Plastic Regrind, Explained: How Runners and Scrap Become Recycled Plastic Pellets

Every injection molded part leaves behind some amount of leftover plastic. Runners, sprues, and the occasional defective part are a normal byproduct of the process, but what happens to that material afterward says a lot about a molder’s operation. At Metro Plastics, plastic regrind doesn’t go into a landfill. It goes through an in-house extrusion and pelletizing process that turns scrap back into usable material, keeping production running and keeping plastic out of the waste stream.

What Is Plastic Regrind?

Plastic regrind is exactly what it sounds like: plastic scrap that has been ground down and reprocessed for reuse. During a typical injection molding process, pellets are heated and pushed through a screw, injected into a mold through a gate, and spread throughout the cavity before the finished part is ejected. The section of plastic between the gate and the part itself, called the runner, isn’t part of the final product. Multiply that by the volume of parts a busy production floor turns out, and it adds up to a significant amount of leftover material every single day.

Instead of treating that leftover material as waste, Metro Plastics treats it as an opportunity. Runners and defective parts are collected, reground, and given a second life as regrind material that can go back into non-critical parts for customers.

From Scrap to Second Life: The Extrusion Process

Turning scrap into something usable starts with a plastic extruder machine. Metro Plastics runs an in-house extruder with a dedicated team assigned to the process, so reprocessing happens on-site rather than through an outside vendor.

Here’s what that process looks like, step by step:

1. Collection. Runners and defective parts are gathered from the production floor rather than discarded.
2. Grinding. The scrap is reground into smaller, uniform pieces so it can move through the extruder consistently.
3. Melting and extrusion. The reground plastic is fed through a second melting screw, which pushes it through the extruder in continuous threads.
4. Cooling. Those threads pass through a cooling chamber to bring them back down to a solid, stable form.
5. Drying. Once cooled, the plastic strands are blown dry to remove any remaining moisture.
6. Repelletizing. Finally, the dried strands are cut down into pellets, ready to be reintroduced into the molding process.

That last step, repelletizing, is what closes the loop. Reprocessed plastic that started as scrap comes out the other end looking and behaving like standard resin, ready to be used again.

Where Recycled Plastic Pellets Fit Into Production

Not every part calls for virgin material, and that’s where recycled plastic pellets come in. Because Metro Plastics controls the entire reprocessing operation in-house, the resulting regrind material can be blended into non-critical parts where full-strength virgin resin isn’t a requirement. This keeps material moving through the plant instead of piling up as postindustrial recycled plastic that never gets used again.

This kind of in-house recycling also gives Metro Plastics more control over consistency. Because the extrusion and pelletizing process happens under the same roof as production, there’s no guesswork about how the regrind material was handled before it comes back into the mix.

Why Plastic Regrind Matters Beyond the Environment

The environmental case for plastic regrind is straightforward: less scrap sent to a landfill, less new resin required, and a smaller footprint per part produced. But there’s a practical business case too, and Metro Plastics saw it play out firsthand.

During the 2021 resin shortage, manufacturers across the plastics industry scrambled to find enough material to keep production on schedule. Metro Plastics had already invested in its extruder and pelletizing setup, which meant it had a reliable internal source of recycled resin when outside supply got tight. While other molders were searching for material, Metro was able to keep jobs moving. That’s the kind of resilience that comes from treating regrind material as a resource instead of an afterthought.

Keeping Regrind Out of the Waterways

Reprocessing scrap is only half the story. Metro Plastics also took a hard look at how plastic was leaving the building in the first place. That review turned up two problem areas: pellets hitching a ride outside on the soles of employees’ shoes, and improper containment of loose material on the production floor. Left unaddressed, either one can send plastic pellets into storm drains and, eventually, local waterways.

To close those gaps, Metro Plastics put designated disposal barrels throughout the plant and tightened clean-up procedures across every shift. Press operators are expected to actively collect plastic shavings and scrap as part of their daily routine, not as an occasional task. It’s a simple change, but it’s made a real difference in keeping plastic regrind contained and headed toward the extruder instead of the environment.

A Process Built on Accountability

Plastic regrind is a small piece of a larger commitment. Metro Plastics has been ISO 9001:2015 certified for years, and that same attention to consistency and process control that governs part quality also shapes how scrap is handled. Reducing defects means less material heading to the extruder in the first place, and reprocessing what does show up keeps the operation efficient from the production floor to the pellet hopper.

For a company that molds more than just plastic, that circular approach to scrap and regrind material is one more way Metro Plastics builds relationships customers can count on, project after project.

Ready to talk about your next injection molding project? Contact Metro Plastics to see how our process, from tooling to regrind, can support your production goals.