Polyester resins are synthetic resins which are insoluble, and polymerize during their curing process. When these resins are combined with glass fibers, plastic fibers, or carbon fibers, the resulting material can be used for different purposes.
The invention of plastics, and in general, polymers, has led to the development of several such similar substances. Plastics, in different stiff and solid forms, are being used in various applications, and even as you glance around, you will find that you are surrounded by several such substances. In fact, the very computer screen on which you happen to be reading this, is also made from countless such polymers. A polyester resin is one such substance that has several industrial and non-industrial applications.
Polyester resin is a thermosetting unsaturated polymer resin, which is formed from the reaction between organic acids and polyhydric alcohols. It is used for various domestic and industrial applications. There are several types of polyesters which are used, and their properties depend upon the acids and alcohols used in their formation. A resin of polyester is obtained from the polymerization of simple molecules of certain compounds, and it is even secreted by coniferous trees.
Process of Formation
Unsaturated polymer resins are formed from condensation action, and hence, they are also known as condensation polymers. In such a reaction, the byproducts are liquids, including either water or methanol. For the creation of polyester resins, two sets of reactants are chiefly used, namely, polyols, which include glycols (e.g.: ethyene glycol), and the acid set, including acids such as phthalic acid or maleic acid. The byproduct, water, is steadily removed till the completion of the reactions. This reaction gives the output in the form of liquid resin. Now, to make the product more usable, it is converted into solid resin, by cross linking the chains of molecules. This is done by adding free radicals to the compound, which causes the unsaturated bonds to go into a set of chain reactions. This reaction causes them to link with each other, thereby changing its state to solid. In order to generate or add a free radical, organic peroxides are used, which easily get decomposed into free radicals.
Uses and Applications
There are several domestic and industrial applications, a common example is the Fiberglass Reinforced Plastic (FRP), that you often see in restaurants, kitchens, and restrooms. The toner of a laser printer is, in fact, also made from polyester resin. Industrial applications include, steel molding compounds, bulk molding compounds, and resin casting.
Now, the actual application is difficult, owing to the fact that the polymer gets cured irreversibly, in an exothermic manner. It means that, the resin is heated during the application process, and it hardens as it cools down, i.e., it is exothermic in nature. The average cure time differs as per the consisting polymer compulsion, though the heat required to apply the polyester is about 200 degrees Celsius. The polyester casting resin, which requires heat, is principally used in industrial applications. Clear polyester resins which have domestic applications, are liquid, viscus, and are combined with a styrene solution to slow down the curing, and also to reduce viscosity. When the total resin is to be applied, a catalyst and accelerator are added to it in order to start the process. The styrene solution gets decomposed, or isolated, and the resin acts with the catalyst and accelerator, thereby curing and solidifying.
Two competitors to polyester resin are vinyl ester and epoxy resins. While comparing the two, you will realize that the polyester resin has less mechanical and strength, plus the water resistance is also quite less. Apart from these two difficulties, the styrene is, to a certain extent, harmful to health and environment, in case of constant exposure.