Cleaner Production for Plastic Recycling and the Issues Affecting this Industry

University Degree Engineering

MASTER OF ENVIRONMENTAL MANAGEMENT

ENVM7104 – Principles of Cleaner Production

Mario E. Fuentes M. Student No. 40908764

Major Assignment:

“Cleaner Production for Plastic Recycling and the Issues Affecting this Industry”

School of Geography, Planning & Architecture

The University of Queensland

Saint Lucia Campus

Date: Monday, November 6th, 2006

CONTENTS

INTRODUCTION …………………………………………………………………………… 3

BACKGROUND TO THE LCA ……………………………………………………………. 4

3. LCA OF PLASTIC PRODUCTS ……………………………………………………………. 5

3.1 Alternatives to Oil Use ……………………………………………………….................. 5

3.2 Energy and Pollution in Production …………………………………………………….. 8

3.2.1 Alternative Energy…………………………………………………………….. 9

4. PLASTIC RECYCLING AND DISPOSAL ……..………………………………………… 11

4.1 Applicability of LCA to Recycling ………..…………………..………………….….... 12

4.2 Main Issues Affecting Plastic Recycling ………………………………………………. 13

FUTURE OF PLASTIC RECYCLING AND CONCLUSIONS ………………………….. 15

LIST OF REFERENCES ………………………………………………………………….. 17

TABLES

1 End uses of plastic material ………………………………………………………………………. 13

2 Specifications of a single plastic and paper bag - the basis products of the LCA …………………14

INTRODUCTION

There is little doubt that plastics have managed to change the way our way of life. Plastics are put to numerous uses from construction, transportation and medical equipment to food packaging and use in high technology goods (Goodship, 2001). In many cases plastic may have replaced a shorter live product that was more expensive. For example, the use of plastics in the construction industry where all types of material from timber to steel has been replaced with a range of plastics (Douglas, 1998, CCC, nd). Other uses, such as some medical uses may otherwise be difficult if not impossible to make from other goods (Stewart, 2005)

‘All plastic materials have the property that at some stage, they have been or can be readily formed or moulded into a useful shape’ (Strong, 2000 p.1). From this perspective plastics are a boom. They have been facilitators and created ease and convenience, increased the quality of life and have also developed markets that have lead to economic wellbeing. However, there has also been a high cost, one that was not originally realised when the plastics industry first developed. The production of plastics as well as its final disposal has a high environment costs with the use of many non renewable sources during production and disposable (Hulse, 2000). The awareness of the problem is increasing, and the pressure to make improvements and develop cleaner plastics production is seen globally but with different levels of commitment and for different bodies. For example, in Ireland there is a € 0.15 tax on all plastic carrier bags used in supermarkets and they are banned in Bangladesh (Knight, 2002). There have also been the passing of legislation in many countries, and consumer pressures but the problems still remain.

This paper will consider the need to find ways for cleaner production, to reduce the waste and pollution of the plastics lifecycle. This will be done with a special focus in the need to recycle efficiently. We will also discuss about the main issues constraining the plastic recycling. The paper will start by considering background to the lifecycle and then take plastics through that lifecycles considering ways that represent more environmentally friendly changes. However, although the focus may be on recycling, the production needs to be considered as well, as it impacts on the level and methods of recycling that can be used and perhaps it is more important than any recycling method developed.

BACKGROUND TO THE LIFECYCLE OF PLASTICS

The entire lifecycle of plastics can be seen as creating harmful emission in some way. It is true that the elaboration of plastics may have some benefits, such as saving the use of timber. However, their production represents a lot of harm as well. Plastics per se make a wide use of fossil fuels, as oil is a main component in its elaboration. For example, PVC is basically made up of two natural resources, salt and oil at a ratio of about 57% to 43% and some additives (British Plastics Federation, 2003). It is not only the components of the plastics that may be seen as depleting the expansible resources, the way plastics are made places higher levels of carbon dioxide into the air with the heating and use of energy in their production as well as their transportation (Hulse, 2000).

