Crystallinity and Hardness Enhancement of Polypropylene using Atmospheric Pressure Plasma Discharge Treatment

Atmospheric pressure plasma was used to treat polypropylene (PP) surfaces.Optical emission spectroscopy (OES) was used to determine the chemical species formed in the plasma as well as the electron temperature and density of the plasma.The flux of species (O and OH) produced during the plasma treatment interact with the polymer surface creating polar groups on the PP surface, which were evaluated by X-ray, Raman, and Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) analyses.Moreover, the thermal properties of PP were investigated by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) analysis.The plasma treatment increased the crystallite size and microhardness.This enhanced effect was produced from high concentrations of O and OH that induced functional polar groups containing C-O, C=O, and C=O-OH bonds appended to the PP surface.The polar groups produced by the air plasma can be attributed primarily to the oxygen radicals in the air plasma hitting the PP surface and to heat-induced oxidation rather than the incorporation of oxygen radicals or UV-induced oxidation from the plasma.The increase in hardness is attributed to the introduction of carbonyl and hydroxyl groups, cross-linking, annealing effects, and chemical etching.