Complete Process of PET Bottle Flake Recycling And Granulation: Equipment Matching From Crushing To Extrusion

PET (polyethylene terephthalate), one of the most widely used plastics, is extensively applied in beverage bottles, food packaging, and other fields. With the increasing awareness of environmental protection, the recycling and regeneration of PET bottle flakes have formed a mature industrial chain. An efficient PET bottle flake recycling and granulation production line requires scientific equipment matching and process design. This article will detailedly explain the complete process from waste PET bottles to recycled pellets and the key equipment configuration.

I. Pretreatment Stage: Sorting and Preliminary Purification

Core Goal: Remove non-PET impurities to lay the foundation for subsequent processing.

Waste PET bottles first enter the pretreatment stage after recycling, which directly affects the purity of the final product:

1. Manual Sorting
    Workers manually pick out mixed HDPE bottles, PVC bottles, aluminum cans, and other foreign objects, as well as severely contaminated or damaged PET

   bottles. For large-scale production lines, automatic sorting equipment can be used to automatically separate different materials through optical identification technology.

2. Label and Cap Removal
    A PET bottle label remover is used to peel off the bottle labels through high-speed rotation and friction, while separating the bottle caps. A high-quality label remover should have a label removal rate of ≥98% to prevent label impurities from entering subsequent processes.

3. Preliminary Crushing
    The sorted PET bottles enter a special crusher and are cut into 20-30mm flakes. The crusher should be equipped with wear-resistant blades and a screen to ensure uniform crushed particles and avoid subsequent cleaning difficulties caused by excessive crushing.

II. Cleaning Stage: Deep Purification Determines Quality

Core Goal: Remove oil, adhesives, dust, and other contaminants on the surface of bottle flakes to make PET bottle flakes meet the standards for recycling processing.

Cleaning is the most critical link in PET recycling, directly affecting the color and mechanical properties of recycled materials. The typical process includes:

1. Pre-washing
    The crushed bottle flakes enter a pre-washing tank, and easily removable impurities such as sediment and beverage residues attached to the surface are removed by high-pressure water flushing. The water temperature is usually controlled at room temperature, and a small amount of cleaning agent can be added for assistance.

2. Hot Alkali Washing
    The pre-washed bottle flakes enter a hot washing cylinder and are soaked and stirred in an alkaline solution at 60-80°C for 15-30 minutes. Adhesives remaining on labels and oil on the bottle surface are decomposed through chemical reactions. The temperature and alkali concentration in this link must be strictly controlled to avoid degradation of PET materials.

3. Friction Cleaning
    The bottle flakes after hot alkali washing enter a friction cleaning machine, and stubborn stains and residual label fragments are peeled off through friction between materials generated by high-speed rotation. The design of lifting blades in the equipment can ensure full contact and friction of materials.

4. Rinsing and Neutralization
    A multi-stage rinsing tank is used to rinse the bottle flakes with clean water to remove residual alkali solution and impurities. Finally, a weakly acidic solution is used to adjust the pH value to neutral (6.5-7.5) to prevent equipment corrosion in subsequent processing.

5. Dehydration and Drying
    The cleaned bottle flakes first pass through a centrifugal dehydrator to remove surface moisture (moisture content reduced to below 10%), and then enter a hot air dryer for further drying. The final moisture content must be controlled below 0.5% to avoid bubbles during granulation.

III. Granulation Stage: Transformation from Bottle Flakes to Pellets

Core Goal: Melt and plasticize clean and dry PET bottle flakes into standardized recycled PET pellets.

1. Selection of Extrusion Granulation Equipment
    PET granulation usually adopts a twin-screw extruder, which is characterized by uniform plasticization and stable output, suitable for processing recycled PET materials. Key configurations include:

• Screw length-diameter ratio (L/D): 36:1-40:1 is recommended to ensure sufficient plasticization.

• Temperature control system: It is necessary to accurately control the temperature of each section.

• Vacuum exhaust system: Remove volatile substances and trace moisture generated during the melting process.

• Filtration system: Equipped with a dual-station screen changer, which can replace the filter screen without stopping the machine to filter tiny impurities.

2. Granulation Process
    The dried PET bottle flakes enter the extruder through a feeder, and after melting, mixing, exhausting, and filtering, they are extruded into filaments through a die head, then cooled and solidified in a water cooling tank, and finally cut into 3-5mm cylindrical pellets by a pelletizer.

3. Quality Inspection
    The finished pellets need to undergo tests on appearance, melt flow index, viscosity and other indicators to ensure they meet downstream application standards.

IV. Core Principles of Equipment Matching

1. Capacity Matching: The capacity of equipment in each link must be consistent to avoid backlog in the previous process or material shortage in the subsequent process.

2. Material Adaptation: Parts of equipment in contact with PET should be made of corrosion-resistant materials (such as 304 stainless steel).

3. Energy-saving Design: Select energy-saving equipment such as variable frequency motors and waste heat recovery to reduce operating costs.

4. Automation Degree: According to labor costs and production scale, reasonably configure automatic equipment to balance efficiency and investment.

PET bottle flake recycling and granulation is a systematic project. Scientific equipment matching can not only improve product quality but also reduce energy consumption and operating costs. Enterprises should customize the most suitable production line scheme according to raw material sources, target markets and investment budgets to achieve sustainable development in the wave of circular economy.