Investigation of Trisodium Salt Management Methods for the Manufacture of Cationic Nylon 6

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Nylene produces stain-resistant cationic nylon 6 polymer, using 5-sodiosulphoisophthalic acid (NaSIP) as an additive in the polymerization reactor to reduce amine end-group concentrations in the final product. Reducing the concentration of amine end groups is important because amine ends react with acidic groups in food and soil, causing stains on nylon carpets. One difficulty with incorporating NaSIP into the nylon 6 reactor is that a series of undesirable side reactions can occur, wherein NaSIP is converted to an insoluble trisodium salt (TriNaSIP). This insoluble salt precipitates from the reaction mixture and leads to fouling of reactor walls and internal structures, especially in the top portion of Nylene's reactor system, near the position where NaSIP is fed and the initial stages of polymerization occur. The degree of build-up of the precipitating trisodium salt has led to severe fouling at Nylene's plant in Arnprior, ON, so that the reactor needs to be shut down for mechanical cleaning. The objectives of this research project are to: 1) quantify the solubility of NaSIP and TriNaSIP in caprolactam and water, 2) develop an improved understanding of the reaction mechanism that generates the trisodium salt, 3) develop mathematical models to describe the rate of TriNaSIP formation under different reactor operating conditions and 4) use the model and knowledge about Nylene's polymerization process to identify operating conditions, process/recipe changes, and/or revised operational strategies to mitigate and/or prevent the fouling of the reactor, without altering the current excellent acid-stain-resistant properties of Nylene's cationic nylon 6 polymer products. A further objective is to initiate a relationship between Nylene and Prof. McAuley's research group at Queen's in the hope that a longer-term research collaboration related to efficient manufacture of new nylon 6 copolymer grades can be developed.