ENStarting point
Filtration and degassing address different problems and have limitations. Developing PCR extrusion should connect input composition, feeding, processing history and the performance of approved material, with records that explain variations.
Extrusion control points
Complementary control areas to evaluate together.
- 01
Feedstock
Identity, moisture and variability before adjustments.
- 02
Filtration
Removable contaminants and system limitations.
- 03
Degassing
Volatile control under validated conditions.
- 04
Material history
Temperature, shear and passes through the process.
- 05
Mass balance
Inputs, approved outputs and other streams.
- 06
Customer validation
Resin performance in the process and application.
Specify the feed before adjusting the machine
PCR describes origin, not a single formulation. Before testing, determine the predominant polymers, contaminants, moisture, particle size, bulk density and presence of fillers. Feeding light flakes may be unstable even when the extruder's rated capacity seems sufficient. This instability may appear as fluctuations in throughput, pressure or properties and be mistaken for a settings problem.
Define which batches may be combined, which need additional preparation and which are unsuitable for the pathway. Coperion's documentation presents feeding, extrusion, filtration and degassing as integrated recycling stages. This description supports a systems view, but manufacturer-stated capabilities require validation with the project's material, configuration and output quality. [1]
Understand what filtration can remove
Melt filtration aims to retain particles that do not pass through the filter element under operating conditions. It does not turn an unknown mixture into pure polymer. Melted, dissolved or sufficiently small components may remain in the stream. Improved appearance therefore does not demonstrate removal of all unwanted substances or suitability for applications with specific requirements.
Selection needs to consider contaminant type and concentration, viscosity, throughput, filtration area and the cleaning or replacement strategy. Record pressure before and after the filter and how it evolves throughout the campaign, always within manufacturer-defined limits. A more restrictive condition may improve a visual attribute while increasing material loss or instability. Compare the full result, including retained residues and the time needed to maintain operation.
Address volatiles without promising universal decontamination
Degassing seeks to remove volatile species under the available conditions of temperature, pressure, exposure and surface renewal. Water and odorous compounds do not necessarily respond in the same way. The presence of a vacuum system does not demonstrate removal of all substances of concern. Effectiveness must be verified for the defined target and the composition actually entering the process.
Include management of condensates and removed streams in the scope, according to the design and relevant requirements. An improvement in odour may matter commercially, but should not replace analyses required for the application. Define the method, sample preparation and odour assessment conditions when this attribute forms part of acceptance; informal comparisons may change with temperature and storage.
Track thermal and mechanical history
The temperature set on the control panel does not by itself describe the condition experienced by the material. Throughput, configuration, speed and residence time influence processing. A change that improves mixing may have another effect on colour, flow or strength. Development aims to find a window that delivers adequate homogeneity and removal while preserving the necessary properties.
To investigate changes, compare input and output using relevant methods. Melt flow rate, addressed by ISO 1133-1, is a measurement under specified conditions; its interpretation depends on the material and test conditions. [2] An isolated increase or decrease does not automatically identify the mechanism involved. Mixing grades, fillers, moisture and degradation may require further investigation, including thermal analysis and mechanical tests.
Use a campaign that allows causes to be distinguished
Select controllable variables and a test sequence that preserves comparability. Keep a record of batch, recipe, preparation, throughput, parameters and sampling time. Wait for the defined stabilisation condition before sampling and separate transition material. If several conditions change simultaneously, acknowledge that attributing the result to one of them will be more difficult.
Include a reference processed under the same general conditions and enough repeats to estimate relevant variation. When input material changes, do not treat the new test as an identical repeat. The report should show which conclusions the campaign supports and which depend on further testing. Validation of batch-to-batch variability complements development of the operating window.
Close the mass balance and yield calculation
A hypothetical example, with all masses on the same basis and no inventory change: a campaign uses 1,000 kg of prepared flakes and 20 kg of additives. It delivers 950 kg of approved pellets, 40 kg of off-specification material and 30 kg accounted for in other outputs. The total balances at 1,020 kg. Approved yield relative to total input is 950 ÷ 1,020 = approximately 93.14%.
Do not claim a 95% overall yield by omitting additives from the denominator. Nor should the 30 kg be assumed to be only lost polymer: identify retained residues, volatiles and other streams. If the flakes contain water, the wet basis must appear in the balance or be converted consistently. Off-specification material remains in that status until a rework pathway or another application is approved.
| Group | Mass | Interpretation |
|---|---|---|
| Prepared flakes | 1,000 kg | Traced input |
| Additives | 20 kg | Additional input |
| Approved pellets | 950 kg | Conforming product |
| Off specification | 40 kg | Not added to approved material |
| Other outputs | 30 kg | Streams identified in the balance |
Validate in the customer's process
Pellets may look good and still fail in the mould or final function. Define with the converter the attributes that limit the application: filling, dimensional stability, strength, surface, odour or another relevant requirement. Use samples linked to campaign data to connect any deviation to the conditions under which they were produced.
Approval should record the formulation, source material and processing range actually tested. Where additives are used, confirm their suitability for the application and their effect on relevant properties. Avoid transferring approval from a non-critical part to another with different thermal, electrical or contact requirements. The commercial goal is to supply a resin with a demonstrated use, while keeping the extent of that demonstration clear.
Turn the test into an operating standard
The final deliverable includes an input specification, validated parameters, sampling points, release criteria and responses to deviations. Also record conditions requiring a stop, technical assessment or recipe review under the facility's procedures. The standard should cover start-up, transition, stable production and shutdown, because losses do not occur only during the period used to present throughput.
Link cost and consumption to approved pellets, as well as tracking tonnes processed. The structuring of PCR supply becomes more consistent when delivered material can be linked to the received batch and campaign. Extrusion provides predictability when the pathway's limits are known and quality can be repeated.
Sources and references
References accessed on 5 October 2026. The numbering in the text indicates the concepts supported by each source.
References to ISO standards use their publicly available scopes; full requirements should be consulted in the respective standards.
Circuvia corporate content to support project discussions. Methods, acceptance criteria and applicable requirements are defined within the scope of each operation.
