Purging compounds are available in several basic classes – chemical, mechanical (sometimes referred to as physical) and hybrid. Chemical purging compounds actually affect the polymer molecules of the production resin, reducing its viscosity so it can be purged out more readily. Mechanical purging compounds rely on differences in “stiffness” to purge out production resin. Hybrid purging compounds blend aspects of these two technologies.
In most cases, mechanical purging compounds are simplest to use. They're appropriate for color and material changes in injection molding systems or small, simple extrusion systems. In contrast, chemical purging compounds are usually a better choice for challenging materials or for large, complex extrusion systems or blow molding systems. Hybrid purging compounds fall between the chemical and mechanical types in both simplicity of use and effectiveness.
Your purging compound supplier can help you to choose the right type of purging product based on the purging task at hand (provided that they offer a full-spectrum product line).