Transesterification Balance

Polymer Stability

Degradation of physical properties occurs when temperature exposure forces the transesterification balance away from the intended stoichiometry. Excessive heat triggers random ester exchange reactions which broaden the molecular weight distribution of the melt. Part strength and impact resistance suffer as the polymer chains shorten through these unwanted reactions.

Tight control over residence time in the barrel limits the progression of such exchange kinetics.

Resin Economics

Virgin material supplies typically possess a controlled thermal history that aligns with the stoichiometric requirements of the base polymer. Recycled resin often contains a higher count of chain ends or impurities that accelerate transesterification balance shifts toward lower viscosity states. Blending regrind requires careful monitoring of melt flow rates to compensate for this inherent chemical drift.

Higher additive loads or shorter cycle times become necessary to prevent part failure in applications using high percentage post-consumer feedstock.

Tooling Interaction

Pressure gradients during the filling phase of injection moulding force localized shear heating that fluctuates the internal chemistry of the melt. Consistent cooling rates prevent the frozen-in stresses that develop when the transesterification balance enters a non-equilibrium state before solidification. Parts with thick sections remain vulnerable to internal structural variations because the heat stays trapped long enough to facilitate further molecular rearrangement.

Properly managed thermal profiles in the mould cavity ensure that the chemical state of the polymer remains fixed throughout the cooling transition.