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Degradation of polyethylene pipes distributing chlorinated water: depletion of stabilizers, release of degraded products and polymer degradation
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
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. , 38 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:10
Keyword [en]
polyethylene pipes, chlorine dioxide, degradation
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-31469ISBN: 978-91-7415-859-5 (print)OAI: oai:DiVA.org:kth-31469DiVA: diva2:404266
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
List of papers
1. A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media
Open this publication in new window or tab >>A new method for assessing the efficiency of stabilizers in polyolefins exposed to chlorinated water media
2009 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 28, no 6, 661-667 p.Article 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.

Keyword
Polyolefins, Antioxidants, Chlorinated water media, polyethylene pipes
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-18713 (URN)10.1016/j.polymertesting.2009.05.010 (DOI)000269295200014 ()2-s2.0-67650087904 (Scopus ID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2017-12-12Bibliographically approved
2. Deterioration of polyethylene pipes exposed to water containing chlorine dioxide
Open this publication in new window or tab >>Deterioration of polyethylene pipes exposed to water containing chlorine dioxide
Show others...
2011 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 96, no 5, 790-797 p.Article in journal (Refereed) Published
Abstract [en]

Chlorine species used as disinfectants in tap water have a deteriorating effect on many materials including polyethylene. There are only very few scientific reports on the effect on polyethylene pipes of water containing chlorine dioxide. Medium-density polyethylene pipes stabilized with hindered phenol and phosphite antioxidants were pressure tested with water containing 4 ppm chlorine dioxide at 90 degrees C and pH = 6.8 as internal medium. The stabilizers were rapidly consumed towards the inner pipe wall; the rate of consumption was four times greater than in chlorinated water (4 ppm, pH = 6.8) at the same temperature. The depletion of stabilizer occurred far into the pipe wall. A supplementary study on a polymer analogue (squalane) containing the same stabilizer package showed that the consumption of the phenolic antioxidant was 2.5 times faster when exposed water containing chlorine dioxide than on exposure to chlorinated water. 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 oxidising 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. Scanning electron microscopy showed that propagation of cracks through the pipe wall was assisted by polymer degradation.

Keyword
polyethylene pipes, chlorine dioxide, degradation
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-31465 (URN)10.1016/j.polymdegradstab.2011.02.009 (DOI)000290078200009 ()2-s2.0-79953673200 (Scopus ID)
Note

QC 20110316 Uppdaterad från submitted till published (20110523).

Available from: 2011-03-16 Created: 2011-03-16 Last updated: 2017-12-11Bibliographically approved
3. Characterization of degradation products from a phenolic antioxidant in squalane exposed to chlorinated aqueous media
Open this publication in new window or tab >>Characterization of degradation products from a phenolic antioxidant in squalane exposed to chlorinated aqueous media
(English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321Article in journal (Other academic) Submitted
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-31468 (URN)
Note
QS 20120328Available from: 2011-03-16 Created: 2011-03-16 Last updated: 2017-12-11Bibliographically approved

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