PRÜFEN UND MESSEN – PMA 2017 TESTING AND MEASURING – PMA 2017

30 KGK · 05 2018 www.kgk-rubberpoint.de

Polyamide 11 (PA 11) micro hardness mechanical properties surface layer β-irradiation FTIR WAXS

The influence of beta radiation on changes in the structure and selected (mechanical and thermal) properties of polymers was proved. The use of low beta radiation doses for polyamide 11 (PA 11) and their influence on the chan-ges of mechanical properties of surface layers has not yet been studied in detail so far. The specimens of PA 11 were ma-de using injection moulding technology and these were irradiated by low doses of beta radiation (0, 132, 165 and 198 kGy). The changes in the microstructure and micromechanical properties of sur-face layer were evaluated using FTIR, WAXS and the instrumented micro-hardness test. The results of the measu-rements showed considerable changes in the mechanical properties.

Der Effekt von Beta-Strahlung auf die mechanischen Eigen-schaften der Oberflächen von spritzgegossenen Polyamid 11 (PA 11) Polyamide 11 (PA 11) Mikrohärte Me-chanische Eigenschaften Oberflächen-schichten β-Strahlung FTIR WAXS

Der Einfluss von Betastrahlung auf die Änderung der Struktur und ausgewähl-ter Eigenschaften (mechanische und thermische) von Polymeren ist unter-sucht worden. Der Einsatz von niedri-gen Dosen an Betastrahlung gegenüber Polyamid 11 (PA 11) und der Einfluss auf die mechanischen Eigenschaften der Oberflächenschichten ist bisher im Detail nicht untersucht worden. Die Probekörper aus PA 11 wurden im Spritzguss hergestellt und mit niedri-gen Dosen an Betastrahlung bestrahlt (0, 132, 165 und 198 kGy). Die Ände-rungen in der Mikrostruktur und der mikromechanischen Eigenschaften der Oberfläche wurden mit FT-IR, WAXS und Mikrohärte-Test untersucht. Die Messergebnisse zeigten eine beträchtli-che Änderung der mechanischen Eigen-schaften (Eindruckhärte, Härte, elasti-scher Modul (Indentation)) bei der Be-strahlung mit Betastrahlen.

Figures and Tables: By a kind approval of the authors

1. IntroductionPolyamides form a particularly interest-ing class of materials in terms of their thermal transition behavior. With few exceptions, the glass transition tempera-tures (T g) for polyamides are independ-ent of the type of polyamide and the length of the paraffinic segment and oc-cur in the range of 40–60 °C. The inde-pendence of the chain length implies the importance of the hydrogen-bonded amide groups and the minor role of the methylene chain mobility in determining the transition temperature. Some stud-ies have performed thorough studies of the effect of processing conditions on the T g of polyamide 11, measured by thermal analysis. Anomalous behavior was noted in terms of aging behavior and annealing treatments. The magni-tude of the T g endotherm increased with aging time as did the position of the T g, the latter moved into the 35–140 °C range. Additionally, annealing treatments at 75°C shifted the endotherm to ≈ 92 °C; followed by aging treatments that pro-duced a second transition back at 40 °C. The free N–H stretching vibration, which absorbs in the 3500–3400 cm−1 region of the infrared spectrum, was used to pos-tulate that the effect of aging and an-nealing treatments on the T g are expli-cable in terms of the slow formation of a hydrogen bonded network in the amor-phous regions. The fact that the mobility of the paraffin segments in the amor-phous regions begins at temperatures well below the T g (≈ −120°C), supports the primary role of amide groups in the T g phenomenon. The explanation pro-posed by Gordon of a disruption of the amorphous hydrogen bonded network to account for the existence of a time and temperature dependent T g seems reasonable in view of the data [1].

The irradiation cross-linking of ther-moplastic materials via electron beam or cobalt 60 (gamma rays), proceeds sepa-rately after processing. The cross-linking level can be adjusted by the irradiation dosage, and often - by means of a cross-

linking booster. The main deferences be-tween β - and γ - rays lie in their differing abilities to penetrate the irradiated ma-terial. γ - rays have a high penetration capacity. The penetration capacity of electron rays depends on the energy of the accelerated electrons.

The thermoplastics used for the pro-duction of various types of products have very different properties. Standard poly-mers - which are easy obtainable with favourable price conditions belong to the main class. The disadvantage of standard polymers is limited by their mechanical and thermal properties. The standard polymer group is the largest, and its share in the production of all polymers is as high as 90%.

Engineering polymers are a very im-portant group that offer much better properties, in comparison to those of standard polymers. Both mechanical and thermal properties are much better than is the case for standard polymers. Pro-duction of these types of polymers repre-sents less than 1 % of all polymers. [1-6].

