Meaning
Trace volatile byproduct concentration measures organic thermal breakdown products contained within polyester matrices. A high acetaldehyde content imparts an off-taste to bottled water and carbonated soft drink containers formed from polyethylene terephthalate. Melt processing temperatures above thermal stability limits accelerate polymer chain scission in the injection barrel.
Control of bottle preform quality relies on head-space gas chromatography testing to verify that volatile levels remain below supplier specification thresholds.
Thermal Degradation
Excessive shear rates and elevated barrel temperatures generate small organic molecules during plasticating. Thermal breakdown increases acetaldehyde content when melt residence time extends beyond recommended processing windows. Screw geometry with aggressive mixing elements generates local hot spots that promote thermal degradation.
Lowering back pressure reduces internal friction within the melting zone.
Container Off-Flavor
Migrated chemical compounds alter the sensory properties of packaged liquids without changing physical bottle strength. Low human perception thresholds for acetaldehyde content make subtle material degradation unacceptable for still water packaging. Regrind inclusion accelerates volatile generation due to previous thermal cycles.
Desiccant Drying
Pre-drying virgin resin reduces hydrolytic degradation before melt processing begins. Effective moisture removal prevents polymer chain cleavage that elevates acetaldehyde content during injection moulding. Automated dry air systems maintain low dew points to protect material integrity.
