Surface functionalization of medical-grade polyvinyl chloride treated with ammonia plasma

Abstract

Polyvinyl chloride (PVC) is often the material of choice for the synthesis of various components used in medical practice, particularly catheters. As-synthesized components may not exhibit appropriate biocompatibility, so the surface should be modified or coated. Amine groups were grafted onto the PVC surface by brief exposure to ammonia plasma generated by a low-pressure inductively coupled radiofrequency discharge in E mode (30 Pa, 25 W). The treatment time ranged from 0.5 to 300 s. The measured density of charged particles was approximately 2 ± 1 × 1015 m−3 and the flux of NH and NH<inf>2</inf> radicals was approximately 3 × 1023 m−2s−1. X-ray photoelectron spectroscopy (XPS) was used to study the evolution of nitrogen-containing functional groups versus the treatment time. The chlorine concentration was not affected much, but the nitrogen concentration in the surface film increased logarithmically with increasing treatment time. The N concentration was approximately 2 at.% after 0.5 s of treatment and reached approximately 9 at.% after 300 s. Some PVC samples were also pretreated with hydrogen plasma. The pretreatment was beneficial for rapid functionalization, as the N concentration reached 6 at.% after 0.5 s of plasma treatment, but the concentration after prolonged treatment was the same as that for a single-step ammonia plasma treatment. High-resolution XPS Cl2p spectra revealed significant modification of the chlorine binding, especially after pretreatment with hydrogen plasma. A possible explanation for this modification is the formation of Cl− binding states, resulting from bond scission by the absorption of VUV radiation in the PVC surface film.