High performance polymers have the best mechanical and thermal properties - but their share in the production and use of all polymers is less than 1 %.

The present work deals with the influ-ence of beta irradiation on the mechani-cal properties of the surface layer of in-jection moulded polyamide 11 (PA 11).

This article is dedicated in memoriam, to Assoc. Prof. David Manas.

Effect of Beta Irradiation on mechanical Properties of Surface Layer of Injection Moulded Poly-amide 11

AuthorsDavid Manas, Pavel Stoklasek, Miroslav Manas, Ales Mizera, Katarina Tomanova, Lenka Hylova, Zlin, Czech Republic

Corresponding Author:CSc., Assoc. Prof Miroslav Manas Tomas Bata UniversityNam. TGM 5555, 760 01 ZlinCzech RepublicE-Mail: manas@fai.utb.cz

PRÜFEN UND MESSEN – PMA 2017 TESTING AND MEASURING – PMA 2017

31KGK · 05 2018www.kgk-rubberpoint.de

2. Experiment

2.1. MaterialPolyamide 11 V-PTS CREAMID-11T* M600/13 was used for this experiment. Irradiation was carried out by the com-pany BGS Beta Gamma Service, GmbH & Co, KG, Saal an der Donau, Germany; us-ing electron rays, electron energy of 10 MeV, minimum doses of 0, 132, 165 and 198 kGy on air by the ambient tem-perature [4,6,14].

2.2. Samples preparationThe samples were made using injection moulding technology on an Arburg All-rounder 420C injection moulding ma-chine. The processing temperature range was 210–240°C, at a mold temperature of 50°C, injection pressure 80 MPa, injec-tion rate 50 mm/s [5, 13].

2.3. Micro-hardnessInstrumented micro-hardness tests were performed using a MicroCombi Tester, CSM Instruments (Switzerland), according to the CSN EN ISO 14577-1. Load and un-load speed was 1 N/min. After a holding time of 90 s at maximum load of 0.5 N the specimens were unloaded. The indenta-tion hardness HIT was calculated as maxi-mum load to the projected area of the hardness impression according to:

pIT A

FH max= (1)

SFhhc

maxmax ε−= (2)

Where, hmax is the indentation depth at Fmax; and hc is the contact depth. In this study, the Oliver and Pharr Method was used in order to calculate initial stiffness and contact depth (hc). The specimens were glued onto metallic sample holders [8, 14].

2.4. Wide-angle X-ray scatteringWide-angle X-ray diffraction patterns were obtained using a PANalytical X´Pert PRO X-ray diffraction system (The Neth-er-lands). The CuKα radiation was Ni-fil-tered. The scans (4.5° 2 Θ/min), in the reflection mode, were taken in the range of 5–30° 2 Θ. The sample crystallinity (X), was calculated from the ratio between the crystal diffraction peaks and the total scattering areas.

The crystall size L110 of α with its most intensive peak at 110 was calculat-ed using the Scherrer equation. As a standard „perfect“ crystal terephthalic

acid with the peak at 2 Θ = 17.4° and the half maximum breadth 0.3 ° 2 Θ was chosen [4-9].

2.5. Fourier transformed infrared spectroscopy (FTIR)The infrared Spectra were measured by means of ATR technology – single reflec-tion ATR - (GladiATR, PIKE Technologies); which was equipped with a diamond crystal a refractive index of 2.4 and im-pact angle 45°). The spectra were meas-ured using an FTIR spectrometer Nicolet 6700 FTIR

(Thermo Nicolet Instruments Co., Madison, USA), blown with dry air. The spectra were measured at the definition of 2 cm-1 and 64 scans. A pure ATR dia-mond crystal was used for the back-ground while ATR correction was used for spectra adjustment. Manipulation of the spectra was done using OMNIC Soft-ware 8.2. Each specimen was measured twice (2 times), on each side [10-14].

3. Results

3.1. Micro hardnessThe development of micro-mechanical properties of irradiated polyamide 11 (PA

11) was characterized by the instrument-ed micro hardness tests, as can be seen in Fig. 1. The highest values (132 MPa) of indentation hardness (HIT), were found at 132 kGy radiation dose, while the low-est value of indentation hard-ness (124 MPa) was measured on a non-irradiated polyamide 11 (PA 11). The increase of in-dentation hardness at 132 kGy radiation dose was by 6 % compared to the non-irradiated polyamide 11 (PA 11). A similar development was recorded for micro stiffness of specimens represented by the elastic modulus of indentation (EIT) illustrated in Fig. 2. The measurement results clearly show that the lowest mi-cro-stiffness values were measured on the non-irradiated polyamide 11 (PA 11) (1.83 GPa), while the highest values were reached in polyamide 11 (PA 11) irradi-ated by 165 kGy dose (1.91 GPa). A sig-nificant increase of micro stiffness (4%) was recorded at the radiation dose of 165 kGy compared to the non-irradiated polyamide 11 (PA 11). Material deforma-tion in time under constant stress (in-dentation creep) measured by instru-mented test of micro hardness showed (Fig. 3) that the highest creep values were measured on the non-irradiated

Fig. 1: Indentation hardness HIT of PA 11 vs. irradiation doses.

