Kinetics of Water Sorption in Single Sterculia and Bauhinia Fibers at Ambient Temperature

Fundamental study on material properties of lignocellulose fiber is important to understand the performance of composite materials. In this study, we explored several material properties of untreated, commercial and wood ash alkali retted fiber obtained from relatively less studied and traditionally important wild plant species Sterculia villosa (local name Murgilo or Mudilo) and Bauhinia vahlii fibers (local name Bharlo). Water sorption kinetics in all fiber types was measured at ambient temperature. Fickian model then was used to fit experimental sorption kinetic data and information on diffusion coefficients at early and late stages of sorption, average diffusion coefficient, sorption coefficient, and water permeability were obtained. The average diffusion coefficient (D) for untreated, wood ash alkali and commercial alkali treated Sterculia was found to be 10.6 x 10-13 m2/ sec, 3.08 x 10-12 m2/sec, and 2.35 x 10-12 m2/sec; respectively. The corresponding values for Bauhinia fiber were found to be 6.8 x 10-13 m2/sec, 3.80 x 10-12 m2/sec, and 3.46 x 10-12 m2/sec; respectively. The equilibrium water sorption in the alkali treated fiber was significantly reduced due to removal of cementing materials and also increase of crystallinity. Significant decrease in mechanical strength of fiber in sorbed state was found. These findings will be useful to understand stability of fiber and potential end products such as paper sheets and reinforced composite materials exposed under different moisture conditions.