Once plastics have been created they are then fairly pollution free, and may be seen as having some positive benefits. For example, 75% of all pipes made of PVC will have a lifetime of more than 40 years and the potential lifetime is up to 100 years, with little or no maintenance (Brydson 1995; British Plastics Federation 2003). The comparison with other material such as metals, would reveal a much lower life expectancy as well as high levels of maintenance, this means not only increased use of the alternative materials, but increased environmental costs associated with their production, transportation maintenance and then more frequent disposal (Andrady, 2003). Therefore there is a positive case for plastics even in environmental terms, but it is more than balanced out when we go on to consider the next stage of the lifecycle of plastics (Lundquist et al, 2001).

Nevertheless, when plastic come to the end of their life there is a major problem, which is the disposal. Plastics are not usually biodegradable, resulting in a long term wastage problem that far outweighs the potential lifetime of the plastic product. The disposal choices are then to either store the long term waste or to dispose of it. Either way there is an increased use of resources and possible pollution in the way the disposal takes place (Curlee & Das, 1991).

The way in which this part of the lifecycle has been managed in the past is with increased attempts to reduce the pollution and create value, with research into recycling. Research has indicated a number of uses for waste plastics. These have ranged from decomposing plastics with the use of a fluidized bed reactor to obtain a new variety of oil, to the reuse of the plastics in new products from housing insulation to packaging (Lundquist et al 2001; Brown & Morgan 1993; Leidner 1981).

The main areas of concern in the lifecycle are the creation of the plastics in the manufacture process and the end of the lifecycle at disposable. At each stage there are potential methodologies to reduce the wastage and pollution that is created resulting in cleaner production.

CLEANER PRODUCTION

As noted the production of plastics takes a high level of energy usage and the take up of exhaustible fossil fuels (Lundquist et al, 2001; Strong 2000; British Plastics Federation 2003; Brydson 1995). In 2002 the worldwide plastics industry was responsible for the consumption of about 270 million tons of oil and gas (Gerngross and Slater, 2003). The extend use of fossil fuels is in the plastic themselves, not only PVC, but also many other common plastics, such as polythene, polystyrene, and polypropylene. The problem of emission and waste is one aspect, but this is also complicated by the expectation of oil and gas to run out at some point in the future. Oils has been estimated at having about 70 years worth of supply left - unless there are major changes in the way oil is used or new oil reserves located - gas 80 years, and coal 700 years (Gerngross and Slater 2003; Modern Plastics 1994; Leidner 1981). The problem is not only with the shortages of these non renewable sources, but also with the costs. The demand for plastics is increasing and so it is the demand for the inputs of production. Any situation of supply and demand will see a situation where supply is running out and demand is increasing resulting in escalating process (Nellis and Parker, 2000).

In contrast with other users of fossil fuels, plastics may be seen as a small consumer, power plants, trucks cars and aircraft account for 90% of the use of all fossil fuels, but it is plastics that account for the majority of the remainder (Gerngross and Slater, 2003).There have been different approaches to the reduction of use of fossil fuels in this process, there have been two main areas of concentration that results in cleaner production which is also economically viable. This concerns the inputs into the main product, and the way that the production is fuelled. We will ...

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3.1 Alternatives to Oil Use

The feedstock used for the manufacture of plastics are gas and oil; coal is used in an insignificant degree. However, the main input into plastic is oil, it is for this reason some of the efforts of plastics recycling has focused in the retrieval of the oil through systems of decomposition. However, if the use of a non renewable product can be substituted for the fossil fuel from a renewable source then the impact in the environment may be lessened especially if the source results in easier disposal. This will also reduce the need for recycling as the products are all biodegradable (Bisio & Xanthos, 1995).

The main drive has been into the use of plant sources. Many plants have been used for many years in order to harvest oil, for example, with hemp and flax there can be the harvesting of both oil and fibres which can be recombined after processing to make plastic composites (Knight, 2002). This is a source that could result in materials that would replace some specific plastics, such as glass-reinforced polyester that is seen used within the automotive industry to make the seatback sections (Hulse 2000; Strong 2000; Asakawa 1992). The benefit is not only the use of a renewable source, simply the need to grow more flax or hemp, but also the benefits at the end of the life when the breakdown of the natural products could be easier than the glass fibres in the glass-reinforced polyester . Unlike the traditional plastics this would be capable of being composted (Knight, 2002).

