Impact of polymer processing on sorption of benzaldehyde vapor in rubbery polypropylene

With the increasing usage of polymers as food and pharmaceutical packaging materials, more information is needed on the barrier properties of these packaging materials. The organic barrier property of polypropylene (PP) was studied in this project. A continuous gravimetric method was developed to study the sorbate uptake and sorption kinetics of benzaldehyde vapor in rubbery PP resin, sheet and polyhedron thermoformed container by using a SGA-100R gravimetric analyzer including Rubotherm magnetic suspension microbalance at 25°C, 0% RH. Solubility coefficients for benzaldehyde sorption in PP resin, sheet and container were determined based on the equilibrium uptake. Diffusion coefficients were also calculated on PP resin and sheet in the Fickian diffusion region. The experimental results demonstrated that the polymer conversion process had a great impact on the mass transfer properties of PP. The sorption of benzaldehyde in the PP polyhedron container was twice that of the sorption in PP sheet at lower vapor activities, and the sorption in sheet was almost three times the sorption of the resin at higher vapor activities. The sorption dynamics among the PP forms were different from each other. This finding emphasizes the need to assess mass transfer of formed polymer sheets or containers to accurately determine the barrier properties of packaging systems.