Introduction to Crosslinking Reagents
What are crosslinking reagents?
Crosslinking reagents, also known as curing reagents, hardeners or maturation reagents, can transform linear or lightly branched macromolecules into three-dimensional networks, improving performance such as strength, heat resistance, wear resistance, solvent resistance, etc. They are used in foaming or non-foaming products.
Crosslinking reagents are substances that can bridge between linear molecules, thus allowing multiple linear molecules to bond together to form a network structure. They promote or regulate the formation of covalent or ionic bonds between polymer molecules.
Crosslinking reagents are called different names in different industries. For example, the rubber industry commonly calls it "vulcanizing reagent"; the plastics industry calls it "hardener", "maturation reagent", "curing reagent"; and in the adhesives or coatings industries, it is called "hardener", "maturation reagent", etc. Although the names are different, the chemical properties and mechanisms they represent are the same.
Principle of action of crosslinking reagents
Crosslinking reagents initiate free radical reactions
Crosslinking reagents can decompose to generate free radicals, which in turn initiate free radical chain reactions of polymers, leading to crosslinking of the polymers. Crosslinking reagents are actually initiators. Organic peroxides are usually used.
The functional groups of the crosslinking reagents react with the polymer
The functional groups (mainly bifunctional, multifunctional, C=C, etc.) of the intramolecular crosslinking reagents react with polymer compounds and crosslink the big macromolecular chains. (a) Crosslinked with a diamine.
Combination of free radical reaction and functional group reaction of crosslinking reagents.
Using the functional groups (mainly bifunctional, multifunctional, C=C, etc.) of the crosslinking reagents to react with polymer compounds and crosslink the big macromolecular chains.
Selection and dosage of crosslinking reagents
L-2 crosslinking reagent
A colorless and odorless liquid generated by the chelation reaction between aluminum ions and ethylenediamine. It does not contaminate the stratum and does not harm the operator. It can make the high polymers crosslink into a structured form, improving the crosslinking strength, salt resistance, and elasticity of the polymer.
Organic boron crosslinking reagents
As a type of organic boron crosslinking reagent, it can improve the temperature resistance due to its benzene ring, but has a strong irritating odor. Because it is a boron sodium salt, it is sensitive to ions and has poor salt resistance.
Organic titanium crosslinking reagents
A brown, viscous liquid with an irritating odor, generated by a chemical reaction with metal titanium compounds. It has a large impact on the stratum and has a high degree of operator risk. It is expensive and requires a large amount, but it can form linear structures between the polymers, resulting in low crosslinking strength, and is commonly used in the crosslinking reaction of polyacrylamide solutions. It has poor salt and temperature resistance.
Dosage
When using crosslinking reagents, it is required to use a small amount of crosslinking reagent, with high crosslinking efficiency and stable crosslinking structure. The crosslinking time should be appropriate, if it is too fast or too slow, it will not be good. It should not affect construction and use performance, and should be non-toxic, non-irritating, and environmentally friendly. It should be low in price and easy to accept, and should have stable storage, not causing adhesives to solidify during storage.
