**4. Proton irradiation of PAs**

Compared to electron and γ-irradiation, there is far less information on proton beam irradia‐ tion in the scientific sources. One possible reason is that proton irradiation is used mostly in the medical domain for therapy and production of isotope-labeled pharmaceutical prepara‐ tions.

Currently, proton beam is used as a direct writing method using focused proton beam to decorate resistant polymers at the nanolevel. In comparison to electron beam, the proton writing offers a unique advantage consisting of the fact that proton penetrates materials more deeply, maintains a straight line, and makes three-dimensional structures with vertical and smooth walls as well as low roughness. This advantage is a consequence of a greater proton mass when compared to electron.

Unlike PAs, some works dealing with other polymers (PMMA, PDMS, fluorinated PI, PP, PTFE, PS, LDPE, PP, PET, and PVC) can be found. Semicrystalline PAs are not typical materials for optical or decorative purposes because of their nontransparency. Maybe this is why studies on PAs irradiated with proton beam are rare if not missing.

Concerning polymers, it is known that also protons affect the polymers mainly through scission and crosslinking of macromolecule chains. Solitary data on PA-6 irradiated by proton beam in air can be found in the paper dealing with Fourier transform infrared (FTIR) spectro‐ scopy comparison of electron with proton beam impact [50]. When irradiating the same PA-6 with an equal dose of 500 kGy, the proton beam generates less gel (57.5%) than the electron beam (67.6%). Therefore, the first DSC melting temperature is a little higher for a protonirradiated sample (217.6°C) than for an electron-irradiated one (216.9°C). Accordingly, the crystallinity for proton-irradiated PA-6 is slightly higher when compared to the corresponding electron-irradiated PA-6, but the difference in the mentioned thermal characteristics is marginal. FTIR spectroscopy shows some differences in the postirradiation species related to nonidentical gel formation. The proton beam irradiation results in a finer structure of some absorption bands, particularly in the range of 400 to 1650 cm-1, indicating the generation of structures that are more varied. The consequence is that the cleavage of PA-6 macromolecules by the proton beam produces fragments containing amine groups and terminal methyl groups, whereas the increase in concentration of these groups in electron-irradiated PA-6 appears to be insignificant in comparison to virgin PA-6. Based on the finding, besides crosslinking [Equation (11)] and oxidation degradation [Equations (13) and (14)], a possible parallel scenario can occur when proton beam interacts with PA:

a) Unsaturated structures formation:

$$\text{[}\text{-CO}-\text{NH}-\text{(CH}\_2\text{)}\_8-\text{]}\_\text{a} \xrightarrow{\text{-2H}^+} \text{[}-\text{CO}-\text{NH}-\text{CH}\_2-\text{CH}=\text{CH}-\text{CH}\_2-\text{CH}\_2-\text{]}\_\text{a} \tag{15}$$

The double bond can occur between any carbons within the ethylene segments.

b) Amine species formation:

**4. Proton irradiation of PAs**

280 Radiation Effects in Materials

mass when compared to electron.

on PAs irradiated with proton beam are rare if not missing.

scenario can occur when proton beam interacts with PA:

2H

o


25 n <sup>2</sup> 2 2 [ CO NH (CH ) ] [ CO NH CH CH CH CH CH ]*<sup>x</sup>*


The double bond can occur between any carbons within the ethylene segments.

a) Unsaturated structures formation:

tions.

Compared to electron and γ-irradiation, there is far less information on proton beam irradia‐ tion in the scientific sources. One possible reason is that proton irradiation is used mostly in the medical domain for therapy and production of isotope-labeled pharmaceutical prepara‐

Currently, proton beam is used as a direct writing method using focused proton beam to decorate resistant polymers at the nanolevel. In comparison to electron beam, the proton writing offers a unique advantage consisting of the fact that proton penetrates materials more deeply, maintains a straight line, and makes three-dimensional structures with vertical and smooth walls as well as low roughness. This advantage is a consequence of a greater proton

Unlike PAs, some works dealing with other polymers (PMMA, PDMS, fluorinated PI, PP, PTFE, PS, LDPE, PP, PET, and PVC) can be found. Semicrystalline PAs are not typical materials for optical or decorative purposes because of their nontransparency. Maybe this is why studies

Concerning polymers, it is known that also protons affect the polymers mainly through scission and crosslinking of macromolecule chains. Solitary data on PA-6 irradiated by proton beam in air can be found in the paper dealing with Fourier transform infrared (FTIR) spectro‐ scopy comparison of electron with proton beam impact [50]. When irradiating the same PA-6 with an equal dose of 500 kGy, the proton beam generates less gel (57.5%) than the electron beam (67.6%). Therefore, the first DSC melting temperature is a little higher for a protonirradiated sample (217.6°C) than for an electron-irradiated one (216.9°C). Accordingly, the crystallinity for proton-irradiated PA-6 is slightly higher when compared to the corresponding electron-irradiated PA-6, but the difference in the mentioned thermal characteristics is marginal. FTIR spectroscopy shows some differences in the postirradiation species related to nonidentical gel formation. The proton beam irradiation results in a finer structure of some absorption bands, particularly in the range of 400 to 1650 cm-1, indicating the generation of structures that are more varied. The consequence is that the cleavage of PA-6 macromolecules by the proton beam produces fragments containing amine groups and terminal methyl groups, whereas the increase in concentration of these groups in electron-irradiated PA-6 appears to be insignificant in comparison to virgin PA-6. Based on the finding, besides crosslinking [Equation (11)] and oxidation degradation [Equations (13) and (14)], a possible parallel

$$\begin{aligned} \left[ \text{-CO}-\text{NH}-(\text{CH}\_{2})\_{5}-\right]\_{\text{a}} & \leadsto \left[ \text{-C}^{\prime}\text{O}-\text{HN}^{\prime}-(\text{CH}\_{2})\_{5}-\right]\_{\text{y}} \\ \xrightarrow{\text{+2H}^{+}} \text{y} & \sim \text{-CHO} + \text{ y} \,\text{H}\_{2}\text{N}-(\text{CH}\_{2})\_{5}-\sim \end{aligned} \tag{16}$$

c) Both methyl-ended and shorter amide chain formation:

$$\begin{aligned} \text{[-CO-NH-(CH\_2)-(CH\_2)\_4-]}\_{\text{at}} & \sim [-\text{CO-N}^\circ\text{H}-\text{C}^\circ\text{H}\_2-(\text{CH}\_2)\_4-]\_\text{t} \\ & \rightarrow \text{z} \sim -\text{CO}-\text{NH}\_2 + \text{z}\,\text{CH}\_3-(\text{CH}\_2)\_4-\sim \end{aligned} \tag{17}$$

The processes reflect some differences also in tensile properties as seen in **Table 4**.


**Table 4.** Relative changes of selected tensile properties for PA-6 irradiated by electron (PA-6/EB) and proton (PA-6/PB) beams in air towards properties of nonirradiated PA-6.

A thorough comparison of the advantages versus disadvantages of the proton beam irradiation in comparison to other radiation technologies in the domain of PAs cannot be concluded unless more data are available.
