Advanced materials with infrared camouflage properties
Authors: Visileanu Emilia , Perdum Elena , Dinca Laurentiu , Salistean Adrian , Dondea Felicia , Scarlat Razvan 
Published: June 2024

Nowadays, textile materials with a protective role must ensure the body's defence against a multitude of threats and fulfil a variety of functional requirements. In particular, textile products intended for military applications require durability, resistance to ballistic threats and environmental conditions (eg, ultraviolet (UV) light, moisture, fire, heat and wind), comfort, etc. In addition, these materials must provide camouflage in various ambient conditions at a wide range of wavelengths in the electromagnetic spectrum such as the near-infrared (NIR) region (750–1200 nm) and far infrared (FIR) (3–5 and 8–14 μm).For the experiments, 3 types of yarns were used with a length density of 49.35 x 1 (20.26 /1) Tex (Nm) - 100% cotton yarn, 19.64 x 2 (50.92 / 2) Tex (Nm) - 100% PA yarn and 20.38 x 2 (49.07 /2) Tex (Nm) - 100% PES yarn. Textile structures in plain weave and ripstop weave (Rips I and Rips II) characterized by tear and abrasion resistance were designed and produced on the STB 2-212 weaving machine. After the finishing operation, the 100% cotton textile structure was treated by impregnation with 70 g/l ITOBINDER AG or 70 g/l PERMUTEX after alkaline boiling phases (8 ml/l caustic soda 38 0 Be, 3 g/l carbonic soda, 3 g/l trisodium phosphate, 2 g/l Kemapon PC/LF; 1,5 ml/l Seghion PC/LF), 4 washes, acidulation: 1 ml/l acetic acid (15 min), rinsing, free drying. The Rips I and Rips II variants have been film-coated on one side by scraping with acrylate paste. The printing samples were made by screen printing technology using water-based inks of the NEWTEX TRANSPARENT HD 10 type and Chromatex HD-10 pigments on automatic machines - carousel type, multi-colour, intermediate drying, Alfa Plus. Reflectance indices and curves were determined using a Perkin Elmer Lambda 950 UV-VIS-NIR Spectrophotometer in the wavelength ranges 860-1200 nm and 1000-1200 nm.To characterize the variability of the reflectivity index of 100% cotton textile structures, Rips I and Rips II, specific descriptive statistical methods were used. Histogram and box-plot graphs were plotted.Assessment of colour difference was carried out after light fastness, alkaline sweat, acid sweat, water and wash tests for the predominant colours of the camouflage colour printed fabric variants. The lightfastness test was performed after 100 hours of exposure on the XENOTEST APOLLO JAMES HEAL machine and colour differences were identified on the HunterLab machine. K/S and reflectance/transmittance (R/T) remission curves were drawn. L*, a*, b* parameters were calculated and interpreted in comparison with the control variants and the colours were fitted into trigonometric quadrants after each resistance test.The colour combination for the samples was made using Optitex pattern design and 3D simulation software (Gina 1 and Gina 2). The determination of the average reflectance was carried out by applying a specific procedure. The following were identified: colour designator, range of colour reflectance, the proportion of area covered by colour in the investigated area, the area covered by colour in the investigated area. To assess the degree of reflectance of each colour in the whole spectral band (860-1200) the median values were calculated.Regression coefficients have been calculated allowing the calculation of the reflectance index at any wavelength in the measured range. In the wavelength range 860-1200 nm all colours in the Gina 1 and Gina 2 structure show reflectance indices between -2.82% (black colour - Gina 2) and 57.68% (green colour - Gina 2). The exception is the beige colour with 92.36% (Gina 1) and 76.49% (Gina 2). In the wavelength range 1000-1200 nm, only the beige colour shows reflectance values >70%, respectively: 89.98% (Gina 1) and 74.25% (Gina 2).The weighted average values of the total reflectance index as a function of the weight of colours in the structures are very good with values <70%, respectively: 35.62% (Gina 1) and 31.48% (Gina 2) in the wavelength range 860-1200 nm and 35.30% (Gina 1) and 32.70% (Gina 2) in the wavelength range 1000-1200 nm.