Carbon Dioxide Laser as a Sustainable Method for Producing a Pattern on Denim Fabric: Evaluation of Colour and Durability

Research Article

Adv Res Text Eng. 2022; 7(1): 1068.

# Carbon Dioxide Laser as a Sustainable Method for Producing a Pattern on Denim Fabric: Evaluation of Colour and Durability

Venkatraman PD*

Manchester Fashion Institute, Faculty of Arts and Humanities, Manchester Metropolitan University, Cavendish Street, Manchester, UK

*Corresponding author: Prabhuraj D. Venkatraman, Manchester Fashion Institute, Faculty of Arts and Humanities, Manchester Metropolitan University, Cavendish Street, M15 6BG Manchester, UK

Received: January 20, 2022; Accepted: February 15, 2022; Published: February 22, 2022

## Abstract

Laser treatment of denim fabrics was demonstrated as one of the methods of producing distressed effects and is continuing to attract textile and fashion designers to develop bespoke designs that appeal to all age groups. Two dark shaded indigo-dyed 100% cotton twill fabric with varying weights representing various garment applications were laser treated using a commercially available pulsed CO2 laser of wavelength 10.62μm. Pulses per inch, which is the degree of closeness of laser irradiation, was maintained at 300 and 400 PPI. Treated denim fabrics were evaluated for tensile strength, colour measurements, including colour hue (H), saturation (S), brightness (B), reflectance, K/S (colour yield), CIE L* a* b*, fabric thickness and colourfastness after wash.

Results indicated that colour contrast of denim fabric enhanced with the increase in grayscale (tone density) for both the LW (lightweight) and HW (heavyweight) fabrics, mainly at lower laser speed (80%) and higher laser power (40%). At higher grayscale (30% GS), surface fibers charred due to laser and the oxidation of cellulose occurred, causing a distinct yellow tone compared to pristine denim. Fabric tensile strength was affected as grayscale and laser parameters increased, the variation from pristine denim for LW fabric was 40 - 45% at 30% GS, whilst for HW fabric, variation was 25-30%. Colourfastness tests revealed limited colour staining, and it removed charred fibers showing a distinct tone change. This research recommends a combination of fabric and laser parameters to produce patterns without affecting the overall quality of the fabric.

Keywords: Denim fabric; CO2 laser; Colour change assessments; Tensile strength and colour fastness

## Introduction

Denim fabric is a popular material for jeans and casual wear [1] and the market for denim fabric is expected to increase by $105 billion by 2023 from$90 billion in 2019 [2]. Approximately 300 denim mills Worldwide produce 6.4 billion meters of fabric, which could reach 8.2 billion meters by 2021 [3]. Due to the rise in awareness among consumers, the demand for innovation in a sustainable, ethically, and environmentally friendly process [1] is rising. Cotton fibre remains the preferred fibre for making denim jeans, and the finishing of denim is the essential aspect to suit consumers’ needs. Indigo dye traditionally used in the dyeing of denim fabric (Indigofera tinctorial plant species) is insoluble in water. It is a vat dye, which provides a brilliant blue hue to the cotton fabric has low colour fastness [4], has a limited affinity to cellulose fibers [5], and it has to be reduced with chemicals to ensure the dye penetrates the fibers. However, synthetic indigo dyes (such as sulphur dyes) are common nowadays due to their better dye affinity to cotton fibers [4]. Traditional denim fabric is durable that has dyed warp yarns interlaced with undyed weft yarns, which has a distinct diagonal line due to warp yarn lifting over or remaining under two or more weft yarns.

Consumers look for some critical aspects when purchasing denim wear: colour/shade, fit, comfort, and finish - distressed or faded jeans. Hence, the finishing of denim is essential to suit consumer demands, and it can be classified as dry and wet finishing. Due to regulatory changes, and increased demand for eco-friendly denim wear [6], several initiatives (yarn dyeing, garment finishing, and use of organic fibers) have been carried out to make denim wear environmentally friendly [7]. Development of surface patterns or decoration or to increase aesthetic appearance is popular globally among all ages, particularly distressed, or faded denim or light washed for men’s and women’s wear [6]. Various finishing techniques enable to produce worn out, faded, or distressed effects, where the dyes are removed or fabrics are abraded or cut. Typical examples of dry finishing include – stone wash, whisker effect, grinding, ripping, etc [8]. Many of these processes are harmful to health, requiring several processing stages, time-consuming and arduous.

