Interfacial Tension Quantification in Mixed Recycled Polyolefin Streams
Dynamic oscillatory rheology coupled with Palierne model inversion quantifies interfacial tension in mixed polyolefins to control compatibilization economics.
Oscillatory Shear Rheology
Meaning
Characterization of the viscoelastic behavior of a polymer melt involves applying a sinusoidal strain and measuring the resulting stress response. This oscillatory shear rheology yields the storage modulus and loss modulus to describe the elastic and viscous behavior of the material. It provides critical insight into the molecular weight and branching of the polymer.
Viscoelastic Measurement
Dynamic testing applies a small-amplitude deformation within the linear viscoelastic region of the polymer melt. Under oscillatory shear rheology, the phase angle between the applied strain and measured stress reveals how the material stores and dissipates energy. Purely elastic materials respond in-phase, while purely viscous fluids show a ninety-degree phase shift.
Thermoplastics exhibit a combination of both responses depending on the oscillation frequency. Low frequencies reveal the long-term relaxation behavior of the chain molecules.
Melt Behavior
Processing techniques like blow molding and thermoforming require high melt strength to prevent parison sag or excessive thinning. This property is tracked via oscillatory shear rheology by examining the low-frequency storage modulus of the polymer. A high storage modulus indicates strong polymer chain entanglement and resistance to stretching.
If the melt strength is too low, the parison will rupture during the blowing cycle. Adjusting the molecular weight distribution helps optimize this behavior.
Quality Check
Degradation of polymers during recycling or processing can be detected by shifts in the crossover frequency where the moduli are equal. Changes in oscillatory shear rheology signify molecular weight reduction due to chain scission or branching from crosslinking. Molders use this method to screen incoming resin lots for processing consistency.
It identifies material that might process differently despite having the same melt flow index.
Quantifying Interfacial Tension Reduction in Recycled Polyolefin Blends
Quantifying polyolefin blend interfacial tension via Palierne rheological modeling confirms compatibilizer migration, reducing droplet size and scrap rates.