Manufacturers generate plastic waste every day. Purgings from extruders, rejected injection molded parts, and packaging film all accumulate on factory floors. While most production managers understand that this material can be recycled, few know what actually happens to it after it leaves their facility. Understanding this process provides valuable insight into why scrap quality matters and how recycled material is produced.
Initial Sorting and Contaminant Removal
When scrap plastic arrives at a reprocessing facility, the first step is evaluation and sorting. Different polymer types cannot be processed together. Polypropylene must be separated from polyethylene, and both must be separated from other materials like styrene or nylon.
Facilities use multiple methods to accomplish this separation. Manual sorting crews remove obvious contaminants. Optical sorting machines use infrared sensors to identify different polymer types at high speed. Density separation tanks separate materials based on whether they sink or float in water. Magnets remove ferrous metals that may have entered the stream.
This stage is critical because contamination directly impacts the quality of the final pellet. A load of scrap that appears clean to the naked eye may contain significant cross-contamination that degrades the finished material.
Size Reduction and Densification
Once sorted, the material must be prepared for processing. Large purgings, thick-walled parts, and bulky items cannot be fed directly into reprocessing equipment. They must first be reduced in size.
Granulators and shredders break the material down into smaller flakes or chips. This increases surface area and creates a consistent feedstock that can be conveyed through the system. For film materials, which are lightweight and take up significant volume, densification may be required. Densifiers use heat and pressure to compress film into a more compact form that flows better through extrusion equipment.
Washing and Separation
For materials that contain surface contamination, washing is necessary. This is particularly common for postconsumer materials, but some postindustrial scrap may also require washing if it contains oils, paper labels, or adhesives.
The ground material passes through friction washers that scrub the surfaces. It then moves through a series of rinse tanks where remaining contaminants are separated by density. Materials lighter than water, such as polypropylene and polyethylene, float to the surface while heavier contaminants sink. The clean material is then dried to remove moisture before further processing.
Extrusion and Filtration
The clean, dry material is fed into an extruder. Inside the extruder barrel, heat and mechanical shear melt the plastic into a homogeneous liquid. As the molten plastic moves through the barrel, it passes through a screen changer.
The screen changer contains fine mesh screens that capture any remaining microscopic contaminants or unmelted particles. This filtration step is essential for producing a clean, consistent material that will perform reliably in molding or extrusion applications. Screens must be changed regularly as they become loaded with captured material.
Pelletizing and Quality Control
After filtration, the molten plastic is forced through a die plate to form strands. These strands are cooled in a water bath, which solidifies the plastic. A pelletizer then cuts the strands into uniform cylindrical or spherical pellets.
These pellets undergo quality testing before shipment. Melt flow rate is measured to ensure consistent viscosity. Physical properties such as tensile strength and impact resistance may be tested. Color and contaminant levels are evaluated against specifications.
The Closed Loop
The finished pellets are packaged and shipped to manufacturers who use them to produce new products. These products may eventually reenter the waste stream and restart the process. At A&A Regenerative Plastics, this cycle represents the fundamental operating principle of the business, transforming manufacturing byproducts back into usable raw material through controlled industrial processing.
