*2.2. Pulping Process*

The olive chips were subjected to a pulping process in a 15 L capacity reactor, heated by an external heating jacket and rotated by means of a horizontal axis. The process carried out was a soda pulping process using 16% NaOH (on dry matter) as a reaction agent, at 170 ◦C for 60 min and a liquid/solid ratio of 8:1. The conditions were selected according to previous studies and the experience of the research group for the production of cellulose pulp for paper production [31,32] After pulping, the treated chips were dispersed in a pulp disintegrator for 30 min at 1200 rpm. Once the chips were disintegrated, the fiber was passed through a Sprout-Bauer beater and separated by sieving through a netting of 0.14 mm mesh size. The cellulosic pulp was centrifuged to remove excess water and left to dry at room temperature until use. Afterwards, the unbleached pulp was subjected to a bleaching process. For this purpose, 0.3 g of sodium chlorite per gram of pulp was incubated in a 0.3% pulp suspension in water at 80 ◦C for 3 h. After cooling, the pulp was filtered and washed with acetone and several cycles of distilled water (Figure S1). This bleaching process allows the removal of practically all the lignin present in the fiber, maintaining the entire carbohydrate composition [33]. This makes it possible to study the effect of lignin on the production of cellulose nanofibers and their characteristics.
