Green based composite polyurethane coatings for steel

The polyurethane composites based on vegetable source were prepared and their properties were investigated. Castor oil was used as polyol and diatomite and birch flour were used as fillers. The introduction of diatomite led to development of ordered quasi-lamellar morphology of polyurethane matrix. This effect in combination with loading of birch flour with fiber structure allowed to obtain polymer composites with improved tensile strength (up to 14 MPa, an increase on five times in comparison with the neat polyurethane). The glass-transition temperatures of polymer composites increased more than 40 °C relative to the neat polymer. Adhesion to steel increased more than in five times in comparison with the neat polyurethane for composite containing 20 wt% diatomite additives). The SEM and FTIR spectroscopy techniques were used to evaluate the microphase structure of the polyurethane composites. SEM micrographs showed that the diatomite particles served as nucleation centers for formation of lamellar-like structure of PU matrix. At the optimal loading (20 wt%) the almost uniform lamellar-like structure of PU matrix was formed, that provided the best mechanical performance of PU composites. However, as FTIR study showed, formation of lamellar-like structure of PU matrix did not induce its inner microphase transformation. The presence of wood fibers in composites, despite their better mechanical performance, led to the decrease of their adhesion to steel. Graphical abstract