Mechanical Potential of Adhesives Elaborated with the Gramineae Stem Lignin

Abstract

The aim of this work is to valorize local materials and to replace synthetic resins in the wood industry with biodegradable resins made from renewable resources such as the dry stems of herbaceous plants. Klason extracted the gramineae stem’s lignins of Andropogon gayanus and Sorghum bicolor and then Soda methods then characterized using attenuated total reflectance Fourier transform spectra in the 4000 and 400 cm^-1 range. Their decompositions were studied using Thermogravimetric Analysis. Their yield from lignins extractions are respectively 19.26% and 24.9%. Guaiacyl, Syringyl, p-hydroxyphenylpropane, phenols and secondary alcohols are present in these lignins. The gel times of their adhesive using paraformaldehyde as hardener decreases as the pH increases. At pH=12, these gel time values are, respectively 6.6 and 7 minutes. These lignins begin to decompose at 291°C. The Modulus of elasticity was studied by thermomechanical analysis and wood particleboards were prepared bonded with these resins. The stiffness of Andropogon gayanus lignin resin is better than that of Sorghum bicolor (4339.08 > 3767.87MPa). The Internal Bond strength of Particleboards manufactured with 10% of total adhesive solids on dry wood particles are respectively 0.37 and 0.41 MPa. These two lignins are good for wood adhesives. The average MOR and MOE values for the manufactured Andropogon gayanus and Sorghum Bicolor particleboards are respectively 14.51MPa and 1850.6MPa and 16.5MPa and 2053.4MPa. The manufactured particleboards have a low resistance to humidity and that they can only be used in a dry environment.