The Significance of Cross-Link Density
Cross-link density refers to the way polymer threads are woven together and the density or packing of those threads. The higher the cross-link density, the better the barrier-type properties of a coating system.
An example illustrating the cross-link densities of two different polyurea coating system formulas is chain link fence vs. chain mail armor. Both are made of metal, are woven together, and offer a certain level of protection. If a circus performer were to throw an ax at you, you could feel equally confident of your safety by standing behind either a section of chain link fence or a section of chain mail armor. In both cases, the molecule size of the ax cannot penetrate the cross-link density of your formula. However, if that same circus performer were to throw a razor-sharp 7” balanced knife at you, you would probably not feel the same level of confidence standing behind the fence as you would the armor. Why? Because the cross-link density of the armor doesn’t allow the small molecule knife to pass through. Which would you choose for protection, the chain mail or the chain link fence?
In comparing Polyurea coating systems, cross-link densities are not all the same. Although similar, the end results, and the level of protection offered, can be very different from one formula to another. By design, coatings with no solvents or volatile organic compounds (VOCs) of any kind (listed, exempt, or other) have the capacity of exhibiting the highest cross-link density.
Don’t be deceived or misled. The use of any solvent in a coating system is both a performance and safety concern. Look for materials which are designed for the specific needs of your project