Abstract:
Colloidal natural rubber (NR) latex is believed to be covered by some
proteins and phospholipids, which derive colloidal stability of natural rubber latex.
The present work is an attempt to study the origin of colloidal behavior of natural
rubber latex and the components, which act to stabilize the colloidal system.
Proteins in the cream fraction of NR latex were decomposed by
treatment with a proteolytic enzyme. Proteins from both cream and serum fractions
were characterized by SDS-PAGE. Then, the latex was further treated with NaOH to
decompose residual proteins and phospholipids. It was found that the rubber particles
in the cream fraction showed different protein compositions from that of the serum
phase. The major proteins in rubber particles and the serum phase were 14.5, 25, 29
kDa, and regions of 6 to more than 200 kDa, respectively. Some molecular weight
proteins were similar to rubber elongation factor (14.5 kDa) and hevamines (29 kDa).
Characterization of the extracted linked phospholipids received from saponification
treatment of dry AENR, was carried out by 13C-NMR spectroscopy and GC-MS,
compared with the data base. The 13C-NMR spectrum of the extracts
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The appearance of these signals indicated that this serum contains phospholipids
linked to a rubber chain. The GC-MS chromatogram also revealed the presence of
linked fatty acids derived from the decomposed phospholipids. The NR particle
surface morphology before and after the removal of proteins and phospholipids was
studied using an SEM and a zeta potential analyzer, with it was found that the surfaces
of the rubber particles were replaced by a surfactant layer after the removal of
phospholipid-protein layers by deproteinization and saponification. Therefore, the
effect of various kinds of surfactants (SDS: anionic surfactant, Triton®X-100: nonionic
surfactant and Levenol-RC: cationic surfactant) on colloidal behavior of the
natural rubber particles during the deproteinization process were elucidated using a
TEM and AFM technique. It was revealed that the deproteinized particles preserved
by cationic surfactant were rapidly destabilized, while natural rubber particles were
stable after deproteinization reaction with non-ionic and anionic surfactants