Influence of moisture and CO₂ on the material behavior of thermoplastic elastomers for beer bottle closures

Metal closures with a polymer-based sealing for beer bottles have been known since the late nineteen-sixties. However, to what extent which parameter of the polymer sealing gasket plays a role in closure performance to keep the beer quality to a highest level possible is not fully understood. For this purpose three thermoplastic elastomer (TPE) liners were investigated by differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectrometry, dynamical mechanical analysis (DMA), scanning electron microscopy (SEM) and surface roughness in order to understand the effect of relative humidity (RH) and carbon dioxide (CO₂) on their physical and chemical properties as well as their macromolecular structures. The TPEs’ viscoelasticity in the frequency domain under different isothermal conditions was evaluated. RH and CO₂ were effective for changes in thermomechanical and surface properties. Liner C was found to have lower seal performance attributed to its relatively higher crystallinity, stiffness, weaker bond structure and rougher surface. Vibrations can lead to seal leakage in Liner B due to its higher damping behavior during production and transportation. Liner A outperforms others due to stabile behavior within the operational temperature range.