- Email: [email protected]
Why green composites?
1 Why green composites? C. B A I L L I E Queen's University, Canada
1.1
Introduction
Often when pursuing research into green composites we say that we are protecting the environment, that we are working for nature. We may as well stop kidding ourselves - nature will be fine; nature will work out OK and adapt to the changes. It's humans that will cease to exist if we continue the way we are at present. Some scientists and engineers have realised that they need to take responsibility for the outcome of their work. Researching ways of creating faster machines and bigger toys, without due consideration of the effects on the environment or on people, is irresponsible. This book represents some of the workers who have, over the last 10 years or so, decided to change the direction of their research to address some of these issues. We have recently been seeing an increase in the number of researchers working in this area and it is time to reflect on the progress and purpose of our work to make sure that we are in fact doing what we say we would like to do.
1.2
An environmental footprint and life cycle assessment
In this context we are defining green composites as composites that are designed with the lowest environmental 'footprint' possible. Furthermore, we are focusing on fibre-reinforced polymer composites in this book as these are the most abundant material group of the composite family in use. In this chapter we will explore some of the assumptions we make and consider the life cycle of such materials, not only from 'cradle to grave' but beyond the grave into the after life. What do we mean by an environmental footprint? What factors must be considered? We consistently hear the terms 'green', ' e c o ' , 'sustainable', 'environmentally conscious', 'life cycle', 'clean' and assume we know what is meant by them. We also often label our work with these terms in order to 1
2
Green composites
generate funding from governmental bodies who in turn use the terms to satisfy their promises. But is anyone actually making any difference to the damage we are doing to our planet? We need to consider the impact that our material choice and design will have on the society and the environment (Rose and Baillie - Navigating the Materials World, Academic Press, 2003). Life cycle assessment is defined as 'an objective process to evaluate the environmental burdens associated with a product, process or activity by identifying energy and materials used and wastes released to the environment, and to evaluate and i m p l e m e n t opportunities to effect environmental improvements' (Society of Environmental Toxicology and Chemistry, SETAC, Code of Practice, 1991). I dispute the objective part of this definition. Life cycle assessments are so difficult, often so subjective in their evaluations and so complex, that they are frequently ignored, or taken as an add on at the end of a project. Many companies insist on carrying out an L C A or life cycle analysis before their design can be realised. An environmental L C A helps us to quantify how much energy and material are used and how much waste is generated at each stage of a product's life. The analysis takes place first but, after this, the life cycle assessment needs to take place, which is where the interpretation and value judgements come in, e.g. • Is it worse to use up more energy in transport or to produce more factories? • Is it worse to burn and create harmful gases or to create landfill? • Is it worse to dump or to use up energy in recycling? • Is it worse to have the risk of food poisoning or waste food or increased packaging? Assessment of the impact on the environment is therefore considered at each stage: resources, production, distribution, use, disposal or re-use. Many such LCAs have actually proved the project to have been a waste of energy in itself. In a recent report from a C R A F T project to produce natural fibre composites in which I was involved ( C R A F T project European Commission report (BES2-3163), 2000) we compared natural mat- (NMT) and glass mat-reinforced thermoplastics (GMT). A comparison was made between G M T and N M T manufactured by a current production method of prepreg followed by compression moulding into an automotive and nonautomotive part. The L C A analysis was performed for both the non-automotive and automotive part and for three different types of performance requirements, i.e. stiffness, strength and impact resistance. The results of L C A showed that, for most cases, the environmental impact of N M T material is higher than the reference GMT. Despite their 'green' image, natural fibre composites are not necessarily an environmentally friendly alternative to glass fibre
Why green composites?
3
composites in applications where strength and impact are the performance drivers. The reasons for this include the need for pesticides and other chemicals to grow the flax fibre and the higher fibre loadings needed to fulfil the impact and strength criteria. Even in the case of stiffness-based non-automotive applications, where no higher fibre loadings are needed to meet the performance requirements, the differences in environmental impact between G M T and N M T are very small and in the current analysis the poorest performance was shown for N M T due to the negative effect of pesticides. In the case of automotive and stiffness critical applications N M T composites do seem to perform better than G M T composites. This reduction in environmental impact for N M T composites is, however, mainly due to the lower weight of natural fibre composite parts, which leads to lower fuel consumption during the use of composites and not so much the result of the use of 'green' natural fibres. Hence, the advantages of natural fibre composites are relevant if weight savings are obtained over glass fibre composites.
