Improving the Deodorizing Ability of Cotton Fabric by Printing with Bamboo Charcoal

ABSTRACT Due to its relatively large specific surface area and microporous structure, bamboo charcoal is widely employed in a variety of industries, including the textile sector. In this investigation, bamboo charcoal powder was formulated as a natural colorant in the pigment print paste and then applied to cotton fabric by screen printing. Colorimetric values were assessed and color fastness to washing, light, and crocking as well as mechanical properties was performed according to related standards. By varying the amount of bamboo charcoal, the printed fabric had a light to dark gray color with good to excellent wash, light, and crock fastness. The combination of binder and fixing agent in the print paste increased fabric tensile strength, elongation, tear strength, and more pronounced stiffness. Besides, the bamboo charcoal printed cotton exhibited a deodorizing rate of 80.3–87.8% against ammonia gas after 40 min and was maintained at 54.8–73.1% after 10 washing cycles.


Introduction
Nowadays textile materials not only possess a pleasant appearance but also offer special functions to satisfy the end-user needs. It was, therefore, vital to incorporate multifunctional characteristics such as moisture management, water repellent, flame retardant, anti-UV, antibacterial, deodorizing, conductive, and electrostatic features to create value-added products (Joshi and Adak 2019). At the same time, when textiles are in use, odors from the environment and the human body accumulate, posing health risks (McQueen and Vaezafshar 2020). To impart or enhance the deodorizing property of textile materials, four approaches, namely enhanced adsorption, catalytic decomposition, source control, and odor masking are normally undertaken (Wang et al. 2020). The enhanced adsorption method relies on the physical adsorption between odor and fiber or other additives, for example, cyclodextrin, chitosan, and porous materials, e.g., zeolite, and activated carbon.
Activated carbon is a carbon-rich material having a well-developed pore structure and is generally produced by carbonization followed by physical or chemical activation processes of coal and biomass (Danish and Ahmad 2018;Reza et al. 2020). With its high surface area ranging from 600-2000 m 2 /g, porous structure, and surface functional groups, activated carbon is utilized in a wide range of applications, e.g., adsorption, filtration, purification, etc. (Benedetti, Patuzzi, and Baratieri 2018;Bhatnagar and Sillanpää 2010). For the adsorption aspect, the activated carbon performed well for volatile organic carbon (VOC), but poorly for polar compounds (Asada et al. 2002;Iyobe et al. 2004).
For functional textile applications, charcoal and activated carbon from biomass have been the subject of intensive investigations. Many attempts have been conducted to add bamboo charcoal particles into spinning solutions during the fabrication of polymeric fibers (An et al. 2008Ho et al. 2015;Lin, Ta-Chung, and Hsu 2007). In addition, the incorporation of biomass charcoal into fabric by coating and printing techniques also offers special properties (Wang et al. 2020). Such charcoal powders from bamboo and neem trees were prepared and then coated to cotton, polyester, and 65/35 polyester/cotton woven fabrics to improve comfort properties such as wetting, wicking, water vapor permeability, air permeability, and thermal characteristics as well as antibacterial and UV protection (Gunasekaran, Prakash, and Periyasamy 2020;Prakash et al. 2021). In one study, the polyester nonwoven fabric was treated with bamboo charcoal and acrylic resin to provide infrared ray and negative ion emission and deodorization functions (Yen et al. 2012). Another research reported the application of activated charcoal powders from coconut and oil palm shells to cotton and polyester fabrics by coating and pigment printing to impart deodorizing ability toward onion odor (Eza, Ahmad, and Ahmad 2012).
The current study is aimed at developing the color and deodorizing ability of cotton fabric using bamboo charcoal powder as a natural colorant in pigment printing. The purpose is to evaluate the influences of bamboo charcoal, binder, and fixing agent on color, color fastness, and mechanical properties. The deodorizing ability against ammonia gas of the printed fabric and its durability to repeated washing is also reported.

Printing process
The printing paste was prepared by first dissolving the thickener (100 g/kg) in hot water to produce a viscous homogenous paste. The required amounts of binder (200, 300, and 400 g/kg), and fixing agent (20, 40, and 60 g/kg), were successively added to the paste with continuous stirring. Finally, the bamboo charcoal powder (10, 30, 50, 70, and 100 g/kg) dispersed in water was added. The viscosity of the print pastes prepared with different binder and bamboo charcoal powder content varied from 1396 to 12,462 cP as measured on a Brookfield DV-II+ viscometer at 21-22°C. The printing paste was manually applied to cotton fabric through the flat screen method. The printed sample was then air dried, fixed in a laboratory mini dryer at 150°C for 5 min, followed by washing in 2 g/L soap solution and thoroughly rinsed with water.

