Analytical Method
Determination of the concentration of chemical bonds between polymer chains establishes the mechanical limits of an elastomer or thermosetting resin. In practice, crosslink density measurement quantifies these bridge points through solvent swelling or dynamic mechanical analysis. The measurement establishes the molar mass between crosslinks, which dictates how the cured network responds to deformation.
If the solvent absorption reaches equilibrium, the calculation uses the Flory-Rehner equation to output a numerical value. Solvent choice determines the accuracy of this swelling method because the interaction parameter must match the polymer chemistry. Dynamic mechanical analysis avoids the solvent hazard by tracking the storage modulus above the glass transition temperature.
Physical Influence
Quantifying the molecular structure allows papermakers to predict the barrier properties and water resistance of coated paperboards. A precise crosslink density measurement indicates how tightly a polymer coating is bonded, which directly controls the migration of grease and moisture. Highly bound networks prevent solvent penetration during the coating process.
When the cure is incomplete, the coating remains porous and susceptible to swelling. This property governs the structural integrity of the barrier layer on food packaging.
Process Application
Industrial control of curing ovens relies on rapid feedback from the laboratory to adjust temperature profiles. While crosslink density measurement remains a laboratory procedure, the resulting values determine the speed of the converting line. An under-cured coating blocks or sticks to adjacent sheets in the rewind roll.
Conversely, over-curing causes the resin to become brittle and crack during folding. Accurate data prevents these runability defects on the factory floor.
