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 their high mechanical properties and customization ability. It is therefore important to systematically estimate the long-term performance of various composite systems.

Environmental exposure causes degradation in composites among which moisture and temperature play dominant roles. Diffusion determines the rate of moisture uptake and hydrolysis the severity of mechanical reduction. The chemical composition, degree of cure, void fraction, filler ratio and size distribution determine diffusion and degradation rate. The extent of these parameters on mechanical properties under various environmental conditions is investigated.

Three different particle-filled composites were stored at temperatures from 21 °C to 40 °C and relative humidities from 25 % to 100 % and characterized within defined time periods. Two bisphenol-based epoxy polymers with low filler content and one vinyl ester-based polymers with high filler content were studied.

Moisture diffusion for the epoxy- and vinyl ester-composites followed a Fickian-type of diffusion. Diffusion mechanisms and kinetics were defined based on the type of filler, the filler ratio and the matrix-filler interphase. A novel Isotherm-Model for moisture saturation was established.

The decline of mechanical properties (tensile strength, shear strength, Young’s Modulus) was directly connected to the moisture, the temperature and the composition and design of the composites.Applied characterization methods:

• Electron Microscopy

• Energy dispersive X-Ray Spectroscopy

• X-Ray Diffractometry

• Differential Scanning Calorimetry

• Mechanical Tests