|April 20, 2016|
|Rick's Tips - Pneumatic troubleshooting charts|
∑ Subscribe to Ahead of the Curve
∑ Ahead of the Curve archived issues
∑ Contact the Editor
ORNL uses lignin to improve thermoplastic
Your car's bumper is probably made of a moldable thermoplastic polymer called ABS, shorthand for its acrylonitrile, butadiene and styrene components. Light, strong and tough, it is also the stuff of ventilation pipes, protective headgear, kitchen appliances, Lego bricks and many other consumer products. Useful as it is, one of its drawbacks is that it is made using chemicals derived from petroleum.
Now, researchers at the Department of Energy's Oak Ridge National Laboratory have made a better thermoplastic by replacing styrene with lignin, a brittle, rigid polymer that, with cellulose, forms the woody cell walls of plants. In doing so, they have invented a solvent-free production process that interconnects equal parts of nanoscale lignin dispersed in a synthetic rubber matrix to produce a meltable, moldable, ductile material that's at least ten times tougher than ABS. The resulting thermoplastic—called ABL for acrylonitrile, butadiene, lignin—is recyclable, as it can be melted three times and still perform well. The results, published in the journal Advanced Functional Materials, may bring cleaner, cheaper raw materials to diverse manufacturers.
“The new ORNL thermoplastic has better performance than commodity plastics like ABS,” said senior author Amit Naskar in ORNL’s Materials Science and Technology Division, who along with co-inventor Chau Tran has filed a patent application for the process to make the new material. “We can call it a green product because 50 percent of its content is renewable, and technology to enable its commercial exploitation would reduce the need for petrochemicals.”
The technology could make use of the lignin-rich biomass byproduct stream from biorefineries and pulp and paper mills. With the prices of natural gas and oil dropping, renewable fuels can’t compete with fossil fuels, so biorefineries are exploring options for developing other economically viable products. Among cellulose, hemicellulose and lignin, the major structural constituents of plants, lignin is the most commercially underutilized. The ORNL study aimed to use it to produce, with an eye toward commercialization, a renewable thermoplastic with properties rivaling those of current petroleum-derived alternatives.
PPI Awards Showcase Innovation
The PPI Awards for 2016 are now open for nominations and entries!
With 10 categories this year—including The Bio-Strategy Award, Environmental Leadership, Innovation in Water Management, and Innovation in Tissue—The PPI Awards provide a platform that honors a multitude of different categories celebrating leadership, vision, innovation and strategic accomplishments within the industry.
The final day for nominations is May 13, 2016. Entries will be evaluated by panels of judges who will independently review the entries against the award criteria set out in each category. The scores of each panel will be collated to determine the winner of the category. Finalists will be announced in July, and the PPI Awards winners for 2016 will be announced at a gala dinner in Brussels on November 21, 2016.
Please visit PPIawards.com for full details and to download entry forms.
To produce an energy-efficient method of synthesizing and extruding high-performance thermoplastic elastomers based on lignin, the ORNL team needed to answer several questions: Can variations in lignin feedstocks be overcome to make a product with superior performance? Can lignin integrate into soft polymer matrices? Can the chemistry and physics of lignin-derived polymers be understood to enable better control of their properties? Can the process to produce lignin-derived polymers be engineered?
“Lignin is a very brittle natural polymer, so it needs to be toughened,” explained Naskar, leader of ORNL’s Carbon and Composites group. A major goal of the group is producing industrial polymers that are strong and tough enough to be deformed without fracturing. “We need to chemically combine soft matter with lignin. That soft matrix would be ductile so that it can be malleable or stretchable. Very rigid lignin segments would offer resistance to deformation and thus provide stiffness.”
All lignins are not equal in terms of heat stability. To determine what type would make the best thermoplastic feedstock, the scientists evaluated lignin from wheat straw, softwoods like pine, and hardwoods like oak. They found hardwood lignin is the most thermally stable, and some types of softwood lignins are also melt-stable.
In a heated chamber with two rotors, the researchers “kneaded” a molten mix of equal parts powdered lignin and nitrile rubber. During mixing, lignin agglomerates broke into interpenetrating layers or sheets of 10 to 200 nanometers that dispersed well in and interacted with the rubber. Without the proper selection of a soft matrix and mixing conditions, lignin agglomerates are at least 10 times larger than those obtained with the ORNL process. The product that formed had properties of neither lignin nor rubber, but something in between, with a combination of lignin's stiffness and nitrile rubber's elasticity. By altering the acrylonitrile amounts in the soft matrix, the researchers hoped to improve the material's mechanical properties further. They tried 33, 41 and 51 percent acrylonitrile and found 41 percent gave an optimal balance between toughness and stiffness.
The title of the published paper is “A New Class of Renewable Thermoplastics with Extraordinary Performance from Nanostructured Lignin-Elastomers.” Future studies will explore different feedstocks, particularly those from biorefineries, and correlations among processing conditions, material structure and performance. Investigations are also planned to study the performance of ORNL’s new thermoplastic in carbon-fiber-reinforced composites.
“More renewable materials will probably be used in the future,” Naskar said. “I'm glad that we could continue work in renewable materials, not only for automotive applications but even for commodity usage.”
Now that you are Ahead of the Curve, stay there by joining TAPPI.
For a modest investment of $174, receive more than US$ 1000 in benefits in return.