Problems with mechanical processing of developing faded denim are high and pose severe health hazards during denim fabric’s surface abrading [8]. Sandblasting (uses sand containing silica) potentially causes silicosis or lung cancer; potassium permanganate spray used to produce colour change can damage the respiratory system; hand scrapping (flying lint, dyes) is another potential health hazard [8,9]. Therefore, conventional denim processing has a negative impact on the environment. Several water-free denim processing technologies have been attempted to counteract these adverse effects, including plasma treatment that produces distressed or faded denim by affecting the dye molecules, ozone treatment (fabric bleached with ozone gas), and enzyme finish. Although these processes have some advantages in reducing water consumption, energy, chemicals, laser processing remains an ideal tool for producing colour fading with good evenness and accurate reproduction [10]. The possibility of developing subtle tonal effects and intricate design patterns or cuts on denim using laser is growing, attracting several designers, and has become a future of denim finishing [11]. Laser systems in textiles use raster marking where laser beam moves in rows successively to produce the marking using a laser beam [12]. The laser beam removes the dye or degrades the fabric surface [13] and produces a localized burning effect on the surface when using a CO2 laser [14].

Various studies have reported the use of laser in apparel for manufacturing [13], fading [15-18], improve appearance [43], changes in the seam properties [44], and producing patterns on denim fabric [19]. Laser application was reported as a cleaner production process for denim processing [17] due to its low hazard, saving energy and time, reducing various processes, and being chemical-free. When using different laser beams, Nd:YAG at 532nm was noted to produce the best effect, and CO2 laser affected textile fibers and produced a distinct effect on the fabric [20]. Much similar to the above, a study that compared three different types of laser beams (Nd:YAG laser 1064nm; CTH: YAG laser 2.09μm; and CO2 laser 10.6μm) indicated pulsed CO2 had a high efficiency, where dimensional shrinkage and tearing strength of laser-treated denim fabrics were not affected. The colourfastness of treated samples revealed that colour change was minimal and that little or no colour transfer was observed [15]. The durability of the fabrics is vital during usage; hence fabric properties such as tensile and tearing strength have been reported. Laser treated denim fabric produced differences in tensile strength, particularly in warp and weft directions [21]. This was attributed to the direction of the laser beam falling on the fabric surface. Owing to these developments, researchers studied various laser variations or equipment to produce surface effects as the process was environmentally friendly compared to conventional methods [17]. Some studies [17,22,23] reported the effect of laser treatment on denim fabrics using pixel time and dots per inch (dpi) as one of the main parameters determining the colour contrast difference between pristine denim and treated denim and affecting other physical properties of the fabric.

Interestingly, when using laser on polyester or polyamide fabrics, increased surface roughness and dye adsorption [24] were noted. Although surface motifs to enhance the appearance of polyester fabrics were also observed at 50dpi and 180μs, any increase in laser parameters melted the fabric [25]. Modification of surface morphology of the fabric structure was of interest to many when applying laser beam. An increase in wetting time (s) of the laser-treated bleached cotton samples were noted when compared to the raw cotton treated sample. Wetting time was zero for bleached cotton laser-treated fabric compared to raw samples [26]. This was attributed to an increase in the porosity of fabric due to fibre loss and the formation of the cellular structure due to laser resulting in increased wetting. In addition, denim treated fabrics, when washed, can produce back staining during denim washing, where removed indigo dye can redeposit on the fabric surface affecting the appearance of the fabric [27].

Some of the shortcomings of previous studies are that most have used higher laser parameters which could affect the durability or performance of the fabrics (that could modify the fabric texture, causing difficulty in handling the fabric during manufacturing or consumer use). Other shortcomings can be limited to one fabric type, use of different equipment, or lack of comparison with different fabric densities or a combination of the above parameters resulting in heterogeneous literature. In this study, we report the application of CO2 laser at a low laser power to create changes in the shade without compromising the fabric properties. Such a comprehensive assessment will serve as a tool for various professionals who apply laser for surface modification, decoration or fading, particularly for lightweight fabrics (shirts, tops, blouses) and heavyweight fabrics (trousers, jackets).

## Objectives of the research

Laser patterning using a commercially available CO2 laser was used to identify a set of laser parameters for developing a pattern using indigo-dyed denim fabrics. Three distinct laser parameters (laser speed, power, and pulses per inch) were varied along with the tone density (grayscale) to determine an ideal combination of laser parameters for differing fabric area densities to produce a distinct contrast in indigo-dyed denim fabric without affecting the durability of the fabric (Figure 1). This research builds on the previous study [19] that reported the potential of producing patterns using a fixed laser speed and pulses per inch laser patterning. In addition, the study adds new information for precisely producing contrast at a lower grayscale (10-30%), which does not affect its physical properties, fabric thickness and tensile strength. Grayscale denotes the tone density, where 10% represents the low tone, and 100% indicates the higher tone density.