HS-SPME - a tool for new insights into the long-term thermo-, Artykuły naukowe, SPME i HS-SPME
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//-->Journal of Chromatography A, 932 (2001) 1–11www.elsevier.com / locate / chromaHeadspace solid-phase microextraction — a tool for new insightsinto the long-term thermo-oxidation mechanism of polyamide 6.6¨Mikael Groning, Minna Hakkarainen*Department of Polymer Technology,The Royal Institute of Technology(KTH),S-100 44Stockholm,SwedenReceived 18 May 2001; received in revised form 21 August 2001; accepted 21 August 2001AbstractLow-molecular-mass products formed during thermo-oxidation of polyamide 6.6 at 1008C were extracted by headspacesolid-phase microextraction and identified by GC–MS. A total of 18 degradation products of polyamide 6.6 were identified.In addition some low-molecular-mass products originating from the lubricants were detected. The identified degradationproducts were categorized into four groups where compounds within each group contain the same structural feature. Ingroups A, B and C several new thermo-oxidation products of polyamide 6.6 were identified including cyclic imides,pyridines and structural fragments from the original polyamide chain. 1-Pentyl-2,5-pyrrolidinedione (pentylsuccinimide)showed the largest increase in abundance during oxidation. The cyclopentanones in group D were already present in theun-aged material. Their amounts decreased during ageing and they are thus not formed during thermo-oxidation ofpolyamide 6.6 at 1008C. The identified thermo-oxidation products can be formed as a result of extensive oxidation of thehexamethylenediamine unit in the polyamide backbone. The degradation products pattern shows that the long-termthermo-oxidative degradation, just like thermal degradation and photo-oxidation of polyamide 6.6, starts at theN-vicinalmethylene groups.©2001 Elsevier Science B.V. All rights reserved.Keywords:Headspace solid-phase microextraction; Thermo-oxidation; Polyamide 6.61. IntroductionThroughout their lifetime, polymers are subjectedto destructive factors such as mechanical stress,chemicals, UV-light and high temperatures. Thesefactors will cause degradation and ultimately affectthe performance and lifetime of the polymers. Dur-ing the last decades, the low-molecular-mass degra-dation products from polymers have been studied todeduce the various mechanisms of degradation andalso to gain a complete knowledge of the environ-*Corresponding author. Fax:146-8-100-775.E-mail address:minna@polymer.kth.se (M. Hakkarainen).mental impact of the polymers [1–3]. Studies ofdegradation mechanisms have not only served as abasis for prolonging the lifetime of polymers, butmany studies have aimed at enhancing the degra-dation rate of large volume plastics, such as poly-ethylene, to overcome the rapidly increasing prob-lems of landfills filling with slowly degrading wasteplastic products [4–6]. Most studies have beenperformed on the large volume plastics, such aspolyethylene (PE) and polypropylene (PP), and littleattention has been given to the engineering plastics.Identification of the low-molecular-mass degra-dation products is a prerequisite in establishing thedegradation mechanisms. Prior to identification0021-9673 / 01 / $ – see front matter©2001 Elsevier Science B.V. All rights reserved.PII: S0021-9673( 01 )01230-42¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11appropriate methods must be developed to separatethe low-molecular-mass products from the polymer.Solid-phase microextraction (SPME) is a relativelynew extraction technique, first presented in 1990 byArthur and Pawliszyn [7]. It is based on a fused-silica fibre coated with a polymeric stationary phase.The fibre is introduced directly into aqueous samplesor the headspace over the liquid or solid samplematrix. During the extraction the analytes partitionbetween the fibre and the sample matrix according totheir partition coefficients. Although the amount ofanalytes recovered by SPME is relatively smallcompared to several other methods, there are noanalyte losses due to sample handling and the entireextraction is desorbed into the injection port of thegas or liquid chromatograph. Several fibre materialswith different polarities are commercially available.The choice of an appropriate stationary phase affectsthe sensitivity of the method. SPME has earlier beensuccessfully applied to the extraction of, for exam-ple, degradation products from low-density poly-ethylene (LDPE) [8] and toxic compounds from soil[9,10].Earlier studies of degradation products from poly-amide 6.6 have focused on degradation under photo,thermal or pyrolytic conditions [11–19], whereasstudies of thermo-oxidation of polyamide 6.6 havefocused on changes taking place in the matrix of