The use of sustainable origin plastics may be interpreted as the next stage on from recycling, instead of dealing with the waste the inputs are being managed to reduce the need for recycling (Bisio & Xanthos, 1995). There are also other sources that have been considered, such as potatoes for their starch, which has been recognised for many years as a potential alternative but has received little research or attention as the cost of using this source as a source for plastics is prohibitively high (Knight, 2002). If we look at the serious research there are three main areas of consideration; the use of plant sugars for conversion into plastics; the production of plastics inside micro-organisms and the growing of plastic in crops such as corn and other industries where suitable crops are harvested for products such as vegetable oils, bio-ethanol and animal feed crops (MacDonald, 2005, Gerngross and Slater, 2003).

The use of plant based oils is already a source that is used, in 1999 15% of the United States corn oil was used for the production of plastics, and this amounted to 39 million tones. The uses that we made for plastics of this type of oil, has been increasing. A joint venture between Cargill and Dow invested $300 million into their NatureWorks factor that makes plastics using this process creating plastics known as polyhydroxyalkanoate (PHA) and polylactide (PLA). In 2005 Cargill bought out Dow for an undisclosed amount and despite the potential the firm has had some difficulties in persuading companies using the products such as drink and shampoo bottles to make the change. The increased cost of oil in the last few years has helped increase the demand and provide a reason to make the move to these PLA’s (MacDonald 2005; Gerngross & Slater 2003).

Very early it was realised that the main barrier to the take up was the cost of production. Looking at the way the plastic competes in the market place it is mainly an alternative for polyethylene (PET), these are recyclable, but are traditional plastics with the problem already discussed. Before the investment in nature works the costs of PLA’s were very prohibitive, (MacDonald, 2005). However, an increased in the oil price ($33 a barrel) helps NatureWorks to stay in market. In fact, this “issue” is generating an opportunity for making PLA’s more feasible (MacDonald, 2005).

On the other hand, Imperial Chemical Industries are focusing in the production of polyhydroxyalkanoate (PHA). PLA and PHA have in common that both are biodegradable and both are made from plant sugars converted directly into plastics (Molinaro, 2004). However there is a difference, in the case of PHA, and is that there is a more direct conversion with the use of a bacterium Ralstonia eutropha that converts sugars directly into the required plastic (Yarnell, 2004). Compared to PLA this is a more effective method of creating clean plastics. PLA needs an external chemical step for the plastic synthesis, but with PHA there is a natural accumulation of the granules in the microbes which make up potentially 90% of each cell mass (Gerngross and Slater, 2003).

PLA may be in commercial production but PHA also has serious potential for creating cleaner plastics production. Both commercial and academic research has been focused on PHA and the use of the approach to the production of plastic; the growing of plastic in crops such as corn. The approach has to be that of genetic engineering, altering the genetic make up of the plant in order to synthesis the plastic while the crop is growing and eliminating the fermentation process. In this process instead of the crop being grown and harvested followed by the extraction of the sugars that are fermented in order to be converted into plastics; this would result in plastics being grown inside the plant, making this more efficient die to the lower level of inputs required and the less greedy manufacturing process, reducing the energy inputs . However this is still a goal and is not yet a reality, but current research is being carried in order to develop this technology in a commercially viable manner. The major threat was that the production may compete with food production, so the research has focused on the non food elements of the plant, the stems and the leaves which are known as stover (Gerngross and Slater 2003).

The raw material inputs are therefore being considered in terms of the way that position can be reduced and the use of exhaustible resources may be lessened. The use of recycling also comes into this, as recycled plastics do not need the same inputs but this will be considered more under the recycling section. The next consideration is the way in which there is entity use in the production of plastics, this is a major source of energy use and as such also presents opportunities for the reduction of energy inputs.

3.2 Energy and Pollution in Production

In looking at the potential of plants there is the need to extract the plastic from the plants, greater concentration of plastics in each cell may increase the yields. However they still need to be extracted. The research has looked at the way in which the plastics can be separated from the plant, which, for the most part are contained in the chloroplasts (Gerngross and Slater, 2003). The process of producing plastics from plants appears to be an ideal solution for cleaner production, but there are also the issues of the process for the separations, the energy requirements and the emissions.

If the process of using plants and the harvesting and extraction is calculated in terms of the energy consumption this takes up more than the traditional processing procedures. For example, looking at the use of the stover (steams and leaves), as considered in section 3.1, this would require the plants to be harvested, dried and stored, then the extraction process, the purification and the separations and recycling of the solvent involved in the production would also have to take place (Gerngross and Slater 2003; Gerngross 1999).

