Mid-infrared emissivity of nylon, cotton, acrylic, and polyester fabrics as a function of moisture content

The effectiveness of material to emit energy as thermal radiation is important in determining the apparent temperature in infrared thermographic measurements. For this reason, a number of measurements of the thermal emissivity in the mid-infrared thermographic (8–12 µm) region have been reported for fabrics. However, many fabrics adsorb moisture from the air, and condensed water has a relatively high thermal emissivity. In this manuscript, we report measurements of adsorption isotherms and mid-infrared thermal emissivity for nylon, cotton, polyester, and acrylic as a function of their moisture content in weight percent at temperatures just above ambient. We find that the order of water mass percentage gain for the fabrics in high humidity conditions are polyester < acrylic < nylon < cotton. The thermal emissivity is ∼0.88 independent of moisture content for the fabrics polyester, cotton, and nylon, while acrylic shows a pronounced increase in thermal emissivity as moisture content increases, ranging from ɛ ∼ 0.81 at low humidity conditions to ɛ ∼ 0.88 under high humidity conditions. In this work, emissivity measurements are made by imaging through a novel infrared window made from household cling wrap and interpreted with equations that are independent of window transmittance and sample temperature.