Agriculture Reference
In-Depth Information
liquid medium for long-term storage. Before use, it undergoes concentration by continuous
centrifugation so that it contains ~60% rubber. The diameters of the NR particle range widely
from 0.01 to 5 μm. NR is widely used in many fields such as tires, medical gloves, condoms
and other products because it has excellent dynamic properties, with a high tear and abrasion
resistance. Before its use, it is vulcanized by one of three methods that include the use of
sulfur, peroxide and irradiation. Considering the limitations of cured rubber after use, the
biggest problem is that it is difficult to degrade in nature and this has led to environmental
pollution. Other drawbacks of NR are its low weathering and oil resistance. This is due to the
NR molecule, which contains carbon-carbon double bonds and is a nonpolar polymer.
Therefore, this chapter describes the modification of the properties of NR so that it could
control the release of fertilizer for an agricultural application. To overcome the limitations of
NR and expand its applications, modification is crucial and three main methods have been
employed (Figure 2). The first is chemical modifications that include cyclisation, degradation,
epoxidization and grafting. Chemical modification can introduce other groups or atoms onto
the NR molecular chains, and thus derive polymers such as epoxidized natural rubber (ENR)
(Riyajan et al., 2009
a
), hydrogenated NR (Piya-areetham et al., 2013), and grafted NR
(Riyajan et al., 2013a,c).
The second is blending with a hydrophilic polymer such as poly (vinyl alcohol) (PVA)
(Riyajan et al., 2009a) and sodium alginate (SA). The third method is by addition of an
additional chemical agent e.g., filler or fiber from a natural source such as sugar cane
(Riyajan et al., 2013c).
Vegetable
Figure 1. Photographs of crops in a tropical country.
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