thematerial [20,21]. Hence, little attention has beengiven to the long-term thermo-oxidation degradationproducts and the mechanisms of their formation. Theaim of the present study was to establish thedegradation processes taking place during long-termthermo-oxidation of polyamide 6.6 at a relativelylow temperature. The low-molecular-mass degrada-tion products were extracted by SPME after differentoxidation times and subsequently identified by GC–MS.contained some lubricant, probably an aliphatic oil,added to the material to facilitate processing opera-tions.2.2.Extrusion of sheetsA counter-rotating twin-screw extruder DSK 35 / 9D from Brabender (Duisburg, Germany) was used toproduce sheets from the polyamide granules. Theextruder was equipped with an adjustable flat sheetdie head (10030.2 mm) giving 200-mm thick poly-amide sheets. During the extrusion operation, thethree heated zones of the extruder were all set to2858C. The screw speed was 30 mm / min. Thegranules were dried for 8 h at 908C in a Piovangranulate dryer (Venezia, Italy) before extrusion.2.3.Thermo-oxidationThe samples were cut out from the extruded sheetsas strips of|1.535cm in size. Strips weighing260.1 were placed in 20-ml closed headspace vials(Chrompack, Middelburg, The Netherlands) with aPTFE-silicone-rubber septum cap from Perkin-Elmer(Stockholm, Sweden). The vials were placed in aconventional circulating air oven (Heraeus, Hanau,Germany) and the samples were thermo-oxidised for25, 100, 500 and 1200 h at 100628C.2.4.ExtractionThree SPME fibres from Supelco (Bellafonte, CA,USA) were tested for the extraction of polyamide 6.6degradation products: polydimethylsiloxane-divinyl-benzene (PDMS-DVB), Carbowax-divinylbenzeneand polyacrylate. PDMS-DVB was found to besuperior in extracting the degradation products as itnot only extracted more products from the headspacebut also generated larger peak areas in the chromato-gram than the other phases and thus was chosen forthe further studies. The degradation products wereextracted on the fibre by subjecting it to the head-space over the films in the vials for 30 min at 808C.To compare the relative amounts of degradationproducts after different oxidation times, an internalstandard was added to each sample prior to ex-traction. By using an internal standard, possibleerrors in the extraction can be eliminated. The2. Experimental2.1.MaterialGranules of a commercially available unstabilisedpolyamide 6.6 (Zytel 101L) were generously sup-plied by DuPont (Stockholm, Sweden). The materialwas not stabilised against thermal oxidation but¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–113relative peak areas of the peaks were calculated bydividing the area of the internal standard by the areasof the peaks. The internal standard also serves as anindicator of repeatability in the performance of theSPME fibre. The internal standard used was an ester,methyl-heptanoate, from PolyScience (Niles, IL,USA). An internal standard solution was prepared bydiluting 5mlof the ester with 10 ml of chromatog-raphy-grade water, LiChrosolv, from Merck (Darm-stadt, Germany). Then 1mlof the standard solutionwas added to each vial prior to extraction.2.5.Gas chromatography–mass spectrometryThe gas chromatography–mass spectrometry anal-yses were performed on a GCQ mass spectrometer´from ThermoFinnigan (San Jose, CA, USA). Thecolumn used was a wall-coated open tubular(WCOT) fused-silica low bleed Cp-Sil 8CB fromSupelco (30 m30.25 mm I.D, film thickness 0.25mm.).The column temperature was initially held at408C for 3 min. The oven temperature was thenincreased to 2508C at a heating rate of 108C / min andthen held at 2508C for 10 min. Helium of scientificgrade purity from AGA (Stockholm, Sweden) wasused as carrier gas with a constant velocity of 40cm / s. The extracted degradation products weredesorbed from the SPME fibre by placing the fibre inthe injector of the GC for 5 min at 2208C. Theinjector was operated in the splitless mode. Toidentify and quantify the products, MS was run inthe EI mode with an electron energy of 70 eV. Thedetector scanned in the mass-range from 35 to 400m/z with a scan time of 0.43 s. The temperatures ofthe ion source and the transfer line were 180 and2758C, respectively. Some samples were also run inthe CI mode using methane as reagent gas to confirmthe molecular ions.desorbing the extracted compounds into the GC–MS.The same GC–MS method was used for the standardcompounds as for the degradation products. Theidentification was positive if the mass spectrum andretention time of the standard compound was identi-cal to the mass spectrum and retention time of thedegradation product.Not all degradation products could be identified bycomparison to authentic compounds since they werenot commercially available. These products wereidentified by comparing their mass spectrums to themass spectrums included in a reference library, NIST98, developed at the National Institute of Standardsand Technology (Gaithersburg, MD, USA). Theidentity of some of the compounds could be furtherconfirmed by literature mass spectrums [22–25].3. Results and discussionFig. 