1

Fig. 2: Indentation elastic modulus EIT of PA 11 vs. irradiation doses.

2

PRÜFEN UND MESSEN – PMA 2017 TESTING AND MEASURING – PMA 2017

32 KGK · 05 2018 www.kgk-rubberpoint.de

polyamide 11 (PA 11) (7.34 %), while the lowest creep value was found in the poly-amide 11 (PA 11) irradiated by a dose of 165 kGy (6.44 %). The creep Factor dropped by 13 % as a result of radiation, which represents a considerable increase of surface layer resistance. Plastic (Wplast) and elastic (Welast) deforma-tion measured during micro hardness test also showed (Fig. 4) that the lowest values were measured at the radiation dose of 132 kGy (Wpl) and 132 kGy (Wel),

while the highest values were found in the non-irradiated polyamide 11 (PA 11). This was also confirmed (Fig. 4) by the results of measurements of reverse re-laxation co-efficient (ηIT).

Radiation, which penetrated through specimens, gradually formed cross-link-ing (3D net), first in the surface layer and then in the total volume, which resulted in considerable changes in specimen be-havior. The 3D net together with crystal-line phase caused changes mainly in the

surface layer, which led to a significant increase of the indentation hardness and micro stiffness of surface layer. This caused the higher resistance of this sur-face layer to wear, scratch, etc. Also, the creep values decreased as a result of changes made after the specimens were subjected to beta radiation.

3.2. Wide-angle X-ray scatteringThe figure 5 and show the typical X-ray diffraction spectrum of the non-irradiat-ed and irradiated polyamide 11 (PA 11). There is an apparent presence of α-phase in the non-irradiated specimen. The greatest growth of the α-phase is seen at the radiation dose of 66 kGy (Fig. 5).

When applying β-radiation the poly-propylene structure undergoes loss and then a grow of the crystalline phase (Table 1). It can be assumed that the size of indi-vidual crystals will correspond with the loss of crystalline phase (crystalline value X calculated lay in the range 35-47%). The greatest size of crystalline phase was found in the case at non-irradiated (47%). The lowest size of crystalline phase was found in the case at the radiation dose of 165 kGy (35%). Its influence on the me-chanical behavior is insignificant. Cross-linking occurs in the remaining non crys-talline part which has a significant influ-ence on the mechanical properties of the surface layer. Its influence on the me-chanical behavior is insignificant.

3.3. Fourier transformed infrared spectroscopy (FTIR)The infrared spectroscopy, IR, is the ver-satile method to follow chemical modifi-cations in a polymeric material. Studies carried out by some researchers [2,3] presented the formation of carbonyl groups.

The results of the infrared spectrosco-py showed changes in the relative repre-sentation of hydroxyl and carbonyl groups in relation to the radiation dose (Fig. 6). For evaluation of the hydroxyl groups pur-poses, we used an area, based on a strip integrated in the area of 3570-3006 cm-1, (Each specimen was measured twice on both sides). For evaluation carbonyl groups we used an area of the strip inte-grated in the area of 1768-1483 cm-1, (Each specimen was measured twice on both sides). When the specimen is irradi-ated, it leads to oxidation on C-H bonds and formation of oxygenic functional groups.

The smallest relative change values representation of hydroxyl and carbonyl

Fig. 3: Indentation creep CIT of PA 11 vs. irradiation doses

3

Fig. 4: Deformation work of PA 11 vs. irradiation doses.

4

Fig. 5: X-ray diffraction of non-irradiated and irradiated PA 11.

5

PRÜFEN UND MESSEN – PMA 2017 TESTING AND MEASURING – PMA 2017

33KGK · 05 2018www.kgk-rubberpoint.de

1 Table 1: X-ray diffraction of non-irra-diated and irradiated PA 11Sample X X-ray, %, ± 1 %0 kGy 47132 kGy 38165 kGy 35

198 kGy 43

groups was found at a radiation dose of 0 and 198 kGy. At this dose the poorer val-ues of mechanical properties of the sur-face layer of the tested polyamide 11 (PA 11) were measured. The greatest change was found at radiation dose of 132 and 165 kGy. These doses showed the best values of the mechanical properties of the surface layer of the tested polyamide 11 (PA 11) sample - as measured.

