Cellulose as a polyol in the synthesis of bio-based polyurethanes with simultaneous film formation

Despite the wide availability of cellulose, this polyhydroxylated polysaccharide has practically not been used in the synthesis of polyurethanes (PUs), a family of polymers with great versatility. Microcrystalline cellulose (MCC) was used as a polyol to synthesize PUs, mostly at room temperature, with no solvent or catalyst, and simultaneous film formation. Castor oil (CO) was used as an additional polyol and MCC dispersant in the reaction medium. 0–60% of MCC was used regarding the concentration of hydroxyl groups in CO. FTIR spectroscopy indicated that all of the isocyanate groups reacted. The films were extensively characterized; in short, they exhibit transparency, high crystallinity (~ 75%; scanning electron microscopy and polarized light microscopy suggest the formation of spherulite), intermediate hydrophobicity (contact angle > 85°). Considering the control film (100% CO as polyol) and the film prepared using 60% MCC, T g ranged from sub-ambient (9 °C) to 78 °C, tensile strength from 0.2 to 14 MPa, Young's modulus from 2 to 474 MPa, and elongation from 21 to 13% (the film prepared using 45% MCC showed 102%). The results from ultraviolet–visible spectroscopy, thermogravimetry, and swelling tests are also shown. The properties of the films formed during the reaction performed at 100 °C (using 60% MCC) were discussed. Biocompatibility tests showed cell viability above 90% after 168 h, indicating non-cytotoxicity for the tested films. The wide range of results demonstrated the feasibility of using MCC as a polyol, indicating applications for the films generated as coatings, packaging, dressings, among others. As far as is known, the approach of this study is unprecedented. Graphical abstract