materials
Article
Properties of Polyethylene Terephthalate (PET) after
Thermo-Oxidative Aging
Robert Panowicz
1
, Marcin Konarzewski
1,
* , Tomasz Durejko
2
, Mateusz Szala
2
, Magdalena Lazi ´ nska
2
,
Magdalena Czerwi ´ nska
3
and Piotr Prasula
3
Citation: Panowicz, R.; Konarzewski,
M.; Durejko, T.; Szala, M.; Lazi´ nska,
M.; Czerwi ´ nska, M.; Prasula, P.
Properties of Polyethylene
Terephthalate (PET) after
Thermo-Oxidative Aging. Materials
2021, 14, 3833. https://doi.org/
10.3390/ma14143833
Received: 23 June 2021
Accepted: 7 July 2021
Published: 8 July 2021
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1
Institute of Mechanics and Computational Engineering, Faculty of Mechanical Engineering,
Military University of Technology, 2,Gen. Kaliskiego Str., 00-908 Warsaw, Poland;
robert.panowicz@wat.edu.pl
2
Institute of Materials Science and Engineering, Faculty of Advanced Technologies and Chemistry,
Military University of Technology, 2,Gen. Kaliskiego Str., 00-908 Warsaw, Poland;
tomasz.durejko@wat.edu.pl (T.D.); mateusz.szala@wat.edu.pl (M.S.); magdalena.lazinska@wat.edu.pl (M.L.)
3
Military Institute of Armament Technology, Prym. S. Wyszynskiego 7 Str., 05-220 Zielonka, Poland;
czerwinskam@witu.mil.pl (M.C.); prasulap@witu.mil.pl (P.P.)
* Correspondence: marcin.konarzewski@wat.edu.pl
Abstract: The influence of the thermo-oxidative aging semi-crystalline polyethylene terephthalate
process on the thermal and mechanical properties was analysed in the article. For this purpose,
PET was aged at 140
◦
C for 21, 35 and 56 days. The research showed that as a result of aging, the
amount of the crystalline phase increases by about 8%, which translates into the properties of the
aged material. The glass transition and melt temperature of lamellar crystals formed during first and
second crystallisation increase with aging. The mechanical properties of the material were analysed
in the temperature range of 25 to 75
◦
C. The tests were showing an increase in Young’s modulus and
a decrease in elongation at the break as a result of aging. This phenomenon was particularly visible
during tests at 75
◦
C and during the morphological observation of the fracture surface, where the
fracture character of the material changes from ductile to brittle. In the case of the material aged for
the longest time, the temperature has a negligible influence on the elongation at break.
Keywords: aging resistance; PET; thermo-oxidation aging; thermal and mechanical properties
1. Introduction
Polyethylene terephthalate (PET) is one of the most popular thermoplastic polymers
and is used primarily for the production of clothing fibres, tanks, bottles and also as a
construction material. The annual production of this material in 2016 was 50.01 MMT [1]
and it is forecast to rise to 87.16 MMT by 2022.
Amorphous PET is used for the production of bottles and packaging due to its high
transparency, which is very similar to that of glass. In other cases, a semi-crystalline state
of polymer is used, which has a milky white colour and is opaque.
Due to such factors as good mechanical properties (abrasion resistance, dimensional
stability-creep resistance, easy processing of details and their surfaces, high impact strength)
even at low temperatures (<−70
◦
C), low water absorption and resistance to inorganic chem-
icals, PET is widely used in a variety of industries (machine, automotive, electromechanical,
electronic). High resistance to various environmental factors along with an absence of
harmful low molecular weight substances make it widely used in applications where it
comes into contact with food (food industry, food packaging, household appliances).
The change in the properties of PET, as well as that of other polymers, is often
influenced by the environment, causing its properties to degrade mainly through random
scission of the polymer chains. Depending on the environmental conditions, thermal,
thermo-oxidative, chemical, radiative, biochemical and hydrolytic degradation processes
Materials 2021, 14, 3833. https://doi.org/10.3390/ma14143833 https://www.mdpi.com/journal/materials