Valorization of Tunisian alfa fibres and sumac tannins for the elaboration of biodegradable insulating panels

Alfa leaves are important renewable raw materials in Tunisia where they are used basically in handcrafts and paper industry. Sumac is also an abundant species in Tunisia known for its high tannin content and is basically used in traditional medicine. To valorize these natural resources, we studied, for the first time, the possibility of making insulating panels based on alfa fibres and sumac tannins based adhesive. Firstly, alfa leaves were treated with an alkali solution as it is one of the standard procedures commonly used in the paper industry to extract cellulosic fibres. Mercerization effects were studied by characterizing fibres thermal properties and fibres surface morphology. Secondly, the sumac tannin based resin was formulated and characterized. Finally, the insulating panel was elaborated and characterized by determining its thermal conductivity. The thermal gravimetric analysis results show improvement in the thermal stability of fibres after alkali treatment. Environmental Scanning Electron Microscopy showed changes on treated alfa surface which could promote the fibre-matrix adhesion. The reactivity of sumac tannins to formaldehyde test (Stiasny number) showed the possible use of sumac tannins in wood adhesive formulation. Thermomechanical analysis and strength analysis of sumac tannin/hexamin based resin highlighted acceptable bonding properties. The thermal conductivity measurement showed an average value equal to 0.110 W/m K.