Isolation of cellulose nanofibers from cassava bagasse and its use as tapioca-film filler

Abstract

Starch-based films limit their application due to poor mechanical properties. An effort to overcome these poor characteristics was using fibers or nanofibers as reinforcement filler. Cassava bagasse, a solid by-product of cassava starch industry, is a source of natural fibers. Cellulose nanofibers from the renewable sources have gained more attention in recent years because of their exceptional mechanical properties and environmental friendly. This research aims: (1) to know of cellulose nanofibers character produced from cassava bagasse; (2) to know physical and mechanical properties of film produced by application of cellulose nanofibers; and (3) to know of mechanical properties stability of film during storage at different environmental humidity conditions. Cellulose nanofibres from cassava bagasse were obtained by three methods, namely method I (alkali treatment + bleaching + mechanical treatment), method II (alkali treatment + bleaching + acid hydrolysis + mechanical treatment), and method III (acid hydrolysis + mechanical treatment). Cellulose nanofibers produced from method I have diameter of 20-30 nm, while cellulose nanofibers produced from method II and III have diameter of 5-8 nm with several micrometer of length. Cellulose nanofibers suspension have good stability, indicated by zeta potential value of method I, II, and III are 46.47 mV, 52.45 mV, and 33.75 mV, respectively. All method improved crystallinity of fibers from 14.52% in cassava bagasse to 33.25% (method I), 39.73% (method II), and 31.23% (method III). It was observed that the addition of cellulose nanofibers was improved tensile strength of films as much as 2.44-2.71 N/mm2, but tends to decrease of elongation at break as much as 16.51-31.14%. Water vapour transmission rate of film in range 143.21-166.56 g/m2.day and water vapoor permeability of film is 28.52-31.98 g.mm/m2.day.kPa. The addition of cellulose nanofibers also decreased the transparency of film. Storage condition with RH 75% for seven days cause tensile strength generally increased but elongation at break is decreased. Modulus of elasticity of film has increased during storage, indicating that the film stiffness also increased. Storage condition with RH 97% for seven days caused tensile strength and elongation at break decreased. Modulus of elasticity of film tends to decrease, indicating film structure getting soft during storage. Stability of cellulose nanofibers suspension not only reflects its ability to be well distributed in the matrix of the film, but also related to the crystallinity of cellulose nanofibers, further affect the mechanical properties of the film, improving the effectiveness cellulose nanofibers as a water vapour transmission barrier, and to support the transparency properties of the film. Cellulose nanofibers with higher crystallinity not only support the increased the strength of the film, but it can increase the effectiveness of the film as a water vapour transmission barrier, as well as inhibit the reduction of film transparency due to the use of fillers.