Abstract
By means of X-ray computed microtomography (XCMT), the existence of a developed porous structure with an average pore diameter of ~3.5 μm and pore content of ~1.1 vol.% has been revealed in unirradiated polytetrafluoroethylene (PTFE). It has been found that the combined action of gamma radiation (absorbed dose per PTFE of ~170 kGy) and high temperatures (327–350 °C) leads to the disappearance of the porous structure and the formation of several large pores with sizes from 30 to 50 μm in the bulk of thermal-radiation modified PTFE (TRM-PTFE). It has been established by X-ray diffraction (XRD) analysis that the thermal-radiation modification of PTFE leads to an increase in the interplanar spacings, the degree of crystallinity and the volume of the unit cell, as well as to a decrease in the size of crystals and the X-ray density of the crystalline phase in comparison with the initial polymer. It is assumed that the previously-established effect of improving the deformation-strength and tribological properties of the TRM-PTFE can be due not only to the radiation cross-linking of polymer chains but also to the disappearance of the pore system and to the ordering of the crystalline phase of PTFE.
Highlights
The study of changes in the microstructure and structure of the crystalline phase of PTFE caused by the combined action of γ-radiation and high temperatures has provided the following conclusions: (i) The existence of a developed porous structure with an average pore diameter of
~3.5 μm and a pore volume content of ~1.1% in PTFE has been revealed by the technique of X-ray computed microtomography
The thermal-radiation modification of PTFE leads to the disappearance of the porous structure and the formation of several large pores with sizes from 30 to 50 μm
Summary
High-temperature radiation modification of polytetrafluoroethylene (PTFE) is a promising method for overcoming the disadvantages of this material-such as cold brittleness, porosity, and low radiation resistance [1,2]. It was found [3,4,5,6] that the combined action of various types of ionizing radiation (γ-radiation, electrons of different energies) and temperatures exceeding the melting point of polymer crystallites can improve the tribological and deformation-strength characteristics of PTFE, change its spectral-luminescent properties, and increase the radiation resistance. The conclusion about the occurrence of radiation-induced cross-linking processes during irradiation of PTFE melt is made mainly on the basis of measurements of the deformation-strength and/or tribological characteristics of the thermal-radiation modified polymer [1,2,3,4,5,6]
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