1. New approaches to Materials Education - a course authored by Mike Ashby and David Cebon, Cambridge, UK, 2007 © MFA and DC 2007 Unit 8. Eco-selection: environmentally informed material choice

2. © MFA and DC 2007 Outline Material consumption and the material life-cycle Analysis of products Strategy for materials selection LCA, problems and solutions Exercises More info:  “Materials: engineering, science, processing and design”, Chapter 20  “Materials Selection in Mechanical Design”, Chapter 16

3. © MFA and DC 2007 Material production Natural fibers: cotton, silk, wool, jute Man-made fibers: polyester, nylon, acrylic, cellulosics

4. © MFA and DC 2007 The product life-cycle

5. © MFA and DC 2007 Life cycle assessment (LCA) Typical LCA output: Resource consumption Energy consumption over life Water consumption Emission of CO 2, NO x, SO x etc Particulates Toxic residues Acidification..Ozone depletion.. Roll up into an Eco-indicator ? Full LCA time consuming, expensive, and requires great detail – and even then is subject to uncertainty What is a designer supposed to do with these numbers? Environmental “stressors” LCA is a product assessment tool, not a design tool

6. © MFA and DC 2007 LCA in the context of design Full LCA A product-assessment tool Concept Embodiment Detail Market need Problem statement Product specification Manufacture, distribution Strategic tools to guide design The need

7. © MFA and DC 2007 Strategies for guiding design Step 1: Seek method that combines acceptable cost burden with adequate accuracy to guide decision making – a design tool Step 2: Seek single measure of stress – energy or CO 2 Eco- screening Streamline LCA Complete LCA Increasing detail, cost and time Scoping LCA Minutes Hours Days Months Step 3: Separate life-phases

8. © MFA and DC 2007 Strategies for guiding design (2) Kyoto Protocol (1997): international agreement to reduce greenhouse gasses Practicality: CO 2 and Energy are related and understood by the public  Why energy or CO 2 ? Cars: use-energy and CO 2 cited Official fuel economy figures: Combined: 6 – 11 litre / 100km CO 2 emissions: 158 – 276 g / km Appliances: use-energy cited Efficiency rating: A Volume0.3 m 3 330 kWhr / year EU directives such as the EuP directive (2006)

9. © MFA and DC 2007 Big picture: energy consumption of products Which phase dominates? Approximate breakdown (Bey, 2000., Allwood, 2006):

10. © MFA and DC 2007 Eco-scoping Aims:  to assess energy or CO 2 burden quickly and cheaply  to explore alternatives What should strategic tools do? Example: drink containers Glass PE PET Aluminum Steel

11. © MFA and DC 2007 Eco-scoping 1. Material production: the embodied energy 2. Bottle manufacture: the processing energy 3. Delivery and use: transport and refrigeration 4. Disposal: collection, recycling, energy recovery Separate the phases of life To assess, need both local and generic data. PET bottle

12. © MFA and DC 2007 What is embodied energy? Transport, MJ / tonne.km  Sea freight 0.11 – 0.15  Barge (river) 0.75 – 0.85  Rail freight 0.80 – 0.9  Truck 0.9 – 1.5  Air freight 8.3 – 15 Transport, MJ / tonne.km  Sea freight 0.11 – 0.15  Barge (river) 0.75 – 0.85  Rail freight 0.80 – 0.9  Truck 0.9 – 1.5  Air freight 8.3 – 15 Material energy MJ / kg  Database of embodied energies for materials Process energy MJ / kg  Database of processing energies for materials Material energy MJ / kg  Database of embodied energies for materials Process energy MJ / kg  Database of processing energies for materials Generic data

13. © MFA and DC 2007 Use (delivery and refrigeration) and disposal 1. Material production: the embodied energy 2. Bottle manufacture: the processing energy 3. Delivery and use: transport and refrigeration 4. Disposal: collection, recycling, energy recovery Refrigeration, MJ/m 3.day  Refrigeration (4 o C)10.5  Freezing (- 5 o C) 13.0 Refrigeration, MJ/m 3.day  Refrigeration (4 o C)10.5  Freezing (- 5 o C) 13.0 Transport, MJ / tonne.km  As before Transport, MJ / tonne.km  As before Generic data

14. © MFA and DC 2007 Disposal: recycling – the problems

15. © MFA and DC 2007 Recycle fractions for commodity materials

16. © MFA and DC 2007 Drink container: the scoping tool Manufacture  PET body moulded 38 g  PP cap moulded 5 g Use  Refrigeration 5 days  Transport 200 km Disposal  Recycling ? Yes  Transport 15,000 km Transport, MJ / tonne.km  Sea freight0.11  Truck1.3 Transport, MJ / tonne.km  Sea freight0.11  Truck1.3 Refrigeration, MJ / m 3.day  Refrigeration (4 o C)10.5  Freezing (-5 o C) 13.0 Refrigeration, MJ / m 3.day  Refrigeration (4 o C)10.5  Freezing (-5 o C) 13.0 Materials  PET body 38 g  PP cap 5 g INPUTS by user RETRIEVE from database Material energy MJ / kg  Embodied energy, PET 85  Energy to blow mould 11 Material energy MJ / kg  Embodied energy, PET 85  Energy to blow mould 11

17. © MFA and DC 2007 CES Edu record for PET General Properties Density