11.4.1 FIBER TREATMENT

11.4.1.1 FIBERS TREATED WITH SINGLE COMPONENT SOLUTIONS

Flax fiber C1 and C2 as described in Table 11.2 was treated with different single component solutions as indicated in Table 11.3 for 120 s using the process P1. Burn­ing tests were conducted in accordance with the general procedure described above and the results from the burning tests are also shown in Table 11.3. It is evident from Table 11.3 that all of the C1 fibers treated with various single component systems are not self-extinguishing, although these treatments slowed down flame propaga­tion. Fibers treated with NaOH or KOH did not continue to burn but did continue to glow. Fibers treated with NaOH and then washed with water did continue to burn, demonstrating that any fire resistant effect afforded by an alkali metal hydroxide alone is easily removed if the fibers get wet. Collectively, Table 11.3 demonstrates that single component systems of metal hydroxides, metal salts or clays do not im­part self-extinguishing properties on fibers treated with the systems.

The difference in surface structure between the untreated and treated flax fibers are illustrated in Fig. 11.3. In general the single component systems do not provide a good coating on the flax fiber surface. Among them LDH and MMT provide better coverage but the can be peeled off easily during handling the fibers. These can be the reason for their poor fire retardant performance.

FIGURE 11.3 SEM image of the flax fibers: treated with a) NaOH, b) BaCl2, c) Ba(OH)2, d) LDH, e) MMT and f) untreated.

11.4.1.2 FIBERS TREATED WITH BI-COMPONENT SOLUTIONS

Flax fiber C1 and C2 were treated with different bi-component systems as indicated in Table 11.4. It is evident that all of the C1 fibers treated with bi-component systems involving the mixture of barium chloride and sodium hydroxide are self-extinguish­ing. Fibers treated with barium chloride alone then with clay or barium hydroxide alone then with clay are not self-extinguishing. Thus, single component systems are not self-extinguishing, even with the subsequent addition of clay. A mixture of both the alkaline metal salt and the alkali metal hydroxide is needed to make the fibers self-extinguishing. It is further clear that washing the fibers after treatment with a bi-component system does not remove the self-extinguishing properties imparted by the treatment. Further, the order in which clay is introduced into the bi-component does not affect the self-extinguishing properties of the fibers after treatment.

For the C2 series fibers treated with (MgCl2+NaOH) and with (CaCl2+NaOH) are self-extinguishing. Fibers treated with (Mg(NO3)2+NaOH) and with (Ca(NO3)2+NaOH) did not burn but continued to glow. Fibers treated with (MgSO4+NaOH) continued to burn, but at a slower rate than untreated fibers. The efficiency of the (MgCl2+NaOH) system is greater than the (Mg(NO3)2+NaOH) sys­tem, which is greater than the (MgSO4+NaOH) system. This is also similar for the calcium-containing systems where the efficiency of the (CaCl2+NaOH) system is
greater than the (Ca(NO3)2+NaOH) system. Thus, chloride is the most preferred counter anion for the alkaline earth metal cation.

Figure 11.4 illustrates the fibers treated with the bi-component systems provid­ing better coating and adhesion of the chemical on the fiber surface thus preventing the treated fiber from burning.

FIGURE 11.4 SEM image of the flax fibers treated with a) NaOH+MgCl2, b) NaOH+BaCl2 and c) NaOH+BaCl2+MMT.

with BaCl2 formed the black char and the fibers treated with (NaOH+BaCl2) or (NaOH+BaCl2+MMT) become self extinguishing. This indicates this treatment method is very effective depending on the selective chemical combination and event the treatment can be performed directly in the fabric and not necessary at individual filament level.