11.4.2.1 PF/FLAX FIBER COMPOSITES

Vertical VC-2 burning test was conducted on the PF composites and the results are shown in Table 11.7. Sample PF-C2 is a comparative example of a PF composite containing untreated flax fiber. PF-C2-21/P2 is PF composite containing flax fibers treated with a bi-component aluminum-containing system. Burning time or burning length are the time or the length it takes for the fire stop after the external ignition flame was removed. Thus, a shorter burning time and length indicate a more fire resistant material. PF is a thermoset resin which itself has considerable resistance to fire. Thus, in the PF composites flax fiber mainly contributes to burning the com­posite specimen. As is evident from Table 11.8, fire-resistant flax fibers of this ap­proach provide a tremendously significant greater resistance to burning in the PF matrix than untreated flax fibers that allows the obtained composite with the treated flax fibers to be classified as self-extinguished (Fig. 11.6).

Figure 11.6 illustrates the remains of the PF composite flax fabric after VC-2 burning test. The PF composite with nontreated flax fabric has burned very much before the fire stops. However, the PF composite with treated flax behaves very dif­ferently, the fire stops very shortly after the torque was removed.

The SEM observation of the fracture composite specimens demonstrates a good fiber-matrix in both the untreated and treated flax composites. Figure 11.7 illustrates the resin sticks on the fracture fibers in both, untreated and treated fiber after ten­sile test. Thus, the treatment does not cause any harm to the fiber-matrix interface, which determines the mechanical properties.

Flexural properties of the PF/flax fiber composite samples are shown in Table 11.8. It is evident that PF composites containing fibers treated with a bi-component aluminum-containing system have comparable flexural properties with the refer­ence if standard deviation is taken into account. It is in coherent with the SEM observation.