Polyamides are polymers whose repeat unit is joined by an amide linkage, and they are produced either by the polycondensation of a diamine with a diacid or by the ring-opening polymerisation of a lactam. The amide groups form hydrogen bonds between chains, which raises the melting point and the strength relative to a polyolefin of comparable chain length [1]. Nylon 6,6 and nylon 6 are the two largest-volume grades, and they differ in melting point because the regularity of the hydrogen-bond pattern differs [2]. Water is absorbed by the amorphous regions and acts as a plasticiser, so the modulus and the dimensions of a part change with humidity [3]. Aromatic polyamides, in which the amide groups sit on benzene rings, give rigid-rod chains with a very high tensile strength and thermal stability [4]. Recycling is mainly mechanical, since hydrolysis of the amide bond requires severe conditions and the resulting monomers must be repolymerised [5].
- amide linkage
- hydrogen bonding
- lactam
- nylon
- moisture absorption
- aromatic polyamide
- polycondensation
References
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- Wang, X.; Wu, G.; Xie, P.; Gao, X.; Yang, W.; Microstructure and Properties of Glass Fiber-Reinforced Polyamide/Nylon Microcellular Foamed Composites. Polymers 2020, 12, 2368, 10.3390/polym12102368.
- Kim, M.K.; Kim, H.I.; Nam, J.D.; Suhr, J.; Polyamide-nylon 6 particulate polycarbonate composites with outstanding energy-absorbing properties. Polymer 2022, 254, 125082, 10.1016/j.polymer.2022.125082.
- Kim, M.S.; Hwang, Y.N.; Kwon, S.T.; Lee, S.G.; Cho, H.H.; Structure and Physical Properties of Hydrophilic Polyamide Copolymers Fiber Based on Nylon 6 and Nylon 4,6. Fibers and Polymers 2020, 21, 2173-2178, 10.1007/s12221-020-9873-0.
- Lee, J.Y.; Oh, B.O.; Cho, H.H.; Yoo, Y.T.; Synthesis of Hydrophilic Polyamide Copolymers Based on Nylon 6 and Nylon 46. Fibers and Polymers 2019, 20, 2227-2235, 10.1007/s12221-019-9098-2.