Curing agent, also known as hardener, maturing agent or setting agent, is a kind of substance or mixture that promotes or controls the curing reaction. Resin curing is an irreversible change process of thermosetting resins through chemical reactions such as condensation, closed-loop, addition or catalysis. Curing is accomplished by adding curing (crosslinking) agents. Curing agent is an indispensable additive. Whether it is used as an adhesive, coating or casting material, a curing agent must be added; otherwise, the epoxy resin cannot cure. The type of curing agent has a significant impact on the mechanical properties, heat resistance, water resistance, corrosion resistance and other aspects of the cured product.
The curing temperature of the curing agent is closely related to the heat resistance of the cured product. Similarly, among the same type of curing agents, although they have the same functional groups, due to different chemical structures, their properties and the characteristics of the cured products are also different. Therefore, a comprehensive understanding of the properties and characteristics of polyamine curing agents with the same functional groups but different chemical structures is very important for the selection of curing agents.
In terms of hue, the alicyclic group is the lightest and basically transparent, while the aliphatic and aromatic groups have a rather significant degree of coloring. In terms of viscosity, there are also significant differences. Alicyclic amines are only a few tenths of a Pa·s, while polyamides are extremely viscous, reaching several Pa·s. Aromatic amines are mostly in solid form. The length of the pot life is exactly the opposite of the curing property. Aliphatic groups have the highest reactivity, while alicyclic groups, amides, and aromatic groups decrease in sequence.
Hue: (Superior) Alicyclic → Aliphatic → Amide → Aromatic Amine (Inferior)
Degree of maturity: (Low) Alicyclic → Aliphatic → Aromatic → Amide (high)
Applicable period: (Long) Aromatic → Amide → alicyclic → aliphatic (short)
Curing property: (fast) Aliphatic → alicyclic → amide → aromatic (slow)
Irritability: (Strong) Aliphatic → Aromatic → alicyclic → Amide (weak)
The chemical structure and properties of polyamine curing agents
In addition, there are certain regularities in terms of luster, softness, adhesion, acid resistance and water resistance.
Luster: (Superior) Aromatic → Alicyclic → Polyamide-aliphatic Amine (Inferior)
Softness: (Soft) Polyamide → Aliphatic → alicyclic → aromatic (rigid)
Adhesion: (Excellent) Polyamide → alicyclic → aliphatic → Aromatic (Good)
Acid resistance: (Excellent) Aromatic → alicyclic → Aliphatic → Polyamide (Poor)
Water resistance: (Excellent) Polyamide → Aliphatic amine → alicyclic amine → aromatic amine (Good
The chemical structure of polyamine curing agents and the properties of the cured products with bisphenol A resin
For luster, aromatic ones are the best, while aliphatic ones are the worst. This property is affected by the curing temperature. As the temperature rises, the gloss improves. As for flexibility, polyamides with longer interfunctional group distances are better, while aromatic amines with higher crosslinking density are inferior. Heat resistance is exactly the opposite of softness, while adhesion is the same as softness. Chemical resistance (acid resistance) is influenced by the chemical structure. Aromatic compounds are relatively superior, while fatty amines and polyamides are prone to corrosion by chemicals. Water resistance is determined by the mass concentration of functional groups. Polyamides with a low mass concentration of functional groups and high hydrophobicity are more water-resistant, while aromatic compounds with a high mass concentration of functional groups are less so.
