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PART 1 – Exploring the Different Types of Epoxy Curing Agents: Advantages, Disadvantages, and Applications in Speciality Polymer Coatings

Epoxy resin systems have revolutionized the world of industrial materials and craftsmanship. As a leading Epoxy Resins Manufacturer, we’ve seen the versatility and durability of these systems in a wide range of applications. Derived from a class of synthetic polymers, epoxy resins have gained popularity due to their exceptional adhesive properties, high strength, and chemical resistance. These systems have found extensive use in various industries, including construction, aerospace, automotive, electronics, and art.

Traditionally, epoxy resin systems consist of two primary components: epoxy resin and a curing agent, commonly referred to as a hardener. When these two components are combined in the correct proportions and subjected to an appropriate curing process, they undergo a chemical reaction known as curing or polymerization. This reaction transforms the liquid epoxy resin into a solid, highly cross-linked structure, resulting in a rigid and durable material with exceptional mechanical and thermal properties.

The most market-dominant epoxy resin is Diglycidyl Ether of Bisphenol A (DGEBA). It is the simplest polymerizable epoxy resin due to its bifunctional molecular structure. On the other hand, there is a wide selection of curing agents available in the market. These curing agents react differently with the epoxy resin, thereby the curing process, curing time and final properties of the cured product can be vastly different.

Here, I will be listing some of the most popular epoxy curing agents (in no particular order), discussing their advantages, disadvantages, and applications.

Types of Epoxy Curing Agents:

1. Amines/ Polyamines:

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Amine curing agents are widely used in epoxy formulations for their ability to initiate and control the curing process. They react with epoxy resins through an amine group, resulting in the formation of a cross-linked network. There are various types of amine curing agents available, including aliphatic amines, cycloaliphatic amines, and aromatic amines. Each type has its own specific characteristics and applications.

  • Aliphatic Amines:
    These curing agents are derived from aliphatic compounds and offer good chemical resistance, adhesion, and flexibility. They are often used in coatings, adhesives, and sealants. NSPC offers Aliphatic Amines CURE-O-POXY 6221, 6231 and 6237.
  • Cycloaliphatic Amines:
    Cycloaliphatic amines provide excellent resistance to UV radiation and yellowing, making them suitable for applications requiring outdoor durability. They are commonly used in epoxy flooring, composites, and coatings. NSPC offers Cycloaliphatic Amines CURE-O-POXY 6050 and 6060, as well as a hybrid cycloaliphatic amine CURE-O-POXY 6129 which blends the benefits of phenalkamines with cycloaliphatic amines.
  • Aromatic Amines:
    Aromatic amines offer high chemical resistance, good adhesion, and mechanical properties. They are utilized in applications such as chemical-resistant coatings, tank linings, and structural adhesives.

Advantages and Disadvantages:

Curing Characteristics:
Amines are known for their relatively faster curing rates compared to other curing agents such as polyamides. This curing time can range from minutes to a few hours. The exact curing time will depend on the specific polyamine type, formulation, and ambient conditions. Polyamines provide rapid curing, which means they require faster handling and application to ensure proper curing before the material becomes too viscous.

Performance Properties:
Polyamines provide good flexibility and toughness. They offer excellent adhesion properties and good chemical resistance. Polyamines are commonly used in applications where fast cure and high adhesion are required, such as epoxy flooring, sealants, and composite materials.

Considerations and Limitations:
While amine curing agents have many advantages, they also have some limitations. For instance, they may exhibit lower heat resistance compared to other curing agents such as anhydrides. Amine-cured epoxy systems can be sensitive to moisture, which can result in blushing or reduced performance if not properly handled. Additionally, some aromatic amines may pose health and environmental concerns, therefore it’s essential to follow proper safety precautions during handling and application.

2. Polyamides/ Polyamidoamines:

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Polyamides are a type of epoxy curing agent derived from the reaction between dimer fatty acids and polyamines. They consist of long-chain structures with amide and amine groups distributed along the chain, resulting in a more complex molecular structure. Resultantly, they offer unique properties and are widely used in various industries. Polyamidoamines are simply lower molecular weight polyamides. At NSPC, we offer standard Polymides CURE-O-POXY 5115, 5125, 5140 and 5115×70.

