Views: 299 Author: Vickey Publish Time: 2023-05-17 Origin: Site
The polyurethane structure of polyols, which are reactive stocks containing at least two functional groups, is created when these groups combine with isocyanate (NCO) groups. Depending on where they are used, polyols can be divided into a number of distinct categories. The two classes of polyols include hydroxyl and amino-terminated groups.One of the two essential elements of polyurethane systems is polyol. At least two hydroxyl functional groups on polyol structures react with isocyanate groups to create polyurethane structures. Numerous industrial applications employ polyurethane, especially in the footwear, building, furniture, automotive, and heating and refrigeration industries.Polyols are the most significant isocyanate reaction partners. Polyethers and polyesters are the two main categories into which polio is divided. Polyether polyols make up 80–90% of the polyols now in use.
Dicarboxylic acids and glycols undergo condensation to form polyester polyols.Polyesterization of glycols, diacids, or their derivatives results in polyester polyols. Based on the diacids utilized in their synthesis, polyester polyols are categorized into three groups: aliphatic polyesters, aromatic polyesters, and caprolactone-based polyesters. Adipic acid, succinic acid, phthalic acid, and maleic anhydride or anhydrides of acids are favored as dicarboxylic acids in aliphatic polyesters. Ethylene glucose, diethylene glucose, propylene glucose, 1.4 butanediol, and 1.6 hexanediol are utilized in aliphatic polyester polyols. Acids with cyclic groups, such as terephthalic acid and isophthalic acid, are employed in aromatic polyester polyols. Comparatively speaking, aromatic polyesters have a lower molecular weight than aliphatic polyesters.
The qualities of the resulting polyurethane material are determined by the weight of the polyester polyol molecules and various monomer combinations. The development of hard polyurethane foam with high temperature and chemical resistance is made possible by the highly branched polyester polyol, whereas flexible polyurethane foam with high elasticity is produced by the less branched polyester polyol. Similar to how flexible polyurethane foam is made, rigid polyurethane foam is made from high-molecular-weight polyester polyols, while the latter is made from low-molecular-weight polyester polyols.Superior characteristic qualities are provided by polyester polyols and polyurethanes. In comparison to polyether polyols, they offer stronger secondary strengths between polyester chains, better crystalline structure inside urethane structures, and heat and fire resistance. In comparison to polyether polyol-based polyurethanes, polyester polyol-based polyurethanes provide superior solvent resistance.
Polyester polyols' tendency to hydrolyze in environments with high humidity and temperatures is a drawback.
Polyether polyols are chains or networks of polymeric structures that have been polymerized in such a way that ether bonds have formed between the monomers. In the process of making polyurethanes, hydroxyl functional oligomers known as polyether polyols are frequently employed. Alkylene oxide is polymerized to create them. By polymerizing cyclic etheric structures, they are produced. They are polymeric structures made when cyclic ethers are ethoxylated or propoxylated in the presence of catalysts. Propylene oxide and ethylene oxide are added together to form polyether polyols.
