The effects of molecular weight and polymorphism on the fracture and thermo-mechanical properties of a carbon-fibre composite modified by electrospun poly (vinylidene fluoride) membranes

The interlaminar toughening of a carbon-fibre reinforced composite by incorporation of electrospun polyvinylidene fluoride (PVDF) nanofibrous membranes was explored in this work. The electrospinning process of low and high molecular weight PVDF was optimised to form nanofibres free of defects with diameters averaging several hundred nanometres. The nanofibres were electrospun directly onto commercial pre-impregnated carbon fibre materials and under these optimised conditions, PVDF primarily crystallised in its beta phase polymorphic form but significant variations were observed between samples. There is strong evidence from DMTA analysis to suggest that a partial miscibility between the amorphous phases of the PVDF nanofibres and the epoxy exists. The improved plastic deformation at the crack tip after inclusion of the nanofibres was directly translated to a 57% increase in the mode II interlaminar fracture toughness (in-plane shear failure). Conversely, the fracture toughness in mode I (opening failure) was slightly lower than the reference by approximately 20%, and the results were interpreted from the complex micromechanisms of failure arising from the changes in polymorphism and molecular weight of the PVDF. (C) 2010 Elsevier Ltd. All rights reserved.