Polypropylene film surface modification for improving its hydrophilicity for innovative applications

Organic polymeric materials, especially polyolefins, contain mainly C and H atoms and thus present serious surface problems due to low surface energy and reactive inertness. Using method developed in this work it is possible to convert the H atoms of the polypropylene (PP) film surface into polar groups by treatment with a mixture of chromic, sulphuric, and phosphoric acids in a short time at elevated temperature. Hydroxyl and carboxyl groups on the surface of materials not only determine their chemical and physical properties, but also provide reactive centers for various applications. Optical microscopy (OM) and atomic force microscopy (AFM) analyses have shown that induced surface modification of the PP film causes mainly physical changes, creating microcraters and surface roughness and hence increasing surface tension, while X-ray diffraction (XRD) analysis has confirmed the absence of phase changes. The attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy analysis has confirmed the grafting of polar groups, such as hydroxyl, carboxyl, and carbonyl onto the surface of the PP. This indicates that used mixture destroyed or at least broke down to some extent the covalent bonds of the main carbon skeletons, which were present on PP substrate surfaces and improved surface wettability and zeta potential. The simultaneous thermal analysis (thermogravimetry (TG) and differential scanning calorimetry (DSC)) results have shown that the presence of polar groups in the PP-[O] film samples affects the melting and decomposition temperatures; they are higher than those of PP film. The change in the enthalpy of melting indicated a change in the surface energy. The band gap (Eg) determined from diffuse reflectance spectra in the UV-visible region by the Kubelka-Munk method has decreased for modified PP films, and they have become more suitable for optoelectronics.