Characterization of Volatile Nylon 6.6 Thermal-Oxidative Degradation Products by Selective Isotopic Labeling and Cryo-GC/MS

Abstract

Aged materials, such as polymers, can exhibit modifications to their chemical structure and physical properties, which may render the material ineffective for its intended purpose. Isotopic labeling was used to characterize low-molecular weight volatile thermal-oxidative degradation products of nylon 6.6 in an effort to better understand and predict changes in the aged polymer. Headspace gas from aged (up to 243 d at 138°C) nylon 6.6 monomers (adipic acid and 1,6-hexanediamine) and polymer were preconcentrated, separated, and detected using cryofocusing gas chromatography mass spectrometry (cryo-GC/MS). Observations regarding the relative concentrations observed in each chromatographic peak with respect to aging time were used in conjunction with mass spectra for samples aged under ambient air to determine the presence and identity of 18 degradation products. A comparison of the National Institute of Standards and Technology (NIST) library, unlabeled, and isotopically labeled mass spectra (C-13 or N-15) and expected fragmentation pathways of each degradation product were used to identify the location of isotopically labeled atoms within the product's chemical structure, which can later be used to determine the exact origin of the species. In addition, observations for unlabeled nylon 6.6 aged in an O-18 enriched atmosphere were used to determine if the source of oxygen in the applicable degradation products was from the gaseous environment or the polymer. Approximations for relative isotopic ratios of unlabeled to labeled products are reported, where appropriate.

Parylene C Aging Studies.

“…Based on these data, the upper limit of annealed Parylene C film accelerated aging temperature was determined to be less than 128 °C and the preliminary annealing conditions were set at 109 °C for 1 hour. The aging temperature upper limit established here is not unlike the temperature limits imposed during previous aging studies of Nylon 6.6 [22,23] or Kevlar [24] .…”

“…Outgassing studies to understand the amount and nature of volatiles species were not performed in the present study although such work has provided valuable insights into degradation mechanisms of polymers such as Nylon 6.6 [23] as well as any compatibility concerns with regard to the materials in the same environment as the Parylene C. This type of work has been performed numerous times in collaboration with the gas analysis expert James Hochrein and should be considered as part of future studies.…”

Identification of volatile butyl rubber thermal-oxidative degradation products by cryofocusing gas chromatography/mass spectrometry (cryo-GC/MS).

“…In the future, the headspace above these materials will be sampled; the degradation species will be characterized; and comparisons will be drawn to samples presented in this manuscript. In addition, these results and those for other polymers can be compared to compounds of interest to the DOE complex that have already been studied by this group: polyethylene [18,19], polypropylene [20][21][22], nylon 6.6 [23][24][25][26], and poly(ethylene-co-vinyl acetate). This information may identify common degradation products and therefore degradation pathways amongst WR materials.…”

Temperature Programmed Desorption of Quench-condensed Krypton and Acetone in Air; Selective Concentration of Ultra-trace Gas Components

“…A number of studies has demonstrated successful application of the cryofocusing-GCmass spectrometry (MS) system to trace gas analysis, such as volatile organic compounds (VOCs) in the air and the exhaled breath. [1][2][3][4][5][6][7][8][9] In the typical cryofocusing-GC-MS system, the cryofocusing typically takes place at the inlet of the GC column. The sample enrichment occurs by quench-condensation at sub-ambient temperature.…”