Table 2
Effect of coagulation systems and incubation times on properties of skim rubber.
Samples
concentration
of H
2
SO
4
Incubation
Times (h)
Properties
Mooney
Viscosity
Po
PRI
Dirt
content
(%)
Ash
content
(%)
Nitrogen
content
(%)
SR
a
98 wt%
0
94
48.5± 0.9
47.4±0.2
0.016
2.89
3.35
10 wt%
0
62
61.0± 0.9
30.3±0.8
0.294
2.17
3.19
SR+NHPA
b
10 wt%
0
98
62.0± 1.0
35.0±0.8
0.151
2.42
3.26
1
60
60.0±11.3
30.3±0.3
0.125
3.07
3.19
3
42
54.0± 0.6
26.9±0.2
0.029
2.33
3.08
6
56
62.0± 0.8
30.6±0.8
0.150
2.51
3.16
12
64
62.0± 0.6
32.8±0.4
0.231
3.33
3.21
24
56
58.0± 0.8
28.0±1.2
0.030
3.15
3.12
Fig. 6.
Appearance of skim rubber (A) coagulated with conc.H
2
SO
4
(B) with 10 wt% H
2
SO
4
and (C) with NHPA + 10
wt% H
2
SO
4
.
Table 2 shows effect of incubation times on properties of skim natural rubber. Fig. 6. shows appearance of
skim rubber coagulated with conc. H
2
SO
4
, 10 wt% H
2
SO
4
and NHPA + 10 wt% H
2
SO
4
. It is seen that the skim rubber
from different coagulation techniques show similar color. It is also seen that incubation of 3 h is an optimum condition
with high level of recovered skim rubber (Table 1). Furthermore, high quality skim rubber included lower Mooney
viscosity, dirt content, and nitrogen content was observed (Table 2). Lower Mooney viscosity contributes to reduce
mixing energy, while lower nitrogen content causes lowering protein allergic risk. The reason behind this process
could be explained that NHPA molecules are capable of coagulating proteins in serum which typically caused
uncoagulation problem (Bunrasri, 1999). The proteins then removed from the surface latex particles which thereafter
increasing capability to coagulate the skim latex by 10 wt% sulfuric acid.
