Which Bottles in the PET Recycling and Washing Line Need to be Manually Pre-sorted?

In the PET bottle recycling and washing production process, in order to ensure the quality of the final PET bottle flakes (recycled materials), the following non-standard PET bottle types must be manually pre-sorted:

I. List of non-standard PET bottles that require manual pre-sorting

Category Need to be sorted out Main reason

II. The adverse effects of not pre-sorting on the quality of the final PET bottle flakes

1. Oil bottles:

Grease residue: Grease is difficult to remove, contaminating the surface of the bottle flakes, hindering subsequent further spinning or blowing processes.

Reduced crystallinity: Affects the melting uniformity and crystallization rate of PET, and weakens the mechanical properties of the product.

2. High barrier layer bottle (EVOH/PA):

Uneven melting: Different melting points of materials such as EVOH and PA will cause gel or black spots to form during the melting process of PET, affecting the quality of the final product.

Decreased IV value: Destroys the cohesion of PET molecules and significantly reduces viscosity and mechanical strength.

Uneven melting:

3. Daily chemical bottles:

Chemical pollution: Residual chemicals in daily chemical bottles will cause bottle flakes to have odor and pollute downstream processing.

Reduced purity: Daily chemical bottles may contain plastics of various components (such as PET, PP, HDPE), which will affect the purity of PET recycled materials.

4. PET blister tray:

Low IV value: The production process of PET tray is different, and its IV value is much lower than that of PET for bottles. After mixing, it will reduce the viscosity of the recycled material.

Contains additives: PET trays may contain additives such as antistatic agents and nucleating agents, which affect the melting uniformity and processing performance of recycled PET.

Reduced transparency: The PET material of the blister tray is usually low-transparency or contains fillers, which will reduce the transparency of the bottle flakes after mixing.

5. Aging PET bottles:

IV value reduction: Long-term exposure to ultraviolet rays and oxidative environments will cause the molecular chains of PET bottles to break, resulting in a decrease in IV value and affecting mechanical properties.

Yellowing: Aging PET bottles turn yellow, reducing the transparency of PET bottle flakes and affecting the appearance of the end product.

6. Recycled bottles:

Performance degradation: After multiple cycles of recycling, the molecular weight and IV value of PET bottles continue to decrease, and the mechanical properties deteriorate.

Poor thermal stability: Repeated melt processing will cause PET degradation, making the thermal stability of recycled flakes worse.

III. Comparison of key indicators of high-quality vs. problematic PET recycled materials

VI. Conclusion and suggestions

Strict manual pre-sorting is the key to ensuring quality: Oil bottles, milk bottles, daily chemical bottles, high barrier bottles, blister trays and other key impurity sources must be strictly eliminated in the front-end manual sorting process. The proportion of aged bottles and recycled bottles must be strictly controlled.

Classification and processing of non-standard bottles: For non-standard PET bottles mixed in batches (such as milk bottles or pallets from specific sources), it is recommended to establish a separate recycling and processing line to prevent them from contaminating mainstream PET bottle flakes.

Goal: Through effective sorting, ensure that the recycled PET bottle flakes have high transparency, stable IV value, excellent melt stability, good mechanical properties, and no odor, meeting high-demand applications such as food-grade contact materials, high-quality spinning, and blow molding.