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Plasticizer loss in a complex system (polyamide 12): Kinetics, prediction and its effects on mechanical properties
KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Fibre- and Polymer Technology.ORCID iD: 0000-0001-7165-793X
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2019 (English)In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 169, no 108985Article in journal (Refereed) Published
Abstract [en]

Plasticizer migration is a major concern for plasticized polymers because it leads to unwanted changes in mechanical properties and, in many cases, contamination of the environment. In cases of slow migration, it is of practical importance to be able to perform accelerated testing and estimate migration rates from high temperature experiments. Despite the importance, a critical evaluation of different ways of extrapolating mass loss data has hitherto not been reported. Therefore, in this article, three different methods (involving for the first time a master-curve approach to mass loss data) to estimate low temperature migration from high temperature data are presented and critically evaluated. The system chosen was a plasticized polyamide 12 pipe, an important component in vehicle fuel-line systems. This system was challenging since the lower part of the temperature range in which the material is used overlaps with the glass transition region. All three methods (using data at 80–145 °C) over-estimated, although to different extents, the low-temperature mass loss rate (60 °C). The main reason for the over-estimation was the partial overlap with the glass transition region. Hence, there is a built-in safety factor when predicting plasticizer loss over glass transition regions, and the predictions are conservative. It was observed that plasticizer loss and annealing effects were the main reasons for changes in mechanical properties (increase in flexural stiffness/strength) during ageing.

Place, publisher, year, edition, pages
Elsevier, 2019. Vol. 169, no 108985
Keywords [en]
Plasticizer, Polyamide, Migration, Diffusion, Evaporation, Ageing, Prediction, Safety factor
National Category
Engineering and Technology
Research subject
Fibre and Polymer Science
Identifiers
URN: urn:nbn:se:kth:diva-260433DOI: 10.1016/j.polymdegradstab.2019.108985ISI: 000501397500007Scopus ID: 2-s2.0-85072653914OAI: oai:DiVA.org:kth-260433DiVA, id: diva2:1355592
Note

QC 20200110

Available from: 2019-09-30 Created: 2019-09-30 Last updated: 2020-01-10Bibliographically approved
In thesis
1. Ageing behavior of plastics used in automotive fuel systems
Open this publication in new window or tab >>Ageing behavior of plastics used in automotive fuel systems
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The increase in service temperature and the use of biobased fuels, such as biodiesel, have raised concerns on the short/long-term performance of plastic components used in automotive fuel systems.

In this work the ageing behavior of unreinforced and glass-fibre reinforced polyamide 12 (PA12), exposed to three different fuels (petroleum diesel, biodiesel, and a mixture of these (80/20)) at high temperature, was investigated. The interactions between the polymer and the fuel, and the associated polymer ageing mechanisms (fuel uptake, extraction of monomer and oligomers, annealing and oxidation), were found to be “generic” in the sense that they occurred, although to various extent, for all fuels. In the glass-fibre reinforced polyamides, the ageing occurred mainly in the polyamide matrix and not in the matrix-fibre interface. The semi-aromatic polyamide showed better performance when exposed to fuels than the aliphatic PA12.  

At a component level, multilayer polyamide-based pipes, with polyamide or fluoropolymer as inner layer, were aged under “in-vehicle” conditions where the pipes were exposed to fuel on the inside and to the air on the outside. All pipes stiffened during ageing but embrittlement occurred only for the pipes with polyamide being the inner layer. Compared to polyamide, the fluoropolymer inner layer showed significantly better barrier properties towards the fuel and no material was extracted into the fuel. The plasticizer loss from the PA12 outer layers into air was diffusion controlled and its diffusivity followed a linear Arrhenius behavior in the high temperature region. Relationships between plasticizer loss and the changes in mechanical properties were established.

The polyamides experienced diffusion-limited oxidation when exposed to air and/or fuel, involving the formation of a thin oxidized surface layer which was responsible for a significant decrease in strain-at-break. 

The fracture behavior of PA 6 in air at high temperature, found to involve three distinct stages, were systematically studied and linked to underlying mechanisms responsible for the reduction in strain-at-break.

Abstract [sv]

En ökning i servicetemperatur och användning av biobaserade drivmedel, t.ex. biodiesel, har väckt frågeställningar om hur detta påverkar egenskaperna på kort och lång sikt hos plastkomponenter som används i fordonsbränslesystem.

I detta arbete har egenskaperna undersökts hos oförstärkt och glasfiberarmerad polyamid 12 (PA12), utsatt för tre olika bränslen (petroleumdiesel, biodiesel och en blandning av dessa (80/20)) vid hög temperatur. Interaktionen mellan polymeren och bränslet och tillhörande åldringsmekanismer hos polymeren (bränsleupptag, extraktion av monomer och oligomer, anlöpning och oxidation) befanns vara "generiska" i den mening att de inträffade, dock i olika grad, för alla bränslen. För glasfiberarmerad polyamid skedde åldrandet huvudsakligen i polyamid-matrisen och inte i gränsskiktet mellan matris och fiber. Semi-aromatisk polyamid visade bättre prestanda än alifatisk PA12 när dessa utsattes för bränslena.

På komponentnivå åldrades flerskikts-polyamid-baserade rör, med polyamid eller fluorpolymer som inre skikt, under ”fordons-lika förhållanden” med bränsle på insidan och luft på utsidan. Alla rör förstyvades under åldrandet men en försprödning inträffade endast för rören med polyamid som inre skikt. Jämfört med polyamiden uppvisade det inre skiktet av fluorpolymer betydligt bättre barriäregenskaper gentemot bränslet och inget material extraherades ut i bränslefasen. Mjukgöraravgången från ytterskikten av PA12 i kontakt med luft var diffusionsstyrd och följde ett linjärt Arrhenius-beteende i högtemperatur-området. Sambanden mellan mjukgöraravgång och förändringar i de mekaniska egenskaperna fastställdes.

Polyamiderna genomgick diffusionsbegränsad oxidation när de utsattes för luft och/eller bränsle, vilket resulterade i bildandet av ett tunt oxiderat ytskikt, vilket i sig bidrog till en avsevärd sänkning i brottöjning.

Brott-beteendet hos PA6 i luft vid hög temperatur studerades systematiskt, vilket ledde till att underliggande mekanismer som var ansvariga för minskningen av brottöjningen i tre distinkta stadier, kunde tas fram.

 

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 65
Series
TRITA-CBH-FOU ; 2019:51
Keywords
Automotive, Ageing, Polyamide, Diesel, Biodiesel, Diffusion, Oxidation, Plasticizer migration, Mechanical properties, Fracture behavior., Fordon, Åldrande, Polyamid, Diesel, Biodiesel, Diffusion, Oxidation, Mjukgöraravgång, Mekaniska egenskaper, Brottegenskaper
National Category
Polymer Technologies
Identifiers
urn:nbn:se:kth:diva-260472 (URN)978-91-7873-320-0 (ISBN)
Public defence
2019-10-25, F3, Lindstedtsvägen 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 2019-10-01

Available from: 2019-10-01 Created: 2019-09-30 Last updated: 2020-02-07Bibliographically approved

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Wei, Xin-FengHedenqvist, Mikael S.

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