Thermodynamic Limits of Solid State Ester Transesterification
Solid-state ester transesterification reaches absolute thermodynamic limits when glycol partial pressure matches local chemical potential in amorphous channels.
Sticky Point Temperature
Meaning
Physical property describing the onset of inter-particle bonding marks the limit for safe handling of resin in dryers. Exceeding the sticky point temperature leads to clumps that stop the flow of material.
Flow Interruption
Movement of granules through a silo or hopper depends on the pellets remaining separate and free. When the operating environment reaches the sticky point temperature, the frictional forces between pellets increase sharply. This change in behavior causes bridging in the discharge cone or the buildup of a skin on the vessel walls.
Maintaining the temperature below this threshold is a requirement for continuous production.
Equipment Safety
High torque loads on agitators and screw feeders can occur if the resin becomes too tacky. Approaching the sticky point temperature forces the machinery to work harder to overcome the increased resistance of the clumped material. In some cases, this can lead to mechanical failure or the tripping of motor safeties.
Monitoring the temperature at several points in the vessel prevents these localized overheating events.
Lattice Stability
Crystalline regions in the polymer provide structural support that resists the softening of the material. Increasing the degree of crystallinity typically raises the sticky point temperature of the resin. This allows the material to be processed at higher temperatures for drying or solid state polymerization.
Amorphous resins are much more sensitive to heat and require careful temperature ramping to avoid fusing into a solid mass.