How to Granulate General Plastic Waste: A Guide for PP, PE, ABS, and Other Common Plastics
Introduction
Plastics processing plants generate waste every day — injection runners, rejects, trial-run material, color-change purge. Discarding this waste is a direct cost loss, but recovering and reusing it starts with one question: can these materials be granulated directly? What equipment is needed? And what happens to the output?
PP, PE, ABS, PS, and PC are all called "general plastics," but they differ considerably in hardness, toughness, and heat sensitivity, and these differences affect how they should be processed. This article is written for equipment buyers and covers the characteristics of each common plastic, the corresponding equipment and blade selection logic, and the downstream processing options.
Material Characteristics and Granulation Difficulty
Before selecting equipment, understanding which category your material falls into is the most critical first step.
PP (Polypropylene)
PP is one of the easiest plastics to granulate. Moderate hardness and low toughness mean a standard blade granulator with SKD11 or SKH-2 blades handles it well. PP waste is common in packaging containers, automotive parts, and appliance housings — varied in shape but generally requiring no special treatment. One thing to watch: thin-wall PP parts can generate static during granulation, causing screen buildup that needs periodic cleaning.
PE (Polyethylene)
PE comes in two forms with notably different characteristics. HDPE is relatively hard and granulates easily. LDPE is soft and elastic — it tends to be pulled rather than cut, requiring higher-speed equipment with sharp blades and a tighter blade clearance setting than harder materials. PE waste is common in bottles, pipe, and film. For film specifically, see the companion article: How to Granulate Plastic Film and Flexible Materials.
ABS (Acrylonitrile Butadiene Styrene)
ABS is hard and tough — one of the more demanding materials for a granulator. Blade wear is faster than with PP or PE; select a higher-hardness blade material and shorten sharpening intervals. ABS waste is common in electronics housings and automotive interiors, and often contains metal inserts or screws. Contaminant removal before feeding is essential — metal hitting blades at speed can cause instant edge chipping.
PS (Polystyrene)
PS is hard and brittle — the easiest of these five plastics to granulate. Brittle materials shatter cleanly under shear rather than stretching like PE, so equipment load is relatively low and blade wear is slow. Note: expanded PS (EPS foam) is a different matter — its extremely low density limits volume reduction during granulation, and the static-charged dust it generates requires dedicated dust collection.
PC (Polycarbonate)
PC is the hardest and toughest of these five materials, placing the highest demands on equipment and blades. SKD11 wears faster on PC than on softer plastics. If PC is your primary material, evaluate carbide-tipped blades — higher upfront cost but better total maintenance economics. PC waste is common in optical lenses, electronics housings, and helmets; it tends to be thick, so confirm feed opening dimensions carefully.
Equipment and Blade Selection
Machine type
A blade granulator is the right choice for all five of these general plastics. Shear-based operation is most effective on tough materials and produces the most uniform output particle size.
The vertical vs. horizontal choice depends on your production mode:
For inline production — granulator running beside a molding machine, processing waste simultaneously — horizontal design provides more consistent output and integrates more easily with conveying systems.
For offline batch processing — collecting waste from multiple processes and granulating in batches — vertical design makes loading easier, especially for larger products.
Blade material
SKD11 tool steel and SKH-2 high-speed steel are the standard blade materials for general plastics — high hardness, re-grindable, excellent cost-efficiency. For PP, PE, and PS, these materials provide a good service life.
For ABS or PC where wear is noticeably faster, consider upgrading to powder-metallurgy high-speed steel (PM-HSS) or carbide-tipped blades. Both carry higher initial cost than SKD11, but their dramatically lower wear rate often makes the overall economics more favorable.
Motor power
Harder and tougher materials require more power. For the same throughput requirement, PC may need a motor one size larger than what PS would require.
Describe your material type and required kg/hr throughput to the supplier and ask for actual capacity data for your specific material — not the generic figures on the spec sheet.
Downstream Processing Options
Direct re-feed to process
For plastics processors, the simplest recovery path is mixing granulated output directly into virgin material and feeding it together into the molding machine. No additional equipment is needed and recovery cost is lowest.
Watch the blend ratio. Regrind proportion varies widely depending on product requirements — anywhere from 20% to 100% is possible. Different materials and processes tolerate different regrind proportions; run small-batch tests first to confirm finished product quality before adjusting the blend ratio.
Pelletizing
If the granulated material will be sold externally or requires more consistent quality, a pelletizing step is typically added. The pelletizer re-melts and extrudes granulated output into uniform-sized pellets. The result is more consistent in quality and more practical to handle than granulated output alone.
Output particle size from the granulator has a direct effect on pelletizer efficiency. Too coarse and the pelletizer feed is uneven — inconsistent melting and potential feed throat jamming. A granulator screen aperture of 8–12 mm generally gives the most pelletizer-friendly output.
Washing and sorting
Plastic waste collected from external sources typically requires washing — before or after granulation — to remove surface oils, labels, and other contaminants. Washing after granulation is more efficient because the total surface area to clean is smaller. Washing before granulation avoids introducing oils into the granulator chamber, reducing cleaning frequency. The right choice depends on your situation.
If incoming waste is mixed-material, density separation or material sorting is needed to separate different plastic types before the regrind is put into use — mixed-material regrind significantly reduces quality.
Pre-Purchase Checklist
Confirm the actual source and condition of your waste
Two batches both labeled "ABS waste" can be very different — electronics housings and automotive parts often use different ABS formulations with different processing difficulty. Bring actual waste samples to the supplier for a trial run before ordering.
Plan for multi-material handling
If your plant processes more than one plastic type, think through the cleaning procedure when switching between materials. Customers with strict regrind purity requirements cannot accept cross-contamination. Plan the changeover cleaning protocol before buying.
Metal contaminant removal
Regardless of which plastic you process, confirm there are no metal contaminants in the waste before feeding. If the waste source is complex and manual inspection is impractical, consider installing a magnetic separator at the feed inlet to intercept ferromagnetic metals and protect blades from instant chipping.
Conclusion
PP, PE, ABS, PS, and PC can all be processed by blade granulators, but differences in hardness and toughness have a meaningful impact on equipment specification and blade selection. Starting from material characteristics leads to better decisions than starting from spec sheets.
For detailed equipment types and selection logic, see: What Types of Granulators Are There? For blade maintenance after installation, see: How Often Should Granulator Blades Be Replaced? and Granulator Maintenance and Care Guide.