Variloft - Adaptive Thermal Insulation
A need exists for adaptive thermal insulation that provides protection over a wide range of temperatures with a single, or at most, couple of garments. Traditional systems rely on layering for effectiveness. This results in bulky, complex clothing systems that impede physical performance. An ideal solution is a system with self-regulating or variable loft capabilities to control the insulation characteristics of the garment.
VARILOFT, short for VARIable-LOFT clothing, is a smart thermal protection system based on the development of thermally responsive fibers. Through the utilization of materials systems (such as smart materials in the form of shape memory polymers) a thermally induced strain is created within the fiber as temperature changes. This concept is integrated into the production of co-extruded, bi-component fibers. Fiber layouts are optimized to transition from a flat, two-dimensional configuration to one that is three-dimensional. With the correct design, a network of fibers creates a self-regulating batting that gradually transitions from a flat, low-loft, low-R configuration to a high-loft, high-R configuration, effectively regulating thermal protection in response to environmental and body temperatures.
One of the direct benefits of this technology is the reduction of complexity in current layered insulation systems, coupled with a weight reduction. Thermal transfer is regulated not only based on the external environment, but also on the internal environment - effectively regulating temperature by balancing the ratio of body heat generation with heat absorption, and limiting heat loss as well as heat buildup. Furthermore, the tools and processes required for manufacture are the same as those used in commercial non-woven products.
Insulation batting materials are found in consumer products in several areas, including outerwear, sleeping bags, and gloves. While much of the commercial focus of Variloft has been on apparel, there are several other industrial uses where Variloft could be beneficial. These include insulation in building products or in automobile headliners. Headliners are currently one of the larger applications for non-wovens due to their low cost, noise reduction, and ability to be recycled. As temperature drops, the headliner contracts, and thus road noise inside the cabin is increased. Variloft can counteract this by expanding during cold weather, thus maintaining the soundproofing in all temperatures.
The VARILOFT thermal protection system combines thermally reactive bi-component structural fibers with thin staple fibers to produce a thermal protection batting that changes thickness based on environmental conditions. The concept optimizes the cross-sectional shape, material pairings, and processing of bi-component fibers and fiber layouts to take advantage of the effects of differential coefficients of thermal expansion (CTE). A helically twisting bi-component fiber is envisaged that transitions into a three-dimensional shape from the baseline to produce the desired variable loft. Increased thermal differentials will cause the fiber to "cork" forming a three-dimensional structure that enhances loft. With the correct design, the network of structural and thermally efficient fibers will produce a self-regulating fabric that gradually transitions from a flat, low loft, low thermal resistance configuration to a sufficiently high loft, high thermal resistance configuration. The overall thickness of the fabric changes when insulation made of the bi-component fiber is exposed to different ambient temperatures.
The composition of the batting will incorporate both non-reactive fibers blended with active bi-component fibers. An ideal batting construction requires bonding between the fibers to be solid yet flexible where structural fibers meet. These bonds will anchor the bi-component fibers so the temperature-induced strains will cause the batting to increase in thickness. If the bonds are not solid, the fibers will change shape, but the loft will only minimally increase thickness, as the straining fibers will slide against each other with only friction anchoring the fibers to produce increased loft. Bonds between the thermal fibers and structural fibers are less important, though ideally they would be bonded together in a non-sliding yet flexible manner as well.
A finite element analysis was conducted to estimate the thickness increase of a fabric made of this fiber as well as to determine evaluate concept feasibility. The Non-Woven Batting model incorporated eight fiber layers per batting with fibers of each layer shifted along their lengths to simulate the random nature of a non-woven batting. Figure 2 shows the result of this analysis for the 15°C and -45°C test temperatures.
The thermal response of a batting made from VARILOFT fibers was modeled to estimate performance with variable ambient temperature. This model comprised 23 distinct layers with linearly varying thickness and a differential CTE of 250 µm/m/°C. Figure 3 shows the results of the matlab simulation.
For more information:
Please email Brian Durant (Products), or call: 781-306-0609 x239