Meaning
Polycondensation occurs within the pellet interior when solid phase transesterification shifts the molecular weight distribution of polyester resins. This process elevates intrinsic viscosity by driving off volatile reaction byproducts while the material remains below the melting temperature. Producers apply this treatment to enhance the thermal stability of polyethylene terephthalate before final injection or extrusion.
Polymer Property
Intrinsic viscosity governs the mechanical integrity of moulded parts and increases predictably during solid phase transesterification. High molecular weight chains improve the tensile strength of the finished product. Failure to control residence time or vacuum pressure leads to inconsistent flow characteristics during subsequent processing stages.
Moulding Requirement
Regrind economics dictate the heavy use of this thermal refinement because reclaimed material often loses polymer chain length during its first melt. Virgin resin specifications rarely require this additional step unless the application demands high chemical resistance or structural permanence. Moulders adjust their machine parameters based on the specific viscosity gain achieved through the reactor cycle.
Operational Constraint
Temperatures must remain just beneath the crystalline melting point to ensure the pellets retain their physical shape during treatment. Heat transfer limitations slow the reaction rate as the pellets grow larger or their density increases. Correct execution prevents premature polymer degradation by balancing the heat input against the oxygen exclusion limits of the vacuum environment.
A successfully treated batch yields predictable viscosity results across entire production runs.
