Recycling the Plastic Package

Location:

Concepts Shown:

Polymer Recycling

Equipment:

Recyclable plastic detergent, shampoo, and soft drink bottles. Plastic products made from recycled plastic (e.g.. Ruffies Eco Choice garbage bags from Carisle plastics).

Procedure:

Considering that the students have spent so much time talking about polymers, it seems apt at this stage to talk about how these materials can be recycled for reuse. Most students are aware about the problems that exist with recycling plastic products. However, they should also be aware of the existing methods of recycling. It is important that as engineers, these students understand that they must take responsibility for the products they will make in the future. A few years ago the emphasis in the plastics industry was on making more durable products. There was almost no effort made to reuse the waste plastic or make it biodegradable. In fact, till last year, only 2 percent of plastic waste in the United States was recycled. However, things have begun to change as people realize that there is neither an unending supply of resources, nor sufficient space to dump our waste. A lot more of the plastic that we use in our daily life (plastic in pop, detergent, and shampoo bottles) is not recyclable.

Science:

At the very start of the plastics lifecycle, virgin resin can be tailored to overcome the effects of future reprocessing. Plastics degrade with repeated heating or mechanical stress. Thus, recycling often reduces the material durability and dimensional stability. But additives such as antioxidants can retard thermal degradation and thus help preserve a plastic�s desirable properties. Also, high-density polyethylene (HDPE) can be more successfully recycled in containers for detergents and cleansers if manufacturers use a type of resin in which one part has a high molecular weight and the rest has a low molecular weight. At the next stage in the material�s lifecycle, packaging production, packaging can be designed to enable an increase in its recycled resin content. For example, Ruffies Eco-Choice garbage bags contain 20 to 30 percent recycled plastic. A common technique is to make a plastic container with several layers, some of which incorporate recycled plastic. The recycled resin is placed in the central layer only, so that it cannot come in contact with the harsh, crack-promoting contents of the bottle, or spoil the bottles appearance. And alternative would be to make single layer plastic containers using a blend of virgin and recycled polymers with acceptable properties to resist chemical damage from contents, and mechanical damage from the reprocessing cycle. The most successfully recycled plastic packaging has been soft drink bottles made of pure polyethylene terephthalate (PET). Perhaps the most powerful set of resin recovery systems to be developed are based on chemical processes. One example is depolymerization systems, whereby heat and pressure are applied to plastics in the presence of chemicals such as methanol. that causes the polymer chains to break down into their monomeric constituents, which can then be recycled to produce virgin resins. Remarks: An entirely different packaging feature is the voluntary code developed by the Society of the Plastics Industry: The by-now-familiar arrows that follow one another in a triangle and are accompanied by numbers and letters. Six of these designate the most common container resins and the seventh designates mixed waste. This allows plastic waste to be sorted manually by resin type.

References:

Author:
Rahul Pinto
Credits:


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