Melt-spinnable polyacrylonitrile copolymer precursors for carbon fibers

This paper describes the feasibility of achieving melt-processable polyacrylonitrile copolymer precursors for producing high strength carbon fibers. High molecular weight poly(acrylonitrile-ran-methyl acrylate) (PAN-MA) copolymers with high acrylonitrile content were mixed were various binary melting point modifiers with one component being water to produce systems that formed stable melts at temperatures below the temperature corresponding to the onset of PAN-MA crosslinking. The structure of the copolymer was 96.5 ± 0.13 mol% AN and 4.40 ± 0.13 mol % MA by ¹H NMR with an M_w = 238 kDa and polydispersity of 1.9 determined by size exclusion chromatography. A reduction in the T_m of the copolymer of 200 °C was established for one of the copolymer/melting point modifier systems, which corresponds to the greatest reduction in a PAN-based copolymer melting temperature yet reported. From isothermal DSC and pressurized capillary rheometry experiments it was found that the stability of the resulting melts shows a strong temperature dependence, but does not show a strong dependence on shear-rate. Copolymer mixtures consisting of H₂O and acetonitrile or adiponitrile were found to be suitable for melt-extrusion at 170 °C with viscosities ranging from 1800 to 2000 Pa*s and stabilities of the melts ≥1 h.