1 shows the GC–MS chromatograms of thelow-molecular-mass products extracted from thepolyamide 6.6 after 25 and 1200 h of thermo-oxida-tion at 1008C. Comparison of Fig. 1a and b clearlyshows how the number and quantity of the productsincreased during the thermo-oxidation. A total ofnine degradation products in low amounts weredetected after 25 h of oxidation. After 1200 h 14degradation products were identified and the amountof several products had increased. However, theamount of some of the products had decreasedduring the ageing and four products that wereidentified after 25 h of ageing were no longer foundafter 1200 h of ageing. Low-molecular-mass prod-ucts were also extracted from un-oxidised polyamide6.6 to see if some of the products are already presentin un-aged samples. These products have beenformed for example during processing of the materi-al. In these chromatograms only a few peaks withsmall peak areas were present. However the actualamounts of low-molecular-mass products in unagedsamples might be somewhat higher because it proba-bly takes more than 30 min (the extraction time) forthe products to migrate from the core of the materialto the headspace where the extraction takes place.Altogether 18 different polyamide degradation prod-ucts were identified. The names and relative areas ofthe identified products are given in Table 1.2.6.Identification of degradation productsThe identity of most of the products was con-firmed by comparison of the recorded mass spectraof the degradation product to the mass spectra andretention time of an authentic compound run underthe same conditions. The latter were generated byexposing the fibre to the headspace over the standardcompounds for a short time,|1or 2 s, and then4¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11Fig. 1. Ion chromatogram of products evolved after (a) 25 h and (b) 1200 h of ageing in 1008C. Numbered peaks are identified in Tables 1and 3. I.S., internal standard. *Peaks corresponding to compounds originating from rubber septum used to seal the vials.¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11Table 1Identified degradation products from thermal oxidation of polyamide 6.6 at 1008C and their relative areasPeakNo.123456789101112131415161718ab5tRCompoundOxidation times (h)2510011619611361376517618615962336314966105363829625009611562496623633568962256510761830664646163611856151200156129652362666237621661386446673863100678267116110668456104.24.65.56.576.638.38.59.29.79.910.611.511.711.812.212.614.016.5Cyclopentanonea2-Methyl-pyridinebPentanoic acidaButanamidea2-Ethyl-cyclopentanonebPentanamidea3-(1-Methylethyl)-pyridinebb2-Butyl-pyridineN,N-hexamethylenebisformamideb2-Butyl-cyclopentanonebGlutarimidea2-Pentyl-cyclopentanoneaCaprolactamaAzepane-2,7-dioneb2-Cyclopentyl-cyclopentanonea1-Butyl-2,5-pyrrolidinedioneb,cc1-Pentyl-2,5-pyrrolidinedione2-Butyl-3,5-dimethylethyl-pyridineb19621763126310618966176396671323682462Identified by comparison with authentic compound.Identified by comparison with NIST 98.cIdentified by comparison with spectrum from literature.Several peaks, identified as compounds originatingfrom lubricants added to the polymer, also appearedin the chromatograms. The peaks were denominatedL1–L7and are marked accordingly in the chromato-grams. The compounds originating from the lubri-cants were identified as linear alkanes or alkeneswith lengths ranging from 10 to 17 carbons. Thenames and relative amounts of these products arepresented in Table 2.The identified polyamide degradation productswere categorized into four different groups accordingto Table 3. Each group shares a common structuralfeature. The products in group A are cyclic imides.The products in group B are pyridine derivatives. Ingroup C all products have structural features that canbe deduced from the repeating unit of the polyamidewhereas the products in group D are cyclopentanonederivatives.3.1.Group A—cyclic imidesSeveral cyclic imides, i.e. 2,6-piperidinedioneTable 2Names and relative amounts of extracted alkanes and alkenes from lubricant added to polymerPeakNo.L1L2L3L4L5L6L7tRCompoundOxidation times (h)2510.813.614.814.916.217.217.3DodecaneTetradecanePentadecenePentadecaneHexadecaneHeptadeceneHeptadecane12648961717865097618186625271676202612100306432161644462319061045261370620263655002566129649163652936301526601776549863112002062576546664163466644653162All compounds were identified by comparison with authentic compound. [ Pobierz całość w formacie PDF ]
