**Abstract**

Polyamide-6,6 (PA-6,6) knitted fabric was coated with a complex combination of liquid-phase oxidized carbon black pigment (CBP) as light absorber and monosulfonated telon violet 3R (TVR) as acid dyes. Nitric acid (NA) moiety was used as liquid-phase oxidation of CBP and hydrophilic transformation of CBP-TVR. Thermoplastic polyurethane (TPU) and N, N-dimethylformamide (DMF) were formulated as cross-linker between composite mixture (CM) and PA-6,6 fabric. Six different CMs were coded for coating of PA-6, 6 fabric such as TPU-DMF, CBP-TPU-DMF, TVR-TPU-DMF, CBP-TVR-TPU-DMF, NA-TVR-TPU-DMF, NA-CBP-TVR-TPU-DMF. Structural, chromatic, and spectral reflection of CM coated PA-6,6 fabric was investigated by scanning electron microscopy, color measurement spectrophotometer, and Fourier transform infrared spectroscopy. CBP formulated PA-6,6 fabric was significantly remarked as maximum light absorber in both visible and near-infrared spectrum without allowing other parameters of treated PA-6,6 fabric. Therefore, minimum light reflection principle of CBP was indicated as camouflage material for camouflage textile coloration/finishing/ patterning of simultaneous spectrum probe in visible and near-infrared spectrum. PA-6,6 fabric is very common fabrication for defense clothing, weapon, and vehicle netting against every combat background. This approach of simultaneous spectrum probe may be extended for concealment of target signature against highperformance defense surveillance.

**Keywords:** camouflage coloration, carbon black pigment, polyurethane, reflection, visible–near infrared

#### **1. Introduction**

Camouflage textiles are incorporated with clothing of special workers and multidimensional equipment in the vein of army, air force, navy, marines, coastal guards, paramilitary forces, uniforms for officers and soldiers in defense forces, tents, shelters and sheets, sandbags, flak jackets, helmets, camouflaged combat and flight uniforms, covering airplanes, guns and boats, creating deceptions, making armored vehicles, and so on [1]. Key parameters of camouflage coloration are spectral bandwidth of target signature, spectral characteristics of combat background, and reflectivity [2, 3]. Reflection of pigment formulation must match with combat background for design of high-performance camouflage textiles. Polyamide and polyester fabric coloration were experimented with carbon black pigment (CBP). The camouflage effect of CBP was recommended in near infrared (NIR), 1000–1200 nm [4]. Camouflage coloration was trialed with CBP for formulation of colorant on synthetic and regenerated textiles [5]. Visible-camouflage coloration was also investigated with pigment, reactive and vat dyes. Combination of CBP with other synthetic colorant depicted more prominent hue of black [6, 7]. CBP was used for camouflage coloration of polyethylene terephthalate textiles in comparison with natural brown hue against desert combat background. Hence, CBP property was also suggested for NIR camouflage [8]. In this experiment, reflection of CBP was compared with a synthetic dyes telon violet 3R (TVR).

#### **1.1 Properties of CBP for suitability of technical coloration**

CBP has versatile industrial applications as a pigment, which imparts a black hue [9, 10]. CBP is the most suitable for defense textiles due to having maximum properties of protection textiles. CBP has weatherability, chemical resistance [11, 12], abrasion resistance [13], electroconductivity [11], alkali resistance, light fastness [7], hydrophobicity [14], which are major considerations for coloration of defense textiles. CBP has ester bond, thioester bond, amide bond, amino bond, carbonyl bond, thiocarbonyl bond, sulfonyl bond [12], aldehyde bond, hydroxyl bond, hydrogen bond [9]. Crystalline CBP shows a high order of reactivity [15]. Quantitatively more application of CBP is found in the rubber industry to accelerate its mechanical properties, such as resistance to abrasion. CBP is generally termed as active carbon for improving the mechanical properties of rubber. CBP is widely used for black coloration in paints, varnishes, carbon paper, ribbons, printing inks [13, 16, 17]. Plastic articles, metal articles, wood, paper, inorganic materials [11], and polyamide fabric coloration with 70% nitric acid (NA) [18]. Oxidization process was used to improve the coloring property of printing inks, paint, and black coloration [13, 16, 17]. Due to hydrophobicity of CBP, it is difficult to apply textile substances. So CBP needs to be oxidized for improving jetness by chromic acid, ozone, hydrogen peroxide, sodium hypochloride, potassium permanganate, NA [14, 19] and sulfuric acid [7, 14]. CBP was grafted with hydrophilic polymeric monomer (alkali or ammonium carboxylate) for improving water compatibility and dispersibility [20]. CBP has dusting tendency [21], it is combined with the carrier to impart chromatic hue. CBP constituted generally as a pigment [22]. CBP with acid surface groupings is particularly suitable with binders [23]. Particle size, surface structure, surface size, pH, and dispersibility of CBP need to be considered for every polymeric binding system [24–26]. Diameter and nigrometer index of CBP critically modify the color of CBP. CBP shows high color for diameter 13 and 15 nm and nigrometer index 63 and 68, respectively. CBP depicts medium color for diameter 17, 20 nm and nigrometer index 71, 76. CBP shows regular color for diameter 25 nm and nigrometer index 80 [11]. Different categories of CBP are fisher lampblack (particle size 44 nm, pH 7, carbon 96.7%, oxygen 0.9%, nitrogen 0.0%, sulfur 1.5%, hydrogen 0.6%), degussa special black (particle size 20 nm, pH 7, carbon 85.6%, oxygen 13.1%, nitrogen 0.3%, sulfur 0.4%, hydrogen 0.6%) and degussa color black FW 200 (particle size 13 nm, pH: 7, carbon 79.2%, oxygen 19.3%, nitrogen

