Analysis of the fracture toughness of the blend PBT / ABS using the technique of essential work of fracture (EWF)

Abstract

The study is about the blend of PBT / ABS. The poly (butylene terephthalate) - PBT, an engineering thermoplastic is very important in many applications because of the good characteristics of stiffness, hardness, resistance to abrasion and solvents. The high sensitivity of the notch and its glass transition temperature (Tg) above room temperature, are a major disadvantage, since it reduces their resistance to impact and shows brittle behavior at low temperatures, respectively. To obtain a more competitive material, these characteristics can be improved by adding some kind of PBT elastomeric polymer such as, for example, the ABS. This copolymer, then, has been used as an impact modifier in many commercial blends. The tenacity is often a key property, which can be determined by various methods of standardized tests such as Izod and Charpy. However, the area of fracture mechanics appears as a viable alternative for the study of the relationship between morphology and fracture toughness of polymeric systems for determining the response of a material to fracture under an applied load. Thus it becomes possible to differentiate the fracture of elastic and plastic energy required to separate the initiation and crack propagation. For ductile polymers, as expected for the blend in question, due to the large plastic zone formed at the end of the crack, enables methods of determining fracture toughness J-Integral and / or Essential Work of Fracture (EWF). The J-integral method is a laborious method, with an integral strain independent of the path around the edge of the crack whereas, concomitantly, the plastic deformation that occurs around the same. However, this approach was initially developed for use in metallic materials presenting ductile fracture, this technique is satisfactory not only for very ductile polymers. For these reasons, the EWF method has received special attention in determining the toughness of highly ductile polymers. Its major advantage over the J-integral method is the clear distinction between the work surface, considered an essential part of the fracture and volume, part not essential, corresponding to plastic flow, in a simplistic way. Therefore, the main objective of this project is the application of the EWF technique for evaluating the fracture toughness of the blend PBT / ABS, obtained by extrusion and using different processing conditions, with subsequent analysis of the morphology obtained. (AU)