Materials and the Environment: Eco-Informed Material Choice

Materials and the. Environment

Michael F. Ashby

The environment is a system. Human society, too, is a system. The sys­tems coexist and interact, weakly in some ways, strongly in others. When two already complex systems interact, the consequences are hard to pre­dict. One consequence has been the damaging impact of industrial society on the environment and the ecosystem in which we live and on which we depend. Some impacts have been evident for more than a century, prompt­ing remedial action that, in many cases, has been successful. Others are emerging only now; among them, one of the most unexpected is changes in global climate that, if allowed to continue, could become very damaging.

These and many other ecoconcerns derive from the ways in which we use energy and materials. If we are going to do anything about it the first step is to understand the origins, the scale, the consequences, and the extent to which, by careful material choice, we can do something about it. And that requires facts.

The book

This text is a response. It aims to cut through some of the oversimplifi­cation and misinformation that is all too obvious in much discussion about the environment, explaining the ways in which we depend on and use materials and the consequences of their use. It introduces methods for thinking about and designing with materials when one of the objectives is to minimize environmental impact—an objective that is often in conflict with others, particularly that of minimizing cost. It does not aim to provide ultimate solutions—that is a task for future scientists, engineers, designers, and politicians. Rather, it is an attempt to provide perspective, background, methods, and data—a toolbox, so to speak—to introduce students to one of the central issues of environmental concerns, that surrounding the use of materials, and to equip them to make their own judgments.

The text is written primarily for students of Engineering and Materials Science in any one of the four years of a typical undergraduate program. It is organized in two parts. The first, Chapters 1 to 11, develops the back­ground and tools required for the materials scientist or engineer to analyze

and respond to environmental imperatives. The second, Chapter 12, is a vii

collection of profiles of materials presenting the data needed for analysis. The two together allow case studies to be developed and provide resources on which students can draw to tackle the exercises at the end of each chapter (for which a solution manual is available) and to explore material - related eco-issues of their own finding.

To understand where we now are, it helps to look back over how we got here. Chapter 1 gives a history of our increasing dependence on mate­rials and energy. Most materials are drawn from nonrenewable resources inherited from the formation of the planet or from geological and biological eras in its history. Like any inheritance, we have a responsibility to pass these resources on to further generations in a state that enables them to meet their aspirations as we now do ours. The volume of these resources is enormous, but so too is the rate at which we are using them. A proper perspective here needs both explanation and modeling. That is what Chapter 2 does.

Products, like plants and animals, have a life cycle, one with a num­ber of phases, starting with the extraction and synthesis of raw materials ("birth"), continuing with their manufacture into products, which are then transported and used ("maturity"), and at the end of life, sent to a landfill or to a recycling facility ("death"). Almost always, one phase of life con­sumes more resources and generates more emissions than all the others put together. The first job is to pin down which phase involves the most consumption. Life-cycle assessment (LCA) seeks to do this, but there are problems: as currently practiced, life-cycle assessment is expensive, slow, and delivers outputs that are unhelpful for engineering design. One way to overcome these issues is to focus on the main culprits: one resource, energy, and one emission, carbon dioxide, CO2. Materials have an embod­ied energy (the energy it takes to create them) and a carbon footprint (the CO2 that creating them releases). So, too, do the other phases of life, and materials play a central role in these also. Heating and cooling and trans­portation, for instance, are among the most energy-gobbling and carbon - belching activities of an industrial society; the right choice of materials can minimize their appetite for both. This line of thinking is developed in Chapters 3 and 4, from which a strategy emerges that forms the structure of the rest of this book.

Governments respond to environmental concerns in a number of ways applied through a combination of "sticks and carrots," or, as they would put it, command and control methods and methods exploiting market instru­ments. The result is a steadily growing mountain of legislation and regula­tion. It is reviewed in Chapter 5.

As engineers and scientists, our first responsibility is to use our particu­lar skills to guide design decisions that minimize or eliminate adverse eco­impacts. Properly informed materials selection is a central aspect of this task, and that needs data for the material attributes that bear most directly on environmental questions. Some, like embodied energy and carbon foot­print, recycle fraction and toxicity, have obvious ecoconnections. But more often it is not these but mechanical, thermal, and electrical properties that have the greatest role in design to minimize eco-impact. The data sheets of Chapter 12 provide all of these properties. Data can be deadly dull. It can be brought to life (a little) by good visual presentations. Chapter 6 intro­duces the material attributes that are central for the material that follows and displays them in ways that give a visual overview.

Now to design. Designers have much on their minds; they can't wait for (or afford) a full LCA to decide between alternative concepts and ways of implementing them. What they need is an eco-audit—a fast assessment of product life phase by phase and the ability to conduct rapid "What if?" studies to compare alternatives. Chapter 7 introduces audit methods with a range of examples and exercises in carrying them out using the data sheets in Chapter 12.

The audit points to the phase of life of most concern. What can be done about it? In particular, what material-related decisions can be made to minimize its eco-impact? Material selection methods are the subject of Chapter 8. They form a central part of the strategy that emerged from Chapter 3. It is important to see them in action. Chapter 9 presents case studies of progressive depth to illustrate ways of using the materials. The exercises suggest more.

Up to this point the book builds on established, well-tried methods of analysis and response, ones that form part of, or are easily accessible to, anyone with a background in engineering science. They provide essential background for an engineering-based approach to address environmental concerns, and they provide an essential underpinning for studies of broader issues. Among these are questions of sustainability (perhaps the most mis­used word in the English language today) and future options, an attempt to foresee future problems and potential solutions. They are the subjects of the last two chapters of Part 1 of the book.

The final chapter is straightforward. It is an assembly of 47 two-page data sheets for engineering metals, polymers, ceramics, composites, and natural materials. Each has a description and an image, a table of mechani­cal, thermal, and electrical properties, and a table of properties related to environmental issues. These data sheets provide a resource that is drawn

on in the text of the book, enables its exercises, and allows you to apply the methods of the book elsewhere.

The approach is developed to a higher level in two further textbooks, the first relating to mechanical design,1 the second to industrial design.[1] [2]