Alkaline twin-screw extrusion pretreatment of sugarcane bagasse for binderless material production by thermocompression

The objective of this study was to assess the effects of alkaline twin-screw extrusion pretreatment on sugarcane bagasse (SCB), including the extraction yield, solid residue chemical composition, and mechanical and water resistance properties of the resulting binderless self-bonded materials made by thermocompression. The parameters investigated were the NaOH concentration in relation to the dry SCB flow rate (0–10% [ w /w]), the screw rotation speed (150–250 rpm) and the effects of a washing step after pretreatment. Soluble molecule extraction from SCB was maximal at a 5.5% ( w /w) NaOH concentration, and the extraction yield increased when the screw rotation speed was reduced. The addition of NaOH reduced the mechanical action of the extruder and fiber defibration, but enhanced the chemical action on the fibers through the cleavage of covalent bonds within the lignocellulosic structure, resulting in increased extraction of molecules. Alkaline pretreatment modified the extrudate chemical composition, leading to increased hemicellulose and lignin solubilization and deacetylation, which resulted in a decline in the mechanical properties and water resistance of the materials obtained. The addition of a washing step removed the residual NaOH and water-soluble molecules in the extrudates, while slightly reducing thickness swelling in the final materials. Material made from the extrudate produced in the presence of 1% ( w /w) NaOH followed by a washing step had superior water resistance and good mechanical properties. The characteristics of the material obtained under these specific conditions were: 1486 kg/m 3 density, 53.8 MPa flexural strength, 5.5 GPa flexural modulus, 76% water absorption and 69% thickness swelling. • Alkaline extrusion pretreatment with NaOH was performed on sugarcane bagasse. • NaOH addition increased the cleavage of covalent bonds within the lignin-carbohydrate complex. • Alkaline pretreatment reduced mechanical action and fiber defibration. • Lower screw rotation speed improved L/S separation and extraction yield. • NaOH pretreatment reduced strength and water resistance of the final materials.