Chemistry Reference
In-Depth Information
OH
O
O
OH
O
O
C
H
2
H
2
H
2
H
2
H
C
H
Cat
+
H
2
C
C
O
C
C
O
C
H
C
O
C
O
C
C
C
CH
2
HOOC
OH
n
O
O
OH
HTME
Gallic acid
O
O
OH
O
O
C
H
2
H
2
H
2
H
2
H
C
H
+
H
2
C
C
O
C
C
O
C
H
C
O
C
O
C
C
C
CH
2
n
OH
OH
OH
OH
COO
OOC
OH
Figure 3.4
Polyol from hydrogenated terpinene-maleic ester type epoxy resin
modified by gallic acid
Two-component polyurethanes exhibit good hardness, excellent adhesion and
strong organic chemical resistance. However, the volatile organic components
in the two-component polyurethane coatings pose a threat to human health and
pollute the environment. Currently, waterborne polyurethane coatings are becoming
increasingly popular. To obtain an eco-friendly two-component polyurethane a
novel, water-dispersible cationic polyol was prepared by modifying HTME with
DEA and polyethylene glycol 200 (PEG200) [9]. PEG200 is a polyethylene glycol
whose average molecular weight is 200 g/mol. The chemical structure of the cationic
polyol is shown in
Figure 3.5
．The DEA, partly neutralised with acetic acid, provides
a cationic group, while the PEG200 is a non-ionic group. Both parts give the polyol
good hydrophilicity, emulsion stability and crosslinking activity with isocyanate. The
properties of the cationic polyol were affected by the ratio of DEA to PEG200. A
good quality polyol could be obtained by reacting 100 g HTME with 12 g DEA and
36 g PEG200 using 2 g zinc chloride as a catalyst. Increasing the proportion of the
PEG200 moiety in the curing agent decreased the glass transition temperature (
T
g
)
of the polyol resin and lowered the viscosity of the dispersion. The increasing DEA
content offers the polyol good emulsion stability but has a detrimental effect on the
glossiness and smoothness of the final coatings. From the particle size analysis, it was
observed that the optimum cationic polyol dispersion had good stability in acidic
conditions and that its particle size was no more than 100 nm. The dispersion of
polyol with high solid content was very thick, but the addition of some inert thinner
such as propylene glycol methyl ether acetate could effectively lower the viscosity.
