Fracture behaviour of thin polyimide films

The deformation and fracture behaviour of aromatic polyimide films (BPDA-PDA, PMDA-ODA, PMDA-BAPB and PMDA-BAPP) was investigated and related with local molecular order. It was found that local molecular order, i.e. bundles of parallel-packed main chains dominated the deformation and fracture behaviour of polyimide films, The fracture behaviour of respective polyimides was heterogeneous over thickness in films with low degree of local molecular order, while this phenomenon disappeared in films with high degree of local molecular order. The tear energy showed maximum value as the degree of local molecular order increased. Also, the deformation behaviour of PMDA-BAPP films with low degree of local molecular order showed a combination of crazing and shear yielding. Other polyimide films with high degree of local molecular order showed only shear yielding in single-edge notched tension test. (C) 1997 Elsevier Science Ltd.