Correlating Dryer Air Dew Point with Karl Fischer Titration Values
Resin moisture correlates to air dew point only at thermodynamic equilibrium; diffusion kinetics and hopper dwell dynamics govern actual Karl Fischer values.
Solid State Post Condensation
Meaning
Chemical enhancement processes increase the molecular weight of semi-crystalline polymers by heating the material in the solid state under a vacuum or an inert gas stream. This technique is commonly applied to polyethylene terephthalate and polyamides to boost their intrinsic viscosity and mechanical performance. Through solid state post condensation, the polymer chains are extended as reaction byproducts like water or ethylene glycol are continuously removed.
Process Mechanism
The reaction occurs at a temperature above the glass transition but below the melting point of the polymer, allowing the chain ends to react without melting the pellets. High vacuum or a dry nitrogen flow sweep away the volatile byproducts, which shifts the chemical equilibrium toward further polymerisation. This process is highly sensitive to the presence of oxygen, which would cause severe thermal oxidation and discolour the resin.
Moulding Advantage
Extruding or moulding resins that have undergone this treatment yields parts with superior tensile strength and toughness. This is particularly beneficial for high-performance applications like beverage bottles or industrial strapping where the polymer must withstand high stress. Using high-viscosity resin also reduces the risk of part failure due to environmental stress cracking.
Industrial Execution
Processing regrind material via this method can restore the mechanical properties that were lost during the initial moulding cycle. This makes it possible to recycle post-consumer waste into high-value applications, reducing the reliance on virgin resins.