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A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media
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), Chemistry, Nuclear Chemistry.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
2009 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 28, no 6, p. 661-667Article in journal (Refereed) Published
Abstract [en]

The chlorine used as disinfectant in tap water degrades most materials, including polyethylene. The most adequate (functional) test method, the pressure test, is complicated and expensive because the chlorinated aqueous media (Cl-2 or ClO2 in water) are unstable and they undergo reactions that are dependent on the pH. A new method which assesses the protection efficiency of phenolic antioxidants in polyolefins was developed. The method uses a liquid hydrocarbon analogue, squalane, in which antioxidants are dissolved. The organic phase was dispersed in the aqueous chlorinated phase (containing 10 ppm of either Cl-2 or ClO2; pH=6.8) at 70 degrees C by intense stirring. The depletion of antioxidant (Irganox 1010) was monitored by standard DSC determination of the oxidation induction time. It was shown that 300 min of exposure was sufficient to obtain useful data.

Place, publisher, year, edition, pages
2009. Vol. 28, no 6, p. 661-667
Keywords [en]
Polyolefins, Antioxidants, Chlorinated water media, polyethylene pipes
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-18713DOI: 10.1016/j.polymertesting.2009.05.010ISI: 000269295200014Scopus ID: 2-s2.0-67650087904OAI: oai:DiVA.org:kth-18713DiVA, id: diva2:336760
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Degradation of polyethylene pipes distributing chlorinated water: depletion of stabilizers, release of degraded products and polymer degradation
Open this publication in new window or tab >>Degradation of polyethylene pipes distributing chlorinated water: depletion of stabilizers, release of degraded products and polymer degradation
2011 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents the study of antioxidants depletions in chlorinated media (10 ppm Cl2 - and ClO2 - aqueous media), polyethylene pipes degradations scenarios and migration of the degraded species to aqueous phase. Pressure testing on pipes and squalane testing with controlled pH aqueous media (6.8 ± 0.2) containing either Cl2 or ClO2 were used for assessing the degradation products. Though squalane test used a liquid hydrocarbon instead of real plastic, it provided reliable data with an efficient and readily way of sampling. Medium density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide (ClO2) at 90 °C as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated (Cl2) aqueous (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizers occurred far into the pipe wall. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that in the surface layer which came into contact with the oxidizing medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains. The depletion rate of the antioxidant exposed to ClO2 - aqueous media was also four times faster than that exposed to Cl2 - aqueous media by squalane test. The aqueous media was extracted to condense the remaining antioxidants and the degraded species from the squalane solution. The absorption spectra from infrared spectroscopy illustrated that carbonyl groups exist in degraded species from both ClO2 - and Cl2 - aqueous, and chlorine-carbon bond presented only in ClO2 - aqueous. It was proved by liquid chromatography that the peaks of oxidizing species formed in ClO2 aqueous media were more intense and they were different from the ones degraded compounds in Cl2.

 

 

 

 

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2011. p. 38
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:10
Keywords
polyethylene pipes, chlorine dioxide, degradation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-31469 (URN)978-91-7415-859-5 (ISBN)
Presentation
2011-03-18, Rånbyrummet, KTH, Teknikringen 56, Stockholm, 14:00 (English)
Opponent
Supervisors
Note
QC 20110316Available from: 2011-03-16 Created: 2011-03-16 Last updated: 2011-03-16Bibliographically approved
2. Deterioration of Polyethylene Exposed to Chlorinated Species in Aqueous Phases: Test Methods, Antioxidants Consumption and Polymer Degradation
Open this publication in new window or tab >>Deterioration of Polyethylene Exposed to Chlorinated Species in Aqueous Phases: Test Methods, Antioxidants Consumption and Polymer Degradation
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis presents a study of antioxidant depletion in water containing chlorinated species (water containing 10 ppm either Cl2 or ClO2, buffered to pH = 6.8), the degradation products in the aqueous phase, and polyethylene pipe degradation scenarios. A low molecular weight hydrocarbon analogue (squalane) was used instead of solid polyethylene as the host material for the antioxidants, and the depletion of antioxidants has been studied. The phenolic antioxidant Irganox 1010 was consumed ca. 4 times faster in water containing 10 ppm ClO2 than in water containing 10 ppm Cl2. The different degradation products in extracts from the aqueous phase identified by infrared, liquid chromatography and mass spectrometry revealed the different degradation mechanisms between ClO2 (" cleavage) and Cl2 (hydrogen substitution). The squalane test shows no energy barrier between 30 and 70 °C, and the activation energy of the antioxidant in solid PE was found to be ca. 21 kJ mol-1. A linear relationship has been established between the time to reach antioxidant depletion in the polyethylene tape samples and the time to reach depletion in samples based on squalane containing the same antioxidants. The surface oxidation and surface embrittlement of PE tape on long time exposure have been studied by IR and SEM. Pressure testing on medium density PE pipes with a controlled pH aqueous media (6.8 ± 0.2) containing 4 ppm either ClO2 or at 90 °C showed that the stabilizers were rapidly consumed towards the inner pipe wall and the rate of consumption in ClO2 was 4 times greater than in Cl2 solution. The subsequent polymer degradation was an immediate surface reaction. It was confirmed by differential scanning calorimetry, infrared spectroscopy and size exclusion chromatography that, in the surface layer which came into contact with the oxidizing medium, the amorphous component of the polymer was heavily oxidized leaving a highly crystalline powder with many carboxylic acid chain ends in extended and once-folded chains.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2013. p. 61
Series
Trita-CHE-Report, ISSN 1654-1081
Keywords
Antioxidants, Polyethylene pipes, Chlorine dioxide, Degradation
National Category
Engineering and Technology
Identifiers
urn:nbn:se:kth:diva-116562 (URN)978-91-7501-533-0 (ISBN)
Public defence
2013-02-01, D3, Lindstedtsvägen 5, KTH, Stockholm, 14:02 (English)
Opponent
Supervisors
Funder
Formas
Note

QC 20130122

Available from: 2013-01-22 Created: 2013-01-21 Last updated: 2013-01-22Bibliographically approved

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