Optimization of Sodium Hydroxide Treatment of Para-Aramid Fibre for Cationic Dyeing

In order to improve the cationic dyeing performance of para-aramid fibre, the optimal conditions of fibre pretreatment were determined through the orthogonal array testing technique with three-factor (sodium hydroxide dosage, treatment temperature and time) and four-level test cases. The tensile strength and apparent colour depth of modified fabrics were the main evaluation criteria. The optimal process for the modification of para-aramid fibre with sodium hydroxide treatment was 2% dosage of sodium hydroxide at 60°C for 30 minutes. Fourier transform infrared analyses were used to study the changes in chemical groups due to fibre modification. The results showed that there was alkali hydrolysis of polymer molecules in the sodium hydroxide modified para-aramid fibre. The treatment increased the number of reactive dyeing sites on fibre surface and consequently improved the dyeing performance of para-aramid fabric. The sodium hydroxide modified and then dyed fabrics showed clearly increased colour depth and colour fastness to rubbing and washing.