S. Kim et al., The effect of crystalline morphology of poly(butylene terephthalate) phases on toughening of poly(butylene terephthalate) epoxy blends, J MATER SCI, 34(1), 1999, pp. 161-168
In an effort to investigate the effect of the crystalline morphology of a p
oly(butylene terephthalate) (PBT) phase on the toughening of PBT/epoxy blen
ds, the blends, having different degrees of perfectness of the PET crystall
ine phase, were prepared by blending PET and epoxy at various temperatures
ranging from 200 to 240 degrees C. As the blending temperature decreases, t
he degree of perfectness of the PET crystalline phase increases as a result
of the increase of crystal growth rate. For PBT/epoxy blends, the change i
n crystalline morphology induced by processing may be the most important ca
use for the dependency of the fracture energy on blending temperatures. It
has been found that PET phases with a well-developed Maltese cross are most
effective for epoxy toughening. This dependency reveals the occurrence of
a phase transformation toughening mechanism. Also, the higher relative enha
ncement of fracture energy of a higher molecular weight epoxy system is fur
ther indirect evidence for a phase transformation toughening mechanism. Som
e other toughening mechanisms observed from the fracture surfaces, such as
crack bifurcation, crack bridging, and ductile fracture of PET phases, have
been found to also be affected by the blending temperatures. (C) 1999 Kluw
er Academic Publishers.