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Assessing the Long-­term Performance of Polyethylene Stabilised WithPhenolic Antioxidants Exposed to Water Containing Chlorine Dioxide
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymeric Materials.
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2013 (English)In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 32, no 2, 359-365 p.Article in journal (Refereed) Published
Abstract [en]

The addition of chlorine dioxide disinfectant to tap water prevents the spread of infection but has a serious drawback in that it degrades materials used in piping, including pipes made of polyethylene. Efficient methods are required to assess the long-term performance of different combinations of antioxidants and polyethylene grades. We have previously presented a screening method which exposes solutions of phenolic antioxidants in squalane (a liquid, low molar mass analogue of polyethylene) to 70 °C water containing either chlorine dioxide or chlorine. This method assesses the stability of the antioxidants towards these aqueous chlorinated media by determining the oxidation induction time through differential scanning calorimetry. The same experimental set-up with two modifications was used in developing a new method. A 0.3 mm thick polyethylene tape replaced the squalane phase and the supply of fresh water containing chlorine dioxide (10 ppm at pH = 6.8) was continuous; this required minimum attention from the operator over the longer exposure time periods used. Tapes of medium-density polyethylene containing 0.1 wt.% of six different phenolic antioxidants were studied. A linear relationship was established between the times to reach antioxidant depletion in the polyethylene tape samples and the times in the squalane samples (with the same antioxidants at the same concentration). A linear relationship was also found between the initial antioxidant consumption rates in polyethylene and squalane. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion.

Place, publisher, year, edition, pages
2013. Vol. 32, no 2, 359-365 p.
Keyword [en]
Polyethylene, Phenolic antioxidants, Chlorine dioxide
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-104734DOI: 10.1016/j.polymertesting.2012.12.003ISI: 000316513300026Scopus ID: 2-s2.0-84872131697OAI: oai:DiVA.org:kth-104734DiVA: diva2:566823
Funder
Formas, 245-2007-473
Note

Updated from submitted to published. QC 20130122

Available from: 2012-11-09 Created: 2012-11-09 Last updated: 2017-12-07Bibliographically approved
In thesis
1. Preparation and long-term performance of poly(ethylene-co-butyl acrylate) nanocomposites and polyethylene
Open this publication in new window or tab >>Preparation and long-term performance of poly(ethylene-co-butyl acrylate) nanocomposites and polyethylene
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The current study discusses the preparation and long-term performance of polymer composites used for various purposes under different ageing conditions.

The first part deals with the preparation and characterization of polymer nanocomposites based on poly(ethylene-co-butyl acrylate) (EBA–13 and EBA–28 with 13 and 28 wt % butyl acrylate, respectively) and 2–12 wt % (0.5–3 vol %) of aluminum oxide nanoparticles (two types with different specific surface areas and different hydroxyl-group concentrations; uncoated and coated with, respectively, octyltriethoxysilane and aminopropyltriethoxysilane). The nanocomposite with EBA–13 showed better overall nanoparticle dispersion while EBA–28 resulted in poor dispersion, probably due to insufficiently high shear forces acting during extrusion mixing which were unable to break down nanoparticle agglomerates.

The activity of hindered phenolic antioxidant (0.2 wt%) in all EBA nanocomposites was assessed by determining the oxidation induction time using DSC. The composites containing uncoated aluminium oxide nanoparticles showed a much shorter initial OIT than the pristine polymer with the same initial concentration of antioxidant, indicating adsorption of antioxidant onto the nanoparticle surfaces. Composites containing coated nanoparticles showed a significantly smaller decrease in the initial OIT, suggesting the replacement of hydroxyl groups with organic silane tails, decreasing the concentration of available adsorption sites on the nanoparticle surfaces. The decrease in OIT with increasing ageing time in dry air at 90 °C of the nanocomposites was slower than

that of the unfilled pristine polymer, suggesting a slow release of antioxidant from adsorption sites.

The EBA nanocomposites exposed to liquid water at 90°C showed faster decrease of OIT than samples exposed to dry or humid air. The migration rate of antioxidant was controlled by the boundary conditions in the case of ageing in humid air and liquid water. The antioxidant diffusivity was lower for the composites containing uncoated ND than for the composites containing ND coated with octyltriethoxysilane or aminopropyltriethoxysilane.

The migration and chemical consumption of deltamethrin DM, (synthetic pyrethroid) and synergist piperonyl butoxide from molded polyethylene sheets was also studied. Deltamethrin and piperonyl butoxide are often used for food  storage and insect control purposes. DM showed no signs of crystallization and remained in a liquid state after being cooled to room temperature. Exposure of polyethylene compound sheets to liquid water (at 80 & 95 °C), caused degradation and hydrolysis of the ester bond in the DM, present in the prepared material, and generated species containing hydroxyl groups. Liquid chromatography and infrared spectroscopy showed a significant migration of the active species in liquid water, whereas in air at 80 °C (60 and 80 %RH) the loss of DM and PBO was negligible over 30 days.

The long-term performance of medium-density polyethylene stabilized with six different phenolic antioxidants (0.1 wt%) in aqueous chlorinated media at 70 °C was studied. The results were compared with data for previously studied solutions of antioxidants in squalane (a liquid, low molar mass analogue of polyethylene). A linear relationship was established between the time to reach antioxidant depletion in polyethylene tape samples and the time in squalane samples. Infrared spectroscopy and scanning electron microscopy of drawn samples revealed the onset of surface oxidation and surface embrittlement in tape samples exposed beyond the time for antioxidant depletion.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2012. 57 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2012:44
Keyword
Polymer nanocomposite, nanoparticles, aluminium oxide, poly(ethylene-co-butyl acrylate), long-term performance, ageing, antioxidant, OIT, aqueous media, silanization, irganox 1010, deltamethrin, piperonyl butoxide, chlorine dioxide, migration of stabilizer
National Category
Polymer Technologies
Research subject
SRA - Production
Identifiers
urn:nbn:se:kth:diva-104685 (URN)978-91-7501-491-3 (ISBN)
Public defence
2012-11-30, Entreplan (F3), Lindstedtsvägen 26, KTH, Stockholm, 13:00 (English)
Opponent
Supervisors
Projects
Cable insulation materialsLoss of deltamethrin and pipronyl butoxide from polyethylenelong-term performance of polyethylene in chlorine dioxide water
Funder
Swedish Research CouncilXPRES - Initiative for excellence in production research
Note

QC 20121109

Available from: 2012-11-09 Created: 2012-11-09 Last updated: 2013-04-19Bibliographically 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. 61 p.
Series
Trita-CHE-Report, ISSN 1654-1081
Keyword
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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