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
| Estágio de processo | 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
O PET é processado a temperaturas que podem causar a desidrocloração do PVC. O cloreto de hidrogénio resultante acelera a degradação do PET e pode provocar amarelecimento, pontos pretos, redução da massa molecular e fragilidade. Um estudo de processamento revisto por pares registou degradação e descoloração mensuráveis do PET com 100 ppm de PVC, mostrando que um fluxo de flocos visualmente limpo pode ainda assim não cumprir a especificação do cliente.
O limite aceitável não é universal. Os compradores de fibra, chapa, cinta e material bottle-to-bottle podem definir limites diferentes, e as aplicações em contacto com alimentos exigem controlos adicionais além do PVC. O objetivo operacional deve, por isso, vir da especificação escrita do comprador dos flocos acabados e de um método laboratorial definido, não de um único valor genérico em 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
Se permanecer PVC após a trituração e lavagem, use um sistema concebido para a apresentação de flocos. Os separadores óticos reconhecem diferenças de polímero ou cor e rejeitam partículas individuais. Sistemas eletrostáticos ou triboelétricos a seco também podem separar flocos de PET e PVC condicionados, mas exigem humidade, distribuição granulométrica, limpeza da superfície e caudal controlados. Um ensaio piloto com o material real da unidade é mais fiável do que uma escolha baseada numa lista genérica de equipamentos.
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?
Estas perguntas determinam se o projeto necessita de um separador de embalagens inteiras, um separador de flocos, um separador eletrostático ou uma combinação por etapas. Também evitam um erro comum de projeto: comprar uma máquina de separação antes de definir a forma do contaminante e o ensaio de aceitação do cliente.
Perguntas frequentes
Por que razão o PVC é um problema na reciclagem de PET?
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.
Como se separa o PVC do PET?
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.
O que acontece se o PVC não for removido do PET?
O PVC residual pode descolorar o PET reciclado, criar pontos pretos, reduzir as propriedades do material, corroer o equipamento de processamento e fazer com que um lote acabado falhe a especificação de contaminação do comprador.
Related PET Recycling Equipment and Guides
- PET linha de lavagem de garrafas e sistema de reciclagem
- Guia de compra de máquinas de reciclagem de PET
- 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
Nenhum separador consegue corrigir todas as fontes de PVC. Comece pelo material recebido, remova a contaminação em peças inteiras antes da trituração, acrescente triagem de flocos apenas quando o risco medido o justificar e teste o produto final segundo a especificação do comprador. Para uma configuração de linha baseada na mistura de garrafas, no rendimento e na classe de flocos pretendida, contact Energycle about a PET recycling project.