It was discovered that to create one kilo of PHA from genetically engineered corn, it would take a total of 29 mega joules, this is 300% more than would be needed to manufacture the same amount of PET. Overall it was determined that usually the benefits of using the corn as the source of the plastics was not of sufficient benefit to off set the increased energy consumption needs. In the current methods of production it would take 2.65 kilo’s of fossil fuel in order to create 1 kilo of PHA, the production of polyethylene (PET), only takes 2.2 kilos of fossil fuels in the form of oils and gas. Only half of this is in the final product, so of the fossil fuels that are used 60% is used as burning to create the energy for production (Gerngross and Slater, 2003).

When looming at the production of the PHA with the use of fermentation a similar pattern was found, with the use of 2.39 kilos to make a single pound of PHA (Gerngross and Martin, 1995). It was due to this realisation and the lack of environmental benefits as well as increased costs that some firms, such as Monsanto withdrew from the high levels of research (Gerngross and Slater, 2003).

The concern over the use of fossil fuels in the position also brings to light the need to conserve fossil fuels and the greater environmental concern with the burning of the fuels. There is a higher level of fuel burned and this means the cleaner sources of plastic are creating a greater level of pollution than the traditional production. Therefore, while using less of the oil it is creating a higher level of carbon dioxide, sulphur dioxide and other greenhouse gases (Flannery 2005; Epstein 2000).

Looking at the problems of the emission these may be seen as uncontrollable any of the ways in which cleaner plastics can be produced. PLA may be commercially viable, but the problem with the emissions needs to be deal first. Boyd et al (2005) argue that the approach should be to look at the sources of energy and move to the use of energy created from biomass.

3.2.1 Alternative Energy

The use of biomass can be seen as having some similarities with the use of plants for the productions of plastics as they look to the same sources so may also find some commonalty in their production. Monsanto and Cargill Dow have both considered the use of biomass as a source.

The favourite appears to be the use of ethanol. The development of ethanol as an alternative fuel provides a renewable source; by the fermentation and distillation of agricultural goods that contain carbohydrates and sugars as well as a reduction in the emission levels with the growth helping to overcome the outputs. Ethanol is also known as ethyl alcohol has the chemical formula of CH3CH2OH (Hayman et al., 1995). It can be gained from different crops, such as corn as well as cellulosic remains from wood or crops (Rendleman and Hohmann, 1993).

This process takes place through four main stages, converting the crops to ethanol. First, the treatment of the crop to make a sugar solution, secondly the treatment of the sugar solution with bacteria or yeast to convert the solution onto ethanol and carbon dioxide, thirdly the distillation of the ethanol from the broth formed in the fermentation process, and lastly ‘dewatering’ the ethanol. It is interesting to note that the production of ethanol is this way only needs the carbohydrates from the crop, all the others parts of the crop, including protein oil, fibre, gum and ash are all surplus to requirements (McCurdy, 1986). In chemical terms we see this in the transformation of the glucose to ethanol; Glucose + 2P + 2ADP + H(+) → 2 ethanol + 2CO2 + 2ATP + 2H2O (Geaney, 2002).

Wet milling is a process that has been available for many years in the production of starch; this has been adapted by those seeking to make ethanol. This method gives a very pure form of starch, however, it is a higher cost with a lower final ethanol yield, but it is popular as it have also been used to find markets for the surplus products such as gluten and protein, and in markets such as animal feed (McCurdy, 1986).

This process will include soaking the corn in a sulphur dioxide solution for one to two days, then grinding it. In soaking it the kernels are disrupted and protein and oil can be removed that the resulting product is starch enriched (McCurdy, 1986). After this has taken place the starch needs to be converted to glucose by using enzymes, then the fermentation of the ethanol is undertaken by adding yeast, usually Saccharamyces cerevisiae. Distillation extracts the ethanol, which leaves stillage behind, which may also be processed further (Hayman et al, 1995).

This process is not suited to all crops, and grain such as wheat and bran are usually processed into ethanol by dry milling. This is a smaller market that is shrinking (Rendleman and Hohmann, 1993). This is due to the way that it has a lower ability to make use of the by products. In this the grain is ground first, and then it is soaked in water and receives heat treatment. Following this, enzymes are added and the sugar that results from the conversion of the starch can then be fermented into ethanol with the use of yeast and then distillation and evaporation. However, the stillage that is left, represents between ten and fifteen time the amount of ethanol that is produced in volume (McCurdy, 1986). The stillage can be centrifuged and separated, and separated using evaporation with the resulting distillers' dried grains (DDG) and distillers' dried soluble (DDS) being used for animal feed. There are also newer methods such as extractive fermentation, developed by Queens University Chemical Engineering Department this is a concurrent process where in a single stage the ethanol is produced and extracted (Hayman et al., 1995).

