Preparative TREF and Size Exclusion Characterization of Olefin Oligomers
Preparative TREF combined with high-temperature SEC isolates and quantifies migrating sub-1000 Da polyolefin oligomers to verify food contact safety compliance.
Olefin Oligomers
Meaning
Low-molecular-weight molecules consisting of a small number of repeating alkene units act as wax-like additives or contaminants within a polymer matrix. Commonly arising from incomplete polymerization or thermal degradation, olefin oligomers can alter the physical and processing characteristics of polyolefin resins. These short chains possess high mobility and migrate easily to the surface of molded components.
Processing Effect
Melt viscosity and flow behavior in the runner system change when low-weight molecules are present in the resin. During extrusion, olefin oligomers act as internal lubricants that reduce the torque required to process the melt. However, they also lower the melt strength of the polymer, which can cause parison sag in blow moulding.
Operators must balance their benefits against the risk of structural defects.
Mould Contamination
High temperatures in the mould cavity cause volatile components to evaporate and condense on polished steel surfaces. During continuous production runs, the buildup of migrated olefin oligomers creates a waxy deposit on the mould vents and cavity walls. This deposit causes surface defects known as plate-out and blocks the escape of trapped air, leading to burn marks on the molded parts.
Frequent cleaning cycles are necessary to maintain part quality.
Resin Quality
Analytical extraction tests determine the suitability of plastic materials for food-contact packaging. Because olefin oligomers can migrate into packaged goods, their concentration in virgin resins is tightly controlled. High levels of these compounds are common in post-consumer recycled polyolefins, which limits the use of recycled materials in sensitive applications.