Meaning
Macroscopic combinations of two or more polyolefin resins prepared to achieve an optimized balance of processability and mechanical properties represent a standard material category in polymer compounding. In the formulation of plastics for automotive and packaging applications, polyolefin blends commonly combine polypropylene and polyethylene to balance stiffness and impact toughness. These systems are typically immiscible and require high-shear mixing or compatibilizers to achieve a stable morphology.
The phase stability of the blend limits its maximum processing temperature and shear rate during extrusion.
Material Formulation
Varying the ratio of the constituent polymers allows the material properties to be tailored. Elastomeric polyolefins are often added to a polypropylene matrix to improve low-temperature impact strength. The selected grades must have compatible melt flow rates to ensure uniform mixing.
Molding Processing
Rheological behavior of the mixture is complex and depends on the shear rate. Injection molders must set melt temperatures that allow both polymers to flow without degrading the more heat-sensitive component. Mold shrinkage can be less predictable than for single-polymer resins.
Performance Attribute
Finished parts display a combination of the properties of the individual components. A blend of high-density polyethylene and linear low-density polyethylene can provide both high tensile strength and excellent puncture resistance. This enables the down-gauging of film products.
