A polymer network of unsaturated polyester and bismaleimide resins: Yielding and fracture behaviour

The yielding and the fracture behaviour of an intercrosslinked polymer network obtained by the simultaneous curing of an unsaturated polyester (UP) and a thermosetting bismaleimide resin (BMI) was investigated in a wide range of temperatures and testing rates. The yield stress sigma(y) and the Young's modulus E increase by increasing the testing rate and decreasing temperature. Moreover, under the same testing conditions, sigma(y) and E increased as the BMI content in the blend was enhanced. On the other hand, it was found that the fracture parameter K-c was not affected by the presence of BMI. The yielding process was analyzed using the theories both of Argon and Bowden and the molecular parameters derived there were related to the molecular structure of the network developed upon curing.