气候变化领域集成服务门户

The degradation of polypropylene (PP) and PP-multiwalled carbon nanotube (PP-MWCNT) panels during environmental weathering resulted in an increased degree of crystallinity, making them brittle, and creating surface cracks. The degradation led to a breakdown of the panels and increased the potential for nanorelease. Thermal analysis revealed that the thickness of the test panels and reinforcement with MWCNTs had a significant influence on the stability of PP-MWCNT composites. Differential scanning calorimetry indicated that the MWCNTs acted as nucleation points, increasing the crystallization temperatures of PP-MWCNT, which reduced the extent of aging. Weathering decreased both the melting and crystallization temperatures of PP by as much as 20 degrees C. The reduction in the temperatures was inversely proportional to the thickness of the panels. The activation energy (E-a) obtained using isoconversional kinetics of the TGA analysis showed that the effective thermo-oxidative degradations of PP changed during aging. The E-a for the initial stages of thermal degradation decreased from similar to 330 kJ/mol to similar to 100 kJ/mol for aged PP. During the late degradation stages, the E-a values increased to similar to 300 kJ/mol. These results suggest that early degradation were altered because of the changes in the molecular structure of the aged PP and a shift in the degradation rate-limiting steps. (C) 2017 Published by Elsevier Ltd.