5.2.3.2 PretreatmentsTypically, to produce CNC, cellulose has to be previously isolated to be directly attacked. The composition of the cellulose sources depends on their origin. In the cases of cotton, BC, and MCC, only cellulose is present. However, when CNC are desired to be obtained from biomass,including wood and agricultural residues, not only cellulose is present but also different extractives, hemicelluloses, lignin, or inorganic particles. In these cases, different pretreatments have been applied prior to acid hydrolysis. A general procedure is often the following:the first step is the removal of extractives (dewaxing) using dichloromethane, acetone, or ethanol/benzene, depending on the raw material [193]. The mixture 2:1 benzene/ethanol often gives the maximum level of extractives since low-molecular-weight carbohydrates and polyphenolsare also dissolved. Depending on the state of the raw material, different proportions solid/liquid have to be used to get the best results.