Anthraquinone and Azo Dyes in Dyeing Processes of PET Films and PET Knitted Fabrics Using Supercritical CO 2 Medium Washington L. F. Santos, 1 Ana P. Moura, 1 Nanci P. Povh, 2 Edvani C. Muniz, 1 Adley F. Rubira * 1 Summary: Dyeing processes using supercritical fluid present advantages over the conventional dyeing process using aqueous medium. Previous works from our group on polymeric fibers such as N,N-dimethylacrylamide (DMAAm) modified poly(ethy- lene terephthalate), PET, showed higher sorption of disperse dyes in supercritical medium. Furthermore, recent studies showed that the association of UV radiation and DMAAm treatment leads to a better incorporation of dyes in modified PET soaked in aqueous medium. In this work, modified and non-modified PET knitted fabrics (KF) were dyed in supercritical CO 2 medium. Azo and anthraquinone dyes were used in order to compare the extent of incorporated dye in PET films and PET KF in supercritical CO 2 . The dyeing process variables were studied by factorial design and by a response surface methodology (RSM) technique. The anthraquinone dye presented a better incorporation in PET than the azo dye. The UV light exposure and the dyeing times inputs showed positive main effects in the incorporation of dyes in PET films and PET KF. From the RSM data, DMAAm and UV light modified PET KF presented 7.43 mg of incorporated azo dye by g of PET if the optimized dyeing conditions, time: 135 min and pressure: 212 bar would be used. In the respective optimized dyeing conditions for the anthraquinone dye, time 150 min and pressure 229 bar, the incorporated dye would be 22.9 mg of dye by g of PET. Keywords: disperse anthraquinone dye; disperse azo dye; PET; supercritical CO 2 Introduction The supercritical fluid technology has increased in the last ten years in Brazil. [1] The dyeing of PET fibers using supercritical fluid presents several advantages in com- parison to the conventional aqueous dyeing process. The dyeing in supercritical fluids does not produce liquid effluents, therefore it decreases the dyeing costs. Dry dyeing has no costs regarding drying stages. The CO 2 can return to the initial step and the remaining dye can be recycled. Recent data in literature indicate that the supercritical CO 2 dissolves a small quantity of disperse dye, [2–7] working as a carrier in order to diffuse itself into the polymeric matrix, resulting in a material which is homoge- neously dyed and presents good fastness properties. [8,9] Supercritical CO 2 decreases the T g of PET, [10] changes the free volume and swells the material, changing the mass transfer properties of the dye to the polymeric matrix. [11,12] Supercritical CO 2 can remove residual monomers and sol- vents from the polymer production pro- cess. [10] The dyeing of PET with disperse dyes has been the main target of the researchers which study the dyeing techno- logy in supercritical medium. [2,4–6,8–10,12–16] This occurs due to the fact that PET possesses a crystalline structure which Macromol. Symp. 2005, 229, 150–159 DOI: 10.1002/masy.200551118 150 1 Universidade Estadual de Maringa ´ , Departamento de Quı ´mica, Brasil Fax: (þ55) 44 3261 4125, E-mail: afrubira@uem.br 2 Universidade Estadual de Maringa ´ , Departamento de Engenharia Quı´mica, Brasil ß 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim