Unsaturated polyester (UP) resins are often used as thermosetting matrices in fiber reinforced applications. They are inexpensive in production and offer a widely adjustable variability of chemical and mechanical properties. However, they are usually very brittle materials, show a high degree of internal stresses due to significant shrinkage during curing, and have a poor ductility because of their highly crosslinked nature.
To overcome these limitations, this study focused on the modification of UP resins by core-shell particles, layered silicates and particulate, inorganic modifiers in the micro to nano-size range. The goal was to evaluate their effect on processability, mechanical properties and impact strength of wet pressed, glass fiber reinforced UP composites (GFR-UP).
All modifiers increased the fracture toughness of the neat resin. However, most of them negatively affected other mechanical properties, such as Young’s modulus and tensile strength as well as the viscosity. Outstanding results were obtained by using a small amount of submicron-sized core-sell-rubber (CSR) particles, which significantly improved the fracture toughness K_Ic of the matrix, while only marginally increasing the viscosity of the reactive mixture. This property improvement was then successfully transferred to the glass fiber reinforced composite, which showed an enhancement of the interlaminar shear strength G_Ic of about 20 %, due to mechanisms such as local shear yielding and an improved fiber-matrix adhesion. Simultaneously, the fracture energy of the GFR-UP under impact conditions increased about 50 %.