NIRA Primary Wavelength Investigations of Nylon Yams

Abstract

Near infrared reflectance analysis (NIRA) is a rapid and accurate technique for measuring the heat set temperature of nylon carpet yams. Several investigations on Suessen heat set nylon 66 yams have yielded empirical prediction equations based on reflectance at three wavelengths, with 2130 nm being common to each investigation. Investigations of the derivatives of the NIRA spectra obtained from various Suessen heat set nylon 66 samples and comparisons of the NIRA spectra to other polymers have yielded new information on probable wavelength structural assignments and the probable rationale for the 2130 nm wavelength's commonality. The 2130 nm wave length is caused by a combination of the C — H stretch/C=O stretch combination and N — H deformation/N—H stretch combination, the 2100 nm wavelength is caused by C = 0 stretch combinations, and the 2270 nm wavelength is caused by various CH/CH2 stretches, bends, and deformations. The 2100 and 2130 nm wave lengths are the primary combination for correlating the crystallinity changes occurring with changing heat set temperature in nylon 66 carpet yams. Derivative spectra indicate that a consistent "slope" change occurs in the original spectra from 2100 to 2130 nm, with increasing absorption at 2100 nm and decreasing absorption at 2130 nm with increasing heat set temperature. This slope change is the driving force in the NIRA's ability to measure the heat set temperature.