Recyclable materials: types, processing and use in manufacturing

Recyclable materials are materials which, after being used or generated during a production process, are prepared for reuse in production. These include plastic, paper, glass, metals and other resources suitable for the manufacture of new products.

In this article, we will look at the main types of recycled materials, the stages involved in processing plastic waste, the areas of application for recycled polymers, and the conditions under which they can be used in injection moulding.

What are secondary raw materials?

Not every used product or production by-product is automatically a secondary raw material. First, the waste must be collected, sorted by material type, cleaned, prepared for recycling and checked to ensure it is suitable for further use.

For example, plastic bottles, films, containers or industrial by-products can only be used as raw materials after they have been sorted by polymer type, had contaminants removed and undergone appropriate processing. For industrial production, the stability of the composition, purity and consistency of the material’s properties are also important.

Recycling should not be confused with reuse. In the case of reuse, a product or its packaging is used again without any significant change to its structure. During recycling, the material is shredded, cleaned, remelted or processed in some other way, after which it becomes a raw material for the manufacture of a new product.

Main types of recyclable materials

Recyclable materials comprise various groups of materials. Separate methods of collection, preparation and processing are used for each of them.

The quality of recycled materials depends directly on proper sorting. For example, different types of plastic must not be mixed indiscriminately, as they have different melting points, shrinkage rates and mechanical properties. Effective separation of waste streams reduces the amount of unwanted impurities and helps to produce a more consistent material.

Where are recycled plastic materials used?

Recycled plastic is used in various industries, but its applications depend on the type of polymer, the origin of the material, its purity and the requirements for the finished product.

Recycled polymers can also be used as part of a material composition alongside virgin raw materials, fillers or modifiers. However, the permissible proportion is not determined by a universal formula, but by the test results for the specific material and component.

For food, medical and other regulated products, compliance of the material with the established requirements must be confirmed separately. The mere fact that the plastic is recycled does not mean that it can be used for any product.

How plastic waste is turned into secondary raw materials

The preparation of plastic depends on its type and degree of contamination. Typical mechanical processing involves several consecutive stages.

1. Collection of materials. Waste is sourced from manufacturing, retail chains, separate collection schemes or specialist operators.
2. Identification and sorting. The material is sorted by polymer type, colour, shape and intended use. This stage is critical in plastic recycling, as mixed polymer streams are more difficult to control.
3. Removal of foreign materials. Metals, labels, adhesive residues, paper, organic impurities and other materials are separated.
4. Cleaning. The plastic is washed to reduce the level of surface contamination.
5. Shredding. Rigid products and films are broken down into fragments or flakes of the required size.
6. Drying. Residual moisture, which may affect the manufacturing process and the properties of the material, is removed.
7. Melting and filtration. The material is melted and purified to remove fine solid inclusions.
8. Pelletisation. The prepared melt is shaped into pellets that are convenient for transport, dosing and further production.
9. Batch inspection. The composition, appearance, uniformity and technical characteristics of the recycled material are checked.

Sorting, washing and shredding are the basic preparatory operations in the mechanical processing of plastics. The exact process may vary depending on the polymer, the type of waste and the requirements for the final material.

Advantages and limitations of using recycled polymers

Incorporating recycled materials into the production cycle can reduce the need for virgin raw materials and support the principles of resource efficiency. However, the technical benefits must be weighed against the potential risks.

Any increase in the proportion of recycled polymer must be technically justified. When a company purchases material by the kilogram or tonne, even slight variations between batches can affect process parameters, the defect rate and the characteristics of the finished parts.

Nor can it be automatically assumed that recycled materials are always cheaper. Their cost may include collection, transport, cleaning, sorting, pelletisation, laboratory testing and stabilisation of properties.

Are recycled polymers suitable for injection moulding?

It is true that certain recycled polymers can be used for injection moulding. However, suitability is not determined by the name of the plastic alone. It is necessary to take into account the origin of the raw material, the uniformity of the batch, the presence of impurities, moisture content, melt behaviour, surface requirements and the loads to which the finished part will be subjected.

During the moulding process, the polymer granules are heated to a viscous-flowing state, after which the melt is injected into the mould. The material cools and takes on the shape of the finished product. Replast uses this technology for the mass production of plastic components and monitors the process parameters at various stages of production.

It is precisely the consistency of these properties that is crucial for achieving repeatable results. If the composition, moisture content or flow properties of the material change in a new batch, this can affect mould filling, shrinkage, the surface finish and the dimensions of the part.

What is checked before the start of mass production

Before using a secondary polymer, the process engineer must assess:

1. type of material and compliance with the declared composition;
2. the origin and traceability of raw materials;
3. consistency of performance across different batches;
4. humidity level;
5. the presence of foreign impurities;
6. fluidity and behaviour of the melt;
7. completing the press form;
8. shrinkage and the geometry of the component;
9. surface quality and colour;
10. the strength of the product under working load;
11. compliance with industry and regulatory requirements;
12. the ability to ensure a stable supply of material for subsequent batches.

When preparing for mass production, it is important to carry out test mouldings, approve samples and establish acceptable process parameters. At Replast, quality control encompasses engineering analysis of the product, material selection, mould testing, mass production and batch consistency checks.