Polymer Architecture
Macromolecular structures in coatings and adhesives gain mechanical strength through the formation of covalent bonds between adjacent polymer chains. Determining the crosslink density allows chemists to measure the concentration of these bridges within a cured film. This structural property influences the hardness, chemical resistance, and thermal stability of barrier coatings on paper substrates.
Higher values restrict chain mobility and limit the penetration of water or oils. By analyzing the molecular gaps, developers can predict the durability and resistance of the final packaging film.
Barrier Resistance
Optimum barrier performance requires balancing the density of crosslinks with the flexibility needed for subsequent converting operations like creasing and folding. Excessively high crosslinking leads to a brittle coating that cracks when the board is folded into cartons. Insufficient curing leaves the surface sticky and susceptible to blocking in rolls.
Process control relies on solvent rub tests or dynamic mechanical analysis.
Reaction Conversion
Energy inputs from ultraviolet light or thermal ovens drive the chemical reaction that connects the functional groups on the prepolymers. Adding functional monomers or catalysts alters the final crosslink density achieved during the brief passage through the curing station. Measuring the degree of conversion ensures that the protective barrier remains intact.
