The Science of Epoxy Coatings

Epoxy coatings are not a one-size-fits-all solution. When it comes to the oil and gas sector, choosing the best protection for various infrastructure requires a great deal of experience. PPG has been doing this for 138 years and provides an in-depth look at the unique chemical characteristics that make up its products. 

In organic chemistry, an epoxide is a cyclic ether formed by an oxygen atom bonded to two carbon atoms that are then bonded to each other through a single covalent bond. Generally, they are liquid, colorless and soluble in alcohol, ether and benzene.

They are named by adding the prefix “epoxi-” to the hydrocarbon that shares the same number of carbon atoms and indicating the carbons bonded to the oxygen.

Epoxide, or epoxy, materials have diverse uses in the industry. In the field of paintings and coatings, they are particularly useful in the elaboration of anticorrosive systems, along with protecting wood and floors. 

Epoxy coatings are extremely versatile and capable of meeting high working standards, such as high mechanical and chemical resistance. This is why they are used in substantially tough environments, such as industrial facilities, vessels, offshore platforms, wind turbines, pipelines and other common structures that require constant protection against environmental degradation.  

To create an epoxy coating that fulfills these requirements, it is fundamental to find the perfect combination of resin and curing agent, which provide characteristics specific to each formulation. 

In all industrial segments in Mexico and in other countries, which include all marine and oil and gas activities, market trends indicate that the two most valued characteristics in epoxy coatings are the following: 

• Highest percentage of volume solids

This is a trend that has been developing for some time; nevertheless, today, this characteristic tends to be obligatory due to national and regional environmental regulations, which include lowering VOC emissions. 

PPG offers a range of products that satisfy the needs of these projects, including PPG-Amerlock 2, PPG-Sigmashield 880 and PPG Sigmashield 1200.

• BA epoxy

This trend is also reinforced by environmental needs, not just lower VOC emissions but also less odor and a reduction in the use of solvents for cleaning. The product can be used beyond the industrial sector, with applications in the healthcare and commercial industries, among others.   

The design of the product’s formulation involves a series of parameters that require care. It is also good to know their basic reactions. 

The process through which epoxy resins are manufactured is an example of the product’s versatility, benefits and varied characteristics. These include the classic formulation that mixes bisphenol A with Epichlorohydrin, along with other possible functionalities within that same structure. 

Bisphenol A, usually abbreviated as BPA, is an essential chemical that has been researched substantially. It is primarily used in the fabrication of durable epoxy resins, along with transparent and resistant polycarbonate plastics. 

In the last few years, a great deal of attention has been given to bisphenol A due to its use in the fabrication of materials that are in contact with food, requiring the approval of the FDA.  

Bisphenol A is an organic compound with two functional groups of phenol. It is a difunctional block of many important plastics and plastic additives. 

• Formula: C15H16O2 

• IUPAC: 4,4'-(propane-2,2-diyl) diphenol

• Molar mass: 228.29 g/mol

• Fusion point: 158 °C

• Soluble in: Ethanol, Base

Epichlorohydrin is an organochlorine compound and an epoxide. It is a colorless liquid with a spicy smell similar to that of garlic. It is moderately water soluble but miscible with most polar organic solvents.

• Formula: C3H5ClO

• Molar mass: 92.52 g/mol

• Density: 1.18 g/cm³

• Boiling point: 117.9 °C

• Fusion point: -25.6 °C

On the other hand, we have bisphenol F, which is a small, organic, aromatic compound with the empirical formula ₂CH ₂. It is related to bisphenol A through its basic structure, since they both belong to the bisphenol category of molecules characterized by two phenolic groups connected by a bonding group.

• Formula:  C13H12O2

• PubChem CID: 12111

• Molar mass: 200.237 g·mol−1

The chemical nature of industry epoxides allows the understanding of part of the characteristics that each formulation provides; for example:

• Fast-drying formulas

Epoxides with this characteristic are the most sought after by clients who require that maintenance on their facilities take place in the shortest amount of time possible to ensure their productivity remains unaffected. 

While fast-drying and rapid-curing epoxides have always existed, they were usually made on the basis of solid resins with a high molecular weight, along with modified amines and accelerators. Nowadays, the same characteristic is achieved through adducts in slow-cured amines, which are generated by the coating manufacturing process itself. 

The use of phenalkamines is an option for fast-curing coatings with high molecular weight that can also have other characteristics, such as cold curing, curing in high humidity conditions and curing on surfaces that have not been adequately prepared.   

Throughout its 138 years of history in the global industry, PPG has maintained several development processes that combine all of these types of chemistry to achieve products with the characteristics that the market needs. Examples of these products include Sigmafast 278, Sigmacover 350 and Amercoat 240. 

• Adducts

The advantages of making adducts in epoxide curing agents are as follows:

• The reaction with the epoxide resin is initiated, leading to a faster curing process.

• The amine’s molecular weight increases, reducing its volatility and absorption time, thus making it healthier to use.

• 100 percent solids translate into greater anti-corrosion protection, chemical resistance and use in concrete floors.

• Low odors and VOC emissions when applied at high thicknesses.

• Like other trends previously mentioned, it has become more common to comply with new regulations and its use has become extensive in confined spaces, interior rooms and low ventilation locations. 

• Resins with 100 percent solids are also of low viscosity to minimize or entirely avoid the use of diluents that affect the coating’s final performance. Hybrid resigns can also provide the product with specific characteristics.  

• Novolacs

Amines are compounds that result from the substitution of one or more hydrogen atoms in ammonia for alkyl radicals (aliphatics) or aryl radicals (aromatics).

The functional group that characterizes amines is known as amino and is represented as (-NH2).

The general formula of an amine is R-NH2 if it is aliphatic and AR-NH2 if it is aromatic. 

For example, in methylamine, a methyl group substitutes a hydrogen atom in ammonia. The bonding of two methyl groups produces dimethylamine and the three methyl groups in trimethylamine substitute all the hydrogen atoms in ammonia. 

Through methods such as these, PPG takes the best chemical characteristics and combinations and uses them to fulfill the objective of consolidating the development of products that help find the best technological solution its clients require. PPG can find these solutions for a tank, a platform, a pipeline or any kind of industrial plant or facility in the world.  

PPG Industries has more than 130 years of experience in the development and supply of paints, coatings and materials. The company serves several industries and operates in more than 70 countries. It specializes in the construction, consumer products, industrial and transportation markets and aftermarkets.