FT–IR spectroscopic study on the photo- and photooxidative degradation of nylons (original) (raw)
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FT–IR spectroscopic study on the thermal and thermal oxidative degradation of nylons
Journal of Polymer Science Part A: Polymer Chemistry, 1987
The effects of heat and oxygen on nylon films were studied by FT-IR spectroscopy. Nylons 6, 66 and nylons containing carbonyl groups in either the diamine or the diacid moiety were prepared. Nylon f i l m s cast on aluminum were studied in an environmental chamber under controlled conditions. The progress of chemical and physical changes was monitored by FT-IR spectroscopy. Thermal energy caused largely an increase in crystallinity due to annealing and also an increase of nonhydrogen-bonded amide groups, which seemed to entail mainly amide groups from the amorphous region. The intensities of IR absorption bands related to the folded structure reduced as soon as heating began. The IR spectra of the carbonyl groups formed by thermal oxidation showed band shapes that indicated that the formed carbonyl groups were of many different origins. The presence of keto groups purposely inserted into the backbone chains increased the rate of oxidation. Pyrolysis of the nylons was also studied to supplement data obtained a t lower temperatures.
Polymer Degradation and Stability, 1984
The thermal and photochemical oxidation of nylon 6,6film (50 l~m thick) has been studied using second-order derivative uv spectroscopy, hydroperoxide analysis and viscometry. During oven ageing the growth and decay of hydroperoxide follows the same pattern as in polyolefins. Subsequent photo-oxidation of the oven aged films results in an initial increase in viscosity due to cross-linking, jbllowed by a rapid decrease due to chain scission. Films of nylon polymer with high initial concentrations of hydroperoxide show little or no initial cross-linking but rapid chain scission, indicating that the latter is induced by hydroperoxides resulting in fl-bond scission to give a free macroalkyl radical and carbonyl group. Using second-order derivative uv spectroscopy, a new intense absorption band is observed at 230 nm. The thermal and photo-chemical behaviour of this band matches that known to be present at 290 nm, confirming the presence of ot,fl-unsaturated carbonyl impurity groups in the polymer.
Photo-oxidative degradation of nylon 66 under accelerated weathering
Polymer, 1998
The photo-oxidative degradation study of nylon 66 was carried out in a polychromatic irradiation chamber (Sepap 12/24, l Ն 290 nm) at 60ЊC in air. The extent of photo-oxidation was monitored by Fourier transform infrared spectrometry. The sample underwent extensive changes in hydroxyl, carbonyl and amorphous region of infrared upon irradiations. The photo-products were characterized by i.r. and ultraviolet spectroscopy. The broadening of hydroxyl and carbonyl absorption bands indicated more than one species. The photo-oxidation mechanism implies the same intermediate photo-products. The kinetics of the photo-degradation also has been studied.
New Vistas in the Photo-Oxidation of Nylon 6
Macromolecules, 2003
Matrix-assisted laser desorption ionization mass spectrometry (MALDI) is an excellent method to use in determining the structure of the molecules produced in the photo-oxidative degradation of nylon 6 at 60°C in air. The MALDI spectra of photo-oxidized nylon 6 (Ny6) show the presence of over 40 compounds, as compared to only 3 in the blank Ny6 sample. The extremely favorable event here is that the MALDI spectra present so many new well-resolved peaks, which provide information on the structure and end groups of the oxidation products. The structural analysis of the photo-oxidation products provided by the MALDI spectra allowed us to draw a detailed map of the photo-oxidation mechanisms of Ny6 . The presence of the majority of the oligomers listed in had not been revealed before. Our results extend and modify the currently accepted picture for the photo-oxidation mechanisms of Ny6. In fact, our results confirm previous insights that the hydrogen abstraction and subsequent formation of a hydroperoxide intermediate actually occur but also reveal that Norrish I and Norrish II chain-cleavage reactions play an important role in the photo-oxidation process of Ny6. This essential feature of the process had been missed in previous studies focused on UV and IR techniques. The peculiarity of our approach consists of using a high-sensitivity and nonaveraging technique such as mass spectrometry, which allows the detection and monitoring of each new oligomers formed during the oxidation process. This is a remarkable result, and it should be expected that future MALDI studies may have an impact on the current views of photo-oxidation processes of other polymer systems.
