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Cellulose Nanomaterials - Come and Get it!
By Clayton Teague, Ph.D., and Colleen Walker, Ph.D.

Cellulose constitutes the most abundant renewable polymer resource available today, and natural cellulose based materials (wood, bagasse, cotton, linen, etc.) have been used by our society as engineering materials for thousands of years. As a chemical raw material, it has been used in the form of fibers or derivatives for nearly 150 years for a wide spectrum of products and materials in daily life.

Although cellulose crystals have been known for over 50 years, what has not been known until relatively recently is that these rod-like crystals are defect free and incredibly strong. Papermakers have been taking advantage of this inherent material in pulp for centuries. But now other researchers are discovering the unique and powerful properties of this renewable, sustainable material.

Potential applications include, but certainly are not limited to, barrier films, antimicrobial films, transparent films, flexible displays, reinforcing for polymer composites, biomedical implants, pharmaceuticals, drug delivery, fibers and textiles, templates for electronic components, separation membranes, batteries, super capacitors, electroactive polymers, and many others.

Samples for Research & Product Development
The availability of high quality cellulose nanocrystals (CNCs) such as the material now being produced at the new Forest Products Laboratory facility, makes possible the full exploration of all these potential applications. This pilot plant is a major step toward the introduction of CNCs into commercial products.

In late July 2012, the U.S. Forest Service Forest Products Laboratory (FPL) celebrated the opening of their $1.7 million pilot plant in Madison, Wisconsin. This investment allows the U.S. FPL to become the country's leading producer of cellulose nanocrystals and TEMPO pretreated cellulose nanofibrils.

This plant produces Cellulose Nanocrystals (CNCs) and TEMPO-based Cellulose Nanofibrils (CNFs) for advanced process and product testing. Both materials are currently being produced from bleached wood pulp in 400 liter glass lined reactors selected to contain the concentrated acid and oxidation conditions necessary for the production of CNCs and CNFs, respectively.

Typically, bleached wood pulp is the starting material for CNCs and CNFs production. The resulting nanocrystals are approximately 5 nm in diameter and 150 nm long, and the fibrils are about 20 nm in diameter and up to 2 ? long. After extraction, both materials undergo extensive purification in the membrane filtration system. CNCs will be available for purchase in an aqueous suspension or freeze dried into a white powder. CNFs can be cast into a clear film or freeze dried into an aerogel or white powder. The substances' unique structural properties enable them to strengthen a wide-range of materials such as films and fiber reinforced composites.

Once CNCs and CNFs are firmly established products and their production processes have been perfected, the pilot plant will be adapted to produce material at a larger scale. The pilot plant was constructed with 4,000 liter reactors currently used as dilution and receiving vessels but also available for a ten-fold scale up once continuous processing methods are worked out for the initial purification. This additional scale-up will begin to demonstrate the process methods suitable for pre-commercial scale.

Over 1600 kilometers away at the University of Maine at Orono, the Process Development Center (PDC) is currently expanding its pilot-scale cellulose nanofibril (CNF) manufacturing plant. The University of Maine PDC is the recipient of a $1.5 million grant from the U.S. Forest Service to upgrade its nanocellulose pilot plant. The new pilot plant will be capable of producing CNFs at a rate of one ton per day. This will be the only facility capable of producing CNFs at this scale in the country. Researchers and industrial companies interested in evaluating CNFs will have a convenient source from which to purchase the material.

Cellulose nanofibrils are valued because of their strength - a strand of it is stronger than steel. It takes on different structures depending on how it is dried. When a sample of the CNF slurry is dried with heat, the material becomes hard, dense and tough, and can be machined into different shapes and sizes. When freeze-dried, the material is light-weight, super-absorbent and demonstrates good insulating properties. The nanocellulose fibrils are about 1,000 times smaller than paper fibers. The material can be made from any lignocellulosic source, such as wood, grasses, corn stalks or wheat straw.

UMaine already produces some cellulose nanofibrills via both mechanical means and chemical means. Researchers and companies will be able to order both CNF and CNC samples by fall of 2012. The PDC's work has already garnered strong interest for the material. Visit http://umaine.edu/pdc/process-and-product-development/selected-projects/nanocellulose-facility/ to learn more, or request a sample of cellulose nanocrystals or nanofibrils.

In February 2012, Glenn Ostle of Paper360° magazine interviewed John Moreau, President and CEO of CelluForce, the first semi-commercial facility to produce nanocellulose. Moreau described the facility and his company's plans (see the AOTC of Feb 1, 2012, "Making nanotechnology pay"). Attendees at TAPPI's 6th International Conference on Nanotechnology for Renewable Materials toured the facility in June 2012.

COLLABORATING FOR SUCCESS
However, before real commercialization of CNCs can be achieved, researchers in academia and in industrial laboratories have outlined a set of very challenging goals for better processing of CNCs, achieving appropriate chemical functionalization of CNCs, better characterization of the mechanical, electrical, optical, and chemical properties of these materials, and understanding how these new materials can be incorporated into polymer and other matrices.

Countries in North America, Europe Asia and elsewhere are currently placing great emphasis on the sustainable and safe use of materials. CNCs are truly a wonderful material because of their inherent sustainability and their low environmental, animal/human health and safety risks; all this in addition to their abundance and promising physical, chemical, and electrical properties.

Clayton Teague is currently a member of the TAPPI Board of Directors (2012-2014 term). From 2003 until he retired in 2011, Dr. Teague was Director, Federal National Nanotechnology Coordination Office. Prior to this position, he was chief of the Manufacturing Metrology Division in the Manufacturing Engineering Laboratory of the National Institute of Standards and Technology, U.S. Department of Commerce. Colleen Walker, Ph.D., is Project Manager and Technical Lead, TAPPI and can be contacted at: [email protected].

 

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