Preparation And Application Of Polyamide 6 Membrane Containing Sulfonic Acid Groups

Two sulfonated polyamide 6（SPA6 and SPAA6）were copolymerized using 5-sulfosalicylic acid（5SA）or 2-amino-5-sulfobenzoic acid（5SAA）monomers withε-caprolactam,respectively.Their films were prepared by nonsolvent induce phase separation（NIPS）method.The optimum conditions of preparing SPA6 membranewas determined by orthogonal test:SPA6 concentration in casting solution was 30wt%,the air-drying time was 120 s,and the thickness of casting stick was 200μm.SPA6 film showed a particles accumulation morphology observed by SEM.S element scanning of EDS showed that S element distributionwas dense and uniform as the increase of SPA6 solid content.The film formation mechanism was explored by TEM.SPA6 self-assembled into micelles in formic acid.After immersing in coagulation bath,the micelles transformed into nanofibers,which solidified into spherical particles during phase inversion.The gaps between particles provided channels full of sulfonic acid groups.Zeta potential test indicated that the membrane was negatively charged.The optimum film,30M,showed congo red,acid blue 93 and methyl orange rejection of 99.21%,85.68%and 63.06%for their 100 mg/L solution,respectively.Rejection of congo red remained at higher than 95.48%in 1500 min.After three rounds of filtration-wash alternative operation,the flux was 91.48%of original values.For SPAA6 membrane,a series of charged surfactants were screened as additive of casting solution to adjust the pores.S20,the self-synthesized surfactant,revealed the best adjustment for the membrane performance in filtration of acid chrome blue K（ABK）.S20 made the film smooth and provided more negative charges.The membrane rejected salts less than 5%for NaCl,Na₂SO₄,MgCl₂ and MgSO₄.Meanwhile,they removd 99.80%congo red,90.81%acid blue 93 and 85.65%methyl orange from their 100 mg/L solution.Congo red rejection was 98.22%for its mixed solution with NaCl,while ABK rejection was 80.18%for its mixed solution with NaCl in 200 h filtration with less than 4%NaCl rejection.They displayed the behavior of loose nanofiltration and a potential for textile wastewater treatment.