Crack propagation and defect formation at polymer interfaces investigated by ultra-small angle X-ray scattering

The double cantilever beam test (DCB) was used to estimate the fracture toughness of poly(methyl-methacrylate) (PMMA). With the help of given neutron reflectometry (NR) results for PMMA a correlation between fracture toughness and interface width was established. It displays a three regime behaviour similar to polystyrene (PS). For the first time, deformation and defect structures in the vicinity of the crack tip were investigated by scanning ultra-small angle X-ray scattering (S-USAX) where a beam from a synchrotron source is scanned over the sample. It is concluded that crack propagation during the DCB measurement is connected with large deformations and defect formation, where the plastic deformation zone extends over a large size (> 400 μm). Following a model for scattering from diffuse boundaries it was concluded that the diffusiveness increases from the outer edges to the centre of the plastic zone. S-USAX thus provides details of sample failure at a microscopic level as well as information about the structure of the defect boundaries and their distribution across the plastic zone.