Nanocellulose Used in Medical Devices

 

Transmission electron microscopy image of freeze-dried CNCs that were redispersed in deionized water and stained with aqueous uranyl acetate.

Transmission electron microscopy image of freeze-dried CNCs that were redispersed in
deionized water and stained with aqueous uranyl acetate.

The Journal of Applied Polymer Science features groundbreaking work from FPL Materials Research Engineer Robert Moon and others. “Enhanced thermal stability of biomedical thermoplastic polyurethane with the addition of cellulose nanocrystals” by Jen-Chieh Liu, Darren J. Martin, Robert J. Moon, and Jeffrey P. Youngblood takes us to the world of nanocellulose in medical devices.

Thermoplastic polyurethanes (TPUs) are used in manufacturing biomedical devices, such as vascular grafts or ventricular assistance devices, where mechanical performance and biocompatibility and nontoxicity are crucial. However, to increase the range of biomedical device applications and improve end use performance, improved thermal stability during fabrication and the ability to controllably manipulate strength and toughness without loss of biocompatibility is required. And because these devices are to be used in the human body, they must be nontoxic. Cellulose nanocrystals (CNCs) are cellulose-based nanoparticles produced from wood or plant fibers. As candidates for nano-reinforcement materials for TPUs, CNCs work well because they have high mechanical properties, good thermal properties, and low toxicity.

In many cases, TPU fabrication (such as extrusion and injection molding) to make products involves high temperatures and long manufacturing time because of blending and homogenization. These factors degrade polymer chains and decrease mechanical properties. If nano-reinforced TPUs can achieve a higher decomposition temperature, they could be processed under a wider range of operation temperatures and manufacturing times without loss of mechanical properties.

This research showed that higher solid loadings of CNCs in a commercial TPU commonly used in biomedical applications resulted in a higher onset degradation temperature of the nanocomposite, providing a wider processing temperature for manufacturing products to be used in biomedical devices without loss of mechanical properties.

FPL cooperated with Purdue University; University of Queensland, Brisbane, Australia; and Georgia Institute of Technology, Atlanta, Georgia, on this project.

 

Documenting the Carbon Impact of Laminated Veneer Lumber Production

 

Laminated veneer lumber

Research Forest Products Technologist Richard D. Bergman continues his good work for the environment with a recent publication, Life-Cycle Inventory Analysis of Laminated Veneer Lumber Production in the United States.

Bergman’s study found that documenting the actual environmental performance of building products is becoming widespread and important because of concerns that some organization’s green-marketing claims are actually misleading. This is known as “greenwashing” in the business and borrows from the term whitewashing.

Developing environmental product declarations (EPDs) for building products is one way to provide scientific documentation that counters efforts to greenwash. Life-cycle inventory (LCI) data are the underlying data for subsequent development of life-cycle assessments (LCAs) and EPDs. EPDs are similar to nutritional labels for food.

This report follows data and reporting requirements as outlined in the Product Category Rules (PCR) for North American Structural and Architectural Wood Products and contains the LCI components for producing a North American EPD. At present, many EPDs for structural wood products made in North America exist. LCI compiles all raw material and energy inputs and outputs associated with the manufacture of a product on a per-unit basis within defined system boundaries. These boundaries can be limited to only one stage within the product life-cycle.

Multiple sequential LCI stages are usually combined to produce an LCA. LCAs describe the total environmental impact for a particular product. Many engineered structural wood products have been developed in the last several decades; for example, laminated veneer lumber (LVL ), which is comprised of many thin layers of dry wood veneers glued together with resins to form lumber-like products. LVL is designed to be used in the same manner as solid wood  products such as sawn lumber. Structural wood products such as LVL used in building construction can store carbon for long periods, which is typically greater or far greater than the carbon dioxide emissions released during manufacturing.

Environmental product declarations based on LCA data are an important means of documenting the environmental performance of building products. The International Organization for Standardization (ISO) requires that underlying LCI data be recent; this study updates the LCI data for LVL needed to develop an updated EPD. The amount of carbon stored in LVL exceeds total CO2 emissions during manufacturing by about 350 percent.

Cooperators include the USDA Forest Service Forest Products Laboratory, Madison, Wisconsin, and the Consortium for Research on Renewable Industrial Materials, Seattle, Washington.

Brashaw Takes the Helm of Forest Products Marketing Unit

The Forest Products Laboratory (FPL) welcomes Brian Brashaw to the position of Program Manager for the Forest Products Marketing Unit (FPMU). He took the helm in early May.

Brashaw comes to the Forest Service from the University of Minnesota Duluth’s Natural Resources Research Institute (NRRI), where he served as Program Manager. In that role, he led a highly successful technology development and transfer group that helped a wide range of wood products businesses in the states of Minnesota, Wisconsin, and Michigan.

Through the NRRI, Brashaw has had a long, productive relationship with the Forest Products Laboratory in the areas of nondestructive evaluation of wood materials, utilization of urban wood waste, and timber bridges. Brashaw has a BS in Forest Management from UW-Stevens Point, a MS in Materials Science from Washington State University, and a PhD in Forest Resources from Mississippi State University. His educational and career path were established living in Wisconsin’s Nicolet National Forest as a youth with goals in forestry and forest products.

