Solid-Phase Microextraction (SPME) Applied to Studies of Polyamide 6.6 Long-Term Thermo-Oxidation and In- Plant Recycling

Headspace solid-phase microextraction was used to extract low-molecular mass degradation products formed during thermo-oxidation of virgin and inplant recycled polyamide 6.6 at 100°C for up to 1200 hours. A total of 20 degradation products were identified using GC-MS. The identified degradation products shared some common structural features and were categorised into four different groups: cyclic imides, pyridines, chain fragments and cyclopentanones. From the structures of the degradation products it was concluded that the thermo-oxidative degradation preferentially starts at the Nvicinal methylene group. The use of an internal standard enabled monitoring of changes in abundance of the identified degradation products during ageing. It was found that N-pentyl-succinimide showed the largest increase in abundance due to ageing. Also the amounts of chain fragments and pyridines increased due to thermo-oxidation. 2-cyclopentyl-cyclopentanone was found in largest amounts in virgin material and the amount of it decreased due to repeated processing, probably due to degradation into lower molecular weight cyclopentanone derivatives. Larger amounts of degradation products were extracted from recycled material compared to virgin material and for some degradation products the increase in amount extracted corresponded almost linearly to the number of processing operations. The increased susceptibility towards thermo-oxidation due to in-plant recycling was verified using tensile testing, DSC and FTIR as it was found that recycled material were affected earlier and more by thermo-oxidation than virgin material. The largest drop in tensile strength coincided with the largest increase in formation of degradation products. The high versatility of HS-SPME-GC-MS was demonstrated as it not only was able to extract a large number of degradation products with a rather wide range of chemical properties but also could be used to track changes caused by degradation already at early stages of degradation when the other techniques employed failed to detect any differences.