Meaning
Analytical procedures specified for the determination of plasticizer migration from polymeric materials into porous substrates govern regulatory compliance for flexible vinyl formulations. The methodology in ISO 16938 defines standardized contact conditions, pressing loads and temperatures to measure compound mass loss over defined exposure intervals. The standard applies to plasticized polyolefins, modified polyurethanes and polyvinychloride compounds containing liquid plasticizers prone to exudation.
Rigid unplasticized engineering thermoplastics, thermoset matrices and vulcanized rubbers with bonded additives lie entirely outside the scope of this protocol.
Extraction Mechanics
Direct contact between the polymer sample and an absorbent substrate like chromatographic paper or microporous membranes induces liquid phase migration. Under the thermal exposure required by ISO 16938, mobile plasticizer molecules diffuse through the amorphous regions of the matrix toward the boundary interface. Capillary forces within the substrate draw the exudate away from the surface, sustaining the concentration gradient across the test piece.
The loss in sample mass or the gravimetric gain of the receiver paper quantifies the exuded mass over forty-eight to one hundred and sixty-eight hours.
Volatility Separation
Elevated temperatures can induce volatile organic compound evaporation simultaneously with liquid absorption, compromising raw gravimetric measurements. Testing according to ISO 16938 separates pure contact migration from mass loss caused by atmospheric vaporization through sealed blank controls. Polymeric plasticizers with high molecular weights resist this surface leaching better than monomeric phthalates like diisononyl phthalate or dioctyl terephthalate.
Virgin PVC dry-blends show lower migration coefficients than recycled scrap contaminated with lower-grade ester plasticizers or process aids.
Substrate Interaction
Surface roughness of the moulded test specimen affects the contact area between the plastic and the absorbing collection material. Inadequate clamping pressure yields incomplete contact, which falsely indicates compliance under ISO 16938 by suppressing the measurable diffusion rate. Excessive clamping force crushes the absorbent media, altering its void volume and retarding oil uptake during high-temperature incubation.
Clean, plane-parallel test plaques molded with mirror-finish tool inserts ensure reproducible migration measurements.
