Stress Dissipation
Temporal intervals required for a polymer or fiber network to relieve internal pressure after a deformation event define its physical behavior. Measuring viscoelastic relaxation times helps predict how a coating or adhesive will flow into surface pores before it solidifies. This property combines the characteristics of both viscous liquids and elastic solids.
Processing Speed
Rapid deformation during high-speed printing forces the molecules in an ink or coating to stretch out of their equilibrium state. If the viscoelastic relaxation times are long, the material remains under tension and may pull away from the substrate or cause misting at the nip. Conversely, a very short interval allows the substance to flow too much and lose its shape before drying.
Temperature plays a major role in this behavior because heat increases molecular mobility and speeds up the relief of stress. Laboratory testing uses oscillatory shear to find the specific frequency where the material shifts from solid-like to liquid-like behavior.
Dimensional Memory
Creasing and folding of paperboard also depend on the ability of the fiber matrix to reorganize. Proper humidity control in the converting facility ensures that the viscoelastic relaxation times of the internal stresses are short enough to maintain the shape of the carton.
