Meaning
Spontaneous movement of low molecular weight polymer chains from the bulk of a plastic material to its surface over time. This process occurs because these shorter molecules possess higher mobility and lower solubility within the polymer matrix than the long-chain resin. The accumulation often appears as a hazy film or a waxy residue that affects the appearance and function of the part.
Surface Accumulation
Bond strength between a moulded part and an adhesive or coating is compromised when a layer of small molecules forms at the interface. The oligomer migration of a polyester or polyamide can create a physical barrier that prevents the chemical bonding of paints and adhesives.
Thermal Influence
Elevated temperatures during storage or use accelerate the diffusion of these molecules through the polymer structure. In food packaging, this movement is monitored closely because the molecules might transfer into the contents and alter the sensory properties of the product.
Batch Variation
Variations in the polymerization process can lead to higher concentrations of short-chain fractions in certain resin lots. Measuring the extractable content of the raw material helps to predict the degree of oligomer migration that will occur in the finished product after it leaves the factory.
