CARBONIZATION AND GRAPHITIZATION OF POLYIMIDE UPILEX

Two-step carbonization was found on a polyimide film, Upilex, similar to that observed on another polyimide, Kapton: large weight loss up to about 22 wt. % and linear shrinkage along the film surface to 30% in a narrow temperature range from 500 to 650-degrees-C, and an additional small weight loss and shrinkage in a wide range between 700 and 1000-degrees-C. The yield of carbonization agreed roughly with that calculated by assuming the release of non-carbon atoms as simple species of CO, O2, and N2. A 25-mu-m Upilex film yielded a relatively high degree of graphitization after heat treatment at 3000-degrees-C: a layered structure under SEM, high magnetoresistance, and a sharp 002 x-ray diffraction peak at a d-spacing of 0.336 nm. The degree of graphitization was lower than for a similar Kapton film, which is attributed to the lack of flatness in the Upilex molecule. A very much lower degree of graphitization was observed for 50-mu-m Upilex films. This difference is tentatively attributed to constraints that must have influenced the orientation of the Upilex molecules near the surface of the films as they were formed.