Development of Degradable Polypropylene by Radiation Grafting and Blending with Polylactic Acid

Abstract

Simultaneous radiation grafting was optimized to graft acrylic acid monomer on the polypropylene (PP) films to make them hydrophilic and enhance their biodegradability. Experiments were designed based on full factorial central composite design (response surface methodology) and influence of monomer concentration, radiation dose, inhibitor concentration, sulfuric acid concentration on degree of grafting was investigated. The extent of grafting was found to increase with increasing monomer concentration, inhibitor concentration and radiation dose. Different degrees of grafted PP were used for different applications. 35% grafted PP was chosen as our optimum grafted material due to desirable tensile strength (above 20 MPa) for packaging application. The targeted 35% grafting could be achieved at the optimum conditions - monomer concentration 12.09 wt%, radiation dose 12.40 kGy, inhibitor concentration 0.07 M and sulfuric acid concentration 0.12 M. The grafted PP films at different degrees of grafting were tested for tensile properties and characterized by swelling test, Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). Successful grafting of acrylic acid onto PP films was indicated by FTIR and confirmed quantitatively by determination of carboxylic groups on the film surface. Tensile strength of grafted PP films decreased with increase in degree of grafting. The crystallinity of the grafted films was lower than that of PP film as indicated by DSC studies. Grafting of acrylic acid increased the roughness on the surface of PP films indicated by SEM studies. Thermal stability and degradation behavior of acrylic acid grafted polypropylene (PP-g-AAc) films were investigated by using thermogravimetric analysis (TGA) at four different heating rates 5, 10, 15 and 20 °C/min over a temperature range of 40 to 550 °C in nitrogen atmosphere.