H. Chen, Y-C Hsu, L-T Hwang, D. Bajaj, D. Patil, N. Verghese, H-J Sue
Texas A&M University,
United States
Keywords: reactive polyetherimide, tetrafunctional epoxy, bismaleimide, fracture toughness, particle bridging
Summary:
Highly crosslinked thermosets exhibit many desirable properties, such as high modulus, high glass transition temperature (Tg), superior thermal stability, solvent resistance, and creep resistance. However, increased crosslink densities tend to decrease their ductility and fracture toughness, rendering them susceptible to detrimental brittle fracture. Numerous effective toughening strategies have been reported over the decades to enhance the fracture toughness of high-performance thermosets. Unfortunately, compromises in their other mechanical and thermal properties usually ensue. The present study focuses on utilizing commercially available reactive amine-functionalized polyetherimide (rPEI) as a toughener for toughening tetraglycidyl diamino diphenyl methane (TGDDM) epoxy and a TGDDM and bismaleimide (BMI) blend systems. As will be shown, rPEI can significantly toughen both thermosetting systems and simultaneously enhance tensile strength and elongation at break. Interestingly, the modulus of the TGDDM-BMI/rPEI blend system can remain similar to the untoughened system even at temperatures above the Tg of rPEI. Possible fundamental reasons behind this unusual phenomenon will be discussed. Furthermore, a set of continuous fiber composite systems based on TGDDM/rPEI were investigated. It is found that the fracture toughness improvement is linearly correlated between the resin castings and the composites counterpart. Implications of the present study for preparation of high-performance toughened composites will be presented.