Review on the production process and uses of controlled rheology polypropylene—Gamma radiation versus electron beam processing

Controlled rheology polypropylene grades are established commodities in the polymer processing market. However, new types, mainly the so-called high melt strength polypropylene (HMSPP) grades, are being introduced in the last two decades and radiation processing has played an important role. The melt strength properties of a polymer increases with molecular weight and with long-chain branching due to the increase in the entanglement level. As polypropylene (PP) is a linear polymer, the way to improve its elongational viscosity is by the production of a bi-modal polymer. Basell's patents claim the production of long-chain branching on PP by irradiating with electrons under oxygen free atmosphere, followed by two heating steps to allow radical recombination and annihilation reaction. Some other companies have issued patents using electron beam processing, but so far there is no actual production other than the Basell one. As a result of a research joint effort, IPEN, BRASKEM (the biggest Brazilian polymer producer) and EMBRARAD (the major Brazilian radiation processing center) developed a new process to produce HMSPP based on gamma processing. This paper will address some characteristics of each technology and the main industrial opportunities.