Chemically Functionalized Cellulose Nanocrystals as Reactive Filler in Bio-Based Polyurethane Foams

Cellulose Nanocrystals, CNC, opportunely functionalized are proposed as reactive fillers inbio-based flexible polyurethane foams to improve, mainly, their mechanical properties. To overcomethe cellulose hydrophilicity, CNC was functionalized on its surface by linking covalently a suitable biobased polyol to obtain a grafted-CNC. The polyols grafted with CNC will react with the isocyanate inthe preparation of the polyurethane foams. An attractive way to introduce functionalities on cellulosesurfaces in aqueous media is silane chemistry by using functional trialkoxy silanes, X-Si (OR)3. Here,we report the synthesis of CNC-grafted-biopolyol to be used as a successful reactive filler in bio-basedpolyurethane foams, PUFs. The alkyl silanes were used as efficient coupling agents for the graftingof CNC and bio-polyols. Four strategies to obtain CNC-grafted-polyol were fine-tuned to use CNCas an active filler in PUFs. The effective grafting of the bio polyol on CNC was evaluated by FTIRanalysis, and the amount of grafted polyol by thermogravimetric analysis. Finally, the morphological,thermal and mechanical properties and hydrophobicity of filled PUFs were thoughtfully assessedas well as the structure of the foams and, in particular, of the edges and walls of the cell foams bymeans of the Gibson-Ashby model. Improved thermal stability and mechanical properties of PUfoams containing CNC-functionalized-polyol are observed. The morphology of the PU foams is alsoinfluenced by the functionalization of the CNC.