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Platinum boat with sampleF. Solid carbon dioxide C. Silver gauze G. Aluminum foil D.

Polyamide fibers are melt spun from linear semicrystalline thermoplastic polymers having recurring amide groups made from diamines and dicarboxylic acids or lactams. Poly(hexamethyleneadipamide), designated as nylon‐6,6, and poly(caprolactam), nylon‐6, account for 98% of the 4 million metric tons of the worldwide annual production of nylon fiber. The attributes of nylon such as high strength, durability, abrasion resistance, resilience, moderate hydrophilicity, ease of dyeability, and low specific gravity have been recognized since its introduction in 1938. Both the inherent properties and those properties that can be engineered into the fiber manufacturing and ultimately into the fabric in downstream mill processing combined with reasonable market pricing account for the diverse end uses and market longevity of nylon. Nylon fiber is offered in the forms of continuous flat and textured filaments, staple, tow and flock for hosiery, apparel, home, flooring, industrial and transportation fabric applications. The physical appearance, functionality, and end‐use performance of nylon fibers can be modified by incorporating additives, eg, delusterants, colorants, antioxidants, or antistats in the polymer, by designing a spinneret hole configuration to impart a desired luster, surface effect or specific dtex‐per‐filament, by spinning bicomponent or biconstituent fibers, and by chemically or mechanically treating the surface of the fiber or fabric.

SynopsisInfrared bands in the 900-1100 cm-1 region are sensitive to thermal energy. These bands can result from intermolecular coupling, producing the crystal lattice, or from intramolecular coupling of the various atomic groups in a regular helix or coiled chain. I n either case an increase in temperature will disrupt the coupling mode, resulting in a form of structural relaxation and a reduction in the integrated absorbance. It is proposed that the temperature at which the peak areas begin to decrease be assigned as the T,. This is measured by continuously scanning a selected peak in the infrared spectrum of a polymer film while it is heated at a rate of about l"C/min. Using this technique polyamides (nos. 6,66, and 610) exhibited transitions in the 30-50°C range, and by studying the increase in the free NH region (3440 cm-' of nylon 66 two other transitions were detected a t 80 and 137OC; the latter represents a change in the nylon 66 crystal state. An amorphous film of poly(ethy1ene terephthalate) displayed a transition at 58-68°C (T,) and at 85"C, which is the crystallization temperature. Films of poly(viny1 acetate) and polyst.yrene exhibited transitions a t 25-37°C and a t 7OoC, respectively.

SynopsisAccording to mechanisms described in the literature, photodecomposition of nylon 66 proceeds through the abstraction of the hydrogen on the carbon u to the amide NH group by a free radical which has been activated by photo absorption. In the p r o p agation phase, the a-carbon radical could readily react with atmospheric oxygen to form a hydroperoxide. The formation of a hydroperoxide in the photodecomposition scheme for nylon 66 has been detected but has not been measured quantitatively.With the colorimetric method described in this paper, it is now possible to determine the peroxide content in a polyamide to a level of 1 Wole/g. with a relative precision of leas than 5%. The polyamide is dissolved in tetrafluoropropanol, to which aliquots of potassium iodide and glacial acetic solutions are added. The absorbance of the liberated iodine is measured in a 1-cm. cell a t 400 mp and the hydroperoxide concentration determined from a calibration curve constructed from hydrogen peroxide solution standards. The rate of peroxide formation, which is dependent on the wavelength of ultraviolet radiation, can be correlated to the strength loss exhibited by a nylon 66 yarn free from antioxidant and delustrant. In addition, an increase in the level of thermal degradation will accelerate yarn strength loss and peroxide formation under ultraviolet exposure. The hydroperoxide begins to decompose a t about 100OC. Yam finish will contribute to the peroxide formation during exposure.