Movements towards the development of cleaner energy as well as more efficient energy useable mean that PLA may be a suitable product in the future. However, we also have to look at the end of the lifecycle and the use of recycling and bridgeable plastics as a way of reducing further pollution at the end of the lifecycle.

PLASTIC RECYCLING AND DISPOSAL

There are several ways of reducing the quantity and environmental impact of plastic waste, and recycling is one helpful alternative (Hulse, 2000). There have been a range of different strategies to deal with plastics that are already in use as well as making plastics that are to be produced more suitable for recycling. Tyre recycling and the reclaiming of oils are only some of the ideas that have been put forward in order to reduce the waste and gain more value from the use of the resources (Leidner, 1981).

In Grangemouth Scotland, BP are undertaking the rendering of plastics to recover oil, the result is a product that is comparable to naptha, with the use of a fluidized bed reactor where the plastics are cracked at temperature between 400 degrees centigrade and 600 degrees centigrade. The energy use here is still very high, however it has also been estimated that for increasing the recovery rate can play an important role in preserving the fossil fuels with every 1% each year increasing the potential consumption by between 2 and 3 years (Smith & Robinson 1997).

We have to bear in mind that the main goal of recycling is to reuse the resources at a lower environmental cost that the creation of new products, such as plastics as well and reducing the impact that wasting them will have directly or indirectly.

In many countries recycling is now an important part of waste minimization programs and Governments have allocated policies and/or programs for ensuring it. For example in 1990 the White paper on the Environment in the UK and in Germany the policies have resulted in Germany being the country with the highest level of recycling (Hulse 2000; Heyde and Kremer 1999).

However, the levels of recycling use compared to landfill disposal are still low. It has been argued that there is a need for recycling, but gaining the products is difficult, it has been noted that only 5% of household waste is being recycled in developed countries such as the UK (Craighill and Powell, 1995). In Canada for instance, it is estimated that 1.5 million tons plastic are buried each year, which means that we are not making use of the energy within plastic materials. In fact, the energy that can be recovered from the incineration of plastics is nearly 10,000 kcal/Kg plastics (Maraghi, 1993).

4.1 Applicability of LCA to plastic recycling

LCA can be used to establish a hierarchy of energy savings. However, this paper will focus on recycling of plastic waste (Bisio & Xanthos, 1995). The types of plastic recycling are:

Mechanical Recycling; this type is concentrated on relatively large and uncontaminated items found mostly in commercial waste. It represents a low percentage of the total plastic recovered.
Feedstock Recycling/Chemical Recycling; this type is mainly used to recover mixed plastic packaging waste. Plastics are used to make raw materials for petrochemical processes. Common examples are cracking and hydrogenation.
Energy Recovery/Incineration; this type of recovering plays an important role by substituting the usage of fossil fuels in combustion plants. Mixed plastic waste posses a high calorific value and can generate heat and/or power. (Goodship 2001; Hulse 2000; Ebert et al 1996).

On the other hand, the following options represent the most common types of end uses for plastic materials:

Regeneration. It is the process of breaking down the polymer molecules in the plastic material into more basic chemicals. The easiest polymers to regenerate are PET plastics and nylon.
Degradation. It means that plastic can break down into smaller molecules by natural means, usually by some biological agent or by sunlight.
Landfills. It is the most commonly used type of disposal. Basically, the rubbish is buried in the ground. It is popular because represents an easier and less expensive option, no sorting is required neither processing (Goodship 2001; Strong 2000; Bureau of Industry Economics 1994).
Incineration. Represent a control burning. The paper, plastics and other flammables are separated from the rest of the waste stream.

Table 2 states the advantages and disadvantages of these four types of disposal for plastic materials.

