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.
Fines Fraction
Meaning
Particulate size measurements quantify the percentage of very small particles or dust present within a batch of bulk resin or regrind. This fines fraction consists of particles that are significantly smaller than the nominal pellet size, usually passing through a standard sieve. Managing these small particles is essential for maintaining uniform extrusion.
Melting Behaviour
Small particles melt much faster than standard pellets due to their higher surface-area-to-volume ratio. This discrepancy caused by the fines fraction leads to premature melting in the feed section of the extruder. The resulting melt pool can block the flow of solid pellets, causing output pressure to fluctuate.
Moulding Defect
Degraded resin from overheated small particles causes cosmetic and structural defects in the final product. These tiny particles spend too much time in contact with the hot screw and barrel, leading to thermal degradation. This deterioration occurs when the fines fraction accumulates in stagnant areas.
For optical or medical parts, these inclusions can cause the batch to be rejected during quality inspection. In addition, the degraded material can reduce the mechanical strength of the part, causing it to fail under impact testing.
Handling System
Pneumatic conveying systems often generate small particles due to high-velocity friction against pipe walls. Removing the fines fraction using dedusting equipment before the material reaches the molding machine stabilizes the process. This filtration reduces both scrap rate and dust hazards.