MODIFICATION OF NANOCRISTALLINE CELLULOSE AS BIO-REINFORCEMENT FOR POLYURETHANES FOAMS

Over the last several years many publications have focused on sustainable monomers to synthesize polymeric materials such as bio-based polyurethane foams (PUs). PUs is a class of materials with a lot of industrial applications (from insulation panels, structural reinforcement, sandwich construction to medical application)1 and are generally composed by polyol, isocyanate and several additives. PUs mechanical and functional properties are determined by the typology of polyols and isocyanate precursors, the distribution of the soft and hard segments from which PUs are composed and by the morphological structure in terms of open or closed cells. To avoid the problem of the big amount of chemicals produced from petroleum source, such as polyols and isocyanate utilized in the PUs formulation (the goal to produce sustainable PUs where both precursors are obtained from renewable resources is still a challenge), nanoparticles made from green and renewable materials are added replacing partially the polyol. Furthermore by modifying the surface of nanoparticle with isocyanate functional group also the amount of isocyanate can be reduced. An example of suitable nanoparticles that could be used is nanocrystalline cellulose (CNC). The combination of cellulose properties, such as low cost, chemical modification capacity, high Young's modulus, biodegradability, and abundance in nature, with features of the nanosized materials such as very large specific surface area, high aspect ratio, light weight, and outstanding reinforcing potential justifies the big interest of scientists towards this issue. On the other hand the cellulose hydrophilicity leads a bad dispersion in non polar matrices, the consequential nanocrystal aggregation decreases thermo-physical and mechanical properties of the nanocomposite. Herein, we propose the use of modified CNC (m-CNC) as reactive filler in polyurethane foams (PUs, fig. 1). To overcome the cellulose hydrophilicity, the CNC has been modified by linking covalently the bio-polyols on the m-CNC surface. In our strategy the silylation reaction in water to modify the surface of CNC followed by bio-polyol grafting was used. The CNC-grafted-polyols has been tested in the preparation of different composite PUs.