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//-->Journal of Chromatography A, 932 (2001) 1–11www.elsevier.com / locate / chromaHeadspace solid-phase microextraction — a tool for new insightsinto the long-term thermo-oxidation mechanism of polyamide 6.6¨Mikael Groning, Minna Hakkarainen*Department of Polymer Technology,The Royal Institute of Technology(KTH),S-100 44Stockholm,SwedenReceived 18 May 2001; received in revised form 21 August 2001; accepted 21 August 2001AbstractLow-molecular-mass products formed during thermo-oxidation of polyamide 6.6 at 1008C were extracted by headspacesolid-phase microextraction and identified by GC–MS. A total of 18 degradation products of polyamide 6.6 were identified.In addition some low-molecular-mass products originating from the lubricants were detected. The identified degradationproducts were categorized into four groups where compounds within each group contain the same structural feature. Ingroups A, B and C several new thermo-oxidation products of polyamide 6.6 were identified including cyclic imides,pyridines and structural fragments from the original polyamide chain. 1-Pentyl-2,5-pyrrolidinedione (pentylsuccinimide)showed the largest increase in abundance during oxidation. The cyclopentanones in group D were already present in theun-aged material. Their amounts decreased during ageing and they are thus not formed during thermo-oxidation ofpolyamide 6.6 at 1008C. The identified thermo-oxidation products can be formed as a result of extensive oxidation of thehexamethylenediamine unit in the polyamide backbone. The degradation products pattern shows that the long-termthermo-oxidative degradation, just like thermal degradation and photo-oxidation of polyamide 6.6, starts at theN-vicinalmethylene groups.©2001 Elsevier Science B.V. All rights reserved.Keywords:Headspace solid-phase microextraction; Thermo-oxidation; Polyamide 6.61. IntroductionThroughout their lifetime, polymers are subjectedto destructive factors such as mechanical stress,chemicals, UV-light and high temperatures. Thesefactors will cause degradation and ultimately affectthe performance and lifetime of the polymers. Dur-ing the last decades, the low-molecular-mass degra-dation products from polymers have been studied todeduce the various mechanisms of degradation andalso to gain a complete knowledge of the environ-*Corresponding author. Fax:146-8-100-775.E-mail address:minna@polymer.kth.se (M. Hakkarainen).mental impact of the polymers [1–3]. Studies ofdegradation mechanisms have not only served as abasis for prolonging the lifetime of polymers, butmany studies have aimed at enhancing the degra-dation rate of large volume plastics, such as poly-ethylene, to overcome the rapidly increasing prob-lems of landfills filling with slowly degrading wasteplastic products [4–6]. Most studies have beenperformed on the large volume plastics, such aspolyethylene (PE) and polypropylene (PP), and littleattention has been given to the engineering plastics.Identification of the low-molecular-mass degra-dation products is a prerequisite in establishing thedegradation mechanisms. Prior to identification0021-9673 / 01 / $ – see front matter©2001 Elsevier Science B.V. All rights reserved.PII: S0021-9673( 01 )01230-42¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11appropriate methods must be developed to separatethe low-molecular-mass products from the polymer.Solid-phase microextraction (SPME) is a relativelynew extraction technique, first presented in 1990 byArthur and Pawliszyn [7]. It is based on a fused-silica fibre coated with a polymeric stationary phase.The fibre is introduced directly into aqueous samplesor the headspace over the liquid or solid samplematrix. During the extraction the analytes partitionbetween the fibre and the sample matrix according totheir partition coefficients. Although the amount ofanalytes recovered by SPME is relatively smallcompared to several other methods, there are noanalyte losses due to sample handling and the entireextraction is desorbed into the injection port of thegas or liquid chromatograph. Several fibre materialswith different polarities are commercially available.The choice of an appropriate stationary phase affectsthe sensitivity of the method. SPME has earlier beensuccessfully applied to the extraction of, for exam-ple, degradation products from low-density poly-ethylene (LDPE) [8] and toxic compounds from soil[9,10].Earlier studies of degradation products from poly-amide 6.6 have focused on degradation under photo,thermal or pyrolytic conditions [11–19], whereasstudies of thermo-oxidation of polyamide 6.6 havefocused on changes taking place in the matrix of thematerial [20,21]. Hence, little attention has