Polyamides thermo-oxidation

A correlation between matrix changes and formation of certain degradation products has also been found for polyamide 6.6 [53]. Especially the amount of cyclic imides increased during thermo-oxidation, of which... 

The HS-SPME method was also developed for the extraction of low molecular weight compounds from virgin or thermo-oxidized polyamide-66 [14,... 

Groning, Hakkarainen [14-16,18] Polyamide 66 thermo-oxidation Cyclopentanones, pyridines, cyclic imides, amides, carhoxyhc acids, caprolactam PDMS-DVB... 

Fig. 6 Chromatograms of extractions from virgin and recycled polyamide 6.6 after 25 h of thermo-oxidation at 100 °C. Identity of the peaks is 1 = cyclopentanone, 2 = 2-methylpyridine, 3 = pentanoic acid, 4 = butanamide, 5 = 2-ethylcyclopentanone, 6 = 2,4,6-trimethylpyridine, 7 = pentanamide, 8 = 3-(l-methylethyl)pyridine, 9 = 2-butylpyridine, 10 = N,N-hexamethylenebisformamide, 11 = 2-butylcyclopentanone, 12 = glutarimide, 13 = l-propyl-2,5-pyrrolidinedione, 14 = 2-pentylcyclopentanone, 15 = caprolactam, 16 = azepane-2,7-dione, 17 = 2-cyclopentyl-cyclopentanone, 18= l-butyl-2,5-pyrrolidinedione, 19 = l-pentyl-2,5-pyrrolidinedione, 20 = 2-butyl-3,5-dimethylethylpyridine, L1-L7 = linear C13-C17 alkanes and alkenes from lubricant, = silicone from septa used to seal vials. Reprinted from [65] with permission of John WUey Sons, Inc. John Wiley Sons, Inc (2002)...

Fig. 11 Decrease in extractable amoimt of 2-cyclopentyl-cyclopentanone from virgin and recycled polyamide 6.6 diming thermo-oxidation at 100 °C. Reprinted from [65] with permission of John Wiley Sons, Inc. John Wiley Sons, Inc (2002)...

During the first 100 h of oxidation there were no significant differences between the samples, i.e. they all seemed unaffected by thermo-oxidation and no influence of repeated processing was found [65]. However, after 500 h of thermo-oxidation, all recycled samples showed a marked deterioration in tensile strength whereas the virgin material remained unaffected. The magnitude of the decrease in tensile strength corresponded well to the number of times the material was extruded. After 1200 h of thermo-oxidation the deterioration in mechanical properties was even more pronounced and at this point the polyamide 6.6 recycled three times retained only 20% of its... 

Thermo-oxidative Degradation of Polyesterimides, Polyamidoimides, Aliphatic-Aromatic Polyamides [7, 21, 40-43]... 

B. L nskd. Thermo-oxidation of lactam-based polyamides with carboxylic end-groups Decomposition of 6-hydroperoxy-6-hexanelactam in the presence of carboxylic acids. Eur. Polym. J., 30(2) 197-204, February 1994. 

Thermogravimetric analyses of various polymer—silica composites including PDMS-sihca [61], polyamide-silica [33,34], polyimide-silica [15,38,47], polybenzoxazole-silica [16,17], polybenzobisthiazole-sihca [16,17] and PDMS -silica-titania [62] have been reported, in all cases indicating that the incorporation of silica raises the temperature of thermo oxidative degradation of the polymer. A possible mechanism for the improvements in degradation temperature could be due to silica inactivating the terminal OH groups... 

Because the thermal stability of polystyrenes and polymethacrylates is limited to 200°C, continuous use of a polymer-supported reactive species tends to be limited to significantly lower temperatures than this (see polymeric sulphonic acids). There is considerable interest in supporting, in particular, alkene oxidation catalysts on polymers and to operate reactions at temperatures above 200°C. To achieve this, novel thermo-oxidatively stable supports are required and some progress has been made in this direction. More details of specific applications will be given later, but supports based on, for example, polyacrylonitrile [50-52], polyamides [53-56], polysulphone [57, 58], polyaniline [59] and polybenzimidazole... 

Degradation behaviour of polyamides continues to be the subject of many papers. The degradation of nylon-6 has been examined by hydrolysis,by photolysis, and ultrasonically. Kinetic studies on chain scission by means of e.s.r. spectroscopy showed that the concentration of free radicals originating from broken chains in nylon-6 fibres could be described by a model system in which crystalline and amorphous layers were sandwiched in the fibre direction. Oxyluminescence has also been used in a study of the kinetics of the thermo-oxidative degradation of nylon-6,6. 

The thermo-oxidative cross-linking of nylon 6 and the resistance to oxidation of its graft copolymers with polyacrylonitrile have been studied. The thermal and thermal oxidative degradation of poly(/w-phenylene isophthalamide) and other aromatic polyamide compositions, together with comparative studies on the mechanisms of degradation of poly(p-benzamide) and poIy(p-phenylene terephalamide) have all been reported. 

The comparison of the results obtained in this study for the LCP degradation imder processing temperatures with the peculiarities of some thermally stable polyheteroaiylenes degradation [14] brings to light some common features carbonization of the structure, H2 evolution, improvement in thermo-oxidative stability with transition metal compoimds. That is why we took into accoimt the stabilization of polysulfones, aiyl-aliphatic polyimides, polyamides etc. The approach to such stabilization is based on the following proposals on the mechanisms of the above said polymer degradation ... 

Kuper, G. Hormes, J. Sommer, K.In situ x-ray absorption spectroscopy at the K-edge of red phosphorus in polyamide 6,6 during a thermo-oxidative degradation. Makromol. Chem. Phys. 1994, 195, 1741-1753. 

DSC was used for samples 1-4 (Table 5.4) at an isothermal temperature of 260 °C. The OIT was determined to be 21.4, 17.8, 14.1 and 8.6 minutes for Samples 1 to 4, respectively. Reprocessed samples exhibit lower OIT values compared with that of the virgin reference samples. The presence of glass fibres in the polyamide matrix seems to decrease the thermo-oxidative stability. 

Darie and co-workers [25] studied the thermal and thermo-oxidative behaviour of isotactic polypropylene/polyamide-6 (PA6) and tertiary isotactic polypropylene, PA6-ethylene-propylene-diene blends by DSC and TGA. 

Figure 5.11 Loss of tensile strength versus the formation of l-pentyl-2,5-pyrrolidinedione during 1200 h of thermo-oxidation of (a) virgin, and (b) once recycled polyamide 6,6 at 100 "C. Reproduced with permission from M. Groning and M. Hakkarainen,/owrn t/ of Applied Polymer Science, 2002, 86,13, 3396.

However, efficient grafting and dispersion was found to reduce the short-term thermally induced morphological changes. Use of efficient heat stabilizers and antioxidants are, of course, necessary to suppress the long term, thermo-oxidative effects of embrittlement in rubber toughened polyamides. 

Forsstrom, D., Terselius, B. R Thermo oxidation stability of polyamide 6 films. I. Mechanical and chemical characterization. Polym. Degrad. Stab. 67, 69-78 (2000)... 

The product studied is obtained as a by-product of nylon 6 manufacture and consists of a mixture of epsilon-caprolactam, low-molecular cyclic and linear polyamides and products of their thermo-oxidative degradation and interaction with sodium hydroxide or other neutralising agents. Data are given on the effect of this secondary vulcanising accelerator on the vulcanisation properties and physico-mechanical properties of various mbbers. 3 refs. Articles from this journal can be requested for translation by subscribers to the Rapra produced International Polymer Science and Technology. 

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