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Long-term properties of polyethylene films: efficiency of a natural antioxidant
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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 [en]
Polymer Technology, alfa-tocopherol, Polyethylene (PE), Thermal aging, Infrared Spectroscopy (FT-IR), Chemiluminescence (CL), Solid-phase microextraction (SPME)
National Category
Chemical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-3972ISBN: 91-7178-357-1 (print)OAI: oai:DiVA.org:kth-3972DiVA: diva2:10231
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
List of papers
1. Process Efficiency and Long-Term Performance of alpha-tocopherol in Film-Blown Linear Low-Density Polyethylene
Open this publication in new window or tab >>Process Efficiency and Long-Term Performance of alpha-tocopherol in Film-Blown Linear Low-Density Polyethylene
2005 (English)In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 98, 2427-2439 p.Article in journal (Refereed) Published
Abstract [en]

Alpha-Tocopherol was compared with a commercial phenolic antioxidant (Irganox 1076) as a long-term and process antioxidant in film-blown and compression-molded linear low-density polyethylene. The antioxiclant function of alpha-tocopherol was high in the film-blown material, especially in the processing, according to oxygen induction time measurements with differential scanning calorimetry. The residual content of alpha-tocopherol after processing, determined with chromatographic techniques, was less than that of the commercial phenolic antioxidant in both the film-blown and compression-molded materials. The process stabilizing efficiency was nevertheless higher for the material containing alpha-tocopherol. During the long-term stabilization, the efficiency of alpha-tocopherol was less than that of the commercial phenolic stabilizer Irganox 1076 in the thin films, according to chemiluminescence and infrared measurements. The long-term efficiency in the compression-molded samples stabilized with alpha-tocopherol or Irganox 1076 was equally good because of the low loss of both alpha-tocopherol and Irganox 1076 from the thicker films

Keyword
ageing, antioxidants, polyethylene (PE)
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5752 (URN)10.1002/app.22435 (DOI)000233091800012 ()2-s2.0-30544440859 (Scopus ID)
Note
QC 20100921Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2017-12-14Bibliographically approved
2. Improvement of α-tocopherol’s Long-Term Efficiency by Modeling Its Heterogeneous Natural Environment in Polyethylene
Open this publication in new window or tab >>Improvement of α-tocopherol’s Long-Term Efficiency by Modeling Its Heterogeneous Natural Environment in Polyethylene
2006 (English)In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 44, no 5, 1660-1666 p.Article in journal (Refereed) Published
Abstract [en]

The natural antioxidant vitamin E (α-tocopherol) is of interest to use in packaging applications to decrease the amount of toxic products migrating into food and drugs. We have earlier shown that the long-term efficiency of α-tocopherol in polyethylene (PE) films is poor. α-Tocopherol is located in the lipid phase of the cell in vivo and it has been revealed that it is more efficient in a polar substrate. PE is more hydrophobic and homogenous than the heterogeneous and hydrophilic lipid phase. Three different additive systems were investigated to model α-tocopherols heterogeneous natural environment in PE. Two of these had carboxylic acid groups, EAA and polyTRIM/PAA core-shell particles (Core), and the third, oat starch, had no carboxylic acid groups. The materials were thermally aged and characterized by chemiluminescence (CL), FTIR, chromatography, and thermal analysis. The EAA system as well as the Core system improved the antioxidant properties of α-tocopherol in PE, and the Core system had the best performance. We know that starch has stabilizing properties in PE, but it had no effect on the efficiency of α-tocopherol.

Keyword
α-tocopherol, Core-shell polymers, Poly(ethylene-co-acrylic acid) (EAA), Polyethylene (PE), Stabilization, Thermal aging
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5753 (URN)10.1002/pola.21286 (DOI)000235526500010 ()2-s2.0-33645012814 (Scopus ID)
Note
QC 20100917Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2017-12-14Bibliographically approved
3. Total Luminescence Intensity (TLI) Offers Superior Early Oxidation Detection in Unstabilised Polyethylene but is no better than FT-IR for Stabilised Polyolefins
Open this publication in new window or tab >>Total Luminescence Intensity (TLI) Offers Superior Early Oxidation Detection in Unstabilised Polyethylene but is no better than FT-IR for Stabilised Polyolefins
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.

Keyword
chemiluminescence (CL), infrared spectroscopy (FT-IR), differential scanning calorimetry (DSC), stabilisation, polyolefins
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5754 (URN)10.1016/j.eurpolymj.2006.02.005 (DOI)000240727000016 ()2-s2.0-33745736601 (Scopus ID)
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
4. Assessment of Carboxylic Acids from Water-Aged and Air-Aged Polyethylene by Head-Space Solid-Phase Microextraction (HS-SPME) and their correlation to Off-Flavours and Carbonyl Index
Open this publication in new window or tab >>Assessment of Carboxylic Acids from Water-Aged and Air-Aged Polyethylene by Head-Space Solid-Phase Microextraction (HS-SPME) and their correlation to Off-Flavours and Carbonyl Index
(English)Article in journal (Refereed) Submitted
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-5755 (URN)
Note
QC 20100921Available from: 2006-05-17 Created: 2006-05-17 Last updated: 2010-09-21Bibliographically approved

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