Silk Fibers and their Unidirectional Polymer Composites - Natural Polymers, Biopolymers, Biomaterials, and Their Composites, Blends, and IPNs - page 77

(b) Sufficient amount of commercial PP was taken in a beaker and weighted. The
20% MAPP was added with it. To prevent voids, water bubbles, poor fiber
matrix adhesion, the PP was dried in an oven at about 100ºC for 3-4 hr.
(c) Mold surface was cleaned very carefully and Teflon sheet was placed over the
mold surface properly for the easy removal of the product.
(d) A layer of PP granule with MAPP was placed in a female mould and 2 mm
thick die was placed surrounding the granule.
(e) Then one layer of continuous fibers was aligned parallel to each other onto
PP granule using glue at the edges of fiber (see Figure 2) and another layer
of fibers was placed over prior layer. And so on to produce as required fiber
volume fraction.
(f) Finally, another layer of mixture of PP and MAPP was placed onto silk fiber
layer.
(g) The female mould with aligned fiber with PP was covered by a male mould
with Teflon sheet.
(h) Plates were placed in hot pressing machine, 185°C temperature and 85 kN
pressure was applied simultaneously for about 15 min and then cooled slowly
using water-cooling system.
(i) At last, the specimen was carefully discharged from the mould.
Figure 2. Unidirectional silk fiber reinforced composite fabrication process.
disCussioN aNd results
tensile testing of Fibers
Stress-strain curves of raw and alkali treated silk fibers (25 mm span) are shown in
Figure 3. Also, uncorrected and corrected extrapolated curves (1/span vs. modulus,
strain to failure and span vs. tensile strength) for the spans of 5, 15, 25, and 35 mm
of raw and alkali treated silk fibers are shown in Figures 4 -6. It seems that with an
increase of span length, Young's modulus increased for uncorrected curves. Some slip-
page portion occurs during tensile testing (which is called machine constant and de-
noted by (α). Larger span length helps to minimize the slippage portion (α) compared
to smaller one as shown in Figure 7. Therefore, modulus of longer span is higher and
strain to failure is lower than smaller span. Total slippage portion of the machine can
be calculated by using the following equations: