Supercritical carbon dioxide-assisted solid-state free radical grafting of methyl methacrylate onto polypropylene

The work reported in this paper was aimed at exploring the advantages of using supercritical carbon dioxide (scCO2) as an environmentally benign solvent and swelling agent for carrying out the free radical grafting process of vinyl monomers onto isotactic polypropylene (PP) in the solid state. Methyl methacrylate (MMA) was chosen as a grafting monomer. Results showed several scientifically interesting and industrially relevant advantages of the scCO2-assisted solid-state grafting process over a classical solid-state or melt process. First, compared to a classical solid-state grafting process the overall reaction rate of the scCO2 assisted one became less diffusion-controlled and more reaction-controlled because of enhanced diffusion of MMA and the initiator in the PP. Second, the CO2 pressure itself constituted an additional and sensitive process parameter capable of significantly modifying the monomer grafting yield and the product quality. Third, the scCO2-assisted solid-state process produced much higher MMA grafting contents and longer MMA grafts than the classical solid-state and melt processes did.