1.3
Drivers for change
From the above it would seem as if only those researchers who are altruistic would be involved in this game. In fact, there are many drivers for the change we currently observe. Global concerns are considered by the Kyoto Protocol, national concerns by government legislation, and local companies in turn make a response to the legislation. All of this will influence funding mechanisms and availability of funds for researchers. Global responses to climate change are critical at the time of writing where countries are deciding upon the Kyoto Protocol. Reports of a lecture by Michael Grubb of Imperial college to the Royal Institute of international Affairs (The Independent, 5 November, 2003) quote him as saying: the US is starting to pour billions of dollars into research on technologies like carbon sequestration and hydrogen. Unfortunately, pursuing climate technology while eschewing emission caps is like designing a fancy car while opposing all efforts to put an engine in it... . Governments are not good at delivering industrial technologies: there has to be a market for them. The argument may be said to be true of green composites in automotive and other applications. In Canada at present there is a push to make a new profitable market from the use of agricultural fibres in composites. Economic arguments alone will not cause this technology to take off. Rumour has it that local industry may not become interested in changing to more ecofriendly products because, even if the Canadian Government encouraged them to do so with legislation, they would simply sell 'over the border'. One of the largest markets for natural fibre composites is the US automotive
4
Green composites
sector who currently do not appear to have the same drivers as the European market. The EU Directive for automotive parts has meant that many companies in Europe have started to consider environmentally friendly alternatives to fuel and materials for production. The Directive stipulates that re-use and recycling of end-of-life vehicles must increase to 9 5 % by 2015. Further details are given by Tucker in Chapter 10. He tells us that disassembly is a concern and costs associated with dismantling plastic components from cars are too high at present. Tucker would suggest 'design for disassembly'. The European Community approach to waste management is based on two complementary strategies: avoiding waste by improving product design and increasing the recycling and re-use of waste. The EU Landfill Directive (1999) states that, by 2010, the amount of biodegradable municipal waste going to landfill must be reduced by 7 5 % of the total produced in 1995. The EU Packaging Waste Directive (1997) states that there must be 5 0 - 6 0 % recovery and 2 5 - 4 5 % recycling by 2006. For a city like London, this means that there must be alternative routes for waste of between 2 and 4 million tonnes per year. The UK has responded by developing its Government Waste Strategy (2000). This states that 30% of all waste produced must be recycled or composted by the year 2010. Furthermore, the UK has responded to the EU Directives by bringing in a landfill tax system that forces companies to think about end of use. Hence, response to EU Directives creates a huge driver and support for research in the green materials area. In the US the Environmental Protection Agency Office of Solid Waste 'supports' reaching a goal of 3 5 % recycling by 2005 (American Plastics Council, 2 0 0 1 , National Post Consumer Plastics Report). Implementation of legislation is, of course, another huge factor. Hence it might be that Liverpool in the UK cannot ask its citizens to take responsibility for the environment as they do not have a collection system in place and the locals would use more energy in fuel driving to the nearest collection point in Chester. Kingston, Ontario in Canada, on the other hand, represents one town that has a well-established curb side collection system in place. However, it is rumoured that much of the plastic waste gets sent to other countries as an export. Those countries obviously do not have enough of their own waste.
1.3.1
Swings and roundabouts
We cannot pour money into environmental research until legislation reinforces the changes that ensue. We cannot encourage participation of profit driven corporations unless legislation supports such changes. Furthermore, we cannot create environmental schemes that rely on the participation of communities of people who produce waste when the infrastructure is not there to support the s c h e m e s . The drivers for, and the national and global e c o n o m i c ,
Why green composites?
5
environmental and social impact of, new directions in research must all be considered before seriously trying to effect change in material usage.
