Quantification Limits of Phase Inversion Boundaries in Recycled Olefin Compound Fractions
Phase inversion boundaries in recycled olefin fractions shift with shear rate, necessitating combined dynamic rheology and thermal analysis for domain sizing.
High Density Polyethylene Domain
Meaning
Individual regions of linear ethylene polymer chains aggregate during the solidification of polyolefin mixtures to form distinct crystalline zones. In a blended compound of polypropylene and polyethylene, a high density polyethylene domain serves as the dispersed phase within the continuous polypropylene matrix. These regions possess high crystallinity and contribute specific ductility to the overall blend.
Dispersion Characteristic
The size and distribution of these zones are dictated by the mixing intensity during compounding. A high density polyethylene domain requires efficient shear during extrusion to prevent large agglomerations that could weaken the material interface. Adding a small amount of block copolymer compatibilizer can stabilize these regions and prevent coalescence during subsequent moulding steps.
Mechanical Performance
Impact toughness in the molded part increases when these dispersed zones are properly sized. The high density polyethylene domain acts to absorb energy during high-speed deformation by initiating localized crazing instead of catastrophic cracking. This mechanism is particularly effective under low-temperature conditions where polypropylene would otherwise become brittle.
Rheological Influence
Melting behaviour during subsequent processing is influenced by the distinct thermal transition of the linear ethylene phase. While the polypropylene matrix melts at a higher temperature, the high density polyethylene domain begins to soften earlier in the heating cycle. This difference requires careful control of the extruder barrel profile to avoid overheating the matrix.
The melt pressure must be monitored to ensure the lower-melting phase is fully integrated during the shearing process.