4.2 Main issues affecting plastic recycle

Historically the main issues constraining plastic recycling have been:

Low perception of recycled plastics, usually they are associated with lower quality.
Higher costs than virgin polymers
Lack of markets
Unreliable availability of good recycled resins (Bureau of Industry Economics 1994; )

Most of the virgin polymers manufacturers do not combine any recycled plastic with the virgin polymer, arguing that recycle plastics have an inferior quality and a higher cost. Therefore, the products made from virgin polymers command a higher price in the market, but are less cost to produce than products made from recycling (Bureau of Industry Economics 1994; Goodship 2001).

The main reason to avoid the usage of recycle plastics has been that recycling is uneconomic and there is a lack of market pressures for the products. Nevertheless, the market agents are increasingly responding to the recycling demand, and in the future the virgin materials producers should emphasised in collection costs, collection and separation technologies, markets for recycled products, and the overall economics of recycling (Bureau of Industry Economics 1994; Goodship 2001).

Moreover, the following example demonstrates that wrong perceptions that may affect waste minimization decisions. The case is about carrier bags which are commonly made of plastic. Usually, it is assumed by the public perception that the use of plastic is more harmful than the use of paper, even when the use of non biodegradable plastic bags is considered. However, interesting results have emerged.

Sevitz (2000) carried a comparison between the footprint of plastic carrier bags and paper bags, the latter of which are considered as more environmentally friendly due to their biodegradable nature. The following table was created when comparing supermarket shopping bags.

Table 2. Specifications of a single plastic and paper bag - the basis products of the LCA

This shows that the paper bags did not make any use of recycled goods. However it was interesting to note that the plastic bags were found to have a much smaller footprint, one plastic bag only created the same level of waste and emission as 2.5 paper bags. There is a point at which the paper bags start to be comparable but they would need to be carrying 7 times the amount of the paper bags.

If we consider this and the lifecycle analysis, which also include disposable and allow level of recycled material being used, the waste is still an issue. If this were then created out of the recyclable plastic then there may be a higher initial cost, but this would still be below the level of the paper bags. However, the cost and waste emission would the end part of the lifecycle would still be reduced.

FUTURE OF PLASTIC RECYCLING AND CONCLUSIONS

Although LCA can help plastics recycling, according to Arsenau (1990) it is necessary to:

Focus the lobby activity on an integrated waste management plan, making an effective use of all the existing waste management options.
Assume/accept the higher cost of recycling.
Fund the extra costs of recycling at the waste or landfill level, not at the consumer level.
Recycling must be integrated to the way in which we do business.
Accept our individual responsibility in regard to recycling.

Plastic recycling is gaining strength due to the increasing opposition of using landfills. Nevertheless, increasing the amount of recycle plastics in the future will require improve, high speed sorting, and new collection techniques. Further research and market development will be required to maximise the value and usage of recycle plastics as well (Bennet, 1992).

Currently the future of plastics is affected by the constant increase of oil price (main source of plastic elaboration), and the growing shortage of this commodity as well; and although it is positive that plastics may be made from vegetable products: cellulose, natural rubber, mollases, soya bean, among others, it will take some time before we could use those materials as our main raw material for plastic (Buekens, 2006).

There is no simple answer, if the overall footprint is considered as the goal, with the need to reduce not only the use of the resources but the level of emissions and pollution that is created, then no single strategy will ever afford this result. The approach has to be a combination of different balances, the use of plastics is not going to diminish and in many cases they may be seen as environmentally favourable to some of the alternatives. However, the way they are made, the products from which they are sources and the way they are dealt with on disposal may also be managed in order to create a cleaner lifecycle.

Considering that decades ago very few people believed that post-consumption plastics were recyclable, and although the amount of plastic recycled at present is still relatively low, we already have the adequate technology for collecting, sorting, cleaning it up and finding markets for recycling products. In spite of this, there is still a lot of work to do on the marketing development. However, it is just a matter of time to happen. Different features will soon increase the present of post-consumer plastics that are recycled (Pearson, 1992).

Moreover, plastics are commonly seen as more detrimental to the environment than perhaps any other material, and this perception is not entirely correct. Recycling is one of several techniques that help to reduce the amount of plastic going to the landfills. Indeed, almost every type of plastic can be recycled as commingled recycle or as fillers in other plastics. However, the last option still represents a high cost option compared to the costs of virgin plastic materials. This compared to the costs of virgin plastic materials. This differential in cost has constrained recycling of many plastics and will continue to be an issue in the short term (Strong, 2000).

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