a comparative study on the environmental friendly bleaching processes of poly(lactic acid) substrate: application of ultraviolet/o3/h2o2 system

Recently, there has been an increasing interest towards the finishing of textiles (fibers, yarns, fabrics and nonwovens) using eco-friendly technology, which can achieve a wide range of functional properties and environmental benefits. this study is related to a modern eco-friendly bleaching technology that relies on ultraviolet/o3 radiation of poly(lactic acid) fabric through simple technique. the effects of ultraviolet/o3 radiation along with the pretreatments with distilled water, hydrogen peroxide, and hydrogen peroxide/sodium silicate solutions on the bleaching of the poly(lactic acid) fabrics were examined using uv-visible and reflectance spectral method and the results were compared with that of virgin untreated samples. ultraviolet/o3 bleaching routes were screened to obtain desired whiteness index (wi), tint factor (tw) , lightness/darkness (l*), redness/greenness (a*), yellowness/ blueness (b*), chroma (c*) and hue (h°) of the bleached poly(lactic acid) fabrics. the optimal properties of the bleached poly(lactic acid) knitted fabric could be obtained at ultraviolet/o3 irradiation for 80 min on the fabrics which preimpregnated in a hydrogen peroxide solution with a wet pick up of 70 %, pressure of 1.1 bar and speed of 2 m/min. (ultraviolet/o3/h2o2 bleaching system). the ultraviolet/o3/h2o2 bleached fabric showed the best colorimetric properties (wi: 87.7, tw: -0.1, l*:94.227, a*:-0.106, b*:0.294, c*:0.2512, h°: 98.6551). moreover, the reflectance of this sample has increased significantly in the range of 400-450 nm which leads to a glossy withe shade on the fibers. the sem images presented that after ultraviolet/o3/h2o2 bleaching process, some fractures with nano scale size (about 130 nm) are formed on the poly(lactic acid) fabric surface. the atr-ir spectrum of ultraviolet/o3/h2o2 bleached poly(lactic acid) fibers displays more intense c–c–o absorption bands (1161 cm^-1).