Meaning
Low molecular weight components within a polymer matrix migrate toward the surface under thermal or mechanical stress. These volatile migrants include additives, residual monomers, or processing aids that separate from the bulk material during injection or extrusion cycles. Their movement alters surface energy, causes adhesion failure, or leaves visible residue on the cavity wall of the tooling.
Thermal Migration
Excessive processing temperatures trigger these species to exit the melt stream early. Heat accumulation inside the barrel increases the kinetic energy of small molecules until they diffuse toward the cool mould surface. Once the cycle repeats, the deposit builds up and disrupts the finish of the moulded parts.
This phenomenon occurs during long residence times where the material remains at high temperatures for extended periods.
Surface Accumulation
Thin films of these substances form an unintended barrier on the tool steel or the cooling channel exits. The presence of such layers requires frequent cleaning intervals to prevent surface defects and loss of detail. A moulder compensates by adjusting venting or lowering the stock temperature to stop the transition from the solid phase to the gas phase inside the mould.
Material Specification
Datasheets define the limits for these components to ensure part performance across various environmental conditions. Manufacturers measure the loss in mass when the polymer undergoes heating to establish the concentration of agents likely to exit the matrix. Stable grades keep these substances locked within the crystalline or amorphous structure until the application requires their release.
Low volatility indicates a material that retains its intended properties throughout the lifespan of the finished part.
