High density polyethylene bottle recycling

At curbside many communities are collecting aluminum and tin cans, glass bottles, newspaper and plastic bottles. High-density polyethylene (HOPE) and polyethylene terephthalate (PET) are the most commonly recycled plastic bottles. Some areas that have a market for other plastics also pick them up for recycling. Sorting is done to some degree by the resident, the collector, and the reprocessor. 

HOPE high density polyethylene milk bottles, detergent bottles, mixing bowls, toys, plastic bags compost bins, detergent bottles, curbside recycling bins... 

Plastics make up only about 8 percent of the volume in the average landfill but represent a huge investment of energy and raw materials. Most plastics produced from petroleum materials by polymerization of monomers such as ethylene or vinyl chloride are thermoplastic materials and can be cleaned, melted, and re-formed. Thermosetting plastics can also be cut into pieces that are mixed with other plastics or used as fillers. High-density polyethylene (HDPE) and polyethylene terephthalate (PETE) are the most widely reused plastic materials, but polyvinyl chloride (PVC), polypropylene, and polystyrene account for 5 percent of the recycled plastics. In 2001 80 million pounds (36 milfion kilograms) of plastics were recycled in the United States. Recycled plastic materials are used in the production of bottles, fabrics, flowerpots, furniture, plastic lumber, injection molded crates, and automobile parts. 

Coextrusion blow molding is often used to produce multilayer plastic containers. A multilayer parison is produced, and subsequent operations are identical to ordinary blow molding. Reuse of flash is more difficult since it will be multilayer. In many cases, the flash is used in an inner layer in the container, either alone or combined with other recycled plastic. High-density polyethylene (HDPE) laundry product bottles, for example, routinely are made with a three-layer structure in which the inner layer contains flash blended with postconsumer recycled HDPE. 

Recycling of high-density polyethylene milk bottles has about as long a history as recycling of PET soft drink bottles, although recycling rates were very much lower for a considerable period of time. 

In the United States, about 20 percent or 81,0001 (90,000 tons) of plastic (polyethylene terephthalate PET) soft-drink bottles are being recycled. The high-density polyethylene (HDPE) milk bottles recycled amount to 36,000 t (40,000 tons) per year. See Chapter 12 for more details on the waste problem. 

The two forms of polyethylene differ slightly in density. Linear polyethylene is referred to in the recycling business as high-density polyethylene, represented by the symbol HDPE 2 on the bottom of a plastic bottle. The corresponding symbol for branched polyethylene is LDPE 4, indicating low-density polyethylene. (The smaller the number, the easier it is to recycle.)... 

Figure 7.4 Classification and image processing results of a typical situation in polymer waste recycling (a) digital image (b) initial classification result (c) calculation of separation data based on the initial classification result (d) classification result after real-time image processing. A, B Polyethylene terephthalate (PET) bottles with paper labels, C PE bottle with paper label, D PE bottle with PE film label, E PP cup, F PS cup. Classification colour code red high-density PE green PS dark blue PET yellow PP light blue paper.

---