1.4
The structure of this book: a life cycle approach
In the light of the above we have decided to arrange this book with a life cycle approach. We consider first the choice of materials that iterates with the design and function or the application. We consider the factors affecting the life cycle analysis. We look at possible fibres to use as reinforcement, as well as potential polymer matrices. In this latter category we need to consider thermoplastics as a source which may be recycled, or as a nonvirgin source; composites as a means of upgrading recycled polymers as well as thermosets which need to be re-used or biodegradable thermosets which degrade. We will look at processing of the composite; its production into components, trying in the meantime not to forget in our discussions the transport of raw materials and parts at each stage and the energy consumed in the production run. We consider a range of applications - replacement for G F R P (glass fibre-reinforced polymers) as well as upgrading of polymer components. Finally, we look at the re-use, recovery and recycling of the composites that we have made. We start the process by reflecting upon 'Design thinking'. Rose takes us on a philosophical pathway through notions of progress and a reflection on our values to the idea of learning from nature about 'ecologically responsible design'. Murphy takes pity on the reader and helps us place this in a more solid context by leading us through those issues which affect the life cycle of a natural fibre composites product. Read this chapter even if you dip in and out of the others. It is necessary to consider all issues impacting our 'footprint' if we are to take ourselves and our research seriously when we say we are working on 'green composites'. The choice of fibre is determined by all of the usual selection criteria such as ultimate mechanical properties, interfacial adhesion with the matrix (high or low for strength or toughness applications respectively), cost, availability of resources, chemical properties, resistance to moisture, etc. It is also determined by the 'green' criteria - whatever those might be. Nishino discusses the potential for natural fibres in composites. They are divided into wood, vegetable, animal and mineral. We have seen different trends in different parts of the world for the uptake of certain fibres. Abundant good quality fibre sources will determine this to an extent and we see far more wood fibres used in North America and more agricultural fibres in Europe. However, it is also lifestyle and marketing that will determine these directions. Hughes discusses the fact that the predominant market for wood plastic composites (WPC) is in decking in North America, whereas the European market for vegetable or agricultural fibres is the automotive sector.
6
Green composites
Nishino's Table 4.6 shows us the main merits and demerits of using natural fibres. Sustainability of natural resources - or the ability to re-grow on an annual basis, together with low energy consumption and biodegradability make them a good environmental or 'green' choice so long as the remainder of the life cycle is properly assessed. For example, we need to think about transport of fibres, moisture resistance, interfacial adhesion, etc. Often, we see arguments comparing glass with natural fibres and suggesting that the only way for natural fibres to be adopted is if their properties can be proved to be 'as good a s ' or better than glass. However, it is also stressed that, unless the new system is cheaper, it will not be adopted. In other words people are not prepared to change anything. This is not the way of nature, which continually adapts to new conditions. The benefits of natural fibres are quite different to those of glass fibres and they should be used to create materials that will better suit the needs of our environment and communities of the future. If we look to see how an ecosystem works, we see that everything is used at its optimal function and no more. There is no waste of material or energy. Peltola focuses more on paper fibres. He states that in the US over 300 kg per capita of paper is used per year. In Europe, of the 35 million tonnes produced in 2002, 3 million tonnes are recycled and 14 million tonnes are used as energy. His argument is that we should divert paper fibre from landfill to a useful composite of waste fibre and plastic. An alternative environmental solution for the choice of fibres is presented by Shanks. He presents the work of researchers who are working with fibre/ matrix of the same thermoplastic material so that, at the end of life, the entire mass can be melted to form a new product. All polypropylene (PP) composites, for example, have great potential environmentally. Even though they do not come from a renewable source - composites made from all P P have at least one more life before incineration or energy recovery. Now we need to turn to the matrix. Of course, it is never possible to deal with the fibre and matrix independently, and all authors do address many other aspects than the one they have been asked to put in focus. In consideration of the choice of matrix, in a way similar to that for the fibre we can select natural sources for sustainability or recyclable polymers. We can also use biodegradable polymers. Thermoplastics are the first matrix of choice as they are recyclable. However, once we have added fibres, they are often rendered non-recyclable so the argument is not well made. Only in the case of all polymer composites such as all PP can the end-of-life be recycling. Adding natural fibres will be better than glass as the composite could be incinerated for energy recovery. However, a better alternative, as discussed earlier, is the use of recycled polymer as source. The addition of fibres will upgrade the polymer. The main thermosets considered are biodegradable. Plackett explains, however, that natural polymer matrices are at varying
Why green composites?
