Meaning
Processing specifications for condensation polymers measure water content against strict upper thresholds to prevent hydrolytic degradation during melt processing. Executing rPET moisture determination establishes the residual water concentration in recycled polyethylene terephthalate flakes or pellets prior to extrusion or injection moulding. Moisture present at elevated melt temperatures causes rapid chain scission, dropping intrinsic viscosity and compromising mechanical strength in preforms and strapping.
Test methods utilize coulometric Karl Fischer titration or specialized desorption systems to quantify water content down to parts-per-million levels. The boundary of effective measurement excludes surface water when testing unconditioned flakes, requiring precise thermal profiling to separate absorbed moisture from superficial wetness.
Hydrolytic Cleavage
Water molecules react with ester linkages in molten polyester, breaking polymer chains into shorter fragments. Performing accurate rPET moisture determination prevents processing resin lots that exceed critical moisture limits, avoiding severe losses in intrinsic viscosity. Chain scission reduces melt strength, leading to structural failures during stretch blow moulding operations.
Dehumidifying dryers must reduce flake moisture below target limits before resin enters the melt stream.
Processing Window
Drying systems must run at controlled temperatures and dew points to remove deep-seated water molecules. Reliable rPET moisture determination verifies that drying cycles reach target thresholds without inducing thermal degradation or agglomeration in recycled flakes. Variable flake geometry and bulk density affect drying rates, necessitating routine moisture testing across production batches.
Consistent drying preserves intrinsic viscosity and maintains stable processing pressures.
Quality Metric
Quality control protocols mandate moisture verification for every raw material lot before processing. Routine rPET moisture determination provides quantitative data that validates dryer performance and prevents costly scrap production during bottle manufacturing. Off-spec moisture levels require immediate re-drying or process adjustments to avoid property loss in final products.
Automated testing systems integrate into production lines to deliver continuous quality assurance.