Polymer Degradation and Stability, 1982
The irradiation of nylon 6,6 film with light of wavelengths greater than 250 nm and 300 nm has been studied using uv derivative absorption spectroscopy. Initially, the polymer showed a strong absorption at 290nm which is associated with an ~,~unsaturated carbonyl species. Changes in the absorption band were found to be dependent on the atmosphere and are discussed in terms of a reversible photolysis versus a photo-induced oxidation process.
Photolysis and photo‐oxidation of unsaturated polyesters
Makromolekulare Chemie. Macromolecular Symposia, 1989
The photolytic and photo‐oxidative evolution of unsaturated polyesters, crosslinked or not, exposed to polychromatic light is studied using IR, FTIR, UV spectrometries. The influence of each elaboration parameter (nature and concentration of diacids like maleic anhydride, fumaric acid or phthalic acids, nature of glycols, nature and concentrations of crosslinking agents, mode of crosslinking) is determined. The mechanism involving primary excitation of the maleate‐fumarate or of phthalate units and radical reactions accounts for the appearance of hydroxylated and carbonylated groups. Photoyellowing of unsaturated polyesters is related either to the styrene oligomers or to the phthalate units. Through parallel studies of photochemistries in polystyrene (PS) and poly(butylene terephthalate) (PBT) at long wavelengths, the different sources of photo‐yellowing are precised.
NMR Analysis of UV and Heat-Aged Nylon6,6
Macromolecules, 1997
Samples of Nylon-6,6 were analyzed by 1-D and 2-D NMR techniques to determine the degradation structures resulting from UV exposure of Nylon films and heat aging of Nylon pellets. The dominant degradation structure in all cases was the terminal methyl group which was attributed to chain scission reactions. Further evidence for chain scission was found through the presence of aldehyde and formamide structures upon UV exposure and heat aging (in the presence of air) and terminal vinyl structures upon UV exposure. The presence of oxygen during UV exposure resulted in OH substitution adjacent to the amide group and at the end of a cleaved alkyl chain. Terminal amide groups were observed in the starting material and did not increase in concentration upon heat aging or UV exposure. In heataged samples, no evidence was found for olefinic or hydroxyl-containing structures in nitrogen, but hydroxyl structures were observed. A degradation mechanism was proposed to account for the structures observed in our work.
2004
Accelerated aging of Nylon 6.6 fibers used in parachutes has been conducted by following the tensile strength loss under both thermaleoxidative and 100% relative humidity conditions. Thermaleoxidative studies (air circulating ovens) were performed for time periods of weeks to years at temperatures ranging from 37 C to 138 C. Accelerated aging humidity experiments (100% RH) were performed under both an argon atmosphere to examine the 'pure' hydrolysis pathway, and under an oxygen atmosphere (oxygen partial pressure close to that occurring in air) to mimic true aging conditions. As expected the results indicated that degradation caused by humidity is much more important than thermaleoxidative degradation. Surprisingly when both oxygen and humidity were present the rate of degradation was dramatically enhanced relative to humidity aging in the absence of oxygen. This significant and previously unknown phenomena underscores the importance of careful accelerated aging that truly mimics real world storage conditions. Published by Elsevier Ltd.
Photosensitized degradation and crosslinking of linear aliphatic polyesters studied by GPC and ESR
Polymer, 2002
Photosensitized reaction on aliphatic polyesters, 3g4 and M 2 3g4, prepared from succinic acid and propanediol derivatives were investigated by spectrophotometry, GPC, and electron spin resonance (ESR) methods. From change of GPC curves for 3g4 polyester doped with N,N,N 0 ,N 0-tetramethyl-p-phenylenediamine (TMPD) as a photosensitizer, it was confirmed that not only degradation but also crosslinking reaction occurred for 3g4, M 2 3g4, and poly(lactic acid), by UV irradiation. By detailed analysis of ESR spectra, it was confirmed that several radical species are produced through photosensitized reaction; TMPD radical cation, ester radial anion of polyester, main chain alkyl radical at the center of diol component, and acyl-type radical. Although there was no direct evidence for producing the main chain scission radical for 3g4 and M 2 3g4, it was strongly suggested that the photosensitized degradation and the crosslinking reactions were originated from the ester radical anion that was produced by electron capturing.