Stealth! Polyurethane-tin oxide composites help you hide.

BACKGROUND:
with the continuous development of science and technology, the military strength of various countries has been increasing. Today, long-range over-the-line warfare has become mainstream. Long-range reconnaissance measurement technology and various kinds of stealth technology are becoming more and more important, among which infrared stealth technology is a kind of technology that makes the infrared radiation emitted by the object as similar as possible to the surrounding background radiation, so that the infrared detection sensor can not distinguish the target object .
for infrared shielding coatings include metal powders, conductive polymers, organic/inorganic composites and semiconductors. In terms of material weight, infrared shielding capability and mechanical properties, tin oxide (ATO) nanoparticles synthesized by a variety of technologies are widely used in infrared and thermal radiation shielding coatings. The unresolved problem is that when ATO nanoparticles are mixed with polymer substates, the mechanical properties of the fibers may decrease. Therefore, it is necessary to develop a wearable infrared (IR) and thermal radiation shielding material, which can effectively improve the shielding efficiency without significantly increasing the weight of the fiber and maintaining the mechanical strength of the fiber.
Highlights
Researchers such as Sang-Mi Jeong of Gyeonggi-do University in South Korea have successfully synthesized polyurethane-tin oxide (PU-ATO) composite fibers, which are pu-ATO composite fiber textiles developed in this study compared to conventional polyester or PU fabrics With excellent IR and thermal radiation shielding performance, the PU-ATO composite fibers are consistent with IR and thermal radiation shielding even when exposed to repeated temperature changes of .20 and .80 degrees C, as well as long-term temperature changes over a 30-day period. The surface of the PU-ATO composite fiber is hydrophobic to prevent IR and thermal radiation deformation due to the moisture moisture absorbed by the PU-ATO composite fiber.
preparation process for the PU-ATO composite fiber
as shown in Figure 1, the best ATO sol is obtained by controlling the concentration of the ATO pre-drive and the aging time of the sol prepared by the sol-gel legal system. Mixing the sol with a preset amount of PU solution, a PU-ATO composite suspension with different components is obtained. Using wet spinning technology, PU-ATO (1-4) composite fibers are prepared using four composite suspensions with different ATO concentrations (0.5, 1.5, 3.0 and 4.0 mmol).
1 ATO sol and PU-ATO composite suspension preparation
. IR and thermal radiation shielding characteristics of PU-ATO composite fibers
As shown in Figure 2, infrared and thermal radiation emitted by the human body can also become visible through the fabric when covered with commonly used polyester or polyurethane fabrics when observing people in visible light and using infrared cameras. Conversely, when a part of the human body is covered with PU-ATO composite fiber clothing, infrared and thermal radiation emitted by the human body is shielded from the IR profile of a person.
Figure 2 Concept Schematic of IR and Thermal Radiation under Visible Light and IR Cameras
The attenuation of fully reflective Fourier Transform infrared spectroscopy (ATR-FTIR) in Figure 3 shows that polyester, PU, and PU-ATO(3) fabrics have infrared pass rates of 40%, 25% and 2%, respectively. Note that the ATR-FTIR spectrum is carried out in the wavelength range of 7 to 14 m, including the entire wavelength range of 7.5 to 13 m detected by the thermal infrared camera. The ATO has excellent infrared and thermal radiation shielding effects due to local surface plasma resonance due to the Sb doping effect. The low infrared pass rate of PU-ATO(3) textiles is the result of the uniform dispersion of ATO sol in the PU substation of the fiber.
3 infrared transmission rates of textiles based on polyester, PU and PU-ATO composites
. Hydrophobicity of PU-ATO composite fibers
Because fiber absorption causes IR image deformation, fiber hydrophobicity is essential to maintain a certain level of infrared and thermal radiation shielding capacity. Use the contact angle analyzer to assess the moisture wetting of the composite fiber. As shown in Figure 4, the water contact angles of pu-ATO (1-4) composite fibers at different concentrations (0.5, 1.5, 3.0 and 4.0 mmol) are ≥130 degrees, indicating hydrophobicity, so that water droplets on the fabric surface are not absorbed, but are easy to roll off.
Figure 4 PU-ATO Composite Fiber Water Contact Angle Map
Infrared and thermal radiation shielding properties of PU-ATO composite fibers in different environments
In order to be used as practical wearable textiles, textiles must maintain their infrared and thermal radiation shielding properties in different environments.
as shown in Figure 5A, the surface temperature of the PU-ATO(3) composite textile remains stable after repeated exposure to high (-80C) and low (-20C) temperatures. These results confirm that the infrared and thermal radiation shielding properties of composite textiles can be maintained even after repeated exposure to high and low temperatures.
5B shows the continuous infrared and thermal radiation shielding properties of PU-ATO(3) composite textiles. The surface temperature of the fabric is measured at a temperature of 40 degrees C for 8 hours a day for a total of 30 days. It was found that even over a long period of time, the surface temperature of the fabric remained at around 25 degrees C.
5 repeatedly evaluates the infrared and thermal radiation shielding properties of PU-ATO(3) composite textiles based on changes in temperature and time. A, after repeated heating (-80 degrees C) and cooling (-20 degrees C) cycle PU-ATO(3) composite textile surface temperature. B. After applying a temperature of 40 degrees C for 8 hours (out of 30 days), the pu-ATO(3) composite textile surface temperature
Conclusion
In this article, the researchers created the PU-ATO composite fiber and used it to weave wear-resistant textiles with IR and thermal radiation shielding properties. At the same time, the fiber has excellent hydrophobicity, which can effectively avoid the IR image deformation caused by fiber absorption. The reliability of pu-ATO composite fibers was confirmed by repeated exposure (ten times) at extreme temperatures of 80 degrees C and 20 degrees C and 30 days of prolonged exposure at 40 degrees C. Pu-ATO composite fibers are expected to drive new markets for wearable infrared stealth products as stealth technology to hide infrared signals from objects continues to evolve.
source: Frontiers in polymer science
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