This study shows the effects of aging on epoxy-based rapid tooling materials. Two epoxy-acrylate resins used for stereolithography and one aluminum powder-filled epoxy used for the high speed machining of plastic injection molds were selected to investigate their aging behavior in different environments. Four different conditions, each characterized by a specific relative humidity, were used to perform a seven week long aging study. Temperature was kept constant at 30°C. Both stereolithographic resins showed a drop in mechanical properties and in their glass transition temperatures in wet environments, whereas aging time showed little influence on these properties. Moisture uptake is mainly responsible for that drop and coefficients of water diffusion were determined. On the other hand, the aluminum powder-filled epoxy showed little humidity-dependent drop in mechanical properties and in its glass transition temperature during aging. This result correlates well with the very low moisture absorption of this material.
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