Melt Shear History and Contaminant Catalyzed Scission in Post Consumer Polyolefin Silo Blends
Deactivate metal catalysts and neutralize acid traces with targeted additives to stabilize viscosity drift and optimize landed cost per good recycled part.
Particle Size Segregation
Meaning
Physical processes cause polymer granules or additive powders of different sizes to separate during storage, handling, or transport. When particle size segregation occurs, it creates non-uniform mixtures of resin and additives. This variation leads to inconsistent melting and erratic behavior in the injection moulding machine.
Ensuring that the material remains homogeneous is necessary for stable production.
Material Handling
Pneumatic conveying systems can cause fine particles to separate from larger resin pellets. Through particle size segregation, the fines accumulate in specific areas of the storage silo.
Defect Prevention
The presence of segregated fine particles in the resin feed can lead to severe defects in moulded parts. When particle size segregation has occurred, the melt temperature fluctuates because fines melt faster than large pellets. This temperature variation causes inconsistent part weight, surface cosmetic defects, and variable shrinkage.
It also leads to incomplete filling of the mould cavities during the injection cycle. This issue can be avoided by maintaining a uniform particle size distribution in the incoming resin.
Silo Design
Silos must be designed to promote mass flow where all the material moves together during discharge. To minimize particle size segregation, engineers specify mass-flow silos with steep hopper angles and smooth internal walls. This configuration ensures that the resin pellets and fines exit the silo at the same rate.
Funnel-flow silos, on the other hand, promote segregation by allowing the material to discharge from the center first. Choosing the correct silo geometry is a reliable way to maintain resin homogeneity.