Synthesis of bio based polyurethane surface coating materials and characterization

During the last few years, there is a continuous search of advanced polymeric materials for coating applications. Polyurethane resins are a class of thermosetting polymer materials largely used in high performance surface coatings and paints. Fast depletion of petroleum stock and increase in their cost puts limit to their use in future for production of petroleum-based resins. Renewable resources used in the preparation of polymers are falling in the class of biomaterials which are rich in hydrocarbons and most of the times obtained from parts of profusely available agriculture feed stock. The current oil based polymers are prepared by consuming petroleum based anhydrides and dicarboxylic acids. Use of non-edible vegetable oils and their fatty acids are currently the raw materials focused in synthesizing polymeric materials as renewable sources due to increasing economic and environmental concerns of petroleums. Polyurethanes have found many applications starting from coating, paint, foam, thermosetting, thermoplastic elastomer to fiber. However, their relatively low abrasion and wear resistance and environmental degradation, limit their application in surface coating. In the past decade, nanostructure organic-inorganic composites based on organic polymer and inorganic materials have attracted great interest of researchers.These composites exhibit the enhanced performance properties compared to conventional composites because of the maximized interfacial contact between the organic and inorganic phases. So, proper design of polyurethane with appropriate structure and composition of the components may result unique and useful properties for its different end applications. In the present work we have attempted to utilize the castor oil for the synthesis of biopolyurethane coating material. The double bonds in triglycerides are not active enough to take part in free radical polymerization reaction generally. Maleation is a method to increase crosslink density of the final polymer thanks to reactive maleate double bonds. To convert maleated oils into polyols, it was first epoxidized. Hydroxylation of castor oil was carried out with hydrogen peroxide. It was further reacted with different isocyanates in different ratios to develop a series of biopolyurethanes. The synthesized polyurethanes were characterized for the evaluation of their chemical and thermal properties and the effect of isocyanates loading into polyurethane on these properties are also being presented. The thermal properties of biopolyurethane coating materials were studied using thermo gravimetric analysis (TGA). The effect of NCO/OH molar ratio on thermal and mechanical properties of coatings was studied for the prepared biopolyurethane coatings.