Abstract

The effect of using different mercerization media on some mechanical properties of local plant bast fibres, Roselle (Hibiscus sabdariffa), kenaf (Hibiscus cannabinus), okra (Hibiscus esculentus), Baobab (Adansonia digitata) respectively, were generally investigated. The fibres from these sources were purified using the retting method which involved heating with 15% ammonium oxalate followed by scouring using 2% sodium hydroxide (NaOH) solution and finally bleaching with 5% hydrogen peroxide (H₂O₂). All the fibres were subsequently mercerized at a temperature of 5°C for 20 min using 10, 15, 20, and 25% NaOH solutions in turn. The parameters used to evaluate their potential as raw materials for textile making under different treatments (different NaOH concentrations) include extension at break, tenacity, specific work of rupture and density. Results show that the variation in the magnitude of extension at break is in the following order: for Roselle we have 25 > 15 > 20 >10%, for Kenaf 10 > 20 > 15 and 25%, for Okra 25 > 15 > 10 > 20% and for Baobab 20 > 15 > 25 > 10%. Tenacity values for the fibres show the following variation in order of magnitude: for Roselle 25 > 20 > 10 > 15%, for Kenaf 10 > 20 > 15 > 25%, for Okra 10 > 20 > 15 > 25%, and Baobab 10 > 20 > 15 > 25%. While specific work of rupture shows the following order: 25 > 10 > 20 > 15% for Roselle, 10 > 20 > 15 > 25%, for Kenaf, 10 > 15 > 20 > 25% for Okra, and 15 > 10 > 20.25% for Baobab. For the Density (g/cm³), the variations are in the following order: For Roselle 10 > 15 > 20 > 25%, for Kenaf 10 > 15 > 20 > 25%, and for Okra and Baobab 10 > 15 > 20 > 25, 10 > 15 > 20 > 25 respectively. From the forgoing, we can say that mercerization condition exert significant effect on the properties of the fibres studied and this may be traced to the structural features of these fibres. Thus, Baobab appears to have high percentage extension at break compared to the other fibres. In all cases investigated, different ranges of values are associated with the parameters involved, thus extension at break range between 2.0 - 7.6 mm, tenacity 0.21 - 1.0 kgf, specific work of rupture 0.01 - 0.28 kgf  while density range between 1.19 - 1.45 g/dm³ for the materials. The relative proportions of amorphous (higher in Baobab) to crystalline regions are presumed to be the major determinant in the variation of these properties.

 Key words: Bast fibre, mercerizations, tenacity, work of rupture.