The factors to be considered in PET bottle recycling directly determine both the quality of the resulting rPET and the overall efficiency of the recycling line.
Raw material quality and sorting
The most critical factor in recycling is the input material. PET bottles should be as homogeneous as possible and free from foreign plastics such as PVC, PS, and PLA, as well as contaminants like metal, glass, and paper. PVC is particularly critical, as even very small amounts can severely degrade PET and must be completely eliminated during the sorting stage. Separating colored and clear bottles also has a significant impact on final product quality.
Label and cap separation
Labels (especially PVC and shrink sleeve labels) and caps (typically HDPE or PP) have different densities and melting behaviors compared to PET. Insufficient label removal or cap separation leads to contamination and black specks during washing and extrusion. High-efficiency label removal systems and proper density separation are therefore essential.
Size reduction and flake size control
Uniform bottle grinding improves washing and drying efficiency. Excessively fine flakes cause material loss and carry-over, while oversized flakes reduce washing effectiveness. Typically, well-cut flakes in the range of 10-14 mm are targeted.
Washing quality and chemical control
Hot washing is a critical step in PET recycling. Adhesive residues, oils, sugars, and organic contaminants can only be removed with the correct temperature, chemical dosage, and sufficient retention time. Inadequate washing may result in yellowing, odor, and reduced IV values. Wastewater management and filtration are also important for process sustainability.
Drying and moisture control
PET is a hygroscopic material and easily absorbs moisture. Moisture in flakes or pellets causes hydrolytic degradation during extrusion, leading to IV loss. Therefore, mechanical drying combined with crystallizers and/or desiccant dryers must be properly applied. The target moisture content is typically 50 ppm or lower.
Extrusion and filtration
In PET extrusion, the temperature profile, screw design, and especially melt filtration are decisive. Insufficient filtration results in gels, black specks, and foreign particle defects. Backflush or automatic self-cleaning filter systems improve both product quality and line continuity.
Degassing and volatile removal
Inks, detergent residues, and low-molecular-weight components must be effectively removed through a proper vacuum degassing system on the extruder. Otherwise, odor issues, discoloration, and loss of mechanical properties may occur.
IV (Intrinsic Viscosity) control
The required IV value depends on the intended application. Fiber, sheet, and bottle-to-bottle applications each demand different IV levels. If necessary, IV can be increased using processes such as Solid State Polycondensation (SSP).
Defining the final application from the beginning
The intended use of recycled PET (fiber, thermoforming, sheet, bottle-to-bottle, etc.) must be clearly defined at the outset. Line configuration, washing intensity, filtration level, and investment budget should all be designed accordingly.
In summary, success in PET bottle recycling depends on an integrated approach that combines correct raw material selection, effective sorting and washing, low-moisture drying, efficient filtration, and a process design aligned with the target application.