A facile approach to modify polypropylene flakes combining O2-plasma treatment and graft polymerization of l-lactic acid

Modification of polypropylene (PP) surface with poly(l-lactic acid) (PLLA) via a facile approach was described. The PP flakes were first treated with O2 plasma and then grafted with l-lactic acid (LLA) monomer in the aqueous solution. The attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS) were employed to probe the surface composition and morphology of the flakes. Water contact angle measurements were used to monitor the change in hydrophilicity of PP flake surface, and tensile strength tests were carried out to monitor the mechanical properties of PP flakes along the treatment procedure. It was found that the PLLA grafting degree increases reasonably with the reaction temperature. At the same time, a grafting polymerization of 6 h of l-lactic acid at 160 °C can lead to obvious IR absorption. PLLA-grafted polypropylene (PP-g-PLLA) was eventually obtained. The higher reaction temperature can bring the detrimental influences to the mechanical properties of PP flakes.