Abstract:

Objective The inner cotton component of polyester-covered cotton fabric is soft, comfortable, sweat-permeable and air-permeable, and the outer polyester component is anti-wrinkle and wear-resistant. Polyester-covered cotton fabric is widely used in daily wear, school uniforms, firefighting apparel, sanitation apparel and other fields. However, the conventional processes for bleaching and dyeing polyester-covered cotton fabrics have problems of high consumptions of water and energy, and low production efficiency. This research aims to use a disperse dye with high resistance to alkalis and peroxides to construct a one-bath process for bleaching and dyeing polyester-covered cotton fabrics.

Method The selected disperse dye was evaluated for its resistance to alkalis and peroxides. Experiments were carried out to investigate the influence of hydrogen peroxide concentration, processing time, and processing temperature on the performances of bleaching and dyeing in one bath. The optimal process was defined by monitoring the whiteness of cotton component and the color depth (K/S) value of the polyester component.

Results The synthesized disperse dye was shown to be of high alkali-resistant and high peroxide-resistant type, withstanding dyeing with at 2 g/L NaOH alkali regulator concentration and 5 g/L H₂O₂ (30%) (Tabs.2 and 4). One-bath process for bleaching and dyeing polyester-covered cotton fabrics was designed based on the synthesized disperse dye with high resistance to alkali and peroxide. The influence of H₂O₂ concentrations and temperature maintaining time on the whiteness and K/S value of polyester-covered cotton fabric treated by one-bath dyeing polyester and bleaching cotton process were tested, respectively. Under the conditions of 2 g/L of H₂O₂ (30%) and a temperature maintaining time of 0 min at 100 ℃, the whiteness of the cotton component of the polyester-covered cotton fabric reached 80, almost the same as the whiteness obtained by the conventional process. In addition, the concentration of H₂O₂ (30%) and temperature maintaining time were shown to have no influence on the K/S value of the polyester component (Fig.5). Therefore, the optimal H₂O₂ (30%) concentration was selected to be 2 g/L and the optimal temperature maintaining time 0 min at 100 ℃. In order to further analyze the bleaching and dyeing effect of polyester-covered cotton fabrics under high temperature and high pressure treatment, the influence of processing time on the whiteness and K/S value of polyester-covered cotton fabrics treated with one-bath dyeing polyester and bleaching cotton process were investigated (Fig.7). It was found that the polyester-covered cotton fabrics could be optimally bleached and dyed in one bath under the conditions of 2 g/L of H₂O₂ (30%), 130 ℃ and 30 min. The one-bath process treated polyester-covered cotton fabric lead to a 8% bursting strength loss, showing around CIE whiteness 80 of cotton component and good moisture permeability (Tabs.5 and 6). Meanwhile, the color difference of dyed polyester component treated by the one-bath process and conventional process was lower than 1.0. The dyed polyester component provided by one-bath process had rubbing and washing color fastness of grade 4-5 or above, and sublimation color fastness of grade 4 or above.

Conclusion One-bath process for bleaching cotton component and dyeing polyester component of polyester-covered cotton fabric has been achieved by a disperse dye with high resistances to alkalis and peroxides. The polyester-covered cotton fabrics could be optimally bleached and dyed in one bath under the conditions of 2 g/L of hydrogen peroxide (30%), 130 ℃ and 30 min. Compared with the conventional process, the one-bath process provided a polyester-covered cotton fabric that had less bursting strength loss, a comparable degree of whiteness (around CIE whiteness 80) and an acceptable color difference (ΔE_CMC< 1.0). The polyester-covered cotton fabric processed in one bath had color fastnesses of grade 4 or above. Therefore, the one-bath process of the polyester-covered cotton fabric for bleaching and dyeing has the advantages in shortening process flow, and saving costs in water and energy.

Key words: disperse dye, polyester-covered cotton fabric, bleaching, dyeing, short process, cotton bleaching and polyester dyeing, one-bath process