Meaning
The increase in the physical volume of a material caused by the absorption of a solvent, water, or other fluid represents a fundamental dimensional change. Packaging films and engineering polymers often undergo volumetric swelling when exposed to high-humidity environments or aggressive chemicals. This change can alter the mechanical integrity and barrier performance of the material.
Dimensional Change
Moisture absorption expands the intermolecular distance between polymer chains. When a design engineer evaluates seals or gaskets, volumetric swelling must be calculated to prevent seal failures in moving parts. This physical expansion reduces the density of the polymer and can cause stress cracking at corners.
Barrier Impact
Fluid ingress opens up the polymer structure and increases the free volume available for penetrant transport. Under conditions of high volumetric swelling, the diffusion rate of gases or water vapor through the polymer increases. This change can accelerate product degradation by allowing more moisture or oxygen to pass through the packaging barrier.
Barrier sheets must be tested under conditions that simulate these saturated states.
Material Degradation
Chemical exposure sometimes leads to irreversible softening and loss of mechanical strength. If a polymer undergoes excessive volumetric swelling, the polymer chains may become permanently displaced or dissolved. This behavior leads to a loss of tensile strength and makes the material susceptible to mechanical failure.
Testing evaluates this risk by measuring weight gain and volume changes after prolonged immersion. Engineers use these measurements to determine the compatibility of the plastic with specific industrial fluids before full-scale deployment.
