InsightsPolymer separation
How do you separate PP from PE?
Direct answer
PP and PE cannot be told apart by eye — they share color, transparency and shape. Separating them needs NIR material recognition, which reads each piece's polymer signature rather than its appearance. For prepared flakes that means a multi-spectral sorter such as MAS-P Pro; for whole bottles, MAS-B Pro. Black pieces have to leave first.
Why a color sorter cannot do it
A color sorter classifies color, transparency, shape and visible defects. It is very good at that: it pulls off-color flakes, black fragments, wood, metal, stone, rubber and paper out of a plastic stream reliably, because those things look clearly different from the plastic around them.
PP and PE do not. A clear PP flake and a clear PE flake present the same color, the same transparency and the same shape to a camera. The difference between them is not visible at all — it is a difference in what the material is, and no amount of image quality turns one into the other.
What NIR reads instead
Near-infrared analysis identifies polymer type by measuring spectral response across multiple wavelengths. Each polymer returns a distinct fingerprint in the near-infrared range, so a piece that is visually identical to its neighbour is still separable by material.
- Polymer signature recognitionEach polymer has a distinct spectral fingerprint, captured across the near-infrared range.
- Multi-wavelength analysisBroad spectral scanning separates plastics that look identical to the human eye or a color camera.
- Real-time classificationWithin milliseconds each particle is classified and routed, so sorting keeps pace with production speed.
“Separate PP from PE” is three different jobs
The same sentence describes three streams that need three different machines. Before anything else, the material form has to be settled: are these whole bottles before shredding, or rigid flakes and fragments after shredding and washing? That answer decides the platform before the polymer question is even reached.
| What you actually have | The decision the sorter makes | Platform |
|---|---|---|
| Whole bottles, mixed polymers, before shredding | Bottle by bottle: PET vs PP vs HDPE vs PVC | MAS-B / MAS-B Pro |
| Washed PET flakes carrying PP and PE contamination | PET vs non-PET — everything that is not PET is a reject | MAS-P |
| Mixed rigid flakes of PP, PE and ABS | One polymer against another | MAS-P Pro |
The middle row is the one most often misread. If the accepted product is PET and PP or PE are simply contaminants in it, the decision is PET vs non-PET and MAS-P is the direction. That machine is not being asked to tell PP from PE — it is being asked to tell PET from everything else, which is a different and easier question.
Black material has to leave first
Black and carbon-black plastics absorb near-infrared light, so NIR cannot identify their polymer type. This is a real constraint, not a caveat to skip past — a stream with a meaningful black fraction will not sort by material until that fraction is gone.
The fix is sequencing rather than a better sensor. Optical color sorting removes black items as visible rejects — MAS-C, MAS-B, MAS-PC and MAS-PC Pro all do this — and the polymer separation runs on what remains. Worth stating precisely: removing black material by color does not mean identifying that black material's polymer type. It means taking it out of the way.
Where this stops applying
- MAS-P is not intended to split the rejected non-PET fraction into individual polymers. Its decision is PET vs non-PET; separating PP from PE within that reject stream is a different machine.
- NIR cannot reliably identify black or carbon-black plastics, which absorb the signal. Remove them by color sorting first.
- Film, plastic bags, soft films and very light flexible plastics are not suitable, because air-jet ejection cannot reliably control their trajectory.
- Mayson's plastic flake sorting machines are not designed for pellet sorting.
- Final machine selection and the achievable separation are confirmed on a representative sample, not from a specification sheet.
Common follow-ups
Can a color sorter separate PP from PE?
No. A color sorter separates by color, transparency and visible appearance, and PP and PE can look identical. Telling one polymer from another needs NIR material recognition, which reads spectral response rather than appearance.
Which machine separates PP from PE in flake form?
MAS-P Pro, the multi-spectral polymer sorter for prepared flakes. It is built for the harder polymer classes — PP, PE, ABS, PC and PMMA — that a PET-focused sorter is not asked to separate from each other.
Can PP and PE be separated while they are still whole bottles?
Yes. MAS-B Pro adds NIR polymer identification to whole-bottle sorting, so PET, PP, HDPE and PVC bottles are separated before shredding rather than after.
Does MAS-P separate PP from PE?
Not as its job. MAS-P purifies PET: it identifies PET and ejects non-PET flakes including PVC, PE, PP, PS, PMMA and PC. It is not intended to sort that rejected non-PET fraction into individual polymer categories.
Why can black PP and black PE not be separated by NIR?
Black and carbon-black plastics absorb near-infrared light, so no spectral fingerprint comes back to read. Black pieces can be removed as visible rejects by optical color sorting, but removing them by color does not identify which polymer they were.