7
stages of development and much work is needed to improve stability, processability, mechanical properties and degradability. Alongside the choice of fibre and matrix will come the choice of processing method - very different for thermoplastics and thermosets. As considered by Aziz and Sain, thermoplastic injection moulded parts can be complex but fibres are short and stiffness low as a result. Furthermore, high temperatures are often needed for adequate viscosity and natural fibres can be damaged. Aziz argues that thermosetting composites have better properties: stiffness can be increased by using longer fibres; interfacial properties will be better because of longer processing times and better fibre wetting. These factors must be weighed against production costs (parts per hour produced) and environmental impact. Natural thermosetting polymers seem to come out quite well in many of the arguments and Aziz considers cashew nut shell liquid resin as an example. Clean processing is discussed more thoroughly by Tucker. He uses Thorpe's (1999 in Tucker) definition: 'a way to reverse our current non-sustainable use of materials and energy'. He tells us that we should move manufacturing from a linear use of resources into the cyclical use of resources that do not produce waste products. He also points out that cleaner production methods must satisfy the triple bottom line: environmental, social and economic. He quotes Thorpe's suggestions for clean production, helping us think about the need rather than the desire for products in the first place, the need for durability rather than for recycling, and reduction of consumption whilst maintaining quality of life. He really seems to balance the three aspects above, but will companies in the current economic system wish to respond? Once we have selected the materials and production method appropriate for our a p p l i c a t i o n , and the properties required, whilst k e e p i n g our environmental impact as low as possible, we must consider the potential for end of use. Already, we have seen this consideration but we now bring this aspect into focus. If we find we will be producing something with one life before landfill, we need to think again. Hodzic reminds us that plastic waste may be reduced to its monomers, recycled or biodegraded. Thermoplastics are not without their problems as they require a high degree of purity of recyclate as well as separation of the matrix from the reinforcement except in the case of all PP, for example. Thermosets are more problematic, as discussed previously, but some chemical additives can help to degrade polymers, although Hodzic warns against possible side effects to the environment. Chemical additives must always be considered in the light of our ecosystem approach. Wherever possible it would be better to use something present within the system to carry out the desired function, as nature would do, rather than adding an alien element that will have a counter effect. Arnold takes us through the whole process of recycling and reprocessing.
8
Green composites
His concern echoes my own - that increases in recycling rates (or use of green composites) will not occur simply by market forces. He stresses that 'design for recycling' is becoming more widespread where legislation is impending as in the automotive sector. This takes us back to the beginning of the book, to Rose's chapter. The cycle begins again, but hopefully next time we will think and act more responsibly and gradually reduce our own footprint as researcher, manufacturer, engineer... .
1.1
Introduction
Often when pursuing research into green composites we say that we are protecting the environment, that we are working for nature. We may as well stop kidding ourselves - nature will be fine; nature will work out OK and adapt to the changes. It's humans that will cease to exist if we continue the way we are at present. Some scientists and engineers have realised that they need to take responsibility for the outcome of their work. Researching ways of creating faster machines and bigger toys, without due consideration of the effects on the environment or on people, is irresponsible. This book represents some of the workers who have, over the last 10 years or so, decided to change the direction of their research to address some of these issues. We have recently been seeing an increase in the number of researchers working in this area and it is time to reflect on the progress and purpose of our work to make sure that we are in fact doing what we say we would like to do.
1.2
An environmental footprint and life cycle assessment
In this context we are defining green composites as composites that are designed with the lowest environmental 'footprint' possible. Furthermore, we are focusing on fibre-reinforced polymer composites in this book as these are the most abundant material group of the composite family in use. In this chapter we will explore some of the assumptions we make and consider the life cycle of such materials, not only from 'cradle to grave' but beyond the grave into the after life. What do we mean by an environmental footprint? What factors must be considered? We consistently hear the terms 'green', ' e c o ' , 'sustainable', 'environmentally conscious', 'life cycle', 'clean' and assume we know what is meant by them. We also often label our work with these terms in order to 1
2
Green composites
generate funding from governmental bodies who in turn use the terms to satisfy their promises. But is anyone actually making any difference to the damage we are doing to our planet? We need to consider the impact that our material choice and design will have on the society and the environment (Rose and Baillie - Navigating the Materials World, Academic Press, 2003). Life cycle assessment is defined as 'an objective process to evaluate the environmental burdens associated with a product, process or activity by identifying energy and materials used and wastes released to the environment, and to evaluate and i m p l e m e n t opportunities to effect environmental improvements' (Society of Environmental Toxicology and Chemistry, SETAC, Code of Practice, 1991). I dispute the objective part of this definition. Life cycle assessments are so difficult, often so subjective in their evaluations and so complex, that they are frequently ignored, or taken as an add on at the end of a project. Many companies insist on carrying out an L C A or life cycle analysis before their design can be realised. An environmental L C A helps us to quantify how much energy and material are used and how much waste is generated at each stage of a product's life. The analysis takes place first but, after this, the life cycle assessment needs to take