Effect of Titanate-Based Compatibilizing Agent Coated Walnut Shell Powder on Rigid Polyurethane Foam Composites

This study aimed to obtain less costly and environmentally friendly polyurethane foam by reducing the petroleum-based chemicals used in the production of rigid polyurethane foam in the industry by adding walnut shell particles compatibilized with titanate as a filler. In this work, after a titanate-based compatibilization of walnut shell particles (Ti-WS), rigid polyurethane (PU) foam composites filled at different Ti-WS weight ratios (1 wt.%, 5 wt.%, 10 wt.%, and 15 wt.%) were produced. Walnut shells used as fillers were first powdered and then compatibilized with titanate-based agent. Afterwards, the polyol and filler were mixed using an ultrasonic homogenizer, isocyanate was added, and the mixture was poured into the mold to finally obtain the polyurethane foam composite. The produced samples were subjected to chemical, microstructure and thermal analyses. From the results, no chemical interaction of the filler with the matrix structure was observed, and the small changes in peak intensities were due to intermolecular interactions occurring at the filler-matrix interface. In addition, it was seen that PU foam composites showed an improvement of the thermal conductivity with the augmentation of Ti-WS weight ratio and Ti-WS15 foam composite exhibited the higher thermal conductivity of 0.09454 W/m.K compared to the pure PU foam (0.02398 W/m.K) with an increase of 394%. Furthermore, as expected an increase of the filler content resulted in a reduction of the mean cell size of the foam up to 180 µm. Thanks to these improved properties, it can be stated that the use of walnut shell as a natural filler in PU foam composites can promote a new application path in converting agricultural waste into useful resources for creating a new class of green materials.