7 criteria for assessing recycled granules

Recycled granules must meet the actual processing conditions and deliver the expected performance in the final product.

An analysis of your quality This is, therefore, the point at which the circular economy becomes a reliable industrial solution: it confirms that recovered waste can be reintroduced into production with consistency, traceability and technical value. But how can we assess its quality before integrating it into the process?

The analysis must take into account seven key criteria: polymer identification, melt flow index, moisture content, particle size distribution and uniformity, colour and homogeneity, thermal and mechanical properties, and consistency and traceability between batches are all fundamental criteria.

In this article, find out whether your company is ready for its industrial application.

Why is the quality analysis of granules so crucial?

The quality of a granulate has a direct impact on productivity, process stability and the conformity of the finished product.

A change in moisture content, particle size distribution, colour or mechanical properties may result in:

• stops
• rejections
• frequent machine adjustments
• differences in the finish of the part

In recycled materials, quality control takes on added importance. The raw material may originate from different industrial streams, each with its own history of use, formulation and level of contamination. The ability to correctly select, separate and process these streams determines the consistency of the final product.

A well-defined quality analysis is not just for identifying non-conformities. It serves to anticipate behaviour, establish realistic specifications and ensure that each batch meets the defined objective.

It is this predictability that makes it possible to replace virgin raw materials, either wholly or in part, in demanding industrial applications.

Quality begins before granulation

No amount of final testing can compensate for poor control at the source. The consistency of the granules is achieved throughout the entire value chain: collection, reception, sorting, decontamination, grinding, processing, filtration, granulation and packaging.

During the collection phase, sorting at source is crucial. Homogeneous industrial waste that is correctly identified and stored better preserves the polymer’s properties and reduces the need for subsequent processing.

On the contrary, mixing incompatible types of plastic or the presence of metals, paper, wood, textiles and other contaminants limits the options for recovery and may affect the performance of the pellets.

Sorting combines knowledge of materials, visual inspection and technologies appropriate to the nature of the feedstock. Accurate identification and separation by polymer type, colour, origin and previous application are essential steps in producing consistent recycled raw materials.

The processing must also protect the material. Excessive temperatures, inappropriate dwell times or insufficient filtration can degrade the polymer. The challenge lies in removing impurities and homogenising the flow without compromising the properties that make the material suitable for a new application.

What to look for in a granulate analysis

The correct specification always depends on the polymer and the end use. A granulate intended for technical components will have different requirements from a material used for non-food packaging, construction profiles or injection-moulded parts. Nevertheless, there are parameters that help to assess the suitability of the material objectively.

Identifying the polymer is the first step. In certain cases, it is also necessary to check for the presence of other resins, mineral fillers, additives or contaminants that may alter the behaviour of the mixture.

The melt flow index is another key indicator, particularly in injection moulding and extrusion processes. This value helps to understand how the material will flow under defined temperature and load conditions. A value that deviates too far from the specification may require changes to the machine parameters or result in a part with properties different from those intended.

Moisture requires particular attention in hygroscopic polymers, such as certain polyamides and polyesters. The presence of water can promote degradation during thermal processing, affect surface appearance and reduce mechanical properties. Depending on the material and application, proper drying prior to processing can be just as important as the composition of the granules themselves.

The particle size, shape and uniformity of the granules influence the feeding of the equipment. A uniform material facilitates dosing, reduces bridging in hoppers and contributes to a more stable operation. Colour, on the other hand, whilst sometimes merely an aesthetic consideration, can reveal variations in the feed flow or guide the selection of material for specific applications.

When the intended use of the granules calls for higher performance, it makes sense to supplement the analysis with thermal, mechanical and density tests. Impact strength, tensile strength, elongation, thermal stability and ash content are examples of data that can support a more reliable technical decision.

From measurement to practical specification

An isolated laboratory result is of little value unless it is linked to a functional specification. For example, knowing that a material has a particular flow index is only useful when that value is compared with the machine’s processing window and the requirements of the part to be produced.

That is why communication between the recycler and the converter is essential. The customer must share critical requirements, processing conditions, the intended use and any limitations of the application.

For its part, the supplier must translate these requirements into an appropriate selection of materials, formulation and quality control. This collaboration reduces unproductive testing and speeds up the qualification of circular alternatives.

Consistency between batches: the true test of reliability

A succession of batches with predictable characteristics is what enables production planning, stock management and the maintenance of product standards. For industry, consistent quality is often more important than an exceptional result achieved on an isolated occasion.

This consistency depends on supply chain management, the separation of material flows, operational discipline and the monitoring of each stage. It also involves traceability: knowing the origin of the material, tracking its recycling journey and linking each batch to the checks carried out.

Traceability is particularly valuable when deviations occur, as it enables:

• quickly identify the cause
• to limit the impact
• implement corrective measures

As well as boosting business confidence, this capability supports the quality systems and environmental commitments of companies that incorporate recycled raw materials.

In the R3 Natura, the recovery of industrial waste is guided by this logic of control and continuity. Turning waste into opportunities requires more than just processing capacity: it requires technical expertise to convert complex waste streams into materials with properties tailored to the needs of industry.

How to incorporate recycled granules without compromising the process

The introduction of a new type of granulate should be treated as a qualification project (and not simply as a change of supplier).

The starting point is to clearly define the application: which properties are essential, which can vary, and what percentage of incorporation is technically feasible.

It is then important to carry out tests under conditions that closely resemble actual production. A laboratory test may indicate compatibility, but only when the material is processed on industrial equipment do factors such as feed rate, pressure, cycles, finish, odour or behaviour in subsequent operations become apparent.

Where necessary, the integration can proceed gradually, starting with a controlled percentage and progressing as the results confirm the desired stability.

It is also important to avoid simplistic comparisons with virgin raw materials. The aim should not be to require all recycled materials to have exactly the same profile as a reference virgin polymer.

In many applications, the best results are achieved by optimising the formulation, adjusting process parameters or selecting an application where the characteristics of the recycled material add value without compromising critical requirements.

Conclusion

Analysing the quality of the granules enables decisions to be made on the basis of verifiable performance, which, in turn, requires data, process control and a close relationship between supplier and customer.

In this way, companies are able to reduce uncertainty when purchasing recycled materials, make better use of waste and move forward with circularity targets which translate into concrete actions.