Meaning
Solvency testing quantifies the amount of non volatile residue that migrates from a polymer sample into a hydrocarbon solvent under controlled temperatures. Compliance with food packaging standards requires n-hexane extraction to prove that the amount of low molecular weight oligomers and waxes is within safe limits. Standard procedures involve weighing a dried sample before and after a period of immersion in the boiling liquid.
Regulatory Compliance
Government agencies set limits for the extractable fraction of polyethylene and polypropylene used in contact with fatty foods. Failing an n-hexane extraction test prevents a material from being used in specific commercial applications.
Polymer Purity
Resin quality is often determined by the consistency of the polymerization process. Excessive n-hexane extraction values indicate a high level of side reactions or poor catalyst performance. Virgin resins typically show lower extractables than recycled materials that may contain degraded chains.
Testing Protocol
Laboratory procedures define the time and temperature required to reach an equilibrium state. The n-hexane extraction process usually runs for two hours at reflux to ensure that all soluble components are removed from the polymer matrix. After the liquid is evaporated, the remaining solids are weighed on an analytical balance.
Precise temperature control is necessary because small fluctuations change the solubility of the waxes.
