Quoc Truong, a physical scientist at the Natick Soldier Research, Development and Engineering Center, is working to develop omniphobic and super-omniphobic textiles, which repel dirt, dust and liquid. Here, he operates a goniometer, which is used to ...
Thinking small is the key to developing future food and clothing technologies for the Soldier -- such is the conclusion of researchers at the U.S. Army Natick Soldier Research, Development and Engineering Center (NSRDEC). Scientists there are using nanotechnology, the engineering or manipulation of materials or systems at an atomic or molecular scale, to improve packaging -- both for the food Soldiers eat and their own packaging -- i.e., clothing.
NSRDEC's efforts include the development of high-barrier, nonfoil food packaging materials -- polymer films that prevent oxygen and water from transporting through them. Nanoparticles within a polymer film make it difficult for gas molecules to get through, improving the barrier to oxygen and moisture, both of which can speed the deterioration of food.
NSRDEC is also working on developing and advancing omniphobic and super-omniphobic textiles and other products, which resist dirt, dust and liquids. Omni means "all," and, in chemistry, phobic doesn't so much mean fearful as it does a chemical aversion. An omniphobic coating, therefore, is averse to both water (hydrophobic) and oils (oleophobic). Omniphobic coatings contain micrometer-sized (one 1 millionth of a meter) particles, such as silica, or a combination of micro- and nanometer scale particles. (A nanometer is one 1 billionth of a meter.) When these coatings are applied onto textiles or hard surfaces, such as glass or metal, their surfaces are modified with micro-and nanoscale surface features. These features are similar to a lotus leaf's hierarchical nonwetting surface, which enables the plant to float and glide on water, or a water strider's feet, which let the insect walk on water without sinking.
By working on the nano level, NSRDEC's scientists and engineers have the opportunity to expand the applications of this technology for the good of the Soldier.
THE PERFECT NONFOIL
The Advanced Materials Engineering Team (AMET), part of NSRDEC's Combat Feeding Directorate (CFD), is investigating high-barrier, polymeric materials for military ration packaging and for food packaging that supports deep space missions for NASA. Nanocomposite materials are an ideal packaging choice for shelf-stable processed foods because they can improve the barrier, mechanical and thermal properties of nonfoil food packaging. Polymeric laminates with foil as the barrier are currently being used for ration packaging. These structures provide an exceptional barrier to oxygen and moisture, but can also experience stress cracking and pin holing.
"The incorporation of nanotechnology into barrier films has proven to be a critical ingredient in our packaging design that will allow us to achieve food protection properties only seen before through the use of foil-based systems," said Dr. Christopher Thellen, a Ph.D. materials engineer in the CFD. "The exfoliated dispersion of nanoparticles in polymers forces penetrating oxygen and water vapor molecules to follow a tortuous pathway through the packaging material, thereby increasing the time needed to penetrate the packaging and improving barrier properties."
Nanocomposite packaging can be lighter in weight and less expensive than foil pouches. That reduction in size can not only reduce the amount of solid waste and enhance the quality of the rations by preserving them better and longer, but it also reduces the warfighter's logistical burden. NSRDEC is exploring technology that is based on incorporating nanoparticles into thermoplastic resins to create a nanocomposite material that is 1,000 times smaller than conventional composite material fillers. Nanoparticles have proven to be cost-effective and compatible with many polymers used in packaging.
As a result, the high-barrier, nonfoil polymeric packaging will comply with the Meal, Ready-to-Eat requirement of maintaining a three-year shelf life. For space applications, it will maintain up to a five-year shelf life.
NOT YOUR GRANDMA'S CANNING
Food sterilization techniques, in combination with proper packaging, play an important role in extending shelf life. Retorting, similar to pressure cooking, is the food industry's most common commercial sterilization process for prepackaged, low-acid foods. This process exposes food packages to high moisture and high temperature conditions under pressures of up to 2.5 atmospheres. In some cases, the long retort process leads to a reduction in food quality and limits the types of packaging materials that can be used.
Dr. Jo Ann Ratto, AMET team leader, whose doctorate is in plastics engineering, said that the implementation of a nonfoil structure into food packaging will make it possible to consider novel sterilization methods, such as microwave-assisted thermal sterilization (MATS) and pressure-assisted thermal sterilization (PATS). MATS and PATS are desirable alternatives to retort sterilization because they reduce the time needed to raise the product temperature to that required for the thermal lethality of target bacteria -- that is, it kills botulism and other toxins faster. A shorter process time can improve food quality and nutrient retention at a lower cost, which is one reason these methods are so attractive for both the U.S. military and NASA.
AMET is exploring polymeric packaging for these novel methods in collaboration with CFD's Food Processing Engineering and Technology Team. The two teams are also studying the effect of the various processing methods on vitamin stability in an effort to preserve freshness and food safety and prevent nutrient loss.
"The nanocomposite research and development work has been challenging and rewarding for the Advanced Materials Engineering Team. After further demonstration and validation work, we will know if these materials have acceptable performance to be considered for incorporation into ration packaging for the warfighter," said Ratto.
'SO' CLEAN
Soldiers are frequently in muddy, dusty and oil-contaminated environments. NSRDEC and its industry partner, Luna Innovations Inc., have worked together to develop omniphobic coatings for fabrics. Omniphobic surfaces do not become wet when exposed to water, liquid chemicals, organic solvents and some oils, such as cooking and motor oils.
