Polyamide | Nylon 6 and Nylon 66

Introduction

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Polyamides are polymers whose monomeric units are joined by the amide (-NH-CO-) linkage (at least 85%).
They contain aliphatic or cyclo-aliphatic units, often known as nylons.
Polyamides are synthesized by a condensation reaction between diamine and diacid, where the repeating units are held together by amide links.
In 1939, the first polyamide in the USA was produced from adipic acid and hexamethylene diamine named polyamide 66.
In 1938, German caprolactam was polymerized to form polyamide 6 (Nylon 6).

Synthesis of Nylon 66

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Synthesis of Nylon 6

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Polyamide fibers/filaments are melt spun.
Dry N₂ is used to prevent oxidation.
Extrusion temperature Nylon 66 (280- 290℃), Nylon 6 (250-270℃).
Spinneret holes dia 0.1-0.4 mm.
Extrusion velocity is normally 1000-1200 meters/min.
After extrusion, it passes through a cooling chamber almost 5 meters long.
The filaments are then moisturized through steam or spin finish to absorb a small amount of water (MR% 4.0-4.5).
The filaments are drawn at a drawing ratio of 4-5 in the cold drawing method for apparel used and carpets.
Stronger yarns are required for demanding applications drawn at a higher temperature, then texturized, and finally heat set.
Heating-Nylon 66 (180-200℃)-Nylon 6 (160-180℃) in the presence of steam.
Induce the annealing process.
The estimated polymer length is 90-140 nm.
The estimated polymer thickness is 0.3 nm.

Specific gravity	1.14
Tenacity	40-60 CN/Tex 90 CN/Tex for higher strength
Elongation at break	20-30%
Elastic recovery	Very good
MR%	4.0-4.5%
Launderability	Should not be washed in hot water (breakage of intermolecular hydrogen bond on the absorption of water)