PVC contamination in PET recycling is difficult to correct after the bottles have been ground. PVC and PET both sink in water, so a standard float-sink tank cannot reliably separate the two polymers. A stable process removes PVC as early as possible, then uses flake-level sorting and quality checks to control what remains.
This guide explains where PVC enters a PET bottle stream, which detection method fits each process stage, and how to set up practical control points without treating one machine as a complete solution.
PVC Contamination Control at a Glance
| Faza procesa | Typical PVC source | Preferred control | Main limitation |
|---|---|---|---|
| Before debaling | Out-of-specification bales | Supplier specification and bale inspection | Inspection cannot find every hidden label or liner |
| Whole-bottle sorting | PVC bottles, sleeves, and safety seals | Manual quality control plus sensor-based polymer sorting | Dirty, overlapping, or black items can reduce detection accuracy |
| After granulation | PVC fragments and label pieces | Flake sorting or dry electrostatic separation | Moisture, particle size, and presentation affect separation |
| Finished PET flakes | Residual PVC missed upstream | Representative sampling and buyer-specific laboratory testing | A small sample may not represent an uneven batch |
Why PVC Is a Serious PET Contaminant
PET se obrađuje pri temperaturama koje mogu izazvati dehidrokloriranje PVC-a. Nastali klorovodik ubrzava razgradnju PET-a i može uzrokovati žućenje, crne točke, smanjenje molekulske mase i krhkost. Recenzirano istraživanje prerade zabilježilo je mjerljivu razgradnju i promjenu boje PET-a pri 100 ppm PVC-a, što pokazuje da vizualno čist tok pahuljica ipak može pasti na specifikaciji kupca.
Prihvatljiva granica nije univerzalna. Kupci vlakana, ploča, traka za vezivanje i proizvoda boca-u-bocu mogu postaviti različite granice, a primjene u dodiru s hranom zahtijevaju dodatne kontrole osim PVC-a. Radni cilj zato treba proizlaziti iz pisane specifikacije kupca gotovih pahuljica i definirane laboratorijske metode, a ne iz jedne opće vrijednosti u ppm.
Where PVC Enters a PET Bottle Stream
- PVC bottles can resemble PET bottles when shape and color are the only sorting criteria.
- Shrink sleeves, tamper-evident seals, and pressure-sensitive label components can remain attached until granulation.
- Closure liners and small PVC components can pass through coarse manual inspection.
- Cross-contamination can occur when conveyors, bunkers, or flake handling equipment process more than one polymer without adequate cleaning.
How to Separate PVC from PET
Whole-Bottle Sorting Before Granulation
Remove PVC while the item is still large enough to identify and eject. Manual quality control can catch obvious PVC bottles and sleeves, while near-infrared or other sensor-based systems classify polymers and trigger air-jet rejection. The sorter must receive a stable, single-layer material presentation; unopened bales, overlapping bottles, dirt, and excessive conveyor loading reduce the value of even a capable sensor.
Why Plain-Water Float-Sink Separation Is Not Enough
Float-sink separation is effective for removing floating PP and PE caps from sinking PET. It does not provide a dependable PET/PVC split because PVC also has a density above water and sinks with PET. The Association of Plastic Recyclers specifically identifies PVC as difficult to remove from PET, particularly after it has become small fragments.
Flake-Level Optical and Electrostatic Sorting
Ako PVC ostane nakon usitnjavanja i pranja, upotrijebite sustav namijenjen pravilnom dovodu pahuljica. Optički sortirnici mogu prepoznati razlike polimera ili boje i izbaciti pojedinačne čestice. Suhi elektrostatski ili triboelektrični sustavi također mogu odvojiti kondicionirane PET i PVC pahuljice, ali zahtijevaju kontroliranu vlagu, raspodjelu veličine čestica, čistoću površine i brzinu dovoda. Pokus s stvarnim materijalom iz pogona pouzdaniji je od odabira prema općem popisu opreme.
Why Thermal Treatment Should Not Be the Primary Control
Heating a mixed PET/PVC stream can expose PVC to the same degradation pathway the recycler is trying to prevent. Any thermal method needs engineered temperature control, corrosion-resistant components, gas capture, and an emissions review. For a PET washing plant, upstream polymer sorting and flake-level rejection are normally safer control points than intentionally heating contamination.
Recommended Control Points in a PET Recycling Line
- Define the incoming bale specification and record contamination by supplier and load.
- Open bales and spread bottles into a consistent single layer before automated sorting.
- Place manual quality control after the primary sorter to monitor misses and changing feedstock.
- Remove labels before granulation whenever the container and label format allow it.
- Use washing and float-sink separation for dirt, adhesive, caps, and polyolefins, but not as the sole PVC control.
- Verify finished flakes with a documented sampling plan and retain samples when investigating a rejected batch.
Quality-Control Questions Before Selecting Equipment
- Is the PVC present as whole containers, labels, or small flakes?
- What PVC limit and test method does the finished-flake buyer require?
- Does the sorter receive dry, clean, separated material within its specified particle-size range?
- Where will rejected material go, and how will the plant measure false rejects and recovery loss?
Ova pitanja određuju treba li projektu sortirnik cijele ambalaže, sortirnik pahuljica, elektrostatski separator ili kombinacija faza. Također sprječavaju čestu projektantsku pogrešku: kupnju stroja za odvajanje prije određivanja oblika onečišćivača i kupčeva testa prihvatljivosti.
Često postavljana pitanja
Zašto je PVC problem u recikliranju PET-a?
PVC can degrade under PET processing conditions and release hydrogen chloride. This accelerates PET degradation and can cause yellowing, black specks, reduced molecular weight, corrosion risk, and brittle recycled products.
Kako se PVC odvaja od PET-a?
Sort PVC from whole bottles before granulation with manual quality control and sensor-based polymer sorting. For washed flakes, use a validated optical flake sorter or a properly conditioned electrostatic process. Plain-water float-sink separation alone cannot reliably separate PET from PVC because both polymers sink.
Što se događa ako se PVC ne ukloni iz PET-a?
Preostali PVC može promijeniti boju recikliranog PET-a, stvoriti crne točke, smanjiti svojstva materijala, korodirati procesnu opremu i uzrokovati da gotova šarža ne zadovolji kupčevu specifikaciju onečišćenja.
Related PET Recycling Equipment and Guides
- PET sustav za pranje boca i recikliranje
- Vodič za kupnju strojeva za recikliranje PET-a
- PET bottle recycling process guide
- PET flake grades and quality requirements
- Sink-float separation tank for PET, PP, and PE
Technical Sources
- Association of Plastic Recyclers: PET Rigid Design Guide
- Peer-reviewed study on small amounts of PVC in recycled PET
- Sensor-based flake sorting equipment reference
Build PVC Control Around the Feedstock
Nijedan separator ne može ispraviti svaki izvor PVC-a. Počnite s ulaznim materijalom, uklonite cijele onečišćivače prije usitnjavanja, dodajte sortiranje pahuljica samo kada to opravdava izmjereni rizik i ispitajte gotov proizvod prema specifikaciji kupca. Za konfiguraciju linije prema mješavini boca, kapacitetu i ciljanoj kvaliteti pahuljica, contact Energycle about a PET recycling project.
