Modification of polymeric substrates using surface-grafted nanoscaffolds
Thompson, Kimberlee Fay
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Surface grafting and modification of poly(acrylic acid) (PAA) were performed on nylon 6,6 carpet fibers to achieve permanent stain and soil resistance. PAA was grafted to nylon and modified with 1H, 1H-pentadecafluorooctyl amine (PDFOA) using an amidation agent, 4-(4,6-dimethoxy-1,3,5-triazin-2-yl)-4-methylmorpholinium chloride (DMTMM). The first goal was to optimize acrylamide modification of PAA in solution. Aqueous reactions with taurine, hydroxyethyl amine, and butyl amine progressed ~100%, while PDFOA reactions in MeOH progressed ~80%. Reaction products precipitated at 77% butyl or 52% PDFOA acrylamide contents. The second goal was to optimize the PAA grafting process. First, PAA was adsorbed onto nylon 6,6 films. Next, DMTMM initiated grafting of adsorbed PAA. PAA surface coverage was ~78%, determined by contact angle analysis of the top 0.1-1 nm and x-ray photoelectron spectroscopy (XPS) analysis of the top 3-10 nm. The third goal was to modify PAA grafted nylon films with butyl amine and PDFOA. Randomly methylated beta-cyclodextrin (RAMEB) solubilized PDFOA in water. Contact angle detected ~ 100% surface reaction for each amine, while XPS detected ~77% butyl amine (H2O) and ~50% for PDFOA (MeOH or H2O pH=7) reactions. In H2O pH=12, the PDFOA reaction progressed ~89%, perhaps due to greater efficiency, access and solubility. The fourth goal was to perform surface depth profiling via angle-resolved XPS analysis (ARXPS). The PAA surface coverage from contact angle and XPS was confirmed. Further, adsorbed PAA was thicker than grafted PAA, supporting the theory that PAA adsorption occurs in thick layers onto nylon followed by DMTMM-activated spreading and grafting of thinner PAA layers across the surface. The PDFOA reaction in MeOH produced a highly fluorinated but thin exterior and an unreacted PAA interior. The PDFOA reaction in H2O pH=12 produced a completely fluorinated exterior and highly fluorinated interior. Thus surface modification levels from contact angle and XPS were confirmed. The final goal was to PAA-graft and PDFOA-modify nylon 6,6 fabrics and carpets. PDFOA modification achieved significant water and oil repellency. Stainblocking was slightly improved for ionized PAA-g-nylon and greatly improved for PDFOA-modified PAA-g-nylon. However, traditional stainblockers may be necessary to completely prevent dye penetration into carpet tufts.