Environmentally friendly approaches for the tuning of cellulosic paper properties through polysaccharide-reinforced silica coatings

Abstract Cellulosic paper, a renewable-based and biodegradable material, is used in various applications, such as writing, filtration, packaging, and insulation. The impact of environmentally friendly coatings on enhancing the mechanical properties of ultrathin specialty paper was investigated in this study. The coatings, composed of organic/inorganic composites representing eco-friendly substances, include silica, which is introduced in an aqueous sol–gel process catalyzed by citric acid and sodium hydroxide, providing a “greener” alternative to traditional methods. TEOS (tetraethyl orthosilicate) sols and TEOS composites enriched with polysaccharides, such as micro-fibrillated cellulose (MFC), cellulose nanofibers (CNF), starch, and alginate, were explored as coatings to tune the paper’s mechanical properties. The coatings were applied by spray-coating, significantly enhancing tensile and flexural strength. TEOS/starch and TEOS/alginate coatings improved the tensile strength from 15 to 31 and 29 MPa, respectively. In contrast, the application of alginate resulted in slightly stiffer papers, and starch in more ductile ones. The flexural strength was notably increased with TEOS/alginate and TEOS/alginate/CNF coatings, from 8 to 15 and 14 MPa, respectively. Mechanical properties normalized to the added coatings’ solid content revealed that the TEOS sol was the most effective approach to boost both parameters. Coated papers showed improved resistance to water and abrasion compared to the reference material. Their surface morphology was analyzed using SEM, and silica/polysaccharide networks were examined with 29 Si NMR spectroscopy. Gelation points were determined by UV/Vis spectrophotometry, and TGA and contact angle measurements showed no significant impact on the related paper properties. These findings demonstrate the potential of TEOS sol and composites to tune and enhance the mechanical performance of ultrathin specialty papers. Graphical abstract