Meaning
Physical dimensions of the distinct regions formed by immiscible components in a polymer blend determine the material’s overall mechanical and optical properties. In thermoplastic compounding, the phase domain size describes the scale of separation between the matrix and the dispersed phase. This variable dictates the efficiency of stress transfer across the phase boundaries.
Optical Clarity
When the domain size is smaller than the wavelength of visible light, the blend can remain transparent despite being multi-phase. Larger domain sizes scatter light, resulting in an opaque or pearlescent appearance in the molded part. Processors must control the compounding shear and temperature to achieve the desired aesthetic finish.
Toughening Mechanism
Optimum impact resistance in polymer blends requires a specific range of domain sizes. If the domains are too large, they act as defect sites that promote premature failure under tensile stress. Conversely, excessively small domains may fail to initiate the cavitation necessary to absorb impact energy.
Process Stability
The stability of the domain size during injection moulding depends on the interfacial tension and melt viscosity. High temperatures or long residence times in the barrel can cause the domains to coalesce, increasing the size and degrading the final properties. Molders use compatibilizers to stabilize these domains against coalescence during the high-shear injection phase.
This stabilization ensures that the parts produced at the start and the end of a production run exhibit identical performance. It also reduces the occurrence of localized mechanical failure across the part surface.
