Investigation of aging effects of polymeric composite materials due to ozone and humidity

Abstract

This study investigates the effect of zinc oxide (ZnO) on the oxidative aging behavior of carbon-epoxy composites exposed to ozone and humidity. Composite samples containing zero, one, two, and four weight percent ZnO were subjected to three ozone concentration levels: 300, 500, and 700 pphm. Their mechanical, chemical, and thermal responses were evaluated through tensile testing, Fourier-transform infrared spectroscopy, thermogravimetric analysis, and differential scanning calorimetry. The results showed that although the untreated composites initially exhibited higher tensile strength, ZnO-doped samples outperformed them following ozone exposure. The sample containing 4% ZnO demonstrated the highest strength at 500 parts per hundred million ozone, with a 27% improvement compared to the neat composite. Spectroscopic analysis indicated that ZnO reduced the formation of oxidation-related carbonyl and hydroxyl groups. Thermal analysis further confirmed enhanced thermal stability and elevated glass transition temperatures in ZnO-modified samples. While the formation of zinc peroxide was suggested as a potential mechanism, this could not be directly confirmed and remains hypothetical. Overall, incorporating 2%-4% ZnO significantly improved the resistance of carbon-epoxy composites to ozone-induced aging, highlighting its potential as a multifunctional additive for long-term durability in harsh environments.