ABSTRACT
Permeabilitymaybeviewedaseitherapositiveornegativefactordependinguponthecircumstances.Ifitisrequiredthatthecontentsofapackage remainuncontaminated,thenhighpermeabilityisnaturallyundesirable.However,ifitisdesiredthatthegaseousproductofareactionescape,highpermeabilitymaybedesirable.Anexampleofthelatteristheoutwarddiffusionofthe respirationproductsfromfruitsandvegetablesthathavebeenpackagedbefore theyarefullyripe.Thepermeabilityofpolyethylenetovariousmoleculesmay alsobeadvantageousbyallowingtheslowreleaseofincorporatedmolecules suchasfragrancesormedications.Otherbeneficialapplicationsofpermeability includethediffusionoflubricants,incorporatedduringfabrication,tothesurface ofamovingpartandthebloomingofsurfacemodifiersinfilmstoaidincling ortopreventblocking.Formanyapplications,however,thediffusionofsmall moleculesthroughpolyethyleneisanundesirabletrait.
