Effects of Gas Adsorption on the Mechanical Properties of Amorphous Polymer

This study investigates the properties of a polymer-gas mixture formed through diffusion, based on the changes in the partial pressure and observed changes in the impact and tensile strengths owing to the gas dissolution. The high-pressure gas dissolves into a solid-state polymer through diffusion based on the difference in the partial pressure. This dissolved gas is present in the amorphous region within the polymeric material temporarily, which results in the polymer exhibiting different mechanical properties, while the gas remains dissolved in the polymer. In this study, the mechanical properties of amorphous polyethylene terephthalate (APET) specimens prepared by dissolving CO₂ using a high-pressure vessel were investigated, and the resulting impact and tensile strengths were measured. These experiments showed that the increase in sorption rate of CO₂ caused an increase in the impact strength. At 2.9% CO₂ absorption, the impact strength of APET increased 956% compared to that of the reference specimen. Furthermore, the tensile strength decreased by up to 71.7% at 5.48% CO₂ sorption; the stress-strain curves varied with the gas sorption rate. This phenomenon can be associated with the change in the volume caused by CO₂ dissolution. When the APET absorbed more than 2.0% CO₂ gas, sample volume increased. A decrease in the network density can occur when the volume is increased while maintaining constant mass. The CO₂ gas in the polymer acted as a cushion in impact tests which have sorption rates above 2%. In addition to the reduction in the network density in the polymer chain, Van Der Waals forces are decreased causing a decrease in tensile strength only while CO₂ is present in the APET. These observations only occur prior to CO₂ desorption from the polymer.