Storage and loss moduli behavior of plasticized epoxy polymers over a frequency and temperature range, and damaging effects assessment by means of the NDT method of ultrasounds and moisture absorption

Abstract

AbstractThe first objective of the present experimental work is to evaluate the storage and loss moduli of plasticized epoxy polymers over a temperature and frequency range, and to correlate with the ability of the ultrasounds for the characterization of such polymers. The materials used were a series of cold‐setting epoxy polymers, plasticized with different amounts of plasticizer. After the investigation of dynamic properties through vibration tests, the velocities of longitudinal and transverse elastic waves, and the acoustic attenuation coefficient a were evaluated and, then, using these quantities, the “dynamic” moduli E′, G′, and ν′ were evaluated. Thereafter, it can be stated that the plasticizer content and measuring frequency range strongly influence the elastic moduli of the material in the sense that the plasticizer tends to reduce, whereas the measuring frequency to increase these. The second objective of this work is to asses and discuss the associated plasticizer‐induced microstructural damaging effects by combined methods of ultrasounds, tensile modulus, as well as moisture absorption testing and then to correlate this assessment with the storage moduli behavior. It was shown that, despite the nonneglecting scatter in the experimental data, certain irresistible general trends might be assessed. In this context, it was found that the damage “response” is markedly sensitive to the respective applied “detection” technique and, therefore, the damage evolution data obtained by these different techniques are comparable only under certain circumstances. By comparison between the applied techniques, it seems reasonable to assume that the “moisture” technique due to its inherent microscopic mass transport processes, in the form of H2O molecules diffusion and therefore its ability to “detect” microstructural detects on a much lower scale, should give a better approach to the internal damage phenomena. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3869–3880, 2006