Color measurement and color fastness testing
The color strength (K/S value), CIE color coordinates (L*, a*, b*), and color difference (ΔE*) were measured using a Datacolor 650 spectrophotometer under illuminant D65 and 10° standard observer. The color fastness to washing was carried out according to ISO 105 C06:2011 (test no. A1S), where the printed sample was treated in 150 mL of 4 g/L standard detergent solution with 10 steel balls at 40°C for 30 min. Color fastness to light and crocking was determined according to ISO 105-B02: 1994 and AATCC Test Method 8-2007, respectively. The color levelness of the printed fabrics was determined by measuring reflectance values (400-700 nm) at 10 different locations on the sample and the relative unlevelness index (RUI) was calculated as in earlier investigations (Chong, Li, and Yeung 1992;Kan 2014;Nakpathom et al. 2020). The degree of color levelness was classified as follows; RUI<0.2 as excellent levelness, 0.2-0.49 as good levelness, 0.5-1.0 as poor levelness, and>1.0 as bad levelness.

Mechanical testing
The tensile property of the bamboo charcoal printed cotton sample was determined according to ASTM 5035-11 using a universal tensile testing machine (Model H5KT, Tenius Olsen Ltd., Redhill, UK). The tearing strength was determined according to ASTM D 1424-09 using an Elmatear digital tear tester (Model 655, James H. Heal & Co., Ltd., Halifax, UK). A Shirley stiffness tester was used to evaluate flexural rigidity following ASTM D 1388-96. For each test, five specimens were performed in the machine direction (MD) and the average of the readings was reported.

Morphological evaluation
Scanning electron microscopy (SEM) images of cotton fabric printed with bamboo charcoal were taken using JEOL JSM-7800F Prime microscope operating at 5 kV.

Deodorizing evaluation
The deodorizing properties of the printed samples against ammonia were evaluated by placing an 8 cm x 10 cm fabric sample in an airtight vessel initially filled with ammonia gas (100 ppm). The change in ammonia concentration was monitored by an ammonia gas detector (Smart Sensor AR8500) over a period of 120 min at 30°C. The deodorization performance (%) was calculated as follows, deodorization performance (%) = (C b -C s )/C b x 100, where C b = the concentration of ammonia in the blank state (without fabric), C s = the concentration of ammonia with the fabric (Lee et al. 2010;Liu, Zhang, and Tang 2013). Five samples were tested for each print paste formula and the average value of deodorization performance was reported.

Effect of bamboo charcoal concentration
In the first part of the investigation, the prepared print pastes containing 400 g/kg binder and different concentrations of bamboo charcoal powder (10, 30, 50, 70, 100 g/kg) were printed on cotton fabric. The resultant color values and color fastness results are presented in Table 1. The color of the obtained prints changed visually from light to dark gray with an increase in bamboo charcoal concentration from 10 to 100 g/kg as indicated by the decreasing L* and increasing K/S values. This darkening of shade corresponded to the relatively high absorption in the visible region, i.e., low reflectance values  (<30%) of the bamboo charcoal printed samples compared to the unprinted (>80%) as illustrated in Figure 1. Additionally, the printed fabric possessed good to excellent levelness as the relative unlevelness index (RUI) values were 0.18-0.27. All printed samples exhibited excellent wash fastness with the ratings of 4-5 or 5 for both color change and staining on the adjacent fabrics. In addition, they had outstanding light fastness, scoring 7-8 on the blue wool scale, which exceeds the level usually provided by natural colorants. Despite the dry crock fastness being excellent, the wet crock fastness declined when the amount of bamboo charcoal was increased. The lower wet crock fastness by 1-3 points at higher bamboo charcoal concentrations suggests that some of the bamboo charcoal particles detached from the fiber surface.

Effect of fixing agent on color fastness properties
The surface morphology of the bamboo charcoal printed cotton is displayed in Figure 2. After printing, a large area of binder films covering the cotton fiber was detected because of the crosslinking reaction during the fixation of bamboo charcoal. Since the deposition of bamboo charcoal particles was more noticeable at higher content (>50 g/kg), some bamboo charcoal particles did not firmly adhere to the fiber, resulting in poorer wet crock fastness. This problem could be solved by adding a fixing agent (20, 40, and 60 g/kg) to the print pastes, which improved the wet crock fastness ratings to a fair to good level as shown in Table 2. In pigment printing, a three-dimensional binder film is formed during the curing process by selfcrosslinking reaction or reaction with other crosslinkers or fixing agents (Gutjahr and Koch 1994;Ibrahim et al. 2019). The role of this continuous film is to hold and adhere pigments to the fiber surface. Based on the results of this study, the use of fixing agent tended to somewhat lower color depth but had no adverse effect on other fastness parameters.

