Chemistry Reference
In-Depth Information
COOH in the structure of HMPAE, which has functionality equal to 3, enhances the
curing process. Thus, electron withdrawing groups adjacent to the epoxide ring often
enhance the reactivity of the epoxy resin nucleophilic reagents (polyamide hardeners),
retading their reactivity toward the electrophilic reagent. It was also noted that
although HAPAE has greater epoxy functionalties than HAbAE, it has lower curing
exotherms at 40
o
C . This can be related to the network formed in HAPAE which
would be very light because some of remaining hydroxyl groups of HAPAE may be
buried in the microgel particles of the epoxy and the further reaction of these groups
with polyamide hardeners requires their diffusion into the core of microgels. This
may lead to increased values of t
max
and decreased T
max
values for HAPAE at lower
temperatures at 40
o
C. Moreover the effect of epoxy functionalities on the curing
behaviour of epoxy binders was observed when the epoxy binders were cured with
different types of hardeners.
The data of curing exotherms of HMPAE and HAPAE epoxy binder with polyamide
based on rosin are listed in Tables 2.8 and 2.9. It was also observed that the curing
exotherms of MA/DAKAE at 40
o
C and 60
o
C have a lower t
max
than those of AA/
DAKAE. This can be attributed to their greater epoxy functionality (equal 4) which
produces a higher crosslink density than in the other resins.
Table 2.8 Curing parameters of the cured HMPAE epoxy/polyamide based
on rosin at different temperatures
Type of
hardener
Temp. 60°C
Temp. 50°C
Temp. 40°C
Theoretical
mixing
ratio
t
max
(min)
T
max
(°C)
t
max
(min)
T
max
(°C)
t
max
(min)
T
max
(°C)
150
77
180
65
210
55.9
2.1
APATA
173
67
193
63
225
55
4
APAPA
142
70
167
66
180
57
1.2
MPATA
160
73
190
59
212
59
1.6
MPAPA
20
83
25
69
40
61
2.3
AA/DAKTA
25
81
39
67
50
59
2.9
AA/DAKPA
29
78
53
63
68
58
1.8
MA/DAKTA
32
76
55
61
71
55
1.8
MA/DAKPA