beengiven to the long-term thermo-oxidation degradationproducts and the mechanisms of their formation. Theaim of the present study was to establish thedegradation processes taking place during long-termthermo-oxidation of polyamide 6.6 at a relativelylow temperature. The low-molecular-mass degrada-tion products were extracted by SPME after differentoxidation times and subsequently identified by GC–MS.contained some lubricant, probably an aliphatic oil,added to the material to facilitate processing opera-tions.2.2.Extrusion of sheetsA counter-rotating twin-screw extruder DSK 35 / 9D from Brabender (Duisburg, Germany) was used toproduce sheets from the polyamide granules. Theextruder was equipped with an adjustable flat sheetdie head (10030.2 mm) giving 200-mm thick poly-amide sheets. During the extrusion operation, thethree heated zones of the extruder were all set to2858C. The screw speed was 30 mm / min. Thegranules were dried for 8 h at 908C in a Piovangranulate dryer (Venezia, Italy) before extrusion.2.3.Thermo-oxidationThe samples were cut out from the extruded sheetsas strips of|1.535cm in size. Strips weighing260.1 were placed in 20-ml closed headspace vials(Chrompack, Middelburg, The Netherlands) with aPTFE-silicone-rubber septum cap from Perkin-Elmer(Stockholm, Sweden). The vials were placed in aconventional circulating air oven (Heraeus, Hanau,Germany) and the samples were thermo-oxidised for25, 100, 500 and 1200 h at 100628C.2.4.ExtractionThree SPME fibres from Supelco (Bellafonte, CA,USA) were tested for the extraction of polyamide 6.6degradation products: polydimethylsiloxane-divinyl-benzene (PDMS-DVB), Carbowax-divinylbenzeneand polyacrylate. PDMS-DVB was found to besuperior in extracting the degradation products as itnot only extracted more products from the headspacebut also generated larger peak areas in the chromato-gram than the other phases and thus was chosen forthe further studies. The degradation products wereextracted on the fibre by subjecting it to the head-space over the films in the vials for 30 min at 808C.To compare the relative amounts of degradationproducts after different oxidation times, an internalstandard was added to each sample prior to ex-traction. By using an internal standard, possibleerrors in the extraction can be eliminated. The2. Experimental2.1.MaterialGranules of a commercially available unstabilisedpolyamide 6.6 (Zytel 101L) were generously sup-plied by DuPont (Stockholm, Sweden). The materialwas not stabilised against thermal oxidation but¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–113relative peak areas of the peaks were calculated bydividing the area of the internal standard by the areasof the peaks. The internal standard also serves as anindicator of repeatability in the performance of theSPME fibre. The internal standard used was an ester,methyl-heptanoate, from PolyScience (Niles, IL,USA). An internal standard solution was prepared bydiluting 5mlof the ester with 10 ml of chromatog-raphy-grade water, LiChrosolv, from Merck (Darm-stadt, Germany). Then 1mlof the standard solutionwas added to each vial prior to extraction.2.5.Gas chromatography–mass spectrometryThe gas chromatography–mass spectrometry anal-yses were performed on a GCQ mass spectrometer´from ThermoFinnigan (San Jose, CA, USA). Thecolumn used was a wall-coated open tubular(WCOT) fused-silica low bleed Cp-Sil 8CB fromSupelco (30 m30.25 mm I.D, film thickness 0.25mm.).The column temperature was initially held at408C for 3 min. The oven temperature was thenincreased to 2508C at a heating rate of 108C / min andthen held at 2508C for 10 min. Helium of scientificgrade purity from AGA (Stockholm, Sweden) wasused as carrier gas with a constant velocity of 40cm / s. The extracted degradation products weredesorbed from the SPME fibre by placing the fibre inthe injector of the GC for 5 min at 2208C. Theinjector was operated in the splitless mode. Toidentify and quantify the products, MS was run inthe EI mode with an electron energy of 70 eV. Thedetector scanned in the mass-range from 35 to 400m/z with a scan time of 0.43 s. The temperatures ofthe ion source and the transfer line were 180 and2758C, respectively. Some samples were also run inthe CI mode using methane as reagent gas to confirmthe molecular ions.desorbing the extracted compounds into the GC–MS.The same GC–MS method was used for the standardcompounds as for the degradation products. Theidentification was positive if the mass spectrum andretention time of the standard compound was identi-cal to the mass spectrum and retention time of thedegradation product.Not all degradation products could be identified bycomparison to authentic compounds since they werenot commercially available. These products wereidentified by comparing their mass spectrums to themass spectrums included in a reference library, NIST98, developed at the National Institute of Standardsand Technology (Gaithersburg, MD, USA). Theidentity of some of the compounds could be furtherconfirmed by literature mass spectrums [22–25].3. Results and discussionFig. 