by josh perry, editor
researchers at the university of maryland (college park, md.) have designed a new thermal insulating material from nanowood that is stronger, more environmentally-friendly, and more effective at insulating than styrofoam and could be a step forward in energy-efficient building materials.
completely derived from natural wood, nanowood with hierarchically aligned cellulose nanofibrils can be used as an anisotropic super thermal insulator. (university of maryland)
according to a report from the university, the idea was based on wood’s ability to conduct heat along the channels that the tree used to carry water to its leaves. when heat went across the grain, it was blocked, so if the wood was oriented in a particular way engineers could block or transmit heat as desired.
“to test how much heat was insulated, they measured the temperature on one side of the nanowood, while on the other side of the wood, shining a light in one test and applying heat in another test,” the report explained. “the nanowood insulated better in both cases.”
in fact, the nanowood blocked 10 degrees more heat than styrofoam or silica aerogel, which had recently been named “best insulator” by the guinness book of world records. it is also white, which allows it to reflect sunlight.
“they also tried to crush it and found that, in one direction, the nanowood was 30 times stronger than commercially used thermal insulation materials such as styrofoam, aerogel or other foams made of cellulose,” the article added. “nanowood’s tiny fibers don’t cause allergic reactions or irritate lung tissues, unlike glass or wool insulators.”
to make the nanowood work, researchers removed the lignin and the short fibers that get tangled with cellulose fibers. the remaining cellulose fibers are aligned and bond with each other to increase the mechanical strength of the material.
the nanotechnologies created by researchers working in the lab are being commercialized through inventwood, which is a spin-off from the university’s research group. the nanowood has been made in blocks or thin, flexible rolls.
the research was recently published in science advances. the abstract read:
“there has been a growing interest in thermal management materials due to the prevailing energy challenges and unfulfilled needs for thermal insulation applications. we demonstrate the exceptional thermal management capabilities of a large-scale, hierarchal alignment of cellulose nanofibrils directly fabricated from wood, hereafter referred to as nanowood.
“nanowood exhibits anisotropic thermal properties with an extremely low thermal conductivity of 0.03 w/m·k in the transverse direction (perpendicular to the nanofibrils) and approximately two times higher thermal conductivity of 0.06 w/m·k in the axial direction due to the hierarchically aligned nanofibrils within the highly porous backbone.
“the anisotropy of the thermal conductivity enables efficient thermal dissipation along the axial direction, thereby preventing local overheating on the illuminated side while yielding improved thermal insulation along the backside that cannot be obtained with isotropic thermal insulators.
“the nanowood also shows a low emissivity of <5% over the solar spectrum with the ability to effectively reflect solar thermal energy. moreover, the nanowood is lightweight yet strong, owing to the effective bonding between the aligned cellulose nanofibrils with a high compressive strength of 13 mpa in the axial direction and 20 mpa in the transverse direction at 75% strain, which exceeds other thermal insulation materials, such as silica and polymer aerogels, styrofoam, and wool.
“the excellent thermal management, abundance, biodegradability, high mechanical strength, low mass density, and manufacturing scalability of the nanowood make this material highly attractive for practical thermal insulation applications.”