Blended polybenzimidazole and melamine-co-formaldehyde thermosets

Abstract

Polybenzimidazole [PBI; poly-2,2′(m-phenylene)-5,5′-bibenzimidazole] is known to have excellent high temperature stability (up to 450°C) and superb H2/CO2 selectivity compared to most high performance (HP) polymers. New blended thermosets were made with PBI and poly(melamine co-formaldehyde) [PMF] to produce stable thin-films after thermal processing at 220–250°C. PBI film formation is difficult, because of challenging processing techniques. As a result, the film tends to fracture and fissure due to processing aids and stabilizers (salt/acid additives) that are found in PBI solutions above 10wt%. Therefore, PBI dense thin-films are fragile and prone to fracturing during film processing. The reported PBI-PMF blended thermosets do not have stabilizers, and can be made into dense thin-films. The PBI-PMF films were analyzed using pure and mixed gas permeability measurement techniques. At 250°C, the data show H2/CO2 gas selectivities greater than 13. Also from the gas permeation data, the energy of activation (Ep) of a mixed gas stream for PBI-PMF shows that hydrogen permeates more easily than the other gases, while the permeabilities for the larger kinetic diameter gases are greatly diminished. In addition, the FT-IR spectra show that the PBI-PMF films have changed from parent PBI after thermal processing, and PMF dominates the spectra even in minor percent compositions. Overall, the reported PBI-PMF thermoset films show good stability which can be used for high temperature gas separation.