CNCs produced are not only in higher yields, but also carry carboxyl surface functional groups, as opposed to the sulfonate groups from typical CNCs hydrolyzed by sulfuric acid. Further reaction optimization to establish charge and yield relationships, as well as characterization of CNFs, will continue in 2018.

Nanocellulose–silica aerogels

A second objective was to more fully utilize rice straw by converting two major rice straw components (cellulose and silica) to nanocellulose–silica aerogel composites.

Cellulose nanofibril (CNF)–silica hydrogels were first fabricated by aging aqueous CNF and sodium silicate precursors in various ratios. CNFs provide the primary skeletal gel structure, while the silica bridges and connects CNFs within the gel network.

These novel nanocellulose–silica aerogel composites take advantage of the complementary qualities of resilient nanocellulose and heat-resistant silica. The pore structure and mechanical properties of CNF–silica aerogels are being characterized. The ability of these rice straw based aerogels to absorb carbon dioxide will be studied for potential carbon sequestering applications.

Amphiphilic nanocellulose aerogels

Nanocellulose aerogel technologies are the most advanced among rice straw based products developed in this project. These aerogels are superabsorbent of both water and oil and their amphiphilicity can be fine-tuned to selectively absorb and remove organic solvents and oils from water.

Significant progress has been made to improve multiple properties of these aerogels. A chemical cross-linking treatment process produced aerogels that were highly effective in separating water and oil through selective absorption or simple filtration. Two papers have been published on this work in 2017.

A provisional patent on nanocellulose aerogels has been filed by the university. Product sponsors have been and will continue to be aggressively sought.

New “green” process

Researchers have tested and validated a new “green” process utilizing a recyclable, multifunctional reagent, solvent, and acid precursor to perform telomerization and hydrolysis that will produce more hydrophobic nanocelluloses.

The cellulose nanofibrils generated are narrower than those previously produced but are far more thermally stable—a significant advantage and important breakthrough. Work will continue in 2018 to optimize this process, improve yield, and characterize CNFs.

One provisional patent on this unique green processing for nanocelluloses was filed in 2017.