Effect of wheat husk surface pre-treatment on the properties of husk-based composite materials

The effect of different types of winter wheat husks treatments (alkaline, hydrothermal and plasma treatment) on the properties of the particle material, as well as on composite materials made from such pre-treated husks, was studied. After pre-treatment, the surface energy, equilibrium moisture content, surface morphology using SEM, elemental content on the surface and the fluorescence life time (FLIM) of husks were estimated, as well as the IR spectra (FTIR) of pre-treated husks. Boards with target density of 450 kg/m(3) were produced using urea-formaldehyde resin (resination 9%) and the equilibrium moisture content, thickness swelling, vertical density profile, internal bonding, bending strength and insulation properties of boards were examined. Modification in 2% sodium hydroxide solution caused noticeable erosion of husks resulting in higher lignin content, higher equilibrium moisture of husks and consequently higher thickness swelling of boards made from pre-treated husks and lower mechanical properties of those boards. Both hydrothermal (boiling in water) and plasma treatment (air plasma at atmospheric pressure, jet system of application) resulted in the desired effect in terms of an increase in the surface energy of husks, decrease of husk equilibrium moisture content and increase of mechanical properties of boards. All of the manufactured boards exhibited low thermal conductivity that ranged from 0.0714 W/(mK) to 0.0783 W/(mK).