PMMA DC surface flashover in vacuum after thermal treatment

Commercial atactic poly (methyl methacrylate) (aPMMA) were tested to study the annealing effects on its DC flashover characteristics in vacuum. The PMMA samples were 60 mm in diameter, 8 mm in height. After cleaning, the samples were thermally treated at Sub-Tg or near Tg in a vacuum oven for 2 hours, and cooled naturally. All DC experiments were done with the pressure below 3E-3 Pa, discharge current less than 20 mA. As expected, the annealing process did increase the surface flahover strength of PMMA. When the samples that annealed near Tg were polished again, their first flashover electrical strength was 80% higher than samples annealed at sub-Tg, and their conditioned flashover electrical strength was 90% higher. X-ray Photo-electron Spectroscopy (XPS), material degassing performance test and Dielectric Spectroscopy analysis were performed to investigate the structure of PMMA. It is speculated that the stereo-complex formation in PMMA will be increased. The PMMA degassing rate was changed dramatically after annealing. The PMMA DC surface flashover strength was negatively correlated with its degassing rate according to experiment results.