The Effect of Mechanocatalytic Pretreatment on the Structure and Depolymerization of Willow

In this study, the effect of a mechanocatalytic pretreatment on the structure of willow and sugar release from pretreated willow was explored. In the mechanocatalytic approach, the pretreatment consists of solvent-free impregnation with sulfuric acid and a mechanical treatment with ball milling. Willow sawdust and pretreated samples were analyzed with field emission scanning electron microscope and X-ray diffraction. The products in the sugar solution were determined as the total reducing sugars with the 3,5-dinitrosalicylic acid method and monosaccharides with capillary electrophoresis. According to the results, milling increased the sugar production, depending on the sulfuric acid load. The milling parameters, such as the rotation speed of the mill, the catalyst-to-willow ratio, and the milling time influenced the amount of sugars in the hydrolysate and the composition of the sugar solution produced. Changes were observed in the surface of the willow particles as well as changes in the crystalline structure. Glucose and xylose yields increased after 15 min of milling and reached their maximum level after 45 min of milling with the 0.5 mmol/g sulfuric acid load.