Meaning
The specific polymer fractions known as POSH Oligomers describe low molecular weight cyclic and linear hydrocarbon species present in polyolefin materials. These contaminants originate from incomplete monomer conversion during synthesis and migrate toward the surface of finished articles under thermal stress. Strict limits govern their presence in food contact applications to prevent organoleptic taint and regulatory noncompliance.
Thermal Degradation
Processing temperatures above two hundred and sixty degrees Celsius accelerate the generation of POSH Oligomers within the barrel of an injection moulding machine. Shear heating compounds this effect by breaking primary polymer chains into smaller volatile fragments before the melt enters the runner system. Resin suppliers control reactor residence time to minimize these low molecular weight components in virgin pellets.
Compounders must dry hygroscopic carrier resins thoroughly to prevent moisture from catalyzing chain scission during compounding operations.
Surface Migration
Internal stresses drive POSH Oligomers outward toward the air interface of a moulded part during cooling stages. This phenomenon creates an oily residue on tool surfaces that accumulates over successive injection cycles and causes cosmetic blemishes. Mould designers incorporate adequate venting channels to allow volatile species to escape before the material freezes against the cavity wall.
Operators evaluate this deposition rate to determine the frequency of scheduled tool cleaning interventions.
Regrind Economics
Incorporating recycled regrind into virgin polymer streams concentrates POSH Oligomers because repeated thermal cycles generate additional low molecular weight fragments. Virgin material must be blended at controlled let down ratios with regrind to keep total volatile content below specification thresholds. Parts produced from heavily degraded regrind exhibit reduced tensile strength and premature surface crazing under mechanical load.
Moulders verify melt flow rate values on incoming regrind batches to detect molecular weight shifts before material reaches the feed throat.
