Impact of processing method and surface functionality on carbon nanofiber dispersion in polyimide matrix and resulting mechanical properties

Composites were produced with functionalized carbon nanofibers (CNF) and polyimide (PI) matrix using either in situ polymerization or blending processes. The impact of the composite processing method, CNF surface chemistry, and fiber loadings on the dispersion of fibers and mechanical properties of composites were investigated. Specifically, functionalization of oxidized CNF with a diamine and polyimide oligomer that mimicked the structure of the base polyimide led to improved dispersion of CNF in the matrix polymer. Samples produced using precipitation blending from hot solvent and in situ polymerization exhibited improved dispersion and reduced agglomeration of CNF relative to samples made using direct blending. While SEM images showed poorly dispersed pristine CNF in PI in the form of agglomerations and thick deposition layer on the bottom of composite film, there was clearly better dispersion for functionalized CNFs. Composites produced with functionalized CNF exhibited improvements in modulus, glass transition temperature and tensile strength relative to the base polyimide. POLYM. COMPOS. 35:1473–1485, 2014. © 2013 Society of Plastics Engineers