Development of eco-friendly water-based polyurethane varnish and investigation of film properties

Various varnishes and coating materials are used to ensure that wooden materials can be used without any problems for many years and to preserve and improve their aesthetically beautiful colors and natural appearance. Water-based polyurethanes (WPU), one of the essential polymer classes commercially used in the surface coating industry today, are an environmentally friendly material that meets the minimum volatile organic component requirements with the advantages of film-forming at room temperature, offering superior performance properties and structural controllability. Recently, due to environmental concerns, a rapid decrease in world crude oil stocks and increasing crude oil prices, the use of polyols obtained from vegetable oils in polyurethane production is very important for sustainable development because they are renewable, low cost and easily modified. On the other hand, it is of great importance to develop new product formulations in order to improve the weak properties of water-based polyurethanes and provide longer-term protection and durability in coating applications. In this thesis, it was aimed to develop environmentally friendly, plant-derived polyol-based and nanocrystalline cellulose (NCC) reinforced water-based polyurethane varnish materials with superior mechanical properties. In the first stage of the study, polyol (UCYOL) with a hydroxyl number of 210 KOH/mg and a molecular weight of 2075 g mol-1 was obtained by the thiol-ene reaction from grape seed oil, and its structure was revealed by FTIR and 1H-NMR analyses. Self-crosslinking water-based polyurethane dispersions (WPU) were synthesized in the presence of a diamine chain extender [3-(2-aminoethyl) amino propyl] trimethoxysilane (AEAPTMS) using the resulting polyol and isophorone diisocyanate (IPDI) as the isocyanate. In order to obtain stable WPU dispersions with desired properties, firstly, a series of experiments were carried out to determine the optimum synthesis conditions. The polyol/isocyanate ratio was kept constant as 1/3, which was used for all experiments. In order to increase the interaction between the WPU matrix and NCC in the preparation of NCC-containing WPU nanocomposites, NCC nanoparticles were modified with AEAPTMS to give SNCC-containing WPUs. WPU dispersions containing three different ratios of NCC and SNCC were prepared to investigate the effect of the modification process on the final product properties. The impact of functional nanoparticle content on the physical, mechanical and thermal properties of the obtained WPU dispersions and films was investigated in detail using various characterization methods. In general, it was observed that the addition of SNCC increases the tensile strength, hydrophobicity, water resistance and thermal stability of the WPU film. In order to test the usability of various water-based polyurethane dispersions obtained at the end of the study as varnish, water-based varnish formulations were prepared by adding auxiliary varnish agents such as wetting agent, defoamer, adhesion promoter and additional solvent to WPU dispersions. The surface appearance, water resistance, anti-adhesion properties and pencil hardness of the obtained water-based varnish films were determined.