Standard Test Methods for Measuring Volatiles in Recycled PET Flake
Accurate rPET flake volatile testing pairs ASTM D6980 sensor drying for moisture with ASTM F2013 headspace gas chromatography for acetaldehyde and solvents.
ASTM D1921
Meaning
Standard protocol designs specify sieve analysis to determine the particle size distribution of plastic materials in various forms. Methodologies under astm d1921 utilize a series of sieves of progressive fineness to separate materials into distinct size fractions.
Particle Size
Flow behaviour in the extruder hopper relies directly on the consistency of the resin’s physical dimensions. Fluctuations in particle dimensions under astm d1921 affect the feed zone efficiency and can lead to erratic melt output. Pellets that exceed the specified size limit cause bridging in the throat, which starves the screw.
Powders that are too fine, conversely, slip past the screw flights and create air pockets.
Processing Impact
Inconsistent melting profiles occur when the feed contains a broad distribution of sizes. Standard astm d1921 testing prevents the inclusion of oversized particles that fail to melt completely during the brief residence time in the barrel. These unmelted regions act as stress concentrators in the finished injection-moulded part.
Moulders utilize these sieve results to adjust the feed section temperature profile.
Economic Consequence
Excessive fines in a shipment of regrind reduce the commercial value of the raw material because they represent lost mass and increased dust hazards during material transfer. Processor margins suffer when feedstock fails the astm d1921 specification, as fines degrade rapidly in the barrel and cause black specks. This test method provides the baseline data to negotiate material returns or price adjustments with resin suppliers.
Accurate testing reduces the risk of running out of specification batches. High percentages of oversized pellets can damage feed throat gates and lead to unscheduled downtime for equipment maintenance.