Properties and Nano-observation of Natural Rubber with Nanomatrix Structure - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 318

Concentration of urea for deproteinization
It is quite important to determine the amount of urea necessary to remove the proteins
from NR. Figure 2 shows the relationship between the total nitrogen content of fresh
NR latex versus concentration of urea after treatment with urea. The nitrogen content
was dependent upon the concentration of urea and was found to be the lowest (i.e.,
0.005 wt%, at urea concentration of 0.1 wt%). The higher nitrogen content of 0.007
wt% at 0.05wt% urea may be due to a lesser amount of urea that interacts with the
proteins present in the rubber. In contrast, the higher nitrogen content at higher con-
centration of urea may be expected to be due to the residual urea that interacts with
the rubber, because the nitrogen content increased linearly as the concentration of urea
increased.
Figure 2. Nitrogen content of fresh U-DPNR versus urea concentration.
Figure 3(A) shows FTIR spectra for fresh U-DPNR, in which the peak at 3,320
cm -1 is identified to mono- or dipeptides, as reported in the previous study (Eng et al.,
1994). In the spectrum of Figure 3(A)a-d, a small peak was observed at 3,450 cm -1 in
addition to the peak at 3,320 cm -1 , the intensity of which increased as the concentra-
tion of urea increased. A mixture of synthetic cis -1,4-polyisoprene with urea showed
a peak at 3,450 cm -1 characteristic of urea in addition to the peak at 3,320 cm -1 , which