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.
Volatile Organic Compound Stripping
Meaning
Purification processes remove residual monomers and reaction byproducts from polymer resins after polymerization or compounding. Implementing volatile organic compound stripping is required to ensure that molded parts do not emit hazardous fumes or unpleasant odors during their end-use lifespan. This process typically involves exposing the polymer melt or pellets to high temperatures under a vacuum or a stream of inert gas.
Thermal Extraction
The thermodynamic driving force of volatile organic compound stripping depends on the vapor pressure of the contaminants and the temperature of the polymer. Heating the polymer increases the molecular mobility, which allows volatile molecules to diffuse through the polymer matrix to the surface where they are swept away. If the stripping temperature is too high, the polymer itself may undergo thermal degradation, which creates more volatile byproducts and reduces the mechanical properties.
Therefore, the process must be carefully optimized to balance the rate of volatile removal against the thermal stability of the resin.
Processing Benefit
In automotive applications, resin that has undergone effective volatile organic compound stripping is preferred to prevent the fogging of interior glass surfaces. It also reduces the exposure of assembly line workers to volatile emissions during high-temperature injection molding. For food-grade plastics, this step ensures compliance with migration limits, guaranteeing that the packaging does not alter the taste or safety of the food product.
Equipment Technology
Standard industrial setups use vented extruders equipped with vacuum ports to extract the volatiles directly from the polymer melt. Alternatively, solid-state pellet stripping can be carried out in heated hopper dryers that circulate nitrogen to continuously remove the extracted vapors.