Interaction of chitosan biopolymer with silica nanoparticles as a novel retention/drainage and reinforcement aid in recycled cellulosic fibers

Processing recycled cellulosic fiber suspension in papermaking has been a main industry concern. Chitosan as a natural biopolymer has been considered recently. The presence of amine groups gives this material an opportunity to gain cationic charge especially in the acidic conditions. Also, its straight polymeric chain consisting of (1–4) linked 2-amino-2-deoxy-β-d-glucan monomer is a unique property for make bridge between fibers, fines and fillers. In this new approach, the performance of chitosan in conjunction with anionic nano-silica as a novel nanoparticle system for improving the drainage/retention and dry strength of recycled waste office pulp was considered. FTIR analysis was used to predict probable interaction between chitosan and nano-silica in suspension. The results indicated that this system could improve drainage and fiber fines/fillers retention. Considering the economical and environmental aspects, 1% chitosan and 0.1% nano-silica was the proper treatment with 42 and 168% gain of drainage and fiber fines/fillers retention in comparison to control pulp, respectively. FE-SEM and ash content analysis of recycled paper also visualized filler retention properly. It seems that micro-flocculation, which may happen according to the semi-reversible bridging mechanism is the main reason for improvement of retention and drainage. Micro-Kjeldahl and EDX results confirmed chitosan retention in final cellulosic paper handsheets. Improving some mechanical and physical properties (apparent density, tensile index, burst index, tear index) seems to complete its mission as proper recycled cellulosic paper reinforcement.