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Beat the Heat or Cold with Phase-Change Materials

Originating in NASA, phase-change materials in specialized clothing change from solid to liquid to maintain a comfortable body temperature in oppressive environments. To measure the dynamic thermal performance of fabrics containing phase-change materials, a new standard is being developed by ASTM Committee D13 on Textiles.

As phase-change materials absorb body heat, they “reduce the distractions of heat and cold fluctuations, providing a new superior level of comfort in clothing,” said Colorado State University professor Doug Hittle, Ph.D., who invented a test instrument and protocol for this innovation with Tifani Andre, a former CSU grad student in Design and Merchandising.

Deciding to release their methodology with ASTM, Hittle and those in attendance at a March meeting of ASTM Subcommittee D13.51 on Chemical Conditioning and Performance formed a task group to draft a voluntary-consensus standard.Among those collaborating with the group are a manufacturer of temperature-regulation products, a U.S. Department of Defense laboratory, a major producer of athletic shoes, and a popular sunglass manufacturer branching into high-tech garments. Further participation is welcomed.A test of performance is needed as phase-change materials increasingly appear in cold-weather gear. “A new metric, the temperature regulating factor (TRF), has been developed to characterize how well a phase change fabric moderates skin temperature. This metric also allows fabrics to be compared,” explained Hittle, a professor of Mechanical Engineering at CSU and director of their solar energy lab.

“A technology company, Outlast Technologies, and its partners in the fabric industry have developed methods for integrating microencapsulated phase change material into the production of fabrics, fibers, and foams for use in the outdoor wear, work wear, and home textiles,” he continued. “The products containing the phase change technology show branding emphasizing that the products with this technology will reduce body temperature fluctuations, and thus increase comfort. The thermal resistance of traditional fabrics is tested using a steady-state procedure whereby a temperature difference is maintained between a simulated skin and a simulated outdoor environment. These procedures are adequate for traditional fabrics. Little or no energy is stored in the fabric. In the case of phase-change products, these tests ignore the fact that during transient temperature fluctuations, energy is stored or released in the phase-change material depending on the activity level of the wearer.”

For further technical information, contact Doug Hittle, Ph.D., Colorado State University, Mechanical Engineering, Solar House II, Fort Collins (phone: 970/491-8617). ASTM Committee D13 meets Oct. 21-24 in Dallas, Texas. For meeting or membership details, contact Staff Manager Bode Hennegan, ASTM (phone: 610/832-9740). //

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