Toughened multiphase thermosetting polymers

Abstract

In recent years a new generation of advanced structural adhesives has become available. They are typically based upon epoxy resins modified by the presence of a second phase of dispersed rubbery particles. This multiphase microstructure results in the material possessing a considerably higher toughness or crack resistance, compared to the unmodified, single-phase resin, but with only a minimal reduction in other important properties such as modulus and high-temperature and creep resistance. Even more recently, polyimide adhesives have also been toughened employing this principle. The present paper considers the following aspects: 1 The chemistry of rubbery-toughened thermosetting polymers developed for adhesive applications. 2 Structure-property relationships of multiphase adhesives which incorporate a dispersed rubbery phase or rigid particulate fillers. The mechanisms of toughening are discussed and related to the microstructure. The effects of volume fraction, particle size and particle size distribution on the polymer's fracture energy are also described 3 The particular problems encountered when using such toughened multiphase adhesives in structural joints are reviewed, including aspects of joint design and environmental effects.