Unlike omniphobic surfaces, which can be found in nature, super-omniphobic (SO) surfaces are purely man-made, engineered surfaces based on a 2007 discovery by the Massachusetts Institute of Technology. SO surfaces are both super-hydrophobic and super-oleophobic and theoretically repel most, if not all, known liquids, including those that with extremely low surface tensions, such as the solvents heptane and hexane, which would make most surfaces, without SO protection, wet.
NSRDEC's research and development of omniphobic and SO technologies, which will be used in protective clothing applications, will improve warfighters' quality of life and lessen their logistical burden. Omniphobic fabrics require much less frequent washing, reducing water and detergent usage. NSRDEC is also investigating the development of SO coatings, inherently SO fibers and micro-and nanosurface transparent films.
Besides being super-repellent to liquids when applied onto protective clothing, SO coatings will also contain an antimicrobial additive to retard the growth of microbes responsible for causing body odors. The SO fibers with the antimicrobial additive will be woven into yarn, made into fabric and finally fabricated into protective clothing that will require no laundering and remain clean, dry and odor free. The hierarchical micro- and nanoscale SO transparent films will be applied onto protective lenses, goggles and visors to provide the Soldiers with "always clear vision" by shedding water, oils and chemicals on the outer lens surface while preventing fog from forming on the inner lens surface. These features will help Soldiers better complete the vision-dependent aspects of their missions, including driving, firing, viewing maps and operating electronic equipment in multiple environments, especially under wet and rainy conditions.
To bring Soldiers the very best science has to offer, NSRDEC is combining its expertise with the expertise of academia and industry. Quoc Truong, an NSRDEC physical scientist, emphasized the importance of these collaborations. "NSRDEC provides concepts and ideas, technical approaches and guidance and methods of testing and evaluation to best meet our Soldiers' needs," Truong said. "We also have a thorough knowledge of user requirements and materials specifications, while our collaborators have expertise, technical knowledge, resources and personnel who are academically trained and also have experience" in a range of related disciplines. Those collaborators include nanomanufacturing experts at the University of Massachusetts Lowell; fiber spinning experts at Clemson University; experts in re-entrant nanosurfaces, theories and modeling at MIT; and experts in omniphobic coating processes at Luna Innovations.
"Single inventors, such as Edison and Einstein, are now much rarer," said Truong. "Our world remains complex, but more and more scientists and engineers are trained in their specialized areas. Therefore, collaboration is a necessity for new inventions and discoveries. This way, we can put our heads together in solving longstanding problems or coming up with new and innovative products and practical solutions, to help our Soldiers complete their mission in the safest and most efficient manner."
INHERENTLY SO
According to Truong, the characteristics of the SO coating will provide a significant improvement over the omniphobic coating. Moreover, SO surfaces will cause most liquid droplets to roll off and will minimize dirt and dust attraction. In addition to coatings, NSRDEC researchers are now working with academia and industry partners to develop fibers and transparent films that are inherently super-liquid-repellent based on their surfaces' physical nanoscale structures and features.
"Clothing and shelters fabricated from fabrics woven using inherently SO fibers will simply stay clean," said Truong, adding that yarns made from inherently SO fibers, then woven into cloth and made into clothing, are expected to be much lighter and more flexible and, therefore, more comfortable to wear. The fabric made from SO fibers will be more breathable because of a physical structure that has multiple "micro-scale" air channels (with nano features on its fiber surface) that run the entire length of the fibers. Since the inherently SO fibers will no longer require the added step of coating, the clothing is also expected to have a lower manufacturing cost.
SO coatings, inherently SO fibers and SO micro- and nano-surface transparent films have different applications. The coatings will be used on soft and hard shelters, textiles, cables, solar panels, intricate shapes and objects, and flexible and hard surfaces, including windows, cars, ships and airplane exteriors. The inherently SO fiber technology will be used on textiles and filtration products.
"With SO technologies, Soldiers will have clothing that always stays clean and fresh," said Truong. "Their goggles, visors, vehicle windshields and windows will always stay clean, which allows them the clear vision to fight and complete their missions. Applying the technologies to ship hulls will allow them to move much faster on the water surface with less fuel consumption."
Like SO coatings, SO films will be used on durable, hard surfaces--solar panels, windows or airplanes, for example--to make them repellent to dust and dirt, and super-repellent to water, oils and other liquids.
"It is my hope that these new breakthrough technologies will help to enhance existing technologies the same way that carbon fibers improved the structural strength of buildings and cars," said Truong. "However, these SO materials, which are just about a year or two away from their formal introduction to commercial applications, will have vastly more potential, especially because of transparent SO film."
Being super-clean means being more mission-ready and more hygienic, with enhanced protection from contaminated water and liquid chemicals. "This exciting research and development project work is underway, and it is expected that sample-size fabrics and lens products will be available for further testing and evaluation by December of 2015," said Truong.
The U.S. Army Natick Soldier Research, Development and Engineering Center is part of the U.S. Army Research, Development and Engineering Command, which has the mission to ensure decisive overmatch for unified land operations to empower the Army, the joint warfighter and our nation. RDECOM is a major subordinate command of the U.S. Army Materiel Command.
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U.S. Army Natick Soldier Research, Development and Engineering Center
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