Advantages and Disadvantages:

Curing Characteristics:
Polyamide curing agents typically provide a relatively long pot life (working time) and a relatively slower cure compared to other curing agents. In most climates this cure time is about 4-8 hours and can be viewed as an advantage as this allows for a long application window for the end user. Although, it can be problematic for colder climates where curing time can extend to days. One can use accelerators to decrease cure time, but it may make more sense to use other curing agents.

Performance Properties:
Polyamides offer good flexibility, toughness, and chemical resistance. They exhibit excellent adhesion to various substrates, making them suitable for applications requiring good chemical resistance and adhesion, such as coatings, adhesives, and laminates.

Considerations and Limitations:
Like polyamines, polyamides exhibit lower heat resistance compared to other curing agents such as anhydrides. Also, polyamide-cured epoxy systems can be sensitive to moisture, which can result in blushing or reduced performance if not properly handled. Furthermore, polyamides tend to have relatively higher viscosities, which can impact the ease of processing and application. Adjustments in formulation or application method may be required.

3. Phenalkamines:

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Phenalkamines are a specific class of epoxy curing agents that combine the properties of aliphatic amines and phenols. Phenalkamines offer unique curing properties and performance characteristics, making them suitable for various applications. At NSPC, we specialize in cardanol (cashew-derived phenol) based Phenalkamines that exhibit excellent corrosion resistance, chemical resistance, flexibility, adhesion, and rapid cure at low temperature. Here is a link to our Phenalkamine offerings.

Advantages and Disadvantages:

Curing Characteristics:
Phenalkamines provide rapid curing, even at low temperatures. They exhibit fast reactivity with epoxy resins, allowing for quick curing times and the ability to achieve high degrees of cure in a relatively short period. They are known for their effective curing (in few hours) in extremely cold weathers where other curing agents can take days to cure. Furthermore, phenalkamines offer superior moisture tolerance during the curing process. They can cure effectively even in the presence of moisture or high humidity, making them suitable for applications in damp or humid environments, and in construction chemicals. Their lower viscosity compared with other curing agents allows for ease of handling during application.

Performance Properties:
Phenalkamines provide excellent corrosion resistance and chemical resistance, offering protection against a wide range of chemicals, solvents, corrosive substances, and water. They are commonly used in applications where resistance to aggressive environments is required, such as tank linings, marine coatings, chemical-resistant coatings, and industrial flooring. Phenalkamines also promote strong adhesion to various substrates, including metals, treated metals and concrete. This property allows for reliable bonding and coating performance. Furthermore, phenalkamine-cured epoxy systems exhibit good flexibility and toughness, which is particularly beneficial in applications where resistance to mechanical stresses, impacts, and vibrations is required. They also offer excellent performance at low temperatures. They maintain their flexibility and mechanical properties even in cold environments, making them suitable for applications in arctic or sub-zero conditions.

Considerations and Limitations:
Phenalkamines generally have a shorter pot life (working time) compared to some other curing agents. Therefore, efficient handling and timely application are necessary to avoid premature curing. Some phenalkamines may undergo color changes or yellowing over time, particularly when exposed at length to UV radiation or outdoor conditions. Finally, while phenalkamines exhibit good moisture tolerance during the curing process, they can be sensitive to moisture during the storage and handling of the uncured material. It is therefore important to store and handle phenalkamine resins in dry conditions to avoid moisture absorption or degradation.

This article will be continued next month with three more curing agents. Make sure you have been subscribed to our Insight Newsletter to be notified.

Further Readings:

  1. Nadkarni SPC – Technology for more on our technology and specialization.
  2. Polymer Science Learning Center for epoxy resin basics.
  3. Composites Australia for more on polyamines.
  4. Future Market Insight for epoxy curing market.

Author:
Shikhin Nadkarni

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sikhin

Shikhin is currently a PhD Student in Coatings and Polymeric Materials Department at North Dakota State University. He is a member of Dr. Dean Webster’s Research Group and his research focuses on Non-Isocyanate Polyurethanes as well as novel Epoxy systems. He is passionate about incorporating bio-based materials in polymers so as to reduce our dependance on petrochemicals.

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