Solid State Polymerization Volatile Stripping Mass Transfer Limits in rPET
Solid state polymerization stripping rate is dictated by internal Fickian diffusion limits of condensation by-products and volatiles within rPET pellet cores.
Micro-Pellet Decontamination
Meaning
Extraction of volatile organic compounds and surface contaminants from small-diameter polymer granules prepares the material for direct food-contact packaging applications. This purification process, termed micro-pellet decontamination, relies on the high surface-area-to-volume ratio of smaller granules to accelerate diffusion of impurities. By utilizing this method, recycling plants can rapidly eliminate odours and harmful chemical residues from post-consumer plastics.
The process is particularly effective for high-density polyethylene and polypropylene recyclates.
Physical Process
Thermal desorption combined with a continuous inert gas purge forces the migration of trapped molecules out of the polymer matrix. Because the diffusion distance is much shorter in smaller granules, micro-pellet decontamination occurs up to three times faster than in standard-sized pellets. The hot gas stream continuously sweeps the released volatiles out of the reactor.
Operational Benefit
Shorter cycle times in the recycling line translate directly to reduced energy consumption per ton of processed material. By optimizing micro-pellet decontamination, a recycling facility can increase its hourly throughput and improve the color quality of the output. The resulting pellets can be blended at higher ratios with virgin polymers.
Equipment Requirement
Specialized desorbing vessels with precise gas distribution plates are needed to handle the fluidization of smaller particles without channel flow. This design avoids stagnant zones where the micro-pellet decontamination would be incomplete. It ensures a uniform thermal history for all processed material.