マウスガードの化学構造と動的粘弾性

Abstract

The chemical structures and dynamic viscoelastic properties of the proprietary mouth-formed and custom-made mouthguards used in contact sports were investigated to evaluate shock absorption and moldability.The infrared spectra of the molecular structure of each material were identified as ethylene-vinyl acetate copolymer (EVA). The contents of vinyl acetate in EVA were 27-39 mass%. The weight average molecular weights measured by the gel permeation chromatography were 99, 000-150, 000.The master curves of storage modulus G′, dynamic viscosity η′ and loss tangent tanδat the reference temperature of 35°C were constructed from the data obtained at different temperatures, by the application of time-temperature superposition principle. By this method, it is possible to evaluate the viscoelastic properties expanded to both higher and lower frequencies than can be obtained experimentally.The difference of G′ and tanδfor each material was due to the vinyl acetate content and molecular weight in EVA. Marked effects of the molecular weight on the master curves of tanδwere observed in a lowfrequency range: the lower the molecular weight, the higher the tanδ.It was suggested that the shock absorption and moldability of mouthguards could be evaluated from the master curve of tanδ.