What should you consider when injection molding recycled plastic?

More and more clients want their products made wholly or partly from recycled plastic. That is a welcome development. However, it is important to know that recycled material is not simply a drop-in replacement for virgin raw material. With the right preparation, it can be processed very well. In this blog, we list the most important considerations.

Why recycled material requires extra attention

Virgin plastic has precise and predictable properties. Every delivery behaves virtually the same in the machine. With recycled material, that is different. Depending on its origin and processing, properties such as flow behavior, mechanical strength and color can vary more widely.

This applies in particular to recycled material purchased as a standard grade on the market. Material compounded specifically for a client and product shows much less variation, because it is tailored to the required specifications in advance.

What it means for the injection molding process

Machine settings

Because of the spread in properties, setting up the machine often takes a little longer. During production, it is also wise to monitor the process closely and adjust where needed. A process that runs stably with virgin material will not automatically run stably with recycled material.

Drying

Some plastics absorb moisture and need to be dried before processing. Recycled material may need to be dried longer or more carefully than its virgin counterpart. Skipping this step can lead to visible defects or reduced strength in the product.

Mold and dimensions

Recycled material can behave slightly differently in the mold than virgin material. This can affect shrinkage and dimensional accuracy, and in some cases cause additional mold wear. For products with tight tolerances, it is therefore wise to test this in advance.

Ensuring quality

Additional inspection

It is still recycled material. An additional incoming inspection and careful monitoring of the first production runs are therefore recommended. Also ask your supplier to include an overview of the technical specifications and processing advice with every delivery.

Clear agreements up front

Good agreements prevent a lot of discussion afterwards. At a minimum, agree on the following in advance:

• the ranges the material must fall within, such as melt flow index, strength and color
• the products the material will be used for
• the requirements the end product must meet
• how to proceed if a delivery deviates

This way, there is a clear reference point as soon as something deviates, and action can be taken quickly.

Choosing smartly per part

Not every part has the same requirements. A few rules of thumb help determine where recycled material is a good fit:

• Functional parts that are not visible, such as fastening clips or connectors, are often very well suited. Color and appearance matter less here.
• Visible parts require more fine-tuning, especially regarding color and surface finish.
• Parts with high technical requirements call for material that is specifically tailored to those requirements.
• Safety-critical and food-related applications are subject to separate regulations and require extensive testing.

Start as early as possible

The earlier in the development process it is clear that recycled material will be used, the better the product design and the mold can be adapted to it. Changes afterwards are often expensive, and sometimes no longer possible at all.

Building a head start

Companies that gain experience with recycled material now will have a head start later. Fine-tuning processes takes time, while demand for recycled raw materials is growing rapidly. Those who only get on board when they have to risk falling behind.

Would you like to know whether your product is suitable for recycled plastic and what that means for production? We are happy to think along with you.