Properties and Nano-observation of Natural Rubber with Nanomatrix Structure - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 326

plateau-modulus is the same as an ideal increase of 1.3 times estimated from the mod-
uli of natural rubber and polystyrene by the following expression (Takayanagi, 1966);

sg = E

ì ü

ï

ï

1 - l l

ï ï

E =+

í ý

ï ï

E f E +- (1 f ) E

ï ï þ

î

PS NR PS

where λ and φ represent volume fractions of the fragments in series and parallel mod-
els, respectively, and E i is a storage modulus of i component, that is, ENR=10 5 Pa and
EPS=10 9 Pa. The large increase in the plateau-modulus is an advantage of the nano-
matrix structure, compared to the island-matrix structure, in which a ratio of natural
rubber to polystyrene is the same, that is, about 90:10. We find a further increase
in the plateau-modulus of the rubber with nanomatrix structure after annealing it at
130°C, above glass transition temperature of polystyrene. The 35 times increase in
the plateau-modulus is a remarkable virtue characteristic of the nanomatrix structure.

Figure 12. Storage modulus at plateau region versus frequency for (A) natural rubber, (B) DPNR-graft-
PS (PS: ca 10%) with island-matrix structure, (C) DPNR-graft-PS (PS: ca 10%) with the nanomatrix
structure annealed at 30 o C and (D) DPNR-graft-PS (PS: ca 10%) with the nanomatrix structure
annealed at 130 o C. The plateau modulus characteristic of the rubbery material increased a little
with the island-matrix-structure and dramatically with the nanomatrix structure, respectively. As for
the nanomatrix structured material, the plateau modulus increased about 35 times as high as that of
natural rubber, after annealing it at 130 o C.

Figure 13 shows a plot of loss tangent, tand, versus frequency at plateau regain.
The value of tand of natural rubber was in a range of 0.1 to 0.15, as in the case of lit-