Effect of binder and bamboo charcoal concentrations on mechanical properties
The influences of binder and bamboo charcoal concentrations on the mechanical properties of the printed cotton fabric are given in Figure 3. The unprinted cotton (control) fabric had 353 N tensile strength, 12.4% elongation, 6.7 N tear strength, 37.7 mg.cm flexural rigidity in the machine direction (MD). It can be seen that there was a slight increase in tensile strength (3.6-26.1%), elongation (2.3-    10.5%), and tear strength (3.1-23.2%) of the printed sample compared to the control. The stiffness, on the other hand, was affected markedly with an increase of about 79.5-182.6%. Higher additions of binder and bamboo charcoal also appeared to intensify this trend due to more binder film development (Shakoor et al. 2017).

Deodorizing properties
The deodorizing performance of the bamboo charcoal printed cotton fabric is denoted by the reduction of ammonia gas as illustrated in Figure 4. Fast deodorization took place in the first 40 min for bamboo charcoal printed samples as the concentration of ammonia gas dropped from 100 ppm to 12.2-19.7 ppm (80.3-87.8% deodorization performance) and subsequently began to level off. Meanwhile, the residual ammonia odor of the unprinted sample was 48.3 ppm (51.7% deodorization performance). The enhanced odor adsorption mainly due to the presence of acidic functional groups on the surface of bamboo charcoal contributed to a greater ability to remove ammonia (Asada et al. 2002(Asada et al. , 2006Iyobe et al. 2004). Moreover, it was found that the higher the amount of bamboo charcoal in the print paste, the better the reduction of ammonia intensity. This could be explained by the larger number of available active surface sites for odor adsorption.
To assess the deodorizing durability to repeated washing, the bamboo charcoal printed cotton fabric had undergone the above deodorizing test after being subjected to 1, 5, and 10 washing cycles (ISO 105 C06 (A1S)). As demonstrated in Figure 5, the deodorizing ability toward ammonia decreased continuously with the number of washings for all samples. For example, in the case of the 50 g/kg bamboo charcoal printed sample, the deodorization performance at 40 min was reduced by 10.3%, 17.4% and 22.2% after 1, 5, and 10 washings, respectively. The overall reduction after 10 washings for all bamboo charcoal content was in the range of 14.7-25.3% (or with the remaining deodorizing performance of 54.8-73.1%). It was also observed that the deodorizing efficiency decreased less as bamboo charcoal content increased from 10 to 100 g/kg. However, the color depth (K/S) and color difference (ΔE*) values of the sample before and after washings were not much different as shown in Table 3, implying that only a small quantity of bamboo charcoal particles was lost. Hence, the reduction of the deodorizing ability of the printed fabric may be because bamboo charcoal could also adsorb detergents in the washing solution, making it less available for ammonia adsorption afterward (Haderiah, Sulasmi, and Erlani 2015;Malhas, Abuknesha, and Price 2002)

Conclusion
The light to dark gray cotton pigment prints with deodorizing activity were fabricated using a natural colorant from bamboo charcoal. The wash fastness ratings for both color change and color staining of the obtained prints were excellent, rated at 4-5 or 5 and the light fastness rating was outstanding with the blue wool scale of 7-8. Good to excellent crock fastness result was also noticed, however, the wet crock fastness is inferior in case of higher bamboo charcoal content, thus requiring the additional fixing agent in the print pastes. Owing to a crosslinked network film formation, when the concentrations of binder and bamboo charcoal were raised, the printed fabric became stiffer as indicated by a large increase in flexural stiffness, while its tensile strength, elongation, and tear strength increased relatively less. Deodorizing ability test revealed that cotton fabric printed with bamboo charcoal could reduce 80.3-87.8% of ammonia gas after 40 min compared to 51.7% of the unprinted. After 10 washing cycles, the deodorization performance of the printed sample remained at 54.8-73.1%. Therefore, cotton fabric printed with bamboo charcoal powder could be a promising candidate to be used for odor masking products such as in furnishing textiles, medical care or sanitary products, and sporting goods.

Research highlights
• Screen printing bamboo charcoal onto cotton fabric produced a light to dark gray color.
• Outstanding light fastness with good to excellent wash and crock fastness were obtained.
• Increasing binder and bamboo charcoal content stiffened the fabric and slightly improved tensile, elongation, and tear strength. • The 80.3-87.8% deodorizing performance against ammonia after 40min was observed.