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Total Luminescence Intensity (TLI) Offers Superior Early Oxidation Detection in Unstabilised Polyethylene but is no better than FT-IR for Stabilised Polyolefins
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2006 (English)In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 42, no 8, 1855-1865 p.Article in journal (Refereed) Published
Abstract [en]

In an earlier study, we have shown that chemiluminescence (CL) and the total luminescence intensity (TLI) method are highly sensitive to oxidation in degradable PE. In this study, stabilised PE and PP were characterised with CL in an inert (TLI) and in an oxygen atmosphere (CL-OIT) and the results were compared to those obtained by the commonly used techniques, FT-IR (carbonyl index (CI)) and thermal analysis (DSC-OIT). PE was aged at a low temperature (80 degrees C) and PP was aged at temperatures between 60 and 120 degrees C. Non-Arrhenius behaviour was observed in the oxidation of PP. This showed the importance of aging at a low temperature to obtain realistic results. TLI and Cl of stabilised PP and most of the stabilised PE gave comparable results with the same sensitivity for oxidation detection. This was in contrast to our previous results for degradable PE. However, TLI of unstabilised PE showed earlier oxidation detection than Cl, which agreed with our earlier results. TLI of PE had a higher sensitivity than CL-OIT, and both TLI and Cl of PP were sufficiently sensitive to detect the effect of aging at different temperatures, whereas DSG-OIT was not.

Place, publisher, year, edition, pages
2006. Vol. 42, no 8, 1855-1865 p.
Keyword [en]
chemiluminescence (CL), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), stabilisation, polyolefins
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-5754DOI: 10.1016/j.eurpolymj.2006.02.005ISI: 000240727000016Scopus ID: 2-s2.0-33745736601OAI: oai:DiVA.org:kth-5754DiVA: diva2:10229
Note

Uppdaterad från in press till published: 20100921 QC 20100921

Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2017-06-13Bibliographically approved
In thesis
1. Long-term properties of polyethylene films: efficiency of a natural antioxidant
Open this publication in new window or tab >>Long-term properties of polyethylene films: efficiency of a natural antioxidant
2006 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

There is a growing awareness of the risks of pollution in biological systems and one potential problem is the synthetic antioxidants, used for e.g. the stabilisation of polymeric materials. Natural antioxidants are an interesting alternative, if the high efficiency and thermal stability of the synthetic compounds can be reached. In the work described in this thesis, vitamin E (alfa-tocopherol) was studied as a natural antioxidant for the stabilisation of one of the major plastics, polyethylene (PE). The dependence of the surrounding environment for the efficiency of alfa-tocopherol in polyethylene (PE), throughout thermal aging, was characterised by sensitive techniques. Two techniques which have shown a high sensitivity in oxidation detection of polymers; chemiluminescence (CL) and gas chromatographic analysis, were compared with the commonly used methods, infrared spectroscopy (FT-IR) and thermal analysis.

Three different additive systems were selected as active domains for -tocopherol in PE. Two of these contained carboxylic acid groups, poly (ethylene-co-acrylic acid) (EAA) and polyTRIM/PAA core-shell particles (Core), and the third, oat starch, had no such groups. The additives containing carboxylic groups improved the long-term efficiency of alfa-tocopherol in PE, according to carbonyl index measurements made by FT-IR, while the additive without carboxylic acid groups gave no improvement. The amount of carboxylic acids emitted from the materials after thermal aging, assessed by head-space solid-phase microextraction (HS-SPME) and gas chromatography-mass spectroscopy (GC-MS), also showed that EAA increased the antioxidant efficiency of alfa-tocopherol, whereas the Core system showed lower antioxidant efficiency. Reference systems containing the synthetic antioxidant Irganox 1076 and EAA or oat starch had the same performance as the materials stabilised with only the antioxidants.

CL measurements in an inert atmosphere (TLI) have earlier been shown to give earlier oxidation detection than carbonyl index measurements in unstabilised PE. In this work, the TLI analysis and the carbonyl index measurements had the same sensitivity in the detection of oxidation in the stabilised materials.

Assessment of low-molecular weight carboxylic acids in PE during the aging was made by gas chromatographic analysis together with solid-phase extraction. Propanoic acid showed the best correlation with the carbonyl index measurements, even if the carbonyl index showed earlier detection of oxidation.

It was also found that TLI and CL in an oxidative atmosphere (CL-OIT) had the same sensitivity and were in accordance for all of the materials, with exception of the materials containing EAA and alfa-tocopherol or Irganox 1076. CL-OIT was also compared to the oxygen induction time determined by thermal analysis.

Place, publisher, year, edition, pages
Stockholm: KTH, 2006. 64 p.
Series
Trita-FPT-Report, ISSN 1652-2443 ; 2006:11
Keyword
Polymer Technology, alfa-tocopherol, Polyethylene (PE), Thermal aging, Infrared Spectroscopy (FT-IR), Chemiluminescence (CL), Solid-phase microextraction (SPME)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-3972 (URN)91-7178-357-1 (ISBN)
Public defence
2006-06-02, K2, K, Teknikringen 28, Stockholm, 13:00
Opponent
Supervisors
Note
QC 20100921Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2010-09-21Bibliographically approved

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