Polyolefin Oligomer Screening in Food Contact Polymers
Polyolefin oligomer screening requires coupled LC-GC-FID quantification of POSH and POAH fractions below ten parts per billion using matched food simulants.
Coextrusion Barrier
Meaning
Polymeric layers constructed to restrict molecular transmission define a coextrusion barrier. These internal film structures prevent oxygen or moisture from migrating through a flexible package. The efficiency of a coextrusion barrier depends upon the chemical polarity of the resin chosen for the core layer.
Polymer Selection
Moulders choose ethylene vinyl alcohol or polyvinylidene chloride to achieve low permeability within a multilayer structure. These specific resins act as a selective gate that slows gas diffusion by creating high crystalline density. Proper adhesion between the core and the adjacent tie layers ensures the film maintains its properties during vacuum forming.
Drifting melt temperatures during the extrusion process often result in degraded resin, which drastically increases the transmission rate of the final film.
Production Economics
Virgin resins possess predictable barrier values whereas regrind materials introduce contaminants that shorten the tortuous path molecules take through the plastic. The inclusion of post-industrial waste material reduces the overall cost of a film but forces a thicker gauge to compensate for lost performance. Consistent control of the feed block geometry allows a facility to minimize the thickness of the expensive high-performance core layer while maintaining the necessary gas resistance.
Stable operating conditions represent the primary method for maintaining cost-effective barrier performance over a long production campaign.
Quality Specification
Laboratory testing of a film sample quantifies the volume of gas that passes through a unit area over a standard timeframe. Moulders define these target oxygen transmission rates on a technical datasheet to verify the consistency of the cooling and orientation steps. A part specification demands a minimum thickness for the barrier layer, but the effective performance remains linked to the total cooling rate of the bubble.
High permeability in the finished product demonstrates a failure of the lamination integrity or a degradation of the resin morphology.