“Under Brian’s leadership, the FPMU will help ensure healthy, sustainable forests that are more resilient to disturbances by creating high-value, high-volume markets from woody biomass,” said Michael T. Rains, Director of the Forest Products Laboratory and Northern Research Station.

Since 1996, the FPMU has maintained a strong partnership with State and Private Forestry and other mission areas of the Forest Service. With its emphasis on technology transfer, the FPMU helps accelerate forest restoration, improve economic conditions, expand wood utilization and marketing opportunities, improve economic conditions, and create new jobs.

Forest biomass cleanup

Forest biomass cleanup

“It has been a dream of mine, growing up in the north woods of Wisconsin, to have the opportunity to work with the U.S. Forest Service.  It is an honor to be a part of this great organization,” said Brashaw.

FPL is excited to have such a qualified and enthusiastic leader on board.

 

Newest Forest Products Journal Features Adhesives: Many FPL Researchers Present

Adhesive-bond

Photomicrograph of an adhesive bond of two pieces of wood. The blue areas show the adhesive penetration into the wood structure.

The latest issue (Volume 54, No. 1/2, 2015) of The Forest Products Journal is all about adhesives. Featuring 10 selected articles addressing a theme of efficient use of wood resources in wood adhesive bonding research presented at the 2013 International Conference on Wood Adhesives in Toronto, Canada, we hear from several FPL scientists.

FPL has played an integral role in developing technical understanding of adhesives and setting product and performance standards by organizations such as the ASTM International (formerly American Society for Testing and Materials), American Institute of Timber Construction (AITC), APA–The Engineered Wood Association (APA), and the American Forest and Paper Association (AF&PA).

The first glue development research at the FPL in 1917 was to improve water resistance of the best glues available for manufacture of WWI aircraft components. At that time, FPL began to develop composites in an attempt to conserve our forests and make use of waste wood. Adhesives for housing, other buildings, timber bridges, and other structures has always been important.

In the Introduction to Special Issue: Wood Adhesives: Past, Present, and Future, Team Leader, Wood Adhesives, Forest Biopolymer Science and Engineering, Charles Frihart provides a comprehensive history and explanation of the important role that adhesives have played in the efficient utilization of wood resources.

Speaking about wood products, Frihart says: “Adhesives will continue to be a growing part of efficient utilization of forest resources. However, acquiring suitable wood resources will continue to be a challenge because of a diminished supply of high-quality wood and competition for wood from wood pellet and biorefinery industries. The challenges involve dealing with species that are not currently being used and with a greater mixture of species. More plantation wood could involve increased porosity and lower strength because of increased proportion of earlywood. The wood may also have increased or more variable moisture content as a result of efforts to reduce drying costs.

Wood products volume should continue to increase especially if engineered wood products replace other building materials for multi-story buildings and if there are sufficient housing starts. One challenge could be in bonding wood to other materials if glulam or laminated veneer lumber start using layers of stronger polymers or composites for greater strength. There also might be markets for bonding to modified wood, such as acetylated wood or heat-treated wood.”

Challenges in our changing forests and in changing construction practices will keep Frihart and his team busy for years to come as they find ways to use their adhesive research to adjust to change and best utilize our natural resources.

 

 

Cellulose Nanocrystals as Filler for Polymers

In a new publication, Supervisory Research Materials Engineer Gregory T. Schueneman reports on his research with cellulose nanocrystals (CNCs). CNCs are a class of renewable bionanomaterials with excellent mechanical properties that have attracted interest as filler for polymers. However, challenges associated with effective CNC dispersion have hindered the production of composites with desired property enhancements.

In Schueneman’s research, composites of polypropylene (PP) and low-density polyethylene (LDPE) with 5–10 wt% unmodified CNC are being produced for the first time with a solventless process, solid-state shear pulverization. Optical and electron microscopy revealed that the CNC dispersed very well and that degradation was strongly suppressed relative to composites made by melt mixing.

Field emission (FE) scanning electron microscope (SEM) images of as-received CNC at different weights.

Field emission (FE) scanning electron microscope (SEM) images of as-received CNC at different weights.

Taking thermal stability into account, this study has produced polyolefin/CNC composites with superior dispersion and property enhancements and has shown that CNC is an attractive and green filler for polymer composites. Over 50 million tons of plastic resins are used annually in the United States to manufacture products for a variety of end uses, including packaging, building materials, vehicles, furniture and furnishings, and electronics and electrical devices.

In this study, solid-state shear pulverization was used for the first time to produce composites of polyolefins and unmodified CNC. Microscopy and improved crystallization rate reveal excellent dispersion and suppression of CNC degradation within the polymer compared with composites made by melt mixing.These composites exhibit substantially greater stiffness, the greatest improvement ever reported for such composites made with unmodified CNC.

This study showed that CNC is an attractive and green filler for polymer composites.

The publication, titled “Cellulose nanocrystal/polyolefin biocomposites prepared by solid-state shear pulverization: Superior dispersion leading to synergistic property enhancements,” will be available online shortly. Cooperators include the USDA Forest Service Forest Products Laboratory, Madison, Wisconsin, and Northwestern University, Evanston, Illinois.