Surface properties of polylactide and hydroxyapatite-based composite materials treated with low-temperature plasma streams

In this work, new unique composite materials based on polylactic acid with hydroxyapatite are being studied, the effect of surface treatment of low-temperature plasma on which has not been previously studied. The purpose of this work is to study the effect of argon flow glow discharge low-temperature atmospheric plasma treatment with pulse durations of 1 /us and 5 /us on the surface physicochemical properties of polylactic acid (PLA) and composite based on polylactic acid and hydroxyapatite with mass ratio of components 70/30 (PLA/HA). In the surface layers in the process of interaction with the plasma, complex physicochemical processes occur that can significantly change the structure and surface properties of materials. The phase composition of surface was investigated by X-ray analysis, and topographic analysis of the sample surface structure was performed by scanning electron microscopy. To estimate wettability of the surface, the sessile drop method was used. According to X-ray analysis, in the initial sample of the PLA and after plasma treatment, there are peaks characteristic of the structure of the L -isomer of polylactic acid. The diffraction patterns of the PLA/HA 70/30 composite contain diffraction lines characteristic of both polylactic acid and hydroxyapatite. The appearance of new reflexes and the shift of diffraction lines is not observed, which indicates the preservation of the chemical composition and crystallographic identity of the initial components after surface modification. It was established that the degree of crystallinity of the PLA samples after low-temperature plasma treatment increases from 68% to 83%, and the PLA/HA 70/30 composite increases from 76% to 82%. According to SEM, low-temperature plasma treatment contributes to an increase in the imperfection, the formation of pores on the surface of PLA and developed surface relief of the composite PLA/HA 70/30. A decrease in the contact angle of all materials is observed, which indicates intense oxidative processes occurring in the surface layers of modified samples, accompanied by an increase in the proportion of high-energy surface adsorption centers. In addition, surface energy increase is observed due to an increase in the polar component and a decrease in the dispersion component of surface energy for the materials after low-temperature plasma treatment. The maximum value of the total surface energy (75 mN/m) is observed for both materials when processed by low-temperature plasma with a pulse duration of 5 /s. An increase in the surface ene rgy of materials indicates an improvement in the adhesive properties of materials.

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