Quantitative and selective study of the effect of O radicals on polypropylene surface treatment

• Published in: Plasma sources science & technology 2023-07, Vol.32 (7), p.75013
• Main Authors: Du, Hao, Komuro, Atsushi, Ono, Ryo
• Format: Article
• Language: English
• Subjects: ATR-FTIR; O radicals; polypropylene; surface modification; water contact angle
• ISSN: 0963-0252; 1361-6595
• DOI: 10.1088/1361-6595/ace5d3

Gaining a comprehensive understanding of the mechanisms underlying plasma-polymer surface treatments using atmospheric pressure plasmas can guide their industrial applications. To this end, a novel vacuum ultraviolet photodissociation reactive species supply (VUV PRS) method, which can quantitatively supply the desired type of reactive species to polymer surfaces, was developed in our previous study. In this study, the innovative approach is used to quantitatively study the effects of O radicals on polypropylene (PP) surface treatment. Specifically, water contact angle (WCA), attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, and atomic force microscopy (AFM) are used to characterize the surface modification. The results show that the surface treatment is dominated by O radicals under the present experimental conditions. The surface modification rate, characterized by the WCA decline rate, is linearly correlated with the concentration of O radicals, that is (surface modification rate) = (8.1 ± 0.4)[O s ] + (0.13 ± 0.02) degrees s −1 , where [O s ] indicates the density of O radicals at PP surface (in ppm). The ATR-FTIR spectra shows that –OH and C=O functional groups are introduced onto the PP surface after the treatment, which results in a decrease in the WCA of the surface. Atomic force microscopy (AFM) analysis shows that the surface morphology of the treated PP remains almost unchanged. Low molecular weight oxidized materials (LMWOMs) on PP surface are generated when the O radical dose that arrives at the PP surface exceeds a certain threshold. More than 60% of the oxygen-containing functional groups exist as LMWOMs when the WCA saturates. The results presented in this paper indicate that the VUV PRS method has the potential to drive the understanding of plasma-polymer surface interactions at the atomic and molecular levels. Moreover, the measured roles of the O radicals on the polymer surface at atmospheric pressure can guide the industrial application of atmospheric pressure plasma treatment.