Suitability of steam exploded residual softwood for the production of binderless panels. Effect of the pre-treatment severity and lignin addition

A steam explosion pre-treatment was applied at various severities to softwood residual substrate to determine the most suitable pre-treatment for the manufacture of binderless panels. The effect of adding acid to the pre-treatment of fibres was also evaluated. The changes in the chemical composition and morphology of the original material were investigated by fractionation analyses and scanning electron micrographs. High severities caused defibrillation of the material allowing to build links to form the panels. Prehydrolysis with acid had a great effect on the structure of the material even at low acid concentration. The physical and mechanical properties of the panel improved as the severity of the pre-treatment increased up to a point where mechanical properties deteriorated. The composites with highest internal bond had a high cellulose content and a medium lignin content. All these factors suggested that steamed pre-treated residual could be improved by adding a natural binder to produce the panels. A test of producing panels with addition of several kinds of lignin (up to 20%) was performed. With no significant changes in density, water stability (thickness swelling and water absorption) internal bond and mechanical properties were greatly improved. Results after accelerated ageing test were also enhanced.