Nanovoids in fracture surface of unsaturated polyester/vinyl ester blends resulting from disruption of the cross-linking of the polymer chain networks

Abstract

A weakness of unsaturated polyester is brittle due to the cross-linking of the UP chain network. Improving the toughness may be carried out by blending with appropriate additives. This work aims to characterize the fracture surface of unsaturated polyester (UP)/vinyl ester (VE) blends with a ratio of 70% and 30% respectively. Addition of VE in UP increases the toughness of the blends resulting from disruption of the cross-linking of the UP chain network. The disrupted network was characterized by the FESEM morphology from fracture surface of the blend which exhibits three different regions i.e., the smooth zone corresponding to the slow crack growth rate (1); a transition zone, where the surface roughness steadily increases (2); a final failure zone with much rougher marks (3). The presence of more nanovoids in region 2 and 3 confirmed the bigger disruption of the crosslinking in UP networks increasing UP chain mobility and toughness of the blends. The nanovoids result in a dimpled appearance of the fracture surface and become points of high-stress concentration from which cracks can initiate. When subjected to a sudden load, many cracks can grow simultaneously forming beach marks where the cleavage from several cracks meets.