Determining the surface free energy of cellulose materials with the powder contact angle method

Different treatment processes such as alkaline washing, bleaching, and slack-mercerization are used to improve the sorption characteristics of cellulose fibers. The differences between the sorption properties of cellulose fibers are measured with tensiometry, and their sorption velocities are measured with liquids of different polarities. From those measurements, contact angles are determined using the Washburn equation. The surface free energy of the cellulose fibers is determined from contact angle data obtained with the Owens-Wendt-Rabel-Kaeble approximation. Results show that among these treatments, slack-mercerization produces the lowest contact angle and the highest surface free fiber energy, and has therefore the largest influence on sorption ability. Viscose fibers (raw and treated) have the lowest contact angle and the highest surface free energy, and are the most hydrophilic compared to lyocell and modal fibers. This is explained by their crystalline structure and the accessibility of their surface groups to polar liquids.