Study On Low-Temperature Bleaching Of Cotton Fabrics

Hydrogen peroxide is an important chlorine free bleaching agent, which iswidely used in the bleaching of fabrics. Bleaching cotton with hydrogen peroxide iscarried out at high pH value, high temperature and long time. In this thesis, alow-temperature bleaching system was carried out, which an activator was addedduring the H₂O₂ bleaching process so as to reach a better whiteness at lowertemperature and pH value.In this study, N-[4-（triethylammoniomethyl） benzoyl] caprolactam chloride（TBCC） was synthesized which being a new cationic bleach activator and was foundto remarkably reduce bleaching temperature and time. First, the optimum syntheticprocess was investigated by single-factor experiments, and the product was analysedby IR spectra. TBCC was added to the bleaching bath of cotton fabric with H₂O₂. Inorder to get the optimal bleaching conditions, the influences of the concentration ofalkali and TBCC, time, pH value on whiteness were investigated. In the third part, theoptimal bleaching conditions of Tetraacetyl-ethylene Diamine （TAED）、Tetraacetylglycoluril（TAGU）、α-glucose penta acetate（PAG）、Sodium nonanoylbenzenesulfonate（NOBS） were determined. The bleaching effect of all activators wascompared with each other and also compared with the traditional bleaching processThe conclusions from exprimental data were as following:1. The synthesis of TBCC was divided into two steps. First,4-（chloromethyl）benzoyl caprolactam was synthesized by the reaction of4-（chloromethyl）benzoyl chloride and caprolactam with methylbenzene as dissolvent.The optimal conditions were: 4-（Chloromethyl）benzoyl chloride was slowly added tohot blends of caprolactam and methylbenzene, the mole ratio being 1:1.5, dosage oftriethylamine was the same as 4-（Chloromethyl）benzoyl chloride, temperature 110℃,time 6h. Second, TBCC was finally synthesized by the reaction of4-（Chloromethyl）benzoyl caprolactam and triethylamine with acetonitrile asdissolvent. The suitable synthesis conditions were: the mole ratio of4-（Chloromethyl）benzoyl caprolactam and triethylamine was 1:1.5, temperature 90℃,time 4h. The chemical structure of TBCC is as following:2. TBCC as an activator could significantly improve the whiteness of fabric ata lower temperature and without any stabilizing agent. The optimal conditions in thisactivated H₂O₂ bleaching system was confirmed by orthogonal experiments. temperature 70℃, H₂O₂ 2g/L, NaOH 2g/L, TBCC 6g/L, time 50min.3 TAED could effectively activate the H₂O₂ bleaching system at a lowertemperature and pH value. In the same way as TBCC, the suitable conditions in thisTAED/ H₂O₂ bleaching system was obtained, temperature 70℃, H₂O₂ :TAED（molratio） = 2:1, Na₂CO₃ 4g/L, first bleaching for 5min and adding TAED, then treatingfor another 55min.4. TAGU used as an activator had the same reaction mechanism and effect asTAED. The optimal conditions for TAGU were as following: temperature 70℃,H₂O₂ :TAGU（mol ratio） = 4:1, H₂O₂ 2～3g/L,Na_CO₃ 3g/L first bleaching for 10minand adding TAED, then treating for another 55min.5 As an activator for H₂O₂ NOBS played a quite important role in bleaching, itcould reach a better whiteness in a relatively less dosage and lower temperature. Theoptimal conditions for this activator were: temperature 60℃, H₂O₂ :NOBS（molratio）=7:1,NaOH 2g/L, first bleaching for 10～15min and adding NOBS, total timebeing 60mn.6 PAG was another activator for H₂O₂ bleaching with the same reactionmechanism as NOBS. The ideal treating conditions in NOBS/ H₂O₂ system was:temperature 60～70℃, H₂O₂ :PAG（mol ratio）=5:1, H₂O₂ （30%）, 2g/L, Na₂CO₃ 3g/L ,first bleaching for 10～15min and adding NOBS, the total reaction time being 60min.7. All kinds of activators could effectively facilitate the decomposition of H₂O₂and improve whiteness at a lower temperature. The processing time was shortenedand the energy was saved. Some activators could act at lower pH value which beingenvironmentally friendly. TBCC was the most effective one and could get higherwhiteness without any stabilizer. The experiments show that H₂O₂ bleaching withTBCC could get the same whiteness at 70℃as traditional bleaching process.