*Evaluation of Camouflage Coloration of Polyamide-6,6 Fabric by Comparing Simultaneous… DOI: http://dx.doi.org/10.5772/intechopen.101537*

0.4%, sulfur 0.4%, hydrogen 0.7%) [27]. Natural gas and hydrocarbon are the raw materials of CBP [28]. Coarser particle of CBP shows lower depth of color, and finer particle shows higher depth of color [23] due to its difference in scattering values with difference in size and surface area. Hence CBP can be applied for chromatic modification of textile substances such as PA-6,6, cotton, wool, and acrylic fabric.

#### **1.2 Properties of TPU for suitability of textile coating**

Thermoplastic polyurethane (TPU) elastomers are a cross-linking agent having low density and high resiliency [29], dispersibility, and polymeric film forming ability was considered the criterion for applying in acid medium coating. TPU is also applicable for printing paste formulation of synthetic fabric coloration [30]. TPU creates capsule shell of CBP [31]. TPU was formulated for the dispersion of pigment [18]. TPU has structural form of hydroxy-terminated polybutadiene and polyetherester based prepolymers with diisocyanates such as hexamethylene diisocyanate [32]. Chemical reaction between polyols and polyisocyanates compounds existing hydroxyl groups reacts with isocyanates [18]. Therefore, structural features and properties of TPU are suitable for textile coating, textile finishing and printing.

#### **2. Technical approach of camouflage textiles formulation with CBP**

Reviewed patent and publications of CBP-based coloration exhibit that CBP has enumerated applications of coloring agent but limited applications on textile coloration. Simultaneous spectrum probe camouflage coloration is almost new concept in camouflage engineering. CBP has harmonized with the demanded textile properties for defense textiles such as low reflection, weatherability, chemical resistance, good rubbing fastness, and light-fastness properties, etc. Light scattering/absorbing principle of CBP materials have been predicted the possibility of deceiving reflection against combat background. CBP has multidimensional color forming functional groups such as carbonyl group, amide group, carboxyl group, which can deceive the surrounding color. The color tone of this functional group differs in spectral responses in Vis–NIR absorbance or reflectance-based spectrophotometric color evaluation and Vis–NIR spectral responses against wavelength. CBP has possibility to modify the hue of other color forming functional group. Light falling on CBP treated fabric diffuses or light is absorbed by the CBP influencing the chromatic hue/hiding the color hue. Hence the chromatic behavior of CBP on textile surface and its moiety with other colorant need to be identified for camouflage coloration. Color combination with CBP may conceal the chromatic hue of red, green, yellow, blue. CBP can be applied on textile substances for special worker's clothing like camouflage textiles as defense wear or protection tents for special requirements. There is very limited research on CBP formulated properties introduced for augmentation of camouflage textiles. Camouflage textiles can be identified by illumination properties of chromatic hue by spectral responses in both visible and NIR ranges as the chromatic hue in Vis and NIR range are not same. The reflectance can be identified by simultaneous spectrum in Vis and NIR region easily by using VIS–NIR/UV–Vis/UV–Vis–NIR reflectance spectroscopy.

#### **3. Materials**

130 GSM PA-6,6 knitted fabric collected from local supplier was used for experimentation. Water-insoluble and laboratory-grade CBP was used for PA-6,6 fabric

#### *Colorimetry*

coloration. TPU-Texalon 598 A in tiny pellet, white color in appearance was selected as cross-linking agent. N, N-dimethylformamide (DMF) was used as solvent for making a viscous solution of TPU. Laboratory-grade NA (70%) moiety was used for liquid-phase oxidation of CBP surface, functioning as hydrophilic vehicle of CBP-TVR into PA-6,6 and overall enhancement of rheopectic property in composite mixture (CM). The components of CM were used without further purification as received from supplier. Mathis laboratory hot plate, Werser Mathis AG, Rutisbergstrasse 3, CH-8156, Oberhasli/Zurich, Switzerland, automatic temperature controllable dryer, and a hand-operated coating processor with 2 mm roller were used for camouflage coloration.

## **3.1 Structure of CBP-TVR-TPU chemical compounds formulated for experimentation**

The chemical structure of CBP [9], TVR [33], TPU compounds [29], and PA-6,6 fabric [34] have been shown below in **Figures 1**–**4**.

**Figure 1.**

*Chemical structure of CBP used in this experimentation.*

**Figure 2.** *Structure of TVR used in this experimentation.*

*Evaluation of Camouflage Coloration of Polyamide-6,6 Fabric by Comparing Simultaneous… DOI: http://dx.doi.org/10.5772/intechopen.101537*

**Figure 3.**

*Polymeric structure of TPU cross-linker used in this experimentation.*

**Figure 4.** *Polymeric structure of PA-6,6 used in this experimentation.*
