after this there was a slight increase Young’s modulus was steady but increased progressively after that Khoathane et al. [1] found that increasing the amount of
bleached hemp fiber (0–30 w/t%) resulted in the initial increase
of tensile strength of the fiber reinforced 1- pentene/polypropylene
(PP1) copolymer composite at 5% fiber content to 30 MPa from
20 MPa for the neat resin as depicted in Fig. 10. The tensile strength
then dropped to a low 23 MPa at 20% fiber loading [1]. After this,
the tensile strength increased again and its value was about at
par with that of 5% fiber content when the fiber was 30% [1].
Fig. 11 illustrated the effect of fiber contents on Young’s modulus
of bleached hemp fiber reinforced PP1 composites [1]. The value
of the Young’s modulus increased by over twice from 1.3 GPa (neat
resin) to 4.4 GPa (30% w/t) [1].
Long-discontinuous natural fibers of kenaf and of jute reinforced
polypropylene (PP) composites fabricated by carding and
hot pressing process with fiber weight fraction varying from 10%
to 70% in steps of 10% were studied [13]. The experimental results
illustrated that the tensile and modulus strength of both kenaf and
jute fiber reinforced PP composites increased with increasing fiber
loading and a maximum was reached before falling back at higher
fiber weight fraction. These were illustrated in Figs. 12 and 13 [13].
From the above citations and discussions, it can be found that
the values of the tensile strength of natural fiber reinforced composites
increased with increasing fiber loading up to a maximum
or optimum value before falling back. However, it is generally true
that the values of the Young’s modulus increased progressively
with increasing fiber loading. On the other hand, some researchers
found totally the opposite trend to the increase of composite
strength with increasing fiber content. This can be attributed to
many factors such as incompatibility between matrix and fibers,
improper manufacturing processes, fiber degradation and others.