place, which is where the interpretation and value judgements come in, e.g. • Is it worse to use up more energy in transport or to produce more factories? • Is it worse to burn and create harmful gases or to create landfill? • Is it worse to dump or to use up energy in recycling? • Is it worse to have the risk of food poisoning or waste food or increased packaging? Assessment of the impact on the environment is therefore considered at each stage: resources, production, distribution, use, disposal or re-use. Many such LCAs have actually proved the project to have been a waste of energy in itself. In a recent report from a C R A F T project to produce natural fibre composites in which I was involved ( C R A F T project European Commission report (BES2-3163), 2000) we compared natural mat- (NMT) and glass mat-reinforced thermoplastics (GMT). A comparison was made between G M T and N M T manufactured by a current production method of prepreg followed by compression moulding into an automotive and nonautomotive part. The L C A analysis was performed for both the non-automotive and automotive part and for three different types of performance requirements, i.e. stiffness, strength and impact resistance. The results of L C A showed that, for most cases, the environmental impact of N M T material is higher than the reference GMT. Despite their 'green' image, natural fibre composites are not necessarily an environmentally friendly alternative to glass fibre
Why green composites?
3
composites in applications where strength and impact are the performance drivers. The reasons for this include the need for pesticides and other chemicals to grow the flax fibre and the higher fibre loadings needed to fulfil the impact and strength criteria. Even in the case of stiffness-based non-automotive applications, where no higher fibre loadings are needed to meet the performance requirements, the differences in environmental impact between G M T and N M T are very small and in the current analysis the poorest performance was shown for N M T due to the negative effect of pesticides. In the case of automotive and stiffness critical applications N M T composites do seem to perform better than G M T composites. This reduction in environmental impact for N M T composites is, however, mainly due to the lower weight of natural fibre composite parts, which leads to lower fuel consumption during the use of composites and not so much the result of the use of 'green' natural fibres. Hence, the advantages of natural fibre composites are relevant if weight savings are obtained over glass fibre composites.
1.3
Drivers for change
From the above it would seem as if only those researchers who are altruistic would be involved in this game. In fact, there are many drivers for the change we currently observe. Global concerns are considered by the Kyoto Protocol, national concerns by government legislation, and local companies in turn make a response to the legislation. All of this will influence funding mechanisms and availability of funds for researchers. Global responses to climate change are critical at the time of writing where countries are deciding upon the Kyoto Protocol. Reports of a lecture by Michael Grubb of Imperial college to the Royal Institute of international Affairs (The Independent, 5 November, 2003) quote him as saying: the US is starting to pour billions of dollars into research on technologies like carbon sequestration and hydrogen. Unfortunately, pursuing climate technology while eschewing emission caps is like designing a fancy car while opposing all efforts to put an engine in it... . Governments are not good at delivering industrial technologies: there has to be a market for them. The argument may be said to be true of green composites in automotive and other applications. In Canada at present there is a push to make a new profitable market from the use of agricultural fibres in composites. Economic arguments alone will not cause this technology to take off. Rumour has it that local industry may not become interested in changing to more ecofriendly products because, even if the Canadian Government encouraged them to do so with legislation, they would simply sell 'over the border'. One of the largest markets for natural fibre composites is the US automotive
4
Green composites
sector who currently do not appear to have the same drivers as the European market. The EU Directive for automotive parts has meant that many companies in Europe have started to consider environmentally friendly alternatives to fuel and materials for production. The Directive stipulates that re-use and recycling of end-of-life vehicles must increase to 9 5 % by 2015. Further details are given by Tucker in Chapter 10. He tells us that disassembly is a concern and costs associated with dismantling plastic components from cars are too high at present. Tucker would suggest 'design for disassembly'. The European Community approach to waste management is based on two complementary strategies: avoiding waste by improving product design and increasing the recycling and re-use of waste. The EU Landfill Directive (1999) states that, by 2010, the amount of biodegradable municipal waste going to landfill must be reduced by 7 5 % of the total produced in 1995. The EU Packaging Waste Directive (1997) states that there must be 5 0 - 6 0 % recovery and 2 5 - 4 5 % recycling by 2006. For a city like London, this means that there must be alternative routes for waste of between 2 and 4 million tonnes per year. The UK has responded by developing its Government Waste Strategy (2000). This states that 30% of all waste produced must be recycled or composted by the year 2010. Furthermore, the UK has responded to the EU Directives by bringing in a landfill tax system that forces companies to think about end of use. Hence, response to EU Directives creates a huge driver and support for research in the green materials area. In the US the Environmental Protection Agency Office of Solid Waste 'supports' reaching a goal of 3 5 % recycling by 2005 (American Plastics Council, 2 0 0 1 , National Post Consumer Plastics Report). Implementation of legislation is, of course, another huge factor. Hence it might be that Liverpool in the UK cannot ask its citizens to take responsibility for the environment as they do not have a collection system in place and the locals would use more energy in fuel driving to the nearest collection point in Chester. Kingston, Ontario in Canada, on the other hand, represents one town that has a well-established curb side collection system in place. However, it is rumoured that much of the plastic waste gets sent to other countries as an export. Those countries obviously do not have enough of their own waste.
