Nano-Mechanical Properties of Surface Layers of Polyethylene Modified by Irradiation

Abstract

This study’s goal was to describe the influence of a wide range of ionizing beta radiation upon the changes in surface layer mechanical properties and structural modifications of selected types of polymer. Radiation crosslinking is a process whereby the impingement of high-energy electrons adjusts test sample structures, thus enhancing the useful properties of the material, e.g., hardness, wear-resistance, and creep, in order that they may function properly during their technical use. The selected polymers tested were polyolefin polymers like polyethylene (Low-density polyethylene LDPE, High-density polyethylene HDPE). These samples underwent exposure to electron radiation of differing dosages (33, 66, 99, 132, 165, and 198 kGy). After the crosslinking process, the samples underwent testing of the nano-mechanical properties of their surface layers. This was done by means of a state-of-the-art indentation technique, i.e., depth-sensing indentation (DSI), which detects the immediate change in the indentation depth associated with the applied force. Indeed, the results indicated that the optimal radiation dosage increased the mechanical properties by up to 57%; however, the beneficial levels of radiation varied with each material. Furthermore, these modifications faced examination from the structural perspective. For this purpose, a gel test, Raman spectroscopy, and crystalline portion determination by X-ray all confirmed the assumed trends.

Polyamide Surface Layer Nano-Indentation and Thermal Properties Modified by Irradiation

“…There are cross-linking actions that happen sequentially in all cases [ 1 ]: Dimensions and polydispersion grow in the first phase. At a certain point, the reaction reaches a gel point in which the molar weight increases beyond all limits and the gel starts to appear in the system.…”

“…After removing the residual xylene, the cross-linked extract was dried for 8 h, in a vacuum, at 100 °C. The dried and cooled residue was weighed again with a precision of five decimal places and compared to the original weight of the sample [ 1 ]. The result is stated in percentage as the degree of cross-linking: where, G i is the degree of cross-linking of each specimen expressed in percent; m 1 is the weight of the cage and lid in milligrams; m 2 is the total weight of the original specimen, cage, and lid in milligrams; and m 3 is the total of the weight of the residue of specimen, cage and lid in milligrams.…”

“…The thermo-mechanical properties were measured using a Perkin-ElmerDMA 7e thermal analyzer (Waltham, MA, USA) which was used for the thermo-mechanical analysis, heated from 50 to 400 °C (depending on the material used) at 20 °C/min, and held for 1 min at 50 °C. This precise temperature resistance evaluation of the polymers (e.g., irradiated, cross-linked polymers) records the displacement of the probe with a loading of 160 mN, which penetrates into the heated material, in a set range of temperatures [ 1 ].…”

“…Although sources focusing on the description of the process are abundant, their scope and complexity do not meet the necessary complexity threshold for a broader understanding. Furthermore, the currently available information about ionized radiation interaction with thermo-mechanical properties is insufficient, and a thorough study of this topic is required [1].…”

“…The mixture's extraction duration was 24 h. Then, the solutes were separated by distillation. After removing the residual xylene, the cross-linked extract was dried for 8 h, in a vacuum, at 100 • C. The dried and cooled residue was weighed again with a precision of five decimal places and compared to the original weight of the sample [1]. The result is stated in percentage as the degree of cross-linking:…”