Chemiluminescence as a condition monitoring method for thermal aging and lifetime prediction of an HTPB elastomer

A rapid and highly sensitive evaluation of polymer composite aging with linear correlation to real-time aging

Evaluation of polymer aging is very important for the long-term performance of polymer materials, but it remains a challenge to correlate accelerated evaluations with the real-time procedures. Here we develop a novel in-situ aging evaluation system for rapid and sensitive aging evaluations of polymer materials within hours under multiple environmental conditions. It is carried out by in-situ detecting the generation rate of trace gaseous degradation products, e.g. CO₂, of polymer materials in a specially designed reaction cell during aging under environmental conditions with various UV irradiation, temperature and humidity. The advantages of this system were demonstrated by applying to evaluate the photo-oxidation of polypropylene (PP)-CaCO₃ composites, including stability evaluation, aging status analysis, aging kinetics measurements and study on effects of UV irradiation intensity and humidity. The CO₂ generation rate of PP-CaCO₃ composites measured in this system is well correlated to carbonyl indices during 120-day natural weathering. A linear relationship was observed between the generation rate of CO₂ and the natural logarithm of the carbonyl index. The activation energy of the photo-oxidation of PP-CaCO₃ composites was calculated based on generation rates of CO₂ at different temperatures in the range of 30-80 °C. The increase of UV irradiation intensity and humidity both enhanced the generation rate of CO₂ of PP composites, and the presence of CaCO₃ fillers promoted the sensitivity of PP photo-oxidation to both of UV irradiation intensity and humidity. This study provides a new approach to rapid and highly sensitive evaluation of polymer composite aging under multiple environmental conditions.

Three-Dimensional Visualization for Early-Stage Evolution of Polymer Aging

Monitoring the evolution of polymer aging, especially early-stage aging, over both time and dimensionality can provide in-depth insight into aging-induced material invalidation and even disastrous accidents. However, it remains a great challenge because currently available methods for polymer aging only provide statistic results at a macroscopic scale. Herein, we report the first three-dimensional early-stage visualization (ESV) technique of polymer aging by using the fluorophore-bonded boronic acid to specifically target aging-induced hydroxyl groups through the B-O click reaction. This method can identify the initial aging of polypropylene (PP) as early as 20.0 min. In contrast, no signals can be detected by conventional infrared spectroscopy even after 21 days of thermal treatment. More importantly, the three-dimensional evolution for early-stage polymer aging was demonstrated: faster aggression in the horizontal plane (4.1 × 10-4 s-1) than in the vertical direction (2.6 × 10-9 m s-1) for PP films. The approach could undoubtedly provide valuable information in elucidating mechanistic details of polymer aging in three-dimensional scale and assessing the utility of advanced antiaging materials.