1.3.1
Swings and roundabouts
We cannot pour money into environmental research until legislation reinforces the changes that ensue. We cannot encourage participation of profit driven corporations unless legislation supports such changes. Furthermore, we cannot create environmental schemes that rely on the participation of communities of people who produce waste when the infrastructure is not there to support the s c h e m e s . The drivers for, and the national and global e c o n o m i c ,
Why green composites?
5
environmental and social impact of, new directions in research must all be considered before seriously trying to effect change in material usage.
1.4
The structure of this book: a life cycle approach
In the light of the above we have decided to arrange this book with a life cycle approach. We consider first the choice of materials that iterates with the design and function or the application. We consider the factors affecting the life cycle analysis. We look at possible fibres to use as reinforcement, as well as potential polymer matrices. In this latter category we need to consider thermoplastics as a source which may be recycled, or as a nonvirgin source; composites as a means of upgrading recycled polymers as well as thermosets which need to be re-used or biodegradable thermosets which degrade. We will look at processing of the composite; its production into components, trying in the meantime not to forget in our discussions the transport of raw materials and parts at each stage and the energy consumed in the production run. We consider a range of applications - replacement for G F R P (glass fibre-reinforced polymers) as well as upgrading of polymer components. Finally, we look at the re-use, recovery and recycling of the composites that we have made. We start the process by reflecting upon 'Design thinking'. Rose takes us on a philosophical pathway through notions of progress and a reflection on our values to the idea of learning from nature about 'ecologically responsible design'. Murphy takes pity on the reader and helps us place this in a more solid context by leading us through those issues which affect the life cycle of a natural fibre composites product. Read this chapter even if you dip in and out of the others. It is necessary to consider all issues impacting our 'footprint' if we are to take ourselves and our research seriously when we say we are working on 'green composites'. The choice of fibre is determined by all of the usual selection criteria such as ultimate mechanical properties, interfacial adhesion with the matrix (high or low for strength or toughness applications respectively), cost, availability of resources, chemical properties, resistance to moisture, etc. It is also determined by the 'green' criteria - whatever those might be. Nishino discusses the potential for natural fibres in composites. They are divided into wood, vegetable, animal and mineral. We have seen different trends in different parts of the world for the uptake of certain fibres. Abundant good quality fibre sources will determine this to an extent and we see far more wood fibres used in North America and more agricultural fibres in Europe. However, it is also lifestyle and marketing that will determine these directions. Hughes discusses the fact that the predominant market for wood plastic composites (WPC) is in decking in North America, whereas the European market for vegetable or agricultural fibres is the automotive sector.
