Evaluating Degradation Mechanisms in Post-Consumer Polyolefin Flake
Polyolefin degradation evaluation requires coupling multi-load melt flow testing and OIT analysis to quantify chain scission and restabilize flake lots.
Bolland-Gee Kinetics
Meaning
A mathematical model describes the rate of oxidation in hydrocarbon polymers by relating oxygen consumption to radical concentrations and reaction temperatures. This theoretical framework, known as bolland-gee kinetics, serves as the basis for predicting the lifetime and degradation rates of polyolefins under thermal stress. The calculations determine how fast oxygen reacts with polymer chains under specific thermal conditions.
Kinetic Model
The reaction rate equations utilize activation energies derived from the oxidation of simple liquid hydrocarbons. These mathematical relationships assume that the concentration of dissolved oxygen remains proportional to the external partial pressure. At high oxygen pressures, the oxidation rate becomes independent of oxygen concentration, while at low pressures it depends linearly on oxygen diffusion.
Polyolefin degradation follows these kinetic rules during both long-term storage and melt processing.
Melt Processing
Melt extrusion occurs under low oxygen concentrations but at extremely high temperatures, which shifts the oxidation dynamics. Applying bolland-gee kinetics to these conditions shows that thermal shear dominates the initial radical formation. The model helps moulders calculate the consumption rate of primary antioxidants during a typical cycle.
Sourcing Decision
Virgin polymers are synthesized with a known level of stability, but recycled batches exhibit variable degradation histories. Moulders use oxidation induction time tests, interpreted through these kinetic equations, to evaluate the remaining lifetime of recycled resins. This evaluation dictates the volume of fresh stabilizers that must be compounded into the regrind.