Headspace solid‐phase microextraction with gas chromatography/mass spectrometry reveals a correlation between the degradation product pattern and changes in the mechanical properties during the thermooxidation of in‐plant recycled polyamide 6,6

Abstract

ABSTRACT:The increased susceptibility of in-plant recycled polyamide 6,6 toward thermooxidation was shown by headspace solid-phase microextraction with gas chromatography/mass spectrometry (HS-SPME/GC-MS), tensile testing, differential scanning calorimetry (DSC), and Fourier transform infrared spectroscopy (FTIR). A correlation between the deterioration in mechanical properties and the formation of degradation products due to thermooxidation was found, and the most prominent decrease in mechanical properties coincided with the largest increase in the abundance of degradation products. The recycled materials had a shorter induction period toward oxidation, and their mechanical properties deteriorated faster than the mechanical properties of virgin material. The same trend was observed with HS-SPME/GC-MS because degradation products were found for recycled materials after oxidation times shorter than those for virgin material. Furthermore, larger amounts of degradation products were formed in the recycled materials. The high sensitivity of HS-SPME/GC-MS as an analytical tool was demonstrated because it was able to detect changes caused by oxidation considerably earlier than the other methods. Unlike DSC and FTIR, it could also show differences between samples recycled for different times. Four groups of degradation products-cyclic imides, pyridines, chain fragments, and cyclopentanones-were identified in thermooxidized polyamide 6,6. After 1200 h of thermooxidation, 1-pentyl-2,5-pyrrolidinedione was the most abundant degradation product. Approximately four times more 1-pentyl-2,5-pyrrolidinedione was formed in polyamide recycled three times than in virgin polyamide. Pyridines and chain fragments behaved toward oxidation and repeated processing like cyclic imides; that is, their amounts increased during oxidation, and larger amounts were formed in recycled materials than in virgin material. The cyclopentanone derivatives were present already in unaged material, and their amounts decreased during oxidation. Cyclopentanones were not formed because of the thermooxidation of polyamide 6,6.

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

“…Cyclopentanone {17} was detected in the adipic acid monomer data. The signal for cyclopentanone {17} relative to the background noise (not necessarily its concentration) intensified with increasing aging time (Figure 1), which largely supports the identification of this species as a thermal-oxidative degradation product for nylon 6.6 and not an impurity from polymer synthesis/processing [19,20]. Moreover, our data support previous work that identified cyclopentanone {17} and its derivatives as nylon 6.6 Figure 5.…”

“…The "red boxes" and "red text" indicate a +1 Da shift was seen in the mass spectrum comparison degradation products where cyclopentanone {17} was postulated to have formed by intramolecular reactions at the adipic acid end groups [17,19] and from within the nylon chain [35]. In addition to varying experimental methodology (cryo-GC/MS vs. SPME-GC/MS) [19], our GC transfer line was held at a much lower temperature (100°C vs. 275°C) [19], which may explain why we did not see the cyclopentanone derivatives.…”

“…Most recently, Gröning and Hakkarainen employed headspace solid-phase microextraction with gas chromatography/mass spectrometry (HS-SPME-GC/MS) to identify and characterize volatile thermal-oxidative degradation species and detailed degradation mechanisms of polyamide 6.6 [18][19][20]. These previous investigations helped increase the understanding of nylon aging, but the specific origin and formation of several degradation species, such as cyclopentanone, remains unclear [21,22].…”

Efficient method of cyclic imides synthesis under ozone influence by the example of ε‐caprolactam oxidation reaction

“…This substance is well known as one of the products of polyamide-6.6 destruction [15]. The mechanism of the reaction of ozone with CL goes through oxidation of C H group adjacent to nitrogen atom with formation of the second carbonyl group.…”

Development of a solid-phase extraction method for simultaneous extraction of adipic acid, succinic acid and 1,4-butanediol formed during hydrolysis of poly(butylene adipate) and poly(butylene succinate)

“…Gas chromatography-mass spectrometry (GC-MS) together with appropriate extraction method is a sensitive tool for detecting early signs of degradation in the material, e.g. solid phase microextraction and GC-MS analysis of the degradation products showed oxidation-induced changes in recycled and thermo-oxidized polyamide 66 considerably earlier than tensile testing, FTIR or DSC [1,2]. The amount and type of degradation products formed was also in good correlation with the degree of degradation in the polymer matrix [2][3][4].…”