EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Polymer composites as high-performance materials are widely used and very specific for numerous applications. In building science, connecting and sealing joints with particle-filled thermoset polymers is a beneficial option due to its high mechanical properties and the ability to customize. It is therefore important to systematically predict the future performance depending on deviations between various composite systems.

Environmental exposure causes degradation in composites among which moisture uptake and hydrolysis can cause severe mechanical reduction. Chemical composition, degree of cure, void fraction, filler ratio, size, and material are determining diffusion and degradation rate.

To assess future behaviour of degrading composites, four different particle-filled polymers were stored in 9 in-house built climate chambers at various temperatures and humidities and characterized within defined storage periods. Two epoxy polymers with 18%vol. filler ratio with quartz or cement and two vinylester-based polymers with 45% or 58%vol. quartz filler ratio were the objects of study.

Applied characterization methods:
ˆ Electron Microscopy
ˆ Energy dispersive X-Ray Spectroscopy
ˆ IR Spectroscopy
ˆ X-Ray Diffractometry
ˆ Differential Scanning Calorimetry
ˆ Mechanical Tests

Moisture diffusion for all epoxy- and vinylester-composites follows a Fickian-type of diffusion. Water Saturation was highest for high humidities. A slight decrease in the saturation level with increasing temperature could be observed for composites with a higher void fraction. Mechanical properties declined proportionally with water absorption for all composites. Post-Curing effects could be observed for the epoxy composite with the smallest particle size distribution for higher temperature and low humidity. Spectroscopy revealed degradation effects due to oxidation.

The main reduction mechanism in mechanical properties for all composites
could be attributed to hydrolysis, scission of polymer chains caused by reaction with water. After 1 ½ year, tensile strength was reduced up to around 25% depending on the humidity level. Higher temperature acted positively on mechanical properties in general.