Development of Novel Toughening Technology for Fusion-Bonded-Epoxy (FBE) Powder Coatings
Many approaches have been used to toughen epoxy systems, often in composite
applications, where toughening agents act through various mechanisms to
dissipate an applied load.3 Among the toughening agents used are liquid rubbers,4-7
core-shell particles,8-10
glass beads11-13 and thermoplastic modified epoxies14-16
as well as combinations of the above.17
Complications with these products may
include significantly increasing the viscosity of formulations containing them,
a dependence of the morphology on cure kinetics, the necessity of vigorous
mixing to disperse the modifiers or the addition of further additives to
prevent particle agglomeration. For example, liquid rubber modifiers, such as
carboxy-terminated butadiene acrylo-nitrile (CTBN), are initially miscible with
the uncured epoxy resins. They phase separate during curing of the epoxy
formulation to typically form spherical inclusions (Figure 1a). The size and
shape of the inclusions are dependent on the cure kinetics. Additionally, the glass
transition temperature (Tg) of these
materials most often decreases because some of the CTBN remains dissolved in
the epoxy matrix and acts as a plasticizer.