M. OVSIK et al.: INFLUENCE OF APPLIED ELECTRON RADIATION ON THE PROPERTIES ...
345–347
INFLUENCE OF APPLIED ELECTRON RADIATION ON THE
PROPERTIES OF A POLYAMIDE 11 SURFACE LAYER
VPLIV OBSEVANJA Z ELEKTRONI NA LASTNOSTI POVR[INSKE
PLASTI POLIAMIDA 11
Martin Ovsik
*
, Petr Fluxa, Michal Stanek, Adam Dockal, Martin Reznicek
Tomas Bata University in Zlín, Vavre~kova 275, 760 01 Zlín, Czech Republic
Prejem rokopisa – received: 2019-07-15; sprejem za objavo – accepted for publication: 2019-12-23
doi:10.17222/mit.2019.155
This article deals with the influence of the radiation cross-linking of polyamide 11 (PA 11) on the mechanical properties. The
aim of this study is to provide more detailed knowledge of the relation between the radiation dosage and the properties of
cross-linked PA 11 and its mechanical behaviour. Electron-beam-unmodified and modified PA 11 test samples were exposed to
electron radiation with dosages from 0 kGy to 198 kGy, which were graded at 33 kGy. The surface-layer properties of the
modified PA 11 were tested using a state-of-the-art indentation technique, which detects the immediate change in the
indentation depth, depending on the applied force. The evaluation of the measured mechanical properties (indentation hardness,
modulus and creep) was done by the Oliver and Pharr method. A significant influence of the radiation cross-linking on the PA
11’s mechanical properties improvement was confirmed by the measurements. This enhancement grows with the increasing
radiation dosage. Due to the electron-radiation modification of PA 11, the mechanical properties of the surface layer were
increased by up to 59 % compared with the unaltered material. Radiation crosslinking is an important thermoplastic
modification method by which the desired properties can be achieved in a relatively short period of time. The main advantage is
that the process is executed on the final product.
Keywords: polyamide, radiation, mechanical properties, indentation hardness
V ~lanku avtorji opisujejo vpliv obsevanja pre~no zamre`enega poliamida 11 (PA11) na mehanske lastnosti. [tudija naj bi
zagotovila bolj natan~en vpogled v poznavanje povezav med dozo obsevanja in lastnostmi pre~no zamre`enega PA 11 ter
njihovim vplivom na mehanske lastnosti. Analizirali so originalne neobsevane vzorce in vzorce PA 11, obsevane s snopom
elektronov z dozami med 0 in 198 kGy v stopnjah po 33 kGy. Lastnosti povr{inske plasti obsevanih vzorcev PA 11 so testirali z
najmodernej{o indentacijsko tehniko, ki takoj zazna spremembe indentacijske (vdorne) globine v odvisnosti od uporabljene sile
vtiskovanja trna (indenterja) v preiskovani material. Avtorji ~lanka so ovrednotili rezultate izmerjenih mehanskih lastnosti
(nanotrdoto, modul in lezenje) z Oliver in Phaar metodo. Rezultati meritev so pokazali pomemben vpliv obsevanja pre~no
zamre`enega PA 11 na mehanske lastnosti. S pove~ano stopnjo obsevanja so se izbolj{evale mehanske lastnosti. Zaradi
obsevanja P11 z elektroni so se mehanske lastnosti povr{inske plasti izbolj{ale za do 59 % v primerjavi z vzorci, ki niso bili
obsevani. Pre~no zamre`enje zaradi obsevanja z elektroni je pomembna metoda termoplasti~ne modifikacije, ki lahko hitro
izbolj{a oz. modificira lastnosti povr{ine izbranega materiala. Pomembna prednost je v tem, da lahko proces izvedemo na
kon~nih izdelkih.
Klju~ne besede: poliamid, obsevanje, mehanske lastnosti, nanotrdota
1 INTRODUCTION
In general, polyamides have medium durability to
ionizing radiation. This durability, for the polyamide
types –CONH-(CH
2
)n-, decreases with the increasing
number of the methyl groups in between the peptide
links. As a result of sample irradiation, a process of
cross-linking as well as fission commences. For most of
the polyamides, the cross-linking process is prevalent,
although, the process of network construction is not very
strong. According to K. Kaindl and E. H. Graul,
1
free
radicals begin to form within the structure during
irradiation. Simultaneously, radicals are created around
the C=N and C=C double bonds. According to K. Kaindl
and E. H. Graul
1
a radiation dosage of 350 kGy with
oxygen present incites the creation of gel. When the
irradiation occurs in a vacuum, the cross-linking process
is prevalent, which leads to changes that improve the
mechanical properties.
Adding a poly-functional monomer, e.g., triallyl iso-
cyanurate (TAIC), enables the polyamides to begin the
cross-linking process after being exposed to relatively
low dosages of radiation, when the oxygen is present.
Finding out the correct dosages for the improvement of
the selected mechanical properties is the goal of this
research paper. First, hydrogen bound to the carbon
neighbouring with the nitrogen of the amide group is
split, leading to the creation of water, carbon monoxide,
carbon dioxide and methane. Three allyl groups of TAIC
can, due to the irradiation, react and create additional
bridges (network) in the polyamide structure.