These changes of the structure corre-spond with the changes of mechanical properties of the modified polyamide 11 (PA 11) by beta radiation.

4. ConclusionThis experimental study has shown that polyamide 11 (PA 11) - modified by beta radiation doses of 0, 132, 165 and 198 kGy showed considerable increases in some mechanical properties of surface layers. In mechanical properties terms, the surface layer indentation hardness values increased by 6 % at a radiation dose of 132 kGy, surface the micro layer surface stiffness by 4% (165 kGy). Micro creep values dropped in irradiated poly-amide 11 (PA11) from 7.34% to 6.44% (165 kGy).

Products made from polyamide 11 (PA 11) by injection moulding methods have a great importance for industry. Their use is mainly extensive in automobile indus-try. Better mechanical properties of sur-face layer of polyamide 11 (PA 11) greatly extends the area of its application. High values of micro hardness and micro stiff-ness extends the area of application of PA 11. It can be used mainly when high resistance to wear and scratch is re-quired. Such resistance values would be hard to achieve in standardly produced PA 11.

AcknowledgementThis paper is supported by the internal grant of TBU in Zlin No. IGA/FT/2017/010 funded from the resources of specific university research and by the Ministry of Education, Youth and Sports of the Czech Republic within the National Sus-tainability Programme project No. LO1303 (MSMT-7778/2014) and also by

the European Regional Development Fund under the project CEBIA-Tech No. CZ.1.05/2.1.00/03.0089. Special thanks also to Dr. Michal Danek (BGS Beta Gam-ma Service GmbH & Co, KG, Germany) for his kind assistance during sample preparation.

References[1] Hsin Her Yu. Vibrational spectroscopic study

of the thermal transition behavior in poly-amide 11, Materials Science and Engineer-ing: A Volume 254, Issues 1-2, 15 October 1998, 53.

[2] Woods RJ, Picaev AK. Applied radiation chemistry: radiation processing. New York: John Wiley, 1994.

[3] Silverstein RM, Bassler GC, Morril TC. Spec-trometric identication of organic com-pounds. New York: John Wiley, 1980.

[4] Chvatalova, L. Navratilova, J., Cermak, R., Raab, M., Obadal, M. 2009. Joint Effects of Molecular Structure and Processing History on Specific Nucleation of Isotactic Polypro-pylene. Macromolecules 42, 7413.

[5] Manas, D., Hribova, M., Manas, M., Ovsik, M., Stanek, M., Samek, D., 2013. The effect of be-ta irradiation on morfology and micro hard-ness of polypropylene thin layers. Thin Solid Films Volume 530, 49.

[6] Manas, D., Manas, M., Stanek, M., Danek, M., 2008. Improvement of plastic properties. Arch. Mater. Sci. Eng. 32 (2), 69.

[7] Shukushima, S., Hayami, H., Ito, T., Nishimoto, S.I., 2001. Modification of radiation cross-linked polypropylene. Radiation Physics and Chemistry 60 (4-5), 489.

[8] Oliver, W.C., Pharr, G.M., 1992 An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation. J. Mater. Res. 7 (6), 1564.

[9] Lalande, A., Gardette, D., 2004. Influence of the structure on the g-irradiation of polypro-

pylene and on the post-irradiation effects. Nucl. Instrum. Methods Phys.Res. B 222, 187.

[10] Oliani, W.L., Lima, L.F.C.P., Parra, D.F., Dias, D.B., Lugao, A.B., 2010. Study of the mor-phology, thermal and mechanical proper-ties of irradiated isotactic poly- propylene films. Radiat. Phys. Chem. 79, 325.

[11] Otaguro, H., Lima, L.F.C.P., Parra, D.F., Lugao, A.B., Chinelatto, M.A., Canevarolo, S.V., 2010. High-energy radiation forming chain scis-sion and branching in polypropylene. Radi-at. Phys. Chem. 79, 318.

[12] Ovsik, M., Manas, D., Manas, M., Stanek, M., Hribova, M, Kocman, K., Samek, D., 2012. Ir-radiated Polypropylene Studied by Micro-hardness and WAXS. Chemicke listy Volume 106, S507.

[13] Ragan, E., Baron, P., Dobránsky, J., 2012. Sucking machinery of transport for dosing granulations of plastics at injection mould-ing. Advanced Materials Research 383, 2813.

[14] Manas, D., Manas, M., Chvatalova, L.,Stanek, M., Bednarik, M., Mizera, A., 2014. Effect of low doses beta irradiation on thermal, mi-cro and macro mechanical properties of ir-radiated polypropylene. Radiation Physics and Chemistry 102, 171.

Fig. 6: Change in the relative representation of hydroxyl and carbonyl groups of PA 11 in relation to the irradiation doses.

6