3.2. Mechanical properties of UHMWPE fi bers/NR composites
3.2.1. Tensile strength
The tensile mechanical behaviors of the NR and UHMWPE fi-
bers/NR composites were characterized at room temperature. The
stress-strain curves of pure NR and 2 wt% UHMWPE fibers/NR
composites are shown in Fig. 5. Pure NR exhibited an elastic
nonlinear behavior typical of amorphous polymers at a temperature above their glass transition temperature, where the stress
continuously increased with the strain, and the stress of pure NR is
lowest among the others. Addition of UHMWPE fibers increases the
stress and beyond a certain strain, the stress starts to level-off
approximately and then, rises up. To clarify the effect of surface
treatment, we compare the two kinds of NR composites with asreceived and treated fibers. In the case of as-received UHMWPE
fibers/NR composites, the composites are apt to stretch at lower
stress with the increase of strain. This may be attributed to a
lubricant-like behavior of untreated UHMWPE fibers which have
only week interaction to the rubber matrix. On the contrary, in the
case of treated UHMWPE fibers/NR composites, it can be seen that
the tensile stress becomes higher than that of NR and as-received
UHMWPE fibers/NR composites. In our study, potassium permanganate solution was used to modify the inert fibers surface, and the
mechanical properties of fibers/NR composites were improved. The
main reason is that the better propagation of tensile stress to
UHMWPE fibers was realized to some extent, because of the
enhancement in the adhesion of fibers to NR matrix, as expected.