2
2 EXPERIMENTAL PART
For this experiment, PA11 called V-PTS-CREAMID-
11T*M600/13 manufactured by PTS was used. To
Materiali in tehnologije / Materials and technology 54 (2020) 3, 345–347 345
UDK 67.017:669.058:544.543.1 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 54(3)345(2020)
*Corresponding author's e-mail:
ovsik@utb.cz (Martin Ovsik)

ensure the radiation induced cross-linking a cross-linking
agent triallyl isocyanurate (TAIC) in 5 % volume was
added. The samples were prepared by injection moulding
on an Allrounder 470E-type ARBURG injection-
moulding machine. The parameters of the machine were
set according to the recommendation of the manufac-
turer. The material that was used was pre-dried in
accordance with the instructions on an ARBURG
THERMOLIFT 100-2 device. The test samples were
prepared in a single-cavity mould in the shape of the
beam, in agreement with the ^SN EN ISO 179 standard.
The test samples were exposed to the radiation in
cooperation with company BGS Beta-Gamma-Service
GmbH & Co. KG in a high-voltage accelerator-type
Rhodotron. The radiation dosages were set to 33 kGy,
66 kGy and 99 kGy.
The mechanical properties of the surface layer were
measured by the depth sensing indentation (DSI) on an
ultra nano-indentation system (UNHT).
3
The parameters
were set to the following values: applied load 50 mN,
loading and de-loading speed 100 mN/min and load
duration 90 s. The measurements were made according
to the ^SN EN ISO 14577 standard and then evaluated
using the Oliver and Pharr method.
3
3 RESULTS
The indentation hardness and modulus of the PA11
modified by various dosages of radiation were measured
by the DSI. Each sample was measured 10 times and the
results were afterwards statistically evaluated.
4 DISCUSSION
As can be seen in Figure 1, the indentation hardness
was gradually increased due to the radiation cross-link-
ing, even at the lower dosages. The highest values were
measured in the material irradiated by a dose of 66 kGy,
in which the indentation hardness rose by 73 % in com-
parison to the unaltered material. It is noteworthy that
even the relatively low amounts of radiation (33 kGy)
increased the indentation modulus by 13 %. Additional
levels of radiation displayed only a minor increase in the
indentation hardness and modulus. In contrast, the use of
radiation dosages of 99 and higher kGy caused the
indentation modulus to decline. Considering the cost of
the irradiation, it is non-profitable to consider higher
dosages than 66 kGy for the indentation modulus.
As is evident from the measurements of the PA11
indentation elastic modulus at room temperature, the
modulus rose with the increasing radiation dosage
(Figure 2). The highest values of the indentation mo-
dulus were measured in the test samples irradiated by a
dosage of 66 kGy. This modulus was 37% higher in
comparison to the virgin material. Indeed, it can be said
that the radiation cross-linking had a positive influence
on the indentation modulus of the PA11. Radiation
dosages higher than 66 kGy displayed a decreasing trend
in the mechanical properties of the surface layer, which
could have been caused the material degradation induced
by the large amounts of radiation.
5 CONCLUSIONS
The measured data indicate that the most suitable
dosage of radiation for the chosen materials appears to
be 66 kGy. This value induced positive changes in the
mechanical properties for each observed test sample. The
improvements to the indentation hardness and inden-
tation modulus directly caused by the radiation cross-
linking are a desired result for some of the technical
applications. The best enhancements of the indentation
hardness were found in the test samples that were
irradiated with dosages of 33 kGy or 66 kGy. Radiation
dosages higher than these proved to significantly de-
crease the indentation modulus and indentation hardness
in the observed test samples. This decline could be
caused by the material degradation induced by the high
dosages of electron radiation.
M. OVSIK et al.: INFLUENCE OF APPLIED ELECTRON RADIATION ON THE PROPERTIES ...
346 Materiali in tehnologije / Materials and technology 54 (2020) 3, 345–347
Figure 2: Indentation modulus Figure 1: Indentation hardness

Acknowledgment
This work was supported by the European Regional
Development Fund under the project CEBIA-Tech
Instrumentation No. CZ.1.05/2.1.00/19.0376 and by the
Ministry of Education, Youth and Sports of the Czech
Republic within the National Sustainability Program
project no. LO1303 (MSMT-7778/2014). Moreover, it
was supported by the Internal Grant Agency of TBU in
Zlin: no. IGA/2020/003.
6 REFERENCES
1
K. Kaindl, E. H. Graul, Strahlenchemie, Dr. Alfred Hüttig Verlag,
Heidelberg, 1967
2
M. Ghidelli, M. Sebastiani, K. E. Johanns, Journal of the American
ceramic society, 100 (2017), 5731–5738
3
W. C. Oliver, G. M. Pharr, Measurement of hardness and elastic mo-
dulus by instrumented indentation, Journal of Materials Research, 19
(2004), 1564–1583
M. OVSIK et al.: INFLUENCE OF APPLIED ELECTRON RADIATION ON THE PROPERTIES ...
Materiali in tehnologije / Materials and technology 54 (2020) 3, 345–347 347