AbstractPolyimides were synthesized from 4,4′‐diamino diphenyl methane and pyromellitic dianhydride using low‐temperature solution polycondensation. Solutions of these polyamic acids in dimethyl‐formamide (DMF) were spun into fibers by the wet spinning technique using a mixture of DMF and water as coagulants. Various spinning parameters such as dope concentration, bath composition, and jet stretch were standardized to get polyimide fibers with optimum properties. It was observed that fibers spun at higher jet stretch did not cyclize satisfactorily. Higher dope concentrations gave fibers with better properties. Cyclodehydrated fibers were hot‐drawn at 300°C. Fibers with a tenacity of 380 mN/tex, an extension at break of 10, and initial modulus of 4060 mN/tex were obtained. Mechanical properties of fibers at elevated temperatures, i.e., 100 and 200°C were also measured. Heat aging at 100, 200, and 300°C was carried out for 10 hr. This resulted in an increase in the initial modulus of fibers. However, a 28 decrease in tenacity was observed when the fibers were heat‐aged at 300°C. The dynamic thermogravimetry in air showed that fibers were stable up to 400°C. The activation energy of decomposition, calculated from these thermograms in the temperature range 540–610
展开▼
