Chemistry Reference
In-Depth Information
epoxy resins has been studied in some detail using normal-phase and reversed-
phase columns, respectively [58]. The difference between taffy-processed and
fusion advancement solid resin can be noted in HPLC chromatograms. In the
advancement process, the even-numbered oligomers predominate, whereas taffy-
produced resins exhibit both even- and odd-numbered oligomers. Compounds
that contribute to hydrolysable chloride and α-glycol content can be quantified
by HPLC. The presence of branched chain components is detectable in studies
using an improved reversed-phase gradient HPLC method.
2.4.1 Characterisation of Epoxy Binders Based on Rosin Adducts
El-Saeed [59], prepared epoxy resins from MPA and APA adducts. Hydroxymethylated
derivatives of condensed product of DEA with MPA and APA (HAPA and HMPA)
were prepared and were reacted with EC in the presence of sodium hydroxide (50
% by weight) as catalyst. The glycidyl ether produced with AbA is referred to here
as HAbAE. While glycidyl ethers of APA and MPA have designated as HAPAE and
HMPAE. The scheme of reactions is illustrated in Scheme 2.6. The liquid epoxy resins
were mainly characterised by EEW, epoxy content, density, viscosity and molecular
weight. The data indicated that the epoxide functionality of HAPAE and HMPAE
epoxy is 2.8 (determined from the molecular weight and EEW values). This indicates
that only trifunctional hydroxyl groups were reacted with EC although the HAPA
derivative also has tetrafunctional hydroxyl derivatives.
This can also be proved from the hydroxyl values of HMPAE and HAPAE which
indicates that only three hydroxyl groups of HAPA and HMPA were reacted with EC.
The lower viscosity values and lower molecular weight of the prepared epoxy indicate
that a side reaction can occur [59]. In this side reaction terminal glycol groups are
formed due to the hydrolysis of epoxy end groups. The presence of terminal glycol
groups can give a lower viscosity resin [59]. The proposed structures of HAbAE,
HMPAE and HAPAE were elucidated by using IR and ¹H-NMR spectroscopy. The
IR spectra showed appearance of new strong peaks at 815 cm
-1
and 780 cmˉ¹, γ
C-O
vibration bending of the ether group of epoxy ring, which indicate the presence of
epoxide rings in the structures of HAbAE, HMPAE and HAPAE. The formation of
glycidyl ether was also proved by ¹H-NMR spectra. Absorptions due to the -OCH
2
groups can be found at 4 ppm whilst those due to the -CH- and -CH
2
- groups of
the epoxide ring occur at 2.9 ppm and 2.2 ppm, respectively. Moreover, ¹H-NMR
spectra can be used to determine the epoxy functionality of HMPAE and HAPAE
through integration of the characteristic signals. For this, the analysis is based on
the integration of two signals, namely, at 2.9 ppm (assigned for the -CH- proton
of the oxirane ring ), and at 2.6 ppm (assigned for unreacted -OH- protons of the
hydroxymethyl group). The ratio of the integrals of these two signals for HAPAE
