CRITICAL MISCIBILITY LIMITS IN BLENDS OF ALIPHATIC POLYAMIDES CONTAINING AN AROMATIC POLYAMIDE

An investigation of the phase behaviour of the aromatic polyamide, nylon 3Me6T, in a specially prepared series of aliphatic copolyamides, (CH2)nNHCO, has allowed for an unambiguous determination of the critical miscibility limits in these blends. The appearance of critical solution behaviour, in the form of an LCST, in a copolymer of caprolactam and laurolactam has identified the upper bound for the volume fraction of methylene units of the latter to correlate perfectly with a value estimated previously to be x = 0.85. A similar evaluation of blends containing copolymers of 2-pyrrolidinone and caprolactam has determined the lower bound to be x = 0.76, which is significantly greater than the estimated value. These observations, when treated within the framework of a mean field binary interaction model, allow for greater precision in projecting the phase behaviour of polyamide blends. The results are also used to corroborate previous findings which describe the phase behaviour of an aromatic polyamide, nylon 6IcoT, in a similar series of aliphatic polyamides. © 1990.