Agriculture Reference
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and has superior mechanical properties. At the present time, the cured NR is widely used in
tires, for shoe soles, hoses, conveyor belts and hockey pucks. Prevulcanized latex (PVL) is
defined as a process in which the crosslinking of the NR occurs with only discrete particles
which are dispersed in a liquid medium, namely serum and it is a very convenient raw
material for the latex goods manufacturing industry. Production of sulfur PVL is carried out
by heating raw NR latex with various compounding ingredients such as an accelerator,
activator and sulfur until the required degree of crosslinking is completed. After the drying
process of PVL, NR latex results in a crosslinked film. To date, there are many methods for
investigation of the extent of crosslinking including the swelling ratio (Riyajan et al., 2003),
stress-relaxation (Sombatsompop, 1998), NMR (Wootthikanokkhan and Clythong, 2003) and
other techniques.
Cyclisation
Cyclisation is a simple reaction that can transform cis- 1,4-polyisoprene to fuse as a six-
membered ring structure, using an acidic reagent as shown in Figure 4. The acidic reagents
used to change the chemical structure of NR include trimethyl silyl triflate (Riyajan and
Sakdapipanich, 2009c) benzotrichloride (Riyajan et al., 2007a) and sulphuric acid (Riyajan et
al., 2006) systems. The advantage of these catalysts is that the cyclized product can be
dissolved in an organic solvent. Moreover, the cyclised NR is a tough, hard and brittle
material. Therefore, it can be used to reinforce resinous materials. When the cyclised NR is
blended with other polymers, the polymer blend has a high modulus, high hardness and low
specific gravity. In addition, it is used for photo resistant applications, pigments for printing
and as a raw material for producing membranes. It is clear that the modulus of the NR
increases with the increase of cyclised NR content in the NR matrix (Riyajan et al., 2007a).
Figure 3. Production of Prevulcanizsed natural rubber latex with sulfur and other compound ingredients
during heat. (http://en.wikipedia.org/wiki/Vulcanisation, 2012).
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