Mechanical vs Chemical Purging Compounds
- UniTemp
- 8 hours ago
- 5 min read
What Plastics Processors Need to Know When Cleaning Extrusion and Injection Molding Equipment (2026)
Plastic processing equipment must remain clean in order to maintain consistent production quality. Over time, polymers degrade inside the screw and barrel, color pigments accumulate, and carbonized residues form on internal metal surfaces.
When contamination builds up, processors rely on purging compounds to restore clean processing conditions.
However, not all purging compounds operate the same way.
Two primary technologies exist in the plastics industry:
Chemical purging compounds
Mechanical purging compounds
Understanding the differences between these approaches helps processors select the most effective cleaning solution for their machines.
This guide explains how each type works and when they are typically used in extrusion and injection molding operations.
Why Plastic Processing Equipment Requires Purging
During normal production runs, plastics processing equipment operates at high temperatures and pressures while moving molten polymer through screw flights and barrels.
Several forms of contamination can develop inside the machine.
Common contamination sources include:
Polymer degradation
Plastic that remains inside the barrel for extended periods can break down and form carbonized deposits.
Color pigments
Pigments used for colored plastics can remain trapped in the screw root and contaminate future production runs.
Additives and fillers
Stabilizers, lubricants, and fillers accumulate over time during repeated material changeovers.
Burned material
Dead zones inside screw geometry can trap plastic that eventually burns and contaminates the melt stream.
These residues can lead to problems such as:
black specks in molded or extruded products
inconsistent color during changeovers
extended startup scrap
reduced product quality
Purging compounds are designed to remove these contaminants and prepare the machine for the next production cycle.
For a broader overview of purging technologies, see the complete guide:
What Is a Chemical Purging Compound?
Chemical purging compounds rely on chemical reactions to help remove contamination from processing equipment.
These materials often contain additives that activate under heat and create gas expansion or chemical reactions inside the machine.
This reaction can help loosen degraded polymer and residue inside the screw and barrel.
Chemical purging compounds are often used when processors want a purge that expands inside the machine to break up contamination.
However, this method may introduce additional considerations.
Potential characteristics of chemical purges include:
gas generation during processing
chemical odor during purging
possible residue inside the machine
limited temperature operating ranges
Because chemical purges rely on reactive agents, processors sometimes need additional purging cycles before introducing production material.
What Is a Mechanical Purging Compound?
Mechanical purging compounds clean equipment using physical cleaning action rather than chemical reactions.
When processed through a machine, the material softens into a dense thermoelastic mass.
This material forms a purge plug inside the screw flights and applies pressure against metal surfaces.
As the purge moves through the machine it:
displaces the existing polymer melt
loosens carbon buildup
scrubs screw and barrel surfaces
pushes contamination out through the die
Mechanical purging compounds maintain pressure inside the barrel during cleaning, which helps remove residue from deep inside the screw root.
Industry publications such as Plastics Technology have described mechanical purging materials as producing a soft scrub cleaning action within processing equipment.
One such example is discussed in this article:
Key Differences Between Mechanical and Chemical Purging Compounds
Although both types are designed to clean plastic processing equipment, their operating methods differ significantly.
Cleaning Mechanism
Chemical purges rely on chemical reactions or gas expansion to loosen contamination.
Mechanical purges rely on physical pressure and scrubbing action.
Residue Risk
Chemical purges may leave reactive agents inside the machine that require additional purging cycles.
Mechanical purges typically exit the machine as a solid mass, displacing existing polymer without introducing chemical byproducts.
Temperature Range
Chemical purges often operate within a limited temperature range depending on their chemical activation properties.
Mechanical purging compounds may operate across a wider range of processing temperatures.
For example, PEKUTHERM® purging compounds can operate across temperature ranges from approximately 175°F to 752°F (79°C–400°C).
Machine Preparation
Some chemical purges require partially empty barrels or special preparation steps before use.
Mechanical purges can typically be introduced directly into the machine during normal processing conditions.
When Mechanical Purging Is Often Preferred
Many processors choose mechanical purging compounds for routine machine cleaning because they can be used quickly during production changeovers.
Common use cases include:
color changes in extrusion or injection molding
switching between different polymer materials
removing carbon buildup
preparing machines for shutdown
troubleshooting contamination problems
Mechanical purging compounds are widely used because they can clean machines without requiring chemical reactions or complex preparation steps.
Processors often report reduced downtime and fewer screw pulls when using mechanical purge compounds as part of regular maintenance routines.
Mechanical Purging in Extrusion and Injection Molding
Mechanical purging compounds can be used in both major plastics processing technologies.
Extrusion
Extrusion machines operate continuously and are particularly prone to contamination buildup over long runs.
Mechanical purging compounds can remove contamination from screw flights while maintaining pressure inside the machine.
Processors often use purging compounds during color changes or material transitions.
A detailed step by step explanation is available here:
Injection Molding
Injection molding equipment also benefits from purging during color or material changes.
Because injection molding cycles are shorter, purging compounds help remove residual polymer from the barrel and screw between runs.
Additional information about injection molding purging is available here:
Choosing the Right Purging Compound
Selecting the correct purge depends on several operational factors including:
processing temperature
machine size
contamination level
polymer type
production schedule
Mechanical purging compounds are often used when processors want a purge that works across multiple materials and temperature ranges.
Many plants also incorporate purging into routine maintenance programs to prevent contamination buildup over time.
Additional application examples and case histories are available here:
Just the Facts
Both chemical and mechanical purging compounds are used in the plastics processing industry to clean extrusion and injection molding equipment.
Chemical purges rely on reactive agents that expand or react inside the machine to loosen contamination.
Mechanical purges rely on physical scrubbing action that displaces polymer and removes residue from internal metal surfaces.
For many processors, mechanical purging compounds provide a simple and effective way to maintain cleaner machines and reduce downtime.
As production requirements increase and machine utilization rises, purging has become an essential part of efficient plastics processing operations.
Mechanical purge compounds are especially effective for removing carbon buildup inside extrusion screws and barrels.
Learn More About PEKUTHERM® Purging Compounds
PEKUTHERM® mechanical purging compounds have been used in continuous plastics processing operations since the mid 1980s and are designed to clean extrusion and injection molding equipment using thermoelastic mechanical action.
If you would like to evaluate how PEKUTHERM® performs in your processing equipment, contact the UniTemp team for product information or technical guidance.