Use of a magnetic suspension microbalance to measure organic vapor sorption for evaluating the impact of polymer converting process

A gravimetric analyzer consisting of a magnetic suspension balance was set up to study the sorption kinetics of benzaldehyde in various forms of polypropylene (PP), including resin, sheet and thermoformed container. Instrument noise was determined throughout the experiments over a maximum of 4000 min or until equilibrium was reached. The sorption of benzaldehyde by PP resin exhibited Fickian sorption kinetics at low vapor activities (0.1-0.5). However, at high vapor activities (0.7 and 0.9), a two-stage sorption involving Fickian diffusion during the initial sorption, followed by a protracted polymer relaxation, which enhanced the sorption capacity, was observed. The converting process of PP resin into sheets and thermoformed containers had a significant impact on the benzaldehyde sorption profile. Benzaldehyde exhibited a much higher solubility in extruded sheet and thermoformed container than in the resin.