Dyeing para‐aramid fabrics in supercritical carbon dioxide with pretreatment of nonthermal plasma induced oil polymers

Abstract It has been a great challenge to effectively dye para‐aramids. This study systematically evaluated the dyeing of textile fabrics made of woven continuous filament, highly crystalline para‐aramids in supercritical carbon dioxide (ScCO 2 ) at various combinations of temperature ( T = 80–160°C) and pressure ( P = 10–20 MPa), focusing on our new pretreatment method of using nonthermal plasma (NTP) to induce oil polymers on the surface of the fabrics for the enhancement of dyeing. We found that, without any pretreatment, the specific para‐aramid fabric used in this study is undyeable (dyed K / S value of ~0.5), even after an NTP surface treatment and undergoing a dyeing process in ScCO 2 , due to its high crystallinity and chemical inertness. Pretreating the para‐aramids with soybean oil, acrylated epoxidized soybean oil (AESO), or a mixture of soybean oil and acrylic acid (AA/Soy) followed by an NTP treatment significantly improved the dyeing color strength, as measured by K / S values up to 9.7. In these cases, AESO and AA/Soy provided comparable results, better than that obtained with soybean oil. The NTP treatment is essential in inducing a cross‐linked polymer network in situ, anchoring the para‐aramids with covalent bonds and also providing functional groups that bind the dye. The new dyeing method did not compromise the strength of the para‐aramids. Further, dyes soluble in ScCO 2 should be selected, since the use of dyes insoluble in ScCO 2 would require the addition of co‐solvents and other auxiliary chemicals, which complicates the downstream separation of these chemicals and decreases the benefit of ScCO 2 dyeing.