27. pVT Analysis of the Effect of Addition of Thermoplastics, Block-Copolymers, or Rubbers on the Curing Behavior and Shrinkage of Epoxy Resins

During curing of epoxy resins shrinkage of the material appears. As long the resin is in the liquid or gel state, the material can easily relax and no stresses appear caused by shrinkage. After vitrification, the mobility of the polymer units is hampered and internal stresses develop. Thus, the shrinkage may cause problems during processing and in the final properties and application. One strategy to reduce the shrinkage is the addition of nonshrinking additives. Favorable is the addition of thermoplastics or rubbers, which in addition to the reduction of cure shrinkage often exhibit a toughening effect to the material. This chapter focuses on the influence of added thermoplastics, hyperbranched polymers, block-copolymers, or rubbers on the cure shrinkage and kinetics. The efficiency of the additives in reduction of shrinkage depends not only on their type and amount but also on their reactivity and the morphology of the blends which develops during the cure process. Beside the shrinkage, also other volumetric properties are discussed like changes in the thermal expansivity.