6
Green composites
Nishino's Table 4.6 shows us the main merits and demerits of using natural fibres. Sustainability of natural resources - or the ability to re-grow on an annual basis, together with low energy consumption and biodegradability make them a good environmental or 'green' choice so long as the remainder of the life cycle is properly assessed. For example, we need to think about transport of fibres, moisture resistance, interfacial adhesion, etc. Often, we see arguments comparing glass with natural fibres and suggesting that the only way for natural fibres to be adopted is if their properties can be proved to be 'as good a s ' or better than glass. However, it is also stressed that, unless the new system is cheaper, it will not be adopted. In other words people are not prepared to change anything. This is not the way of nature, which continually adapts to new conditions. The benefits of natural fibres are quite different to those of glass fibres and they should be used to create materials that will better suit the needs of our environment and communities of the future. If we look to see how an ecosystem works, we see that everything is used at its optimal function and no more. There is no waste of material or energy. Peltola focuses more on paper fibres. He states that in the US over 300 kg per capita of paper is used per year. In Europe, of the 35 million tonnes produced in 2002, 3 million tonnes are recycled and 14 million tonnes are used as energy. His argument is that we should divert paper fibre from landfill to a useful composite of waste fibre and plastic. An alternative environmental solution for the choice of fibres is presented by Shanks. He presents the work of researchers who are working with fibre/ matrix of the same thermoplastic material so that, at the end of life, the entire mass can be melted to form a new product. All polypropylene (PP) composites, for example, have great potential environmentally. Even though they do not come from a renewable source - composites made from all P P have at least one more life before incineration or energy recovery. Now we need to turn to the matrix. Of course, it is never possible to deal with the fibre and matrix independently, and all authors do address many other aspects than the one they have been asked to put in focus. In consideration of the choice of matrix, in a way similar to that for the fibre we can select natural sources for sustainability or recyclable polymers. We can also use biodegradable polymers. Thermoplastics are the first matrix of choice as they are recyclable. However, once we have added fibres, they are often rendered non-recyclable so the argument is not well made. Only in the case of all polymer composites such as all PP can the end-of-life be recycling. Adding natural fibres will be better than glass as the composite could be incinerated for energy recovery. However, a better alternative, as discussed earlier, is the use of recycled polymer as source. The addition of fibres will upgrade the polymer. The main thermosets considered are biodegradable. Plackett explains, however, that natural polymer matrices are at varying
Why green composites?
7
stages of development and much work is needed to improve stability, processability, mechanical properties and degradability. Alongside the choice of fibre and matrix will come the choice of processing method - very different for thermoplastics and thermosets. As considered by Aziz and Sain, thermoplastic injection moulded parts can be complex but fibres are short and stiffness low as a result. Furthermore, high temperatures are often needed for adequate viscosity and natural fibres can be damaged. Aziz argues that thermosetting composites have better properties: stiffness can be increased by using longer fibres; interfacial properties will be better because of longer processing times and better fibre wetting. These factors must be weighed against production costs (parts per hour produced) and environmental impact. Natural thermosetting polymers seem to come out quite well in many of the arguments and Aziz considers cashew nut shell liquid resin as an example. Clean processing is discussed more thoroughly by Tucker. He uses Thorpe's (1999 in Tucker) definition: 'a way to reverse our current non-sustainable use of materials and energy'. He tells us that we should move manufacturing from a linear use of resources into the cyclical use of resources that do not produce waste products. He also points out that cleaner production methods must satisfy the triple bottom line: environmental, social and economic. He quotes Thorpe's suggestions for clean production, helping us think about the need rather than the desire for products in the first place, the need for durability rather than for recycling, and reduction of consumption whilst maintaining quality of life. He really seems to balance the three aspects above, but will companies in the current economic system wish to respond? Once we have selected the materials and production method appropriate for our a p p l i c a t i o n , and the properties required, whilst k e e p i n g our environmental impact as low as possible, we must consider the potential for end of use. Already, we have seen this consideration but we now bring this aspect into focus. If we find we will be producing something with one life before landfill, we need to think again. Hodzic reminds us that plastic waste may be reduced to its monomers, recycled or biodegraded. Thermoplastics are not without their problems as they require a high degree of purity of recyclate as well as separation of the matrix from the reinforcement except in the case of all PP, for example. Thermosets are more problematic, as discussed previously, but some chemical additives can help to degrade polymers, although Hodzic warns against possible side effects to the environment. Chemical additives must always be considered in the light of our ecosystem approach. Wherever possible it would be better to use something present within the system to carry out the desired function, as nature would do, rather than adding an alien element that will have a counter effect. Arnold takes us through the whole process of recycling and reprocessing.
8
Green composites
His concern echoes my own - that increases in recycling rates (or use of green composites) will not occur simply by market forces. He stresses that 'design for recycling' is becoming more widespread where legislation is impending as in the automotive sector. This takes us back to the beginning of the book, to Rose's chapter. The cycle begins again, but hopefully next time we will think and act more responsibly and gradually reduce our own footprint as researcher, manufacturer, engineer... .