Plastic And Glass

The recycling and reuse of plastics are not easily accomplished because each type of plastic must go through a different process before being reused. Hundreds of different types of plastics exist, but 80% of the plastics used in consumer products is either HDPE (milk and detergent bottles) or polyethylene terephthalate (PET) (large soda bottles). The most common items produced from postconsumer HDPE are detergent bottles and motor oil containers. Detergent bottles are usually made of three layers, with the center layer containing the recycled material.

Most plastic container manufacturers code their products. The code is a triangle with a number in the center and letters underneath. The number and letter indicate the resin from which the container is made:

1 = PET (polyethylene terephthalate)

2 = HDPE (high-density polyethylene)

4 = LDPE (low-density polyethylene)

5 = PP (polypropylene)

6 = PS (polystyrene)

7 = Other (all other resins and multilayered material)

Still, keeping plastics separate is not easy. The most notorious look alikes are PET, the clear, shiny plastic that soda bottles are made from, and PVC, another clear plastic used mainly for packaging cooking oil. Because PVC starts to decompose at the temperature at which PET is just beginning to melt, one stray PVC bottle in a melt of 10,000 PET bottles can ruin the entire batch.

Container glass is the only glass being recycled today. Window panes, light bulbs, mirrors, ceramic dishes and pots, glassware, crystal, ovenware, and fiberglass are not recyclable with container glass and are considered contaminants in container glass recycling.

The consideration in container glass marketing is color separation. Permanent dyes are used to make different colored glass containers. The most common colors are green, brown, and clear (or colorless). In the industry, green glass is called emerald, brown glass is amber, and clear glass is flint. For bottles and jars to meet strict manufacturing specifications, only emerald or amber cullet (crushed glass) can be used for green and brown bottles, respectively.

At the MRF, the collection vehicle discharges the commingled plastic and glass into a hoppered bin, which discharges to a conveyor belt. The material is transported to a sorting area, where the plastic and glass are separated manually from the other materials. The remaining glass is color sorted and sent to a glass crusher. The waste is discharged to vibrating screens where broken glass falls through the openings in the screen. Any residual materials is collected at the end of the vibrating screen. The crushed glass is loaded onto large trailers and transported to the vibrating screen. The residual material is disposed of in a landfill. The commingled plastic is separated further by visual inspection or according to the type (PET and HDPE) based on the imprinted code adopted by the plastic industry.

In a glass bottle manufacturing plant, specialized ben-eficiation equipment performs final cleaning to remove residual metals, plastic, and paper labels. The cullet is then mixed with the raw material used in the production of glass. After the batch is mixed, it is melted in a furnace at temperatures ranging from 2600 to 2800°F. The mix can burn at low temperatures if more cullets are used. The melted glass is dropped into a forming machine where it is blown or pressed into shape. The newly formed glass containers are slowly cooled in an annealing lehr. They are inspected for defects, packed, and shipped to the bottler.

At a reclamation facility, PET bottles and HDPE jugs are transformed into clean flakes. A resin reclamation facility chops and washes the chips to remove labels, adhe-sives, and dirt and separates the material from their com-

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