SEM Analysis of CO 2 Laser Treated Cotton Grey Fabric

A. Méndez-Vilas and J. Díaz (Eds.) SEM Analysis of CO 2 Laser Treated Cotton Grey Fabric Y. L. Chow, C. K. Chan, and C. W. Kan Institute of Textiles and Clothing, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China In this paper, the surface morphology of the laser treated fabrics was studied which showed a characteristics sponge-like structure on cotton fibres after treating with 10.6µm CO 2 laser irradiation. The degree of surface modification was changed accordingly with various laser treatment parameters, the laser beam parameters ranging from 100 to 150 pixel time and 40 to 70 dot per inch (dpi) were irradiated on the grey cotton fabrics directly. After the cotton fabrics were irradiated with laser directly, they were undergone three wet processes including desizing, scouring and bleaching. The cotton morphology with a sponge-like surface structure was still found. The surface morphology of cotton fibres treating with laser were evaluated using Scanning Electron Microscope (SEM). Keywords Laser, Cotton, SEM 1. Introduction As for textile materials, surface modification by chemical finishing methods is not environmentally friendly and can cause safety and pollution problems [1]. As a result, laser technology applied as physical treatment methods is becoming more popular, and can be used in different applications to make an improvement and even eliminate several problems from the traditional processes [2]. The laser impact on grey cotton fabric was evaluated in the study by SEM. The effect of different laser parameters on grey cotton fabric was studied so as to examine the effectiveness of laser treatment applied on textiles fabrics. There are two parameters are used to study the surface modification by laser, which are resolution and pixel time. The range of resolution from 40 to 70 dpi and the pixel time from 100 to 150µs are studied. 2. Experimental 2.1 Sample Preparation 100% pure plain weave grey cotton fabric (density:60 ends/inch & 60 picks/inch; yarn count: 20x20 tex ) with the fabric weight of 156g/m 2. The fabric was conditioned at 21 ± 1 and 65 ± 5% relative humidity for 24 hours before the experiments and evaluations. 2.2 Laser Irradiation Irradiation was performed using a commercial pulsed CO 2 laser (GFK Marcatex FLEXI-150) under atmospheric condition in air. The samples were irradiated from the laser beam directly. The pulse energy of the laser beam was in the range from 5mJ to 230mJ and the wavelength was 10.6µm. The two parameters of resolution (40, 50, 60 and 70dpi) and the pixel time (0, 100, 110, 120, 130, 140 and 150µs) were varied to study the effect of different laser conditions on grey cotton fabric.. 2.3 Desizing treatment Laser treated grey cotton fabrics were desized with super rapidase (Supplier: Ciba Specialty Chemicals) (5g/l, liquor-togoods ratio: 200:1) at 70 for 1 hour. The desized fabrics were rinsed with hot water and then cold water and ovendried at 75, and then were conditioned at 21 ± 1 and 65 ± 5% RH for 24 hours prior to any evaluations. 2.4 Scouring treatment Desized laser treated grey cotton fabrics were scoured with sodium hydroxide (Supplier: Oriental Chemicals & Lab Supplies LTD) (20g/l, liquor-to-goods ratio: 200:1) at boil for 1 hour. The scoured fabrics were rinsed with hot water first and then cold water. The fabrics were neutralized with cold 0.5% Acetic Acid (Supplier: Oriental Chemicals & Lab Supplies LTD) and then rinsed with cold water again, finally the farbics were oven-dried at 75 and then were conditioned at 21 ± 1 and 65 ± 5% RH for 24 hours prior to any evaluations. 1860

