Infrared and Thermal Fingerprinting Protocols for Polyolefin Blends
Infrared and thermal fingerprinting verifies polyolefin blend composition, oxidation levels, and phase contamination to enforce supplier compliance and landed part cost.
Phase Co-Crystallization
Meaning
Solidification processes where different polymer chains with compatible structures organize into a single, shared crystalline lattice represent a distinct mechanism of polymer crystallization. In the compounding of polyolefin blends, phase co-crystallization occurs when segments of linear low-density polyethylene and high-density polyethylene crystallize together during cooling. This cooperative packing is restricted to polymers with highly similar monomer sequences and chain conformations.
The phenomenon does not occur if the cooling rate is too high or the polymer structures are incompatible.
Thermodynamic Process
Lattice matching requires the constituent polymer chains to have similar chain dimensions and crystallographic structures. The onset temperature of crystallization lies between the transition points of the individual polymers. This creates a homogeneous crystalline phase instead of separate, distinct crystal populations.
Melt Compounding
Intimate mixing of the polymer phases must be achieved in the melt prior to cooling. Twin-screw extruders are configured to provide high shear to distribute the different resins uniformly. Poor mixing leads to phase separation and prevents the co-crystallization process.
Physical Property
Mechanical performance of the blended part is enhanced by this cooperative crystal structure. The co-crystallized regions act as ties between different polymer domains, improving impact strength and environmental stress crack resistance. This enables molders to use recycled blends in demanding applications.