Meaning
Cyclic oligomer comprising three repeating units of ethylene terephthalate forms during the polycondensation stage of resin manufacture. This chemical byproduct remains trapped within the amorphous regions of the polymer matrix at concentrations typically reaching nearly two percent by weight. Extrusion temperatures above three hundred degrees Celsius cause cyclic trimer migration toward the metal surfaces of injection moulds during high-speed production runs.
Accumulation of this cyclic ester within the venting channels creates white powdery deposits that eventually interrupt continuous output by fouling mould release mechanisms.
Thermal Yield
Chemical equilibrium during melt polymerization governs the exact concentration of low molecular weight cyclic species locked inside polyester pellets. Vacuum drying removes superficial moisture but leaves internal oligomers untouched within the core of every pellet. Thermal degradation accelerates when hopper temperatures exceed safe limits because excessive heat liberates trapped cyclic molecules from the polymer chains.
Increased shear rates inside the plasticating screw generate localized hotspots that promote further oligomer formation prior to gate injection.
Mould Deposition
Volatilized cyclic fractions condense rapidly upon contacting cold tooling surfaces situated near core pins and slide interfaces. Cavity venting efficiency deteriorates steadily as powdery deposits narrow the micro-air-channels required for proper gas evacuation during cavity filling. Tool maintenance schedules must account for deposit accumulation rates to prevent surface hazing on transparent packaging items and electronic housings.
Part ejection forces rise noticeably once mould fouling disrupts the uniform release behavior across complex geometries.
Extraction Limits
Analytical gas chromatography quantifies residual oligomer fractions within moulded components to verify compliance with food contact migration thresholds. Solvent extraction protocols isolate cyclic species from ground polymer samples for precise mass balance verification before mass production begins. Virgin resin processing maintains predictable extraction baselines whereas high percentages of recycled regrind elevate starting cyclic levels above standard specification limits.
Finished component crystallinity determines the final diffusion rate of remaining oligomers toward external surfaces over time.