1 shows the GC–MS chromatograms of thelow-molecular-mass products extracted from thepolyamide 6.6 after 25 and 1200 h of thermo-oxida-tion at 1008C. Comparison of Fig. 1a and b clearlyshows how the number and quantity of the productsincreased during the thermo-oxidation. A total ofnine degradation products in low amounts weredetected after 25 h of oxidation. After 1200 h 14degradation products were identified and the amountof several products had increased. However, theamount of some of the products had decreasedduring the ageing and four products that wereidentified after 25 h of ageing were no longer foundafter 1200 h of ageing. Low-molecular-mass prod-ucts were also extracted from un-oxidised polyamide6.6 to see if some of the products are already presentin un-aged samples. These products have beenformed for example during processing of the materi-al. In these chromatograms only a few peaks withsmall peak areas were present. However the actualamounts of low-molecular-mass products in unagedsamples might be somewhat higher because it proba-bly takes more than 30 min (the extraction time) forthe products to migrate from the core of the materialto the headspace where the extraction takes place.Altogether 18 different polyamide degradation prod-ucts were identified. The names and relative areas ofthe identified products are given in Table 1.2.6.Identification of degradation productsThe identity of most of the products was con-firmed by comparison of the recorded mass spectraof the degradation product to the mass spectra andretention time of an authentic compound run underthe same conditions. The latter were generated byexposing the fibre to the headspace over the standardcompounds for a short time,|1or 2 s, and then4¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11Fig. 1. Ion chromatogram of products evolved after (a) 25 h and (b) 1200 h of ageing in 1008C. Numbered peaks are identified in Tables 1and 3. I.S., internal standard. *Peaks corresponding to compounds originating from rubber septum used to seal the vials.¨M.Groning,M.Hakkarainen/J.Chromatogr.A 932 (2001) 1–11Table 1Identified degradation products from thermal oxidation of polyamide 6.6 at 1008C and their relative areasPeakNo.123456789101112131415161718ab5tRCompoundOxidation times (h)2510011619611361376517618615962336314966105363829625009611562496623633568962256510761830664646163611856151200156129652362666237621661386446673863100678267116110668456104.24.65.56.576.638.38.59.29.79.910.611.511.711.812.212.614.016.5Cyclopentanonea2-Methyl-pyridinebPentanoic acidaButanamidea2-Ethyl-cyclopentanonebPentanamidea3-(1-Methylethyl)-pyridinebb2-Butyl-pyridineN,N-hexamethylenebisformamideb2-Butyl-cyclopentanonebGlutarimidea2-Pentyl-cyclopentanoneaCaprolactamaAzepane-2,7-dioneb2-Cyclopentyl-cyclopentanonea1-Butyl-2,5-pyrrolidinedioneb,cc1-Pentyl-2,5-pyrrolidinedione2-Butyl-3,5-dimethylethyl-pyridineb19621763126310618966176396671323682462Identified by comparison with authentic compound.Identified by comparison with NIST 98.cIdentified by comparison with spectrum from literature.Several peaks, identified as compounds originatingfrom lubricants added to the polymer, also appearedin the chromatograms. The peaks were denominatedL1–L7and are marked accordingly in the chromato-grams. The compounds originating from the lubri-cants were identified as linear alkanes or alkeneswith lengths ranging from 10 to 17 carbons. Thenames and relative amounts of these products arepresented in Table 2.The identified polyamide degradation productswere categorized into four different groups accordingto Table 3. Each group shares a common structuralfeature. The products in group A are cyclic imides.The products in group B are pyridine derivatives. Ingroup C all products have structural features that canbe deduced from the repeating unit of the polyamidewhereas the products in group D are cyclopentanonederivatives.3.1.Group A—cyclic imidesSeveral cyclic imides, i.e. 2,6-piperidinedioneTable 2Names and relative amounts of extracted alkanes and alkenes from lubricant added to polymerPeakNo.L1L2L3L4L5L6L7tRCompoundOxidation times (h)2510.813.614.814.916.217.217.3DodecaneTetradecanePentadecenePentadecaneHexadecaneHeptadeceneHeptadecane12648961717865097618186625271676202612100306432161644462319061045261370620263655002566129649163652936301526601776549863112002062576546664163466644653162All compounds were identified by comparison with authentic compound. [ Pobierz całość w formacie PDF ]