Silk Fibers and their Unidirectional Polymer Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 83

Figure 14. Comparison between longitudinal and transverse loading results.
microscopic observations of tensile specimens
The fracture surfaces of the tensile test specimens were examined by SEM. To study
the surface morphology of the prepared composites, SEM photographs were taken
for 30, 35, 40, and 45% fiber volume fraction, as shown in Figure 15. The SEM of
fracture surface of composite indicates that fiber pullout occurs. This is due to lack of
interfacial adhesion between silk and PP matrix. Due to intermolecular hydrogen bond
formation between silk fibers and hydrophobic nature of PP matrix, hydrophilic silk fi-
bers tend to agglomerate into bundles (Figure 15(d)), and become unevenly distributed
throughout the matrix. It is seen that for 40% fiber volume fraction composite, less
fiber pullout happens, better interfacial adhesion between silk and PP matrix occurs.
Figure 15. SEM micrographs of fracture surface of silk fiber-reinforced composite with various fiber
volume fractions (200X).