Synergistic effect between phenoxy and CNTs on the delamination toughness of modified epoxy based composites

Details

Supervisors

Bailly, Christian

Faculty

Ecole polytechnique de Louvain

Degree label

Master [120] : ingénieur civil en chimie et science des matériaux

Abstract

Epoxy resins are horse-work of the advanced polymer matrix composites (PMC) which are widely used in automotive and aerospace industries. High mechanical properties with low density and excellent chemical resistance are main advantages of these PMCs. On the other hand due to high crosslinked network, these PMCs are inherently brittle and have limited fracture toughness and impact resistance compared to metallic alternatives. Among resin additives, thermoplastics and nanoparticles have been used as toughening agents for the past decades. In this work synergistic effect of thermoplastic phenoxy phase and multi- walled carbon nanotubes (MWCNTs) as toughening agents of epoxy system made of tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) and 4,4′-diaminodiphenylsulfone (DDS) has been studied. Two different methods are used for epoxy modifications, one is adding them separately and the other one is using nanocomposites of phenoxy and CNTs. Three points SENB tests are done to evaluate the fracture toughness. Transmission electron microscopy (TEM) is used to study microstructure and degree of dispersion of the bulk of the samples and scanning electron microscopy (SEM) is used to study fracture surfaces and figure out toughening mechanisms. It is observed that in the case of adding separately, synergistic effect only exists when 0.3 wt% CNTs and 9.7 wt% phenoxy is added and 114% increase in GIc is achieved. On the other hand when nanocomposites are used synergistic effect is seen when adding 0.6 wt% CNTs and 9.4 wt% phenoxy; with 107% increase in G¬Ic. TEM observations prove that in the case of using nanocomposites CNTs are more at the interfaces of phenoxy nodules after reaction phase induce separation (RIPS). SEM shows that at the lower amounts of CNTs, 0.1 wt%, toughening mechanisms is mainly crack path deflection, and in samples with higher amounts on CNTs beside crack path deflection shear banding due to pull out of MWCNTs is also identified as toughening mechanism.