Agriculture Reference
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The possible mechanism of grafting M-SPNR with cellulose fiber by using BPO and
K
2
S
2
O
8
at 80
o
C
is presented in Figure 10. Free radicals from BPO attacked the carbon-carbon
double bonds of MA, which then reacted
with the carbon-carbon double bonds of the SPNR
molecules activated by K
2
S
2
O
8
leading to the formation of M-SPNR. When the M-SPNR
reacted with cellulose fiber, an M-SPNR-g-cellulose fiber was generated. In addition, the
crosslinks between the M-SPNR and cellulose fiber might occur through MA bridging.
Polymer Blends
A polymer blend is a heterogenous material that consists of two polymers. The properties
of NR are modified with a hydrophilic polymer such as PVA as described earlier. NR
(Riyajan et al., 2008) or ENR (Riyajan et al., 2009a) latex was blended with 5%w/w of a
PVA aqueous solution in the presence of different concentrations of maleic acid as a
crosslinking agent. The possible chemical reaction of the blend between PVA and maleic acid
at 120
o
C is displayed in Figure 11. After heating, the hydroxyl group of PVA is crosslinked
with the carboxylic group from MA to form the crosslinked PVA through esterification.
The swelling of any polymer blend film in a solvent depends upon the diffusion
coefficient of the solvent, the relaxation rate of the amorphous regions of the polymer chain
and its degree of crystallinity. In polymer gels, there are two different categories, i.e., a
physical gel and a chemical gel. In a physical gel the junction points of the network arise due
to the physical bonding like Van Der Waals interactions, hydrogen bonding, the presence of
crystallites, etc.; hence, in a good solvent such networks exhibit a large degree of volume
change owing to the facile penetration of the solvent. The PVA selected for the present study
possessed a degree of hydrolysis of 98%. The swelling ratio of a semi-interpenetrating sample
could be practically used to approximate the crosslinking density in the sample. The swelling
ratio of the maleic acid crosslinked PVA was based on the NR/PVA blend having different
maleic acid contents but all were cured at 120ºC for 60 min and studied in water after keeping
the samples immersed in solvents for 5 days. The polymer blend based on NR and PVA
showed a lower swelling ratio after being cured with maleic acid (Figure 12), when compared
with the uncured measurement. This indicated the chemical reaction that occurred between
the PVA and maleic acid. When the amount of maleic acid increased in the blend, the
swelling ratio of the polymer blend slightly increased. This was due to the solubility of the
excess maleic acid. The swelling ratio of the sample in water decreased as a function of the
amount of maleic acid in the sample as shown in Figure 13. The water resistance of the
ENR/PVA blend system also increased with an increasing amount of maleic acid in the
sample after curing. The swelling ratio of the semi-IPN ENR/PVA blend with 10% w/w
maleic acid was 130%. When the maleic acid contents in the sample were increased from 10
to 30% w/w, the swelling ratio of the ENR/PVA blend was 80%.
The morphology of the ENR/PVA blend was observed under TEM as shown in Figure
14. The images show that the PVA molecules penetrated into the ENR particles. The tensile
strength of the ENR/PVA blend was higher than that for the NR or ENR due to the increase in
miscibility between the ENR and PVA. The properties of polymer blend were also improved
after the addition of maleic acid to the blend. The tensile strength of the NR/PVA blends as a
function of curing times and the maleic acid contents are presented in Figure 15. The results
indicated that the tensile strength of the polymer blend based on the ENR/PVA blend
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