Environmental resistance of high performance polymeric matrices and composites

The issue of environmental resistance of Polymer Matrix Composites (PMC) is addressed focusing on the effects of low molecular weight (m.w.) compounds including, among them, moisture. Sorption thermodynamics and mass transport of low m.w. compounds is first reviewed with reference to neat polymer matrices, illustrating Fickian and anomalous diffusion and describing the role of stresses which develop within the polymer in association with mass transport. The cases of thermoplastic and thermoset polymers, both in the glassy and rubbery states, are treated under the theoretical and experimental viewpoints. The effect of penetrant sorption in glassy polymers is then analyzed in terms of depression of glass transition temperature. Theoretical approaches are reviewed, aimed at the quantitative prediction of plasticization of glassy polymers. Subsequently, the specific case of PMCs is addressed, highlighting the role of the geometric effect and of the mechanical constraint effect of reinforcing elements on mass transport and associated stress development. The role of damage development, in terms of micro-cracking, debonding and macrocracking, which occur as a consequence of penetrant ingress into the composite, is analyzed evidencing its contribution to mass transport mechanism