Hydrophilization of Polypropylene by Gaseous Plasma Treatments and Hydrophobic Recovery

Although polypropylene (PP) is among the most widely used polymers with adequate chemical and mechanical properties, its poor wettability prevents adhesive joints needed for sticking with other materials, printing, etc. Plasma treatment, an established method for increasing wettability, is presented, and relevant literature is analyzed. A comparison of different reviewed articles shows little influence of the discharge parameters on PP wettability, and that the methods for achieving a super-hydrophilic surface of this polymer have yet to be developed. The peculiarities of PP prevent stable surface functionalization, although the formation of molecular fragments is the predominant effect of plasma treatments. The key conclusion after analyzing the reviewed literature is that the washing of PP following plasma treatment will cause a low level of wettability regardless of the peculiarities of the plasmas or discharges, including the treatment time, and all authors reported a water contact angle between about 75 and 80° after washing the plasma-treated PP. The hydrophobic recovery of washed plasma-treated PP was not addressed in any reviewed article.