The key difference between saturated and unsaturated polyester resin is that the saturated polyester resins have no double bonds in their main chain whereas the unsaturated polyester resins have double bonds in their main chain.
A polyester is a polymer compound that forms from the condensation reaction between a polyol and an acid. Therefore, we can categorize them as condensation polymers. The most common and very useful form is the unsaturated form. However, there is a saturated form as well.
CONTENTS
1. Overview and Key Difference
2. What is Saturated Polyester Resin
3. What is Unsaturated Polyester Resin
4. Side by Side Comparison – Saturated vs Unsaturated Polyester Resin in Tabular Form
5. Summary
What is Saturated Polyester Resin?
Saturated polyester resin is a polymer that has no double or triple bonds in its backbone (main carbon chain of the polymer). Though the most common form is the unsaturated resin, we can obtain this saturated form by using excessive polyol (glycol) in the reaction process. The result can be either a hydroxyl terminated polyester or a carboxyl terminated one. However, the common form is the hydroxyl terminated polyester resin. Most of the times, we use acids such as Isophthalic Acid, Phthalic Anhydride, Adipic Acid and glycols like Neopentyl Glycol, Propylene Glycol, Di-ethylene Glycol, Glycerine, etc. in the production process.
Figure 01: Saturated Polyester Resin as a Raw Material for Coil Coatings
The major use of this resin includes the production of coil coatings. However, it depends on the properties and structure of the resin; we can use them for coating, primer and backing paint for coil coatings. Moreover, it is useful in the production of printing inks and thermally coated coils as well.
Characteristics Saturated Polyester Resin
The important characteristics of this polymer are as follows.
- Versatility and weather resistance
- Prominent hardness and toughness
- Resistance to dirt
- Suitable for general requirements; cost effective.
What is Unsaturated Polyester Resin?
Unsaturated polyester resin is the most common type of resin, and it has double bonds in its backbone (main carbon chain). We can produce this form via the condensation reaction between unsaturated dicarboxylic acids. This polymer is a linear polymer with ester bonds and double bonds. The uses of this polymer include production of sheet moulding compound, bulk moulding compound, toners and laser printers.
Characteristics Unsaturated Polyester Resin
The important characteristics of this polymer include the followings:
- Heat resistance
- High tensile and compression strength
- High bending strength
- Resistance to chemical corrosion
- Excellent dielectric properties
- Good fluidity when heated
What is the Difference Between Saturated and Unsaturated Polyester Resin?
Saturated polyester resin is a polymer that has no double or triple bonds in its backbone. Therefore, there is no unsaturation is this polymer. On the other hand, the unsaturated polyester resin is the most common type of resin, and it has double bonds in its backbone; thus, it has unsaturation. This is the key difference between saturated and unsaturated polyester resin.
Furthermore, we can produce both by condensation reaction but, in the production of saturated polyester resins, the reaction takes place between acids and glycols with an excessive amount of glycol. Whereas, in the production of unsaturated polyester resin, the reaction takes place between unsaturated dicarboxylic acids. Looking at more differences, the saturated polyester resin has its major use in the production of coil coatings whereas, the unsaturated polyester resin is useful in producing sheet moulding compound, bulk moulding compound, toners and laser printers.
The below infographic presents the difference between saturated and unsaturated polyester resin in tabular form.
Summary – Saturated vs Unsaturated Polyester Resin
The polyesters are important thermoplastic polymers. There are two types of polyester resins based on the chemical nature of the backbone of the polymer; they are the saturated and unsaturated form of polyester resins. The key difference between saturated and unsaturated polyester resin is that the saturated polyester resin has no double bonds in its main chain but the unsaturated polyester resin has double bonds in the main chain.
Reference:
1. “Polyester Resin.” Wikipedia, Wikimedia Foundation, 3 July 2018. Available here
2. HE, Ben. “BEN.” The Difference between Saturated and Unsaturated Resins. Available here
Image Courtesy:
1.”Pulverlackbindemittel Polyester”By Hardcoreraveman – Own work, (Public Domain) via Commons Wikimedia