by certain compounds by either deliberate addition or contamination.
Added structures include filler pigments, dyes, or compounds admixed to affect polymer stability. More recent methods for determining basic groups, acidity, acyl groups, comonomers, molecular weights, delustering agents, and techniques for chemical and physicochemical analyses of polyamide fibers have also been reviewed [373].
Nylon fiber for outdoor uses, such as flags, decorative banners, and personal flotation device covers, must be protected from the ultraviolet light to extend its useful life. Therefore, light stabilizers are generally added during the nylon polymerization process.
By reacting a sufficient number of amine or amide-forming functional groups of a hindered amine with the end groups of the polyamide precursor at polymerization temperature, the hindered amine are bound to the polyamide and inhibit migration, leaching, and volatilization of the hindered amine.
Thus, a light-stabilized polyamide is formed as illustrated in several recent U.S. patents [374 376]. Hence, the articles manufactured from such a polyamide will retain their breaking strength and ultimate elongation even after many hours of outdoor exposure to ultraviolet light under the sun.