A. Méndez-Vilas and J. Díaz (Eds.) 2.5 Bleaching treatment After desizing and scouring, the fabrics were bleached with hydrogen peroxide (Supplier: Oriental Chemicals & Lab Supplies LTD) (conc. 35%) with liquor ratio of 200:1 at 90-95 at ph10.5-11.0 for 1 hour. The bleached fabrics were rinsed with cold water and oven-dried at 75, and then were conditioned at 21 ± 1 and 65 ± 5% RH for 24 hours prior to any evaluations. 2.6 Scanning Electron Microscopy (SEM) Surface morphology of cotton specimens was investigated by the JEOL JSM-6490 Scanning Electron Microscope (SEM) at the magnifications upto 3000X. 3. Result and Discussion Fig. 1 and 2 reveal the SEM images of grey control sample at magnification of 1000X and 3000X respectively, which were the cotton sample without treating with any laser treatment. The SEM results showed the convolution of cotton fibre and the fibre surface was smooth. Fig. 1. SEM image of control sample at 1000X Fig. 2. SEM image of control sample at 3000X Fig. 3 to 6 present the SEM images of grey cotton sample treated with laser beam at 40 dpi and 100µs pixel time and then undergone desizing, scouring and bleaching respectively at the magnification of 3000X. Fig. 4 to 6, after treating with laser irradiation, the cotton samples were undergone a series of wet processes, including desizing, scouring and bleaching. The surface of the fibres was damaged after treating with laser, in which laser irradiation developed various sizes of pores on the cotton fibre and resulting in a sponge-like structure [3]. As for the CO2 laser used is a kind of pulsed laser, thus lots of pores were formed by the pulsed laser irradiation. The sponge-like structure was still can be found even the treated samples underwent desizing, scouring and bleaching processes. Fig. 3. Laser treated grey cotton sample Fig. 4. Laser treated desized cotton sample 1861

A. Méndez-Vilas and J. Díaz (Eds.) Fig. 5. Laser treated desized and scoured cotton sample Fig. 6. Laser treated desized, scoured and bleached cotton sample Fig. 7 (a) to (f) illustrate the SEM images of grey cotton sample treated with laser directly at different pixel time and without any post treatment at 200X, 1000X and 3000X respectively. As shown from these SEM images, the sponge-like structure is limited to a surface layer of fibres [3]. As the smooth and without damaged cotton fibres from the inner part of the fabric were also shown clearly. The resolution was at 40 dpi and the pixel time was increased from 100µs to 150µs. The SEM images showed when the pixel time increased, the surface damage became more serious. Furthermore, the laser irradiation is capable of etching away the cotton fibres, in which a lot of short fibres with free ends were obtained. (a) Resolution: 40 dpi; Pixel time: 100µs (b) Resolution: 40 dpi; Pixel Time: 110µs (c) Resolution: 40 dpi; Pixel time: 120µs 1862

A. Méndez-Vilas and J. Díaz (Eds.) (d) Resolution: 40 dpi; Pixel time: 130µs (e) Resolution: 40 dpi; Pixel time: 140µs (f) Resolution: 40 dpi; Pixel time: 150µs Fig. 7. Relationship between the fibre surface morphological modification and pixel time of laser irradiation of the laser treated grey cotton fabric at 200X and 1000X. Fig. 8 (a) to (d) demonstrate the grey cotton treated with laser beam at different resolution. From the SEM images, the fibres with a higher resolution laser treatment, the amount of pores and free ends short fibres were more densely developed. For example, the laser induced pores were distributed over nearly all the fibres surface at 70 dpi. Since the yarns were sized to enhance the yarn strength before weaving process, CO2 laser beam is a kind of infrared laser which could give thermal energy and the sizes may be melt and adhered on the fibre surface resulting in a rougher surface [4]. (a) Resolution: 40 dpi; Pixel time: 150µs (b) Resolution: 50 dpi; Pixel time: 150µs 1863

A. Méndez-Vilas and J. Díaz (Eds.) (c) Resolution: 60 dpi; Pixel time: 150µs (d) Resolution: 70 dpi; Pixel time: 150µs Fig. 8. Relationship between the fibre surface morphological modification and resolution of laser irradiation of the scoured laser treated grey cotton fabric at 200X. Fig. 9 (a) to (f) show the SEM images of the grey cotton samples underwent desizing process after treating with laser. It was obvious that the unfixed fragments were removed in desizing and clearer pores and cracks were obtained. Besides, when the pixel time was increased the formation of pores was increased accordingly. The level of fibre damage by laser increased with the pixel time increased that more fibres were etched away. As in Fig. 9(f), the laser irradiation could be penetrated into inner part of fibres and even a whole bundle of fibre could be cut away at greater pixel time. (a) Resolution: 40 dpi; Pixel time: 100µs (b) Resolution: 40 dpi; Pixel time: 110µs (c) Resolution: 40 dpi; Pixel time: 120µs (d) Resolution: 40 dpi; Pixel time: 130µs (e) Resolution: 40 dpi; Pixel time: 140µs (f) Resolution: 40 dpi; Pixel time: 150µs Fig. 9. Relationship between the fibre surface morphological modification and pixel time of laser irradiation of the desized laser treated grey cotton fabric at 1000X. 1864

