Cure Terms Glossary

Crosslink Density

The crosslink density can be defined in various ways. One way is as the number of chain segments (between crosslinks) per unit volume - designated ν.

Another way of expressing this is in terms of the average molecular weight between crosslinks - designated as Mc. These two conventions can be related numerically, since the average segment weight (in grams) is Mc / N (where N is the Avogadro number) and the average segment volume is therefore Mc / Nρ (where ρ is the material density). Thus the average number of chains per unit volume is given by,

ν = Nρ / Mc

Hence crosslink density is inversely proportional to Mc. Increasing crosslink density increases material stiffness, and various expressions have been derived linking modulus to ν or Mc. The basis of any direct correlation relies on the crosslink providing the only restriction on segmental mobility (i.e. the hypothetical freely-jointed chain) and the closest approximation is for crosslinked materials in their rubbery state, especially when swollen.