Silk Fibers and their Unidirectional Polymer Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 80

table 1. Tensile properties of silk fiber.
Fiber types Average Tensile Stress (MPa) Average E-modulus (GPa) Average strain (%)

Raw silk
Alkali Treated silk

227
319

9.56
15.45

23.53
25.67

surface morphology of Fibers
Surface morphology of raw and alkali treated silk fibers was observed by using SEM.
It is shown in Figure 8. Raw silk surface contains fibroin and siricin (Figure 8(a)).
Siricin is a hard and gummy matter that binds fibroin together. Fibroin gives the fiber
strength. Fiber defects can be seen in Figure 8(b), which reduce the fiber strength. Silk
fibers after treated with alkali show rather smooth surface and reduction in diameter as
compared to raw fibers. Alkali treated silk fiber contains small amount siricin than raw
silk. For that reason, alkali treated silk fibers give better properties than raw silk fibers.

Figure 8. Surface morphology of silk fibers (500X).

thermo-gravimetric analysis (tGa) of silk Fibers
From TGA curves of raw and alkali treated silk fibers (Figure 9), it is seen that raw silk
fiber is stable up to 281°C and alkali treated silk fiber is stable up to 265°C.

Figure 9. Thermo-gravimetric analysis (TGA) curves of silk fibers.