A. Méndez-Vilas and J. Díaz (Eds.) Fig. 10 (a) to (d) present the SEM images of the laser treated cotton samples underwent desizing with various resolution at 200X. The fragments and impurities were removed in desizing, thus the free ends short fibres formed due to laser irradiation became more obvious than the samples showed in Fig. 8. In addition, the sizing materials were removed from desizing process, the fibres are not held firmly together and hence the free ends of fibres were observed. When the resolution increased from 40 dpi to 60 dpi, the amount of free ends of fibres was increased. Since the higher resolution represents there are more dots per inch will irradiated on the samples, the laser power is higher and the amount of cut away fibres may be increased. (a)resolution: 40 dpi; Pixel time: 150µs (b)resolution: 50 dpi; Pixel time: 150µs (c)resolution: 60 dpi; Pixel time: 150µs (d)resolution: 70 dpi; Pixel time: 150µs Fig. 10. Relationship between the fibre surface morphological modification and resolution of laser irradiation of the desized laser treated grey cotton fabric at 200X. Fig. 11 (a) to (f) indicate the SEM images of the cotton samples which were scoured after treating with laser and desizing at 1000X. The sponge-like structure was still very clear after the two wet processes. Also the laser induced pores were more densely distributed at 150µs pixel time. Therefore, the laser engraving result increased when the pixel time increased. The impact of laser irradiartion is permanent and the induced morphological modification can still be found even undergone desizing and scouring. Moreover, the more the laser induced fragments removed in scouring process when compared with Fig. 9, in which there were still some fragments and residuals remained. (a) Resolution: 40 dpi; Pixel time: 100µs (b) Resolution: 40 dpi; Pixel time: 110µs 1865

A. Méndez-Vilas and J. Díaz (Eds.) (c) Resolution: 40 dpi; Pixel time: 120µs (d) Resolution: 40 dpi; Pixel time: 130µs (e) Resolution: 40 dpi; Pixel time: 140µs (f) Resolution: 40 dpi; Pixel time: 150µs Fig. 11. Relationship between the fibre surface morphological modification and pixel time of laser irradiation of the scoured laser treated grey cotton fabric at 1000X. Fig. 12 (a) to (f) show the SEM images of the laser treated cotton samples after desizing, scouring and bleaching at 1000X. When compared with Fig. 9 and 11 the SEM images of laser treated grey cotton fabric, the sponge-like structure became clearer as the samples were conducted three wet processes subsequently in which the fragments, unfixed short fibres and the melted parts of fibres were removed. Moreover, the formation of pores on the cutting area indicated the fibres were etched away by laser beam. 1866 (a) Resolution: 40 dpi; Pixel time: 100µs (b) Resolution: 40 dpi; Pixel time: 110µs (c) Resolution: 40 dpi; Pixel time: 120µs (d) Resolution: 40 dpi; Pixel time: 130µs

A. Méndez-Vilas and J. Díaz (Eds.) (e) Resolution: 40 dpi; Pixel time: 140µs (f) Resolution: 40 dpi; Pixel time: 150µs Fig. 12. Relationship between the fibre surface morphological modification and pixel time of laser irradiation of the bleached laser treated grey cotton fabric at 1000X. 4. Conclusion According to the SEM pictures, the CO2 laser could cause surface modification on grey cotton fabric and give a characteristics sponge-like structure on fibre surface. This morphological modification was permanent and can last for several wet processing, such as desizing, scouring and bleaching. Besides, by changing the resolution and pixel time of laser irradiation, the degree of laser induced modification is different. By adjusting the two parameters, resolution and pixel time, the level of laser effect could be controlled and give a desired result. Acknowledgements. The authors want to express the gratitude to the Hong Kong Polytechnic University for the financial assistance. References [1] Esterves F, Alonso H. Effect of CO2 laser radiation on surface properties of synethics fibres. Research Journal of Textile and Apparel. 2007;11(3):42. [2] Ortiz-Morales M, Poterasu M, Acosta-Ortiz S.E, Compan I, Hernandex-Alvarado M.R. A comparison between characteristics of various laser-based denim fading processes. Optics and Lasers in Engineering. 2003;39:15-34. [3] Ferrero F, Testore F, Innocenti R, Tonin C. Surface degradation of linen textiles induced by laser treatment: comparsion with electron beam and heat source. AUTEX Research Journal. 2002;2(3). [4] Dadbin S. Surface modification of LDPE film by CO2 pulsed laser irradiation. European Polymer Journal. 2002;38;24892495. 1867