Introduction

In daily life, we consume a large amount of milk every day, and the ones that carry this milk are mostly white or opaque plastic bottles made of HDPE. HDPE material is sturdy and corrosion-resistant, making it an ideal choice for storing milk and washing products. Through professional recycling and cleaning lines, these used dirty milk bottles can be converted into high-purity HDPE recycled plastic sheets, becoming valuable raw materials for manufacturing new bottles, pipes, benches, and other products, achieving resource recycling.

Process flow of HDPE milk bottle recycling and cleaning line

Pre-sorting and Initial Impurity Removal
At this stage, manual laborers or robotic arms remove foreign objects clearly not made from HDPE (e.g., bottles of other materials, large contaminants) from the conveyor belt. Simultaneously, equipment utilizes methods such as vibratory screening to remove fine particulate impurities like sand, soil, and glass fragments lodged within the bottle mass.

Label Separation
The plastic film or paper labels on milk bottles are processed by a specialized delabeling machine. This equipment effectively detaches the majority of labels from the bottle bodies through friction and tumbling action, with a suction system then collecting the waste labels.

Precision Sorting and Metal Detection
On the sorting platform, workers perform a refined manual sort, typically by color (e.g., separating white from mixed-color HDPE bottles), to ensure the purity and value of the final recycled flakes. Concurrently, the production line is equipped with a metal detector to ensure any inadvertently mixed metal impurities are promptly removed, thereby protecting subsequent crushing equipment from damage.

Size Reduction (Crushing into Flakes)
The sorted, whole bottles are fed into a wet-type crusher. Here, they are pulverized into uniformly sized HDPE flakes (typically 12-18mm) with water providing both cooling and lubrication. This wet crushing process effectively prevents material oxidation and yellowing caused by frictional heat, preserving quality.

Floatation Washing (Critical Step)
This is one of the core stages in HDPE washing. As HDPE has a density greater than water, it sinks. In the floatation sink-float tank, the crushed flakes are mixed with water. Lighter impurities (such as residual PP/PE cap fragments, incompletely removed label pieces, etc.) float to the surface and are skimmed off, while the purified HDPE flakes settle to the bottom and are collected for the next process stage.

Hot Caustic Washing
Residual organic contaminants like proteins and fats adhering to the inner walls of the milk bottles are a primary cleaning focus. The hot washer utilizes heated water and dedicated, food-grade cleaning agents to vigorously break down and emulsify these stubborn stains and any potential adhesive residues.

High-Speed Friction Washing
To thoroughly remove the last traces of contaminants adhering to the flake surfaces, the high-speed friction washer comes into play. It generates intense friction and collision between the HDPE flakes within its chamber, utilizing physical force to “scrub” off tenacious dirt, achieving a deep cleaning effect.

Rinsing
Following the intensive friction washing, the flakes enter a clean water tank for a final rinse. This step washes away all suspended soils and chemical residues generated in the previous stages, ensuring the ultimate cleanliness of the flakes.

Dewatering and Drying
The cleaned flakes still retain significant surface moisture. First, a dewatering machine (centrifuge) employs powerful centrifugal force to remove the vast majority of surface water. Subsequently, the flakes enter a pneumatic (pipe) dryer, where they are thoroughly dried by a stream of hot air, resulting in the final dry, free-flowing product.

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