Chemistry Reference
In-Depth Information
2.2.3 Synthesis of Epoxy Binders from Rosin Hydroxyl Derivatives
Epoxy binders are prepared by the reaction of compounds containing an active
hydrogen group with (EC), followed by dehydrohalogenation in the presence of
sodium hydroxide. The ability to prepare epoxy resins from modified hydroxyl
derivatives of resin acids will be discussed in this section.
It was proved that the functionality of rosin acid can be increased by introducing
new functional groups through the condensation of rosin acid with formaldehyde
(FA), the formation of Diels- Alder adducts of resin acids with MA and AA or by the
dimerisation of rosin acid. It was also noted that multifunctional hydroxyl derivatives
of rosin acid can be obtained. Cycloaliphatic epoxy resins based on rosin acids
were synthesised from Diels-Alder adducts and condensed rosin acid-FA resins. The
structure of the produced resins was determined by infrared (IR) and proton nuclear
magnetic resonance (
1
H-NMR) analysis. The molecular weight of the produced resins
was determined by gel permeation chromatography (GPC). Series of poly(amide-imide)
hardeners were prepared from the condensation of Diels-Alder adducts of rosin acid-
MA and AA with triethylenetetramine (TETA) and pentaethylenehexamine (PEHA).
These amines were also condensed with Diels-Alder adducts of rosin ketones. The
curing exotherms of the produced epoxy resins with poly(amide-imide) hardeners were
investigated. The observed mechanical properties, solvent resistance and chemical
resistance indicated the superior adhesion properties of the cured epoxy resins based
on rosin acid formaldehyde resins.
2.2.3.1 Production of Epoxy Resins from Diels-Alder Rosin Adducts
Tetrafunctional epoxy resins were prepared from rosin acids. These were obtained
from reactions of diethanolamine with Diels-Alder adducts of rosin ketone. It is well
known that AbA, when heated, undergoes various transformations such as oxidation,
dehydrogenation, decarboxylation and polymerisation. As an example, AbA heated
at moderate temperatures and in the presence of 80-85% sulfuric acid solution
polymerises in a high proportion [28, 29]. A new and very interesting transformation
was observed when AbA was heated in the presence of small quantities of sulfonic
derivatives such as
p
- toluenesulfonic acid (PTSA) or macroporous sulfonic derivatives
[30]. Much work [30, 31] has been centred around the reaction conditions necessary
for dimerising the rosin acids because of the increasing commercial use of dimerised
rosin in adhesives, lacquers, varnishes and printing inks. The present work describes
the synthesis and the characterisation of the hydroxyl derivatives produced from the
condensation reaction (dimerisation) of AbA in the presence of PTSA as the catalyst.
Bicu and co-workers [30, 32] reported that when AbA, as its isomer pimaric acid, was
heated in the presence of PTSA as the catalyst it underwent a dehydrodecarboxylation
