Meaning
Physical expansion occurs when a polymer absorbs a solvent without undergoing total dissolution. This solvent swelling happens because the liquid molecules occupy spaces between polymer chains, pushing them apart and increasing the overall volume. The degree of expansion depends on the thermodynamic compatibility between the liquid and the resin.
Measurement Value
Determining the crosslink density of elastomers often relies on the extent of the volume change. When solvent swelling is measured in a laboratory, it indicates how well a moulded seal will perform in contact with oils or fuels. Excessive expansion can lead to the mechanical failure of a joint or gasket.
Process Interference
Residual chemicals from the cleaning of moulds can trigger this effect in sensitive resins. If solvent swelling occurs unexpectedly during a production run, it may cause dimensional inaccuracies or surface defects like blistering. Moulders must ensure that all cleaning agents are fully evaporated before starting the cycle.
Material Selection
High crystallinity generally reduces the susceptibility of a polymer to this type of penetration. Because solvent swelling is more pronounced in amorphous regions, materials like PET or nylon are chosen for chemical transport. Understanding this boundary helps engineers specify the right material for harsh environments.
