Unusual role of labile phenolics in imparting flame resistance to polyamide

In the quest for development of halogen-free FR additive and better understanding of the structureflammability relationship, here we report the synthesis and characterization of a series of phenolic and benzylic succinamides, with and without aliphatic hydroxyl groups. These compounds allow for detailed investigation of the influence of these functional groups on thermal stability and FR properties in their native form and as coatings on Nylon 66 fabric. The thermal stability, char formation, heat release characteristics and thermal decomposition pathway of synthesized succinamides were studied by thermogravimetric analysis (TGA), microscale combustion calorimetry (MCC) and TGA-FTIR (Fourier Transform Infrared Spectroscopy). Phenolic succinamide, 2,3 dihydroxy-N-1,N-4-bis(4-hydroxybenzyl) succinamide (C1) and N-1,N-4-bis(4-hydroxybenzyl)succinamide (C3), exhibits about 20% char yield with low heat release characteristics while benzylic succinamides, N-1,N-4-dibenzyl-2,3-dihydroxysuccinamide (C2) and N-1,N-4-dibenzylsuccinamide (C4), exhibit poor char yield and high heat release characteristics. Thermal decomposition followed by evolved gas analysis of all these succinamides indicate that the decomposition pathway is very much dependent on the presence of phenolic moieties. Heat release characteristic and flammability of Nylon 66 coated with succinamides (10% by weight) clearly indicate that the coating of Cl and C3 impart flame resistance to Nylon 66. These studies clearly reveal that phenolic derivatives are essential for improving the thermal stability, flame resistance and lowering the heat release characteristics of Nylon 66 through char formation. (C) 2020 Elsevier Ltd. All rights reserved.