Saturated Polyester Polyols for Polyurethane Coatings
When we learn what polyurethane is, and where it is used in the industry of many items we use in construction and daily life, it is surprising to everyone. Learning about the history and present of polyurethanes, which are used in practically every aspect of our lives, is intriguing.
Polyurethanes are a form of polymer that can be used in a variety of applications. They are polymers made up of organic molecules bonded together by urethane. Polyurethane is available in a variety of shapes and sizes.
Most of them are thermoset. 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 all common in our daily lives.
Polyurethanes are produced by the reaction of polyols with isocyanates. The first findings were given by Bayer and colleagues in 1937 [1]. Polyurethane materials are used as rigid and flexible foams, elastomers, adhesives, varnishes and resins and have a wide variety
of properties. Rigid and flexible foams are the most typical polyurethane applications.
It is used in the construction, transportation, bedding and furniture and packaging industries [2]. The properties of polyurethane materials are determined by the different
molecular weights and ratios of the monomers of the polyester polyol from which it is made.
Polyurethane foam formed with multi-branched polyol is resistant to chemicals and high temperatures. More flexible polyurethane foams have less branching 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 polyol structure, polyester polyols are classified
as aliphatic or aromatic polyester polyols. The most typically used dicarboxylic acids/anhydrides in the production of aliphatic and aromatic polyester polyols, respectively, are adipic acid and phthalic anhydride.
Figure 1 shows typical polyester polyols formed by adipic acid and 1,4-butanediol or phthalic anhydride and diethylene glycol. Aromatic polyester polyols are harder than aliphatic polyester polyols and are commonly used to produce flame resistant rigid polyurethane foams.
Although isocyanates can be utilized to manufacture polyurethanes, polyol-isocyanate reactions are the most popular, especially in commercial polyurethane production. Several routes are implicated, including type monomer reactions [5], self-condensation of type
AB monomers with hydroxyl and acyl azide groups [6], trans-urethane reactions between diurethanes and diols, and AB containing hydroxyl and methyl carbamate groups for polyurethanes generated without isocyanates.
Polymeric polyols are high molecular weight polymers that serve as the building blocks for polyurethane backbones. The most popular polymeric polyols are polyether and polyester polyols.
Base-catalyzed alkoxylation of alkylene oxide monomers such as ethylene oxide, propylene oxide, or combinations of these two monomers, with a multi-hydroxyl alcohol (e.g. glycerol, pentaerythritol) as an initiator, is a typical way to make petroleum-based polyether polyols.
The alkoxylation process frequently employs base catalysts such as alkali metal hydroxides [7]. The mechanical and thermal properties of PUs are frequently used to classify them.
Additional performance qualities for specific end users are evaluated, such as thermal conductivity for PU insulation boards, water and organic solvent resistance capabilities, and/or weathering properties for PU coatings.
Coatings
Polyurethane compounds are commonly used as topcoats and varnishes to preserve or seal wood. According to some, this process creates a robust, wear-resistant, and long-lasting coating that is preferred for hardwood floors but difficult or unsuited for finishing
furniture or other intricate components.
Polyurethane coatings are produced in two-component, isocyanate-free reactive and one-component systems, and the first two are most commonly used [7, 8]. A polyol and an isocyanate are mixed prior to application and then cured at room temperature in two-component solutions. Prior to curing, a polyol is combined with a blocked isocyanate to make oven cured two-component polyurethane coatings.
When heated, the blocked isocyanate dissolves the blockage, allowing the isocyanate groups to react with the polyol. Non-isocyanate reactive solutions do not require further reaction with isocyanates in applications such as water-based polyurethane dispersions.
They’re sometimes referred to as moisture-curing systems as a result of this. In the same way as SEM, DMA, and/or DSC and TGA are used to characterize the morphology and thermal properties of polyurethane foams, they are also used to characterize the morphology and thermal properties of their coatings.
Adhesion, bending, hardness, water and organic solvent resistance, viscosity, and tensile strength are all qualities that are commonly assessed in coating applications. Based on the polyol structure, PU coatings produced from polyether and polyester polyols perform differently (Table 1) [8].
Polyurethane coatings are widely used in a range of industries, including automotive, electronics, wood goods, and equipment [9], because to its hardness combined with high chemical, solvent, and abrasion resistance as well as outstanding low temperature
flexibility.
Izel Kimya conducts 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 dispersionsbased on hydroxylterminated polybutadiene and poly (propylene glycol): synthesis and characterization. J Appl Polym Sci 80:566– 572.
M.Sc. Canan Aslan
R&D Senior Researcher
İzel Kimya
Dr. Cemil Dizman
R&D Manager
İzel Kimya
