Dissolution and regeneration of nylons utilizing superbase-acid conjugate ionic liquids

Abstract

Synthetic polyamides (nylons) are widely used in our daily life and in technical applications due to the good mechanical properties, as well as good resistance towards chemicals and sunlight. The recycling of nylons is challenging even as pure materials, however their structural diversity further complicates the recycling of mixed nylon waste. The mechanical strength and stiffness of nylons arise from interchain hydrogen bonding of the polymer chains resulting poor solubility in common solvents. The solubility of cellulose is also hindered by a strong hydrogen bonding network, yet it is well known that many superbase ionic liquids (SB-ILs) are efficient for dissolution and regeneration of cellulose. It turns out that many of the known cellulose dissolving SB-ILs can also dissolve nylon polymers, but efficiency increases towards more hydrophobic superbase cations. From the screened SB-ILs, the 5/7-methyl-3,3-dimethyl-1,5,7-triazabicyclo[4.4.0]dec-5-enium acetate ([dm₃-mTBDH][OAc], a mixture of isomers) showed good performance in a dissolution-regeneration process of nylons. No degradation of the regenerated nylon polymer was observed upon comparison with the virgin ones and the SB-IL was stable through repeated dissolution-regeneration cycles. The solubility of nylons in SB-ILs enable novel tools for characterization of nylon polymers and opens possibilities towards efficient and sustainable recycling of nylons.