Emissivity Measurement of Semitransparent Textiles

In the textiles production industry it is more and more common to advertise new textiles, especially for sportswear, by claiming their ability to emit IR radiation in the long wave band at a higher degree with respect to normal clothes, that is highly beneficial to improve sporting performances. Three textiles are compared, one normal and two “special,” with Ag+ ions and carbon powder added, with different colors. The emissivity of the textiles has been measured to determine if it is increased in the “special” textiles with respect to the normal one. No substantial increase has been noticed. Nonetheless, the test implied some nonstandard procedures due to the semitransparent nature of the textiles, in comparison with the normal procedure that is commonly used on opaque surfaces. 1. Introduction Two textiles are made of polypropylene (PP) and charged with Ag+ ions and Carbon powder. They differ from the color that is green for the first and blue for the second. They are compared with a third “normal” PP textile of green color and the same weft of the previous. The purpose is to demonstrate if the emissivity in the Infrared-Long Wave band (IR-LW) [1–3] of the charged textiles is increased or not due to the presence of the charging elements. The measurement is carried out in the wavelength interval 8–14？μm; it is an integral measurement; that is, it represents the average value of the spectral emissivity in the considered interval [4]. The measurement is carried out by means of a microbolometric camera that exhibits an almost flat spectral response at the various wavelengths. Therefore, it is not taken into account any spectral response of the detector even because of the comparative nature of the measurement [5, 6]. Any evaluation of the taking angle is neglected and so the dependence of the emissivity with the view angle. The measurement is performed with a normal view with respect to the textiles [7]. The measurement technique consists in laying down the charged textiles, to be measured, and the “normal” (the reference) one, side by side and in contact with a thick aluminum plate that is assumed to be as much isothermal as possible. Observing the two textiles (that own the same temperature) by an IR camera allows to evaluate the IR radiation emitted by their surfaces. The possible difference in the radiation collected by the IR camera in correspondence of the “measured” textiles and the “reference” one is due to the emissivity difference. In this case the measurement is more difficult than the one for an opaque surface in so far the textiles are