Introduction

It would be hard to imagine a modern society today without plastics. Plastics have found a myriad of uses in fields as diverse as household appliances, packaging, construction, medicine, electronics, and automotive and aerospace components. As can be seen from this list, plastic technology can be applied with great success in a variety of ways.

So what makes plastic such a versatile material?

The reason for its success in replacing traditional materials such as metals, wood and glass in such a diverse range of applications, is the ability to modify its properties to meet a vast array of designers' needs. This, plus the ease with which plastics can be processed, makes them ideal materials for the production of a variety of components. A quick rummage around the office soon found a whole host of plastic items, the result is shown in Figure 1.1. Look around and you'll be surprised to see just how many different uses plastics have found and how big a market the plastic industry supports.

The plastic material used to make many of these products is what is called 'virgin' grade. These are materials which have come straight from the polymer manufacturer to the factory and have not yet been processed. If these materials later come to be reprocessed, they are then called 'recyclates'. However not all plastic materials are reprocessed, most are simply thrown away, leading to the need to dispose of them. A continued increase in the use of plastics has led

Figure 1.1 Various plastic items

to an increasing amount of plastics ending up in the waste stream. To get an idea of the size of the market, the Western European consumption of plastics in 2005 was 43.5 million tonnes [1], with the UK accounting for 4.8 million tonnes [2] of this with the majority of post consumer plastic waste ending up in landfill.

'The UK currently recycles or recovers approximately 19% of all plastic consumed. This is set to increase to over 25% by 2010 [3].'

Management of waste is one of the major problems facing modern society and is not just limited to plastics. However, a combination of legislative measures and government initiatives, the increasing cost of landfill disposal and public interest in support of recycling has meant that plastics recycling must increase. Generally, plastics are made from crude oil. Recycling of plastics therefore helps to conserve this natural resource.

Any strategy for waste management is based around three guidelines.

  • Avoidance, i.e., reducing and, if possible, avoiding producing waste at source. No waste = no problem.
  • Reclamation, the recovery of materials from the waste stream for recycling.
  • Elimination, the disposal of non-recyclable materials, for example by landfill.

The second point can be applied to the problems of plastic waste by reclaiming material that is destined for landfill. Hence, plastic material recovered from the waste stream is termed 'reclaim'. A summary of the terms introduced so far is given in Table 1.1.

Table 1.1 Summary of common terms

Term

Meaning

Virgin grade

A material that has not yet been processed

Recyclate

A material that has already been processed

Reclaim

A material reclaimed from the waste stream for recycling

A material is reclaimable when both a treatment technology and a market for the resulting new material are available [3]. This book concentrates on the reclamation and recycling of plastics. There are several options for how this can be done: reuse, mechanical recycling, feedstock recycling and energy recovery. These are defined next.

Reuse: the most common examples of reuse are with glass containers, where milk and drinks bottles are returned to be cleaned and used again. Reuse is not widely practised in relation to plastic packaging - plastic products in general tend to be discarded after first use. However, there are examples of reuse in the marketplace. For example, a number of detergent manufacturers market refill sachets for bottled washing liquids and fabric softeners. Consumers can refill and hence reuse their plastic bottles at home.

Mechanical recycling: also known as physical recycling. The plastic is ground down and then reprocessed to produce a new component that may or may not be the same as its original use.

Feedstock recycling: the polymer is turned back into its oil/ hydrocarbon component for use as raw materials for new polymer production. This is also known as chemical recycling.

Energy recovery: the materials are incinerated to recover their inherent energy.

Mechanical recycling is the most widely practised of these methods and will be the focus of much of the further chapters. However, the others are valuable options for waste disposal, especially for materials that do not meet the criteria for mechanical recycling for reasons of practicality or cost-effectiveness.

A number of technologies are available for recovering and recycling plastics. Some are currently in use by industry and capable of processing large quantities of material in a cost-effective manner, whilst others currently exist only in laboratories. Plastic recycling is an area that is constantly developing to try to meet the often competing demands of legislation, market forces and environmental pressure. The inter-relationship is complex and is illustrated in Figure 1.2. No manufacturer wishing to stay in business can recycle materials if it is not profitable to do so. Recycled plastics are used

in the same market in which they originated. They replace and compete against virgin materials. The price recyclate can command will depend on both the price of the virgin materials and the quality of the recyclate. The price of virgin materials can vary greatly as it is linked to both oil prices and supply and demand within the market. This in turn means that the price that recyclate can command varies greatly.

Environmental pressure may create a demand from the consumer for recycled goods. By creating such a market, a manufacturer can see a profit to be made, and will therefore begin to produce and sell recycled goods. This business will also be subject to the effects of market forces, supply and demand. Environmental pressure may also result in legislation forcing manufacturers to use recycled materials. In this case, a market may not exist already and this legislation will impact upon the 'natural' market force. The result may be less profitable and require subsidies to kick-start such activity. For long-term growth however, the activity must be self-supporting.

A fully sustainable infrastructure for the recycling and recovery of plastics is required if the vast quantities of plastic material available are to be diverted from landfill. However, this will occur only when the demand is created for the end product materials and it is economically viable to recycle them. Currently, this has meant that recycling activities need to be subsidised if they are not commercially profitable. Therefore it is paramount that the plastic industry continues to educate the public and potential recyclate users in order to create and develop the supply and demand for these materials.

Before recycling methods are discussed in more depth, a familiarity with some of the fundamentals of polymer science is required. This will be introduced in Chapter 2.

Waste Management And Control

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Responses

  • robur goldworthy
    What makes plastics so diverse?
    8 years ago

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