Strengthening fibre/matrix interphase by fibre surface modification and nanoparticle incorporation into the matrix

Fibre reinforced polymers (FRPs) generally consist of different phases including the matrix phase, the fibres as the dispersed phase and the fibre/matrix interphase. Of great importance for the FRP properties such as mechanical strength is the contact between the fibre and the matrix. In this work modification of the fibre surface was investigated with the aim to strengthen the contact between fibre and matrix by increasing the surface of fibre and matrix as well as using the atomic forces through nanoparticles. These modifications are to enhance properties of the composite such as tensile strength and interfacial strength. One approach used to achieve this was the modification of the fibre surface by coating it with a resin containing nanoscaled particles including purified carbon nanotubes (CNTs), carbon nanotubes functionalized with carboxyl groups or amino groups as well as boehmite nanoparticles functionalized with taurine. Another approach was to modify the fibres with various treatments. In this approach the fibres were plasma treated, coated using a sizing agent with carbon nanotubes dispersed in it or treated in liquid nitrogen. Properties of the composites produced such as strength and effectiveness of the composites were investigated using the tensile fibre bundle test as well as the single fibre pullout test. Scanning electron microscopy (SEM) was used to examine the homogeneity of the dispersions and fracture areas of samples that underwent fracture testing. Results obtained in this work show that considerable enhancement of the interphase and mechanical strength of the FRP can be achieved with composites that contained suitably treated fibres. Particular improvements were achieved with the plasma treatment of carbon fibres in an Ar/O2 atmosphere as well as a combination of CNTs and boehmite nanoparticles in the resin.