Saturated Polyester Polyols for Polyurethane Coatings

Saturated Polyester Polyols for Polyurethane Coatings When everyone learns what polyurethane is and where it is used in industry—a material used in the manufacture of many items in the construction sector and in everyday life—they are surprised. Learning about the history and current state of polyurethanes, which are used in virtually every area of our lives, is thought-provoking. Polyurethanes are a form of polymer that can be used in various applications. They are polymers composed of organic molecules bonded together through urethane linkages. Polyurethane exists in various shapes and sizes. Most are thermosets. They do not melt at high temperatures and retain their solid state. Thermoplastic polyurethanes melt when exposed to a certain amount of heat. Both flexible and rigid foams, films, and coatings are common in our daily lives. Polyurethanes are produced as a result of the reaction of polyols with isocyanates. The first findings were reported by Bayer and colleagues in 1937 [1]. Polyurethane materials are used as rigid and flexible foams, elastomers, adhesives, varnishes, and resins and have widely varying properties. Rigid and flexible foams are the most typical polyurethane applications. They are used in the construction, transportation, bedding and furniture, and packaging sectors [2]. The properties of polyurethane materials are determined by the different molecular weights and ratios of the monomers of the polyester polyol from which they are made. Polyurethane foam created with a highly branched polyol is resistant to chemicals and high temperatures. More flexible polyurethane foams have less branched polyols. Condensation polymerization of dicarboxylic acids or their esters or anhydrides with monomeric diols such as diethylene glycol and 1,4-butanediol produces polyester polyols with linear structures. Branched polyester polyols can be formed by combining triols such as glycerol and 1,1,1-trimethylol propane. According to their poliol structures, polyester polyols are classified as aliphatic or aromatic polyester polyols. The dicarboxylic acids/anhydrides most typically used in the production of aliphatic and aromatic polyester polyols are adipic acid and phthalic anhydride, respectively. Figure 1 shows typical polyester polyols formed by adipic acid and 1,4-butanediol or phthalic anhydride and diethylene glycol. Aromatic polyester polyols are stiffer than aliphatic polyester polyols and are widely used to produce fire-resistant rigid polyurethane foams. While isocyanates can be used in polyurethane production, poliol-isocyanate reactions are the most popular, especially in commercial polyurethane production. Various routes are implied, including type monomer reactions [5], self-condensation of AB-type monomers with hydroxyl and acyl azide groups [6], trans-urethane reactions between diurethanes and diols, and AB-containing hydroxyl and methyl carbamate groups for the produced polyurethanes, without isocyanates. Polymeric polyols serve as building blocks for polyurethane backbones, being high molecular weight polymers. The most popular polymeric polyols are polyether and polyester polyols. Alkylene oxide monomers such as ethylene oxide and propylene oxide, or combinations of these two monomers, using a multi-hydroxyl alcohol as an initiator (e.g., the alkoxylation process often uses base catalysts such as alkali metal hydroxides [7]). The mechanical and thermal properties of PUs are frequently used to classify them. For specific end users such as thermal conductivity for PU insulation boards, water and organic solvent resistance properties, and/or weather resistance properties for PU coatings, additional performance characteristics are evaluated. Coatings Polyurethane compounds are widely used as topcoats and varnishes to protect or insulate wood. According to some, this process creates a solid, wear-resistant, and long-lasting coating, preferred for parquet floors, but difficult or unsuitable for finishing furniture or other complex components. Polyurethane coatings are produced in two-component, isocyanate-free reactive, and single-component systems, with the first two being most commonly used [7, 8]. A polyol and an isocyanate are mixed before application and then cure at room temperature in two-component solutions. Before hardening, a polyol is combined with a blocked isocyanate to produce oven-cured two-component polyurethane coatings. When heated, the blocked isocyanate breaks down, allowing the isocyanate groups to react with the polyol. Isocyanate-free reactive solutions, such as in applications like water-based polyurethane dispersions, do not require further reaction with isocyanates. In single-component systems, prepolymers with low isocyanate content harden by reacting with moisture. As a result, they are sometimes referred to as moisture-curing systems. SEM, DMA, and/or DSC and TGA are used to characterize the morphology and thermal properties of polyurethane foams, as well as to characterize the morphology and thermal properties of their coatings. Adhesion, flexibility, hardness, water and organic solvent resistance, viscosity, and tensile strength are commonly evaluated characteristics in coating applications. PU coatings produced from polyether and polyester polyols show different performance depending on the poliol structure (Table 1) [8]. Polyurethane coatings are widely used in a number of industries, including automotive, electronics, wood products, and equipment [9], due to their hardness combined with exceptional low-temperature flexibility, as well as high chemical, solvent, and wear resistance. İzel Kimya is conducting research on the use of bio-based raw materials in the production of saturated polyester polyols and their applications in can and coil coatings. References 1. Bayer O, Siefken W, Rinke H, Orthner L, Schild H (1937) A process for the production of polyurethanes and polyureas. German Patent DRP 728981. 2. https://www.marketsandmarkets.com/Market-Reports/polyurethane-foams-market-1251.html. 3. Mahendran AR, Aust N, Wuzella G, Müller U, Kandelbauer A (2012) Bio-based non-isocyanate urethane derived from plant oil. J Polym Environ 20:926–931. 4. Fleischer M, Blattmann H, Mülhaupt R (2013) Glycerol-, pentaerythritol-and trimethylolpropane-based polyurethanes and their cellulose carbonate composites prepared via the non-isocyanate route with catalytic carbon dioxide fixation. Green Chem 15:934–942. 5. Deepa P, Jayakannan M (2008) Solvent-free and nonisocyanate melt transurethane reaction for aliphatic polyurethanes and mechanistic aspects. J polym Sci A Polym Chem 46:2445–2458. 6. Palaskar DV, Boyer A, Cloutet E, Alfos C, Cramail H (2010) Synthesis of biobased polyurethane from oleic and ricinoleic acids as the renewable resources via the AB-type self-condensation approach. Biomacromolecules 11:1202–1211. 7. Szycher M (1999) Szycher's handbook of polyurethanes. CRC Press, Florida. 8. Randall D, Lee S (2002) The polyurethanes book. John Wiley & Sons Ltd., UK. 9. Coutinho F, Delpech MC, Alves LS (2001) Anionic waterborne polyurethane dispersions based on hydroxylterminated polybutadiene and poly (propylene glycol): synthesis and characterization. J Appl Polym Sci 80:566–572. Dr. Cemil Dizman R&D Director İzel Kimya M.Sc. Canan Aslan R&D Specialist Researcher İzel Kimya