Chemistry Reference
In-Depth Information
Scheme 9.15 Physical appearance of MHHPA-cured EGS/ESO-DGEBA polymers and
uncured monomer blends: (a) EGS-DGEBA (90 : 10); (b) ESO-DGEBA
(90 : 10) pre-cured at 145 1C for 10 min; (c) ESO-DGEBA (90 : 10)
without pre-curing; and (d) pure ESO inducted for 12 h.
a two-phase structure with a dispersed domain size of about 100 nm, i.e.,
smaller in size than the wavelength of visible light.
Due to the even lower reactivity of EVOs with amine curing agents than
anhydrides, compared to that of DGEBA, an EVO component in EVO-DGEBA
blends is either not reactive or proceeds via different reaction mechanisms.
Therefore, heterogeneous structures such as phase separation are more
common than in anhydride polymerization but are still related to the EVO
structure, concentration, reaction process and conditions. Using epoxidized
crambe oil as an epoxy monomer and an MDA curing agent, Raghavachar
et al.
129
found the epoxidized crambe oil was only partially compatible with
the DGEBA and formed a two-phase structure after direct mixing and curing.
ESO of molecular weight lower than epoxidized crambe oil is more com-
patible with DGEBA.
Using TETA as curing agent, a plasticizing effect was observed when dir-
ectly mixing ESO into DGEBA followed by polymerization. Phase separation
could be induced by two-stage mixing where ESO was first reacted with TETA
to form pre-polymers.
130
Similar research was also conducted by Sarwono
et al.
131
in an epoxidized palm oil (EPO)-DGEBA system cross-linked
by xylylenediamine. Mixing 10 wt% EPO into DGEBA or EPO pre-polymers
