Optimizing Desiccant Drying Parameters to Prevent Hydrolytic Degradation in Recycled Polyester
Optimize rPET desiccant drying at 160-170°C with -45°C dew point dry air to maintain moisture under 30 ppm and prevent intrinsic viscosity drop.
Sieve Analysis
Meaning
Particle size distribution measurement through mechanical screening classifies powder and pellet feeds before polymer processing begins. Granular polymer stocks and dry powder additives undergo mechanical separation through calibrated wire mesh layers to verify conformity to purchasing specifications. Feedstock grading prevents downstream equipment blockage and ensures uniform melting behaviour inside an extruder barrel.
Undersized fines and oversized agglomerates alter bulk density and cause erratic screw feeding during injection moulding. Resin compounding operations rely on this separation method to maintain consistent filler dispersion and avoid moulded part voids caused by moisture trapped in fine fractions.
Particle Separation
Mechanical agitation forces dry polymer powders through stacked wire cloth screens of descending aperture sizes during a fixed operational duration. Vibratory motors impart horizontal and vertical acceleration to carry particles across each mesh surface until apertures present a clear path for smaller fractions. Screen blinding occurs when soft polymer particles deform under friction and wedge inside the wire openings.
Operators prevent blinding by introducing anti-static agents or rubber clearing cubes beneath the wire cloth during the test cycle. Retained mass on each individual screen is weighed on a precision balance to construct a cumulative particle size distribution curve.
Regrind Economics
Mechanical recycling mills apply particle grading to mixed plastic regrind before blending post-consumer output with virgin polymer feedstocks. Shredded plastic scrap generates excessive airborne dust and broad particle size distributions that destabilise volumetric hopper feed rates. Melt filtration pressures spike inside the plasticising unit when fine particulate loads exceed established thresholds within recycled polymer batches.
Virgin resin replacement economics depend entirely on maintaining a consistent regrind particle profile that matches the virgin pellet geometry. Downstream thermal degradation accelerates rapidly if oversized flake fractions pass through the feed throat without achieving complete prior plastification.
Moulding Defects
Hopper bridging and erratic throat feeding originate from improper powder grading and produce severe shot weight variations in moulded components. Excessive dust fractions melt prematurely against barrel walls, causing localized thermal degradation and black speck formation in transparent optical parts. Oversized agglomerates create unmelted domains inside the screw channel that transfer unplasticised inclusions directly into the runner system and weaken the structural integrity of thin-walled mouldings.
Precise powder classification eliminates inconsistent packing density inside the mould cavity and prevents dimensional distortion across high-volume production runs.