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Synergistic effects involved in the environmental degradation of Glass Reinforced Polymer (GRP) composites were examined in this research. Six GRPs based on E-glass and ECR-glass fibers with four different polymer resins were exposed either individually or in combination to ultraviolet (UV) radiation, water condensation and elevated temperature for approximately 1000 hours. The composites were monitored for weight changes as a function of time and their surfaces were examined after the tests using optical and scanning electron microscopes. A new model of synergistic aging of polymers under UV and water contestation was also proposed. It has been shown that the selected aging conditions created noticeable synergistic effects causing extensive erosion of the polymer matrices of the tested composites which appeared to be much stronger under the combined actions than under individual exposures. The differences in the aging rates under the individual and combined situations were adequately explained using the newly proposed model. It is suggested that the surface erosion of polymer matrices of the GRPs by combined UV and water condensation creates the most effective condition for small polymer particles formed by UV to be subsequently removed by water condensation exposing fresh still undamaged surfaces to further UV degradation. It has also been shown that depending on the size of the particles different particle removal mechanisms occur on polymer surfaces eroded by a cyclic exposure to UV and water condensation.

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