Polymer Scission
Heat-driven molecular chain breakdown occurs when processing equipment imparts excessive mechanical shear and elevated temperature to thermoplastic coatings during high-speed extrusion coating runs. Extrusion thermal degradation reduces the molecular weight of low density polyethylene layers, which lowers melt strength and causes pinholes in the substrate barrier film. Converting plants monitor barrel temperature profiles closely to prevent polymer chain scission before molten resin contacts the moving paperboard web.
Viscosity Shift
Polymer melt viscosity drops sharply as elevated barrel heat destroys long-chain branching within the polyethylene extrudate. Lower melt elasticity destabilizes the fluid curtain exiting the flat die, producing uneven edge bead formation and fluctuating caliper across the packaging substrate. Operators adjust screw speed and cooling water temperature to stabilize melt flow rates when compounding variations trigger localized overheating inside the extruder barrel.
Barrier Failure
Excessive processing heat destroys the moisture vapor transmission resistance of extruded polymer films by creating microscopic fractures in the laminated coating layer. Degraded polymer molecules crystallize irregularly upon contact with chilled press rollers, leaving minute voids that compromise grease and liquid containment properties in folding carton stock. Finished packaging materials fail seal integrity tests whenever polymer degradation alters the chemical composition of the extrusion layer beyond acceptable tolerance limits.
