Swelling of polyethylene particles and its relation to sorption equilibria under gas‐phase polymerization conditions

The attempts to predict the swelling of semicrystalline polyolefins using equations of state have not been successful so far and the few conducted experimental investigations have been limited to a narrow range of samples and conditions. This article presents a systematic video‐microscopic study of the swelling induced in various grades of PE particles by the sorption of ethylene and co‐monomers (propylene, 1‐hexene) at condition relevant to gas‐phase polymerization. Based on experimental data for various PE densities, the swelling factor H was evaluated, which enables the prediction of PE swelling by ethylene. The swelling data were compared with the corresponding gravimetrically measured sorption isotherms. In the case of ethylene and propylene sorption, the swelling significantly influences the evaluation of sorption isotherms. Conversely, the effect of swelling was negligible for higher hydrocarbons. The observed impact of swelling on the sorption is discussed based on the evaluated partial molar volumes of penetrants. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45035.