Change of notch impact strength depending on radiation dose and test temperature

The main purpose of this paper has been determine the effect of radiation crosslinking on the notch impact strength of polyamides filled with fiberglass. These properties were examined in dependence on the dosage of the ionizing beta radiation (non-irradiated samples and those irradiated by dosage 66 and 132 kGy were compared) and on the test temperature (23 – 150 oC).


Introduction
The modification of polymer properties by irradiation is constantly evolving area. Ionic and ionizing radiation are the main types of radiation which are used for the polymer modification. Gamma radiation created from radioactive isotope Co-60 (60Co) belongs to ionizing radiation as well as beta radiation (electron beam) and X-ray radiation. All of these types significantly differ, however during these all process the energy transfer to atoms of irradiated material occurs [1][2][3][4][5][6]. As stated in previous investigations [6][7][8][9][10][11][12][13][14][15][16], it is possible to effectively change physical, mechanical and biological properties of irradiated material by ionizing radiation. These changes are probably caused by primary and secondary processes which are created due to interaction of ionizing radiation with polymer [1,2]. The crosslinking level can be adjusted by irradiation dosage and often by means of a crosslinking booster. The main difference between electron beta and photon gamma is in their different abilities of penetrating the irradiated material. Gamma rays have a high penetration capacity. The penetration capacity of electron rays depends on the energy of the accelerated electrons. Due to accelerated electron the required dose may be applied for seconds, whereas several hours are required on the gamma radiation plant. The electron accelerators operate on the principle of the Braun tube, whereby a hot cathode is heated in vacuum to such a degree that electrons are released [17][18][19][20][21]. This study deals with the influence of different doses of ionizing beta radiation (66 and 132 kGy) on notch impact strength of polyamides under thermal loading and follows previous studies [3,5,7,9,10], which described the change of mechanical properties of selected types thermoplastics. The previous study [3,5,7,9,10] proved the positive irradiation effect on mechanical of selected types polymers. Nevertheless, some findings are not explained yet, namely the change of dynamic properties during the application of beta radiation on material under thermal loading. Each new finding on the effect of radiation crosslinking on the properties of polymer materials may thus contribute to a better understanding of the issue and can extend the field of new applications.

Materials
For this experiment two types polyamides were used. Both materials are filled with glass fibers and their commercial names are: -Polyamide 66 GF 30 -V -PTS -CREAMID A3H7.2G 6*M0129A Schwarz -Polyamide 7T GF 56 -V -DURAMID TH7 G12.0SZB*9207 The basic properties of used materials are shown in Table 1 and 2.   In the case of test temperature 23 ºC the highest value of notch impact strength was achieved by the irradiation with dose of 132 kGy and the highest value of maximum force was achieved by the irradiation with dose 66 kGy (referring to: Fig. 1). In the case of test temperature 50 ºC the highest value of notch impact strength and maximum force was achieved at non-irradiated samples (referring to: Fig. 2). In the case of test temperature 75 ºC the highest value of notch impact strength was achieved at non-irradiated samples and the highest value of maximum force was achieved by the irradiation with dose 66 kGy (referring to: Fig. 3). In the case of test temperature 100 ºC the highest value of notch impact strength was achieved at non-irradiated  Fig. 4). In the case of test temperature 125 ºC the highest value of notch impact strength was achieved at non-irradiated samples and the highest value of maximum force was achieved by the irradiation with dose 132 kGy (referring to: Fig. 5). In the case of test temperature 150 ºC the highest value of notch impact strength was achieved at non-irradiated samples and the highest value of maximum force was achieved by the irradiation with dose 132 kGy (referring to: Fig. 6).

Notch impact strength -PA 7T GF 56
Comparison of notch impact strength and maximum force (at 23, 50, 75, 100, 125, and 150 ºC) of PA 7T GF 56 before and after irradiation is given in the Figures 7 to 12.  In the case of test temperature 50 ºC the highest value of notch impact strength and maximum force was achieved by the irradiation with dose of 132 kGy. The value of notch impact strength increased from 20.7 kJ/m 2 (nonirradiated samples) to 22.9 kJ/m 2 (dose of 132 kGy), which is a hike of approximately 10 % (referring to: Fig.  8).
In the case of test temperature 75 ºC the highest value of notch impact strength and maximum force was achieved by the irradiation with dose of 132 kGy. The value of notch impact strength increased from 27.2 kJ/m 2 (nonirradiated samples) to 32.2 kJ/m 2 (dose of 132 kGy), which is a hike of approximately 18 % (referring to: Fig.  9). In the case of test temperature 100 ºC the highest value of notch impact strength and maximum force was achieved by the irradiation with dose of 66 kGy. The value of notch impact strength increased from 34.9 kJ/m 2 (non-irradiated samples) to 36.7 kJ/m 2 (dose of 66 kGy), which is a hike of approximately 5 % (referring to: Fig.  10). In the case of test temperature 125 ºC the highest value of notch impact strength and maximum force was achieved by the irradiation with dose of 66 kGy. (referring to: Fig. 11). In the case of test temperature 150 ºC the highest value of notch impact strength and maximum force was achieved by the irradiation with dose of 66 kGy. (referring to: Fig. 11).

Conclusion
This article describes the effect of radiation crosslinking on the notch impact strength of polyamides (with glass fiber filler) under thermal stress. Changes due to irradiation were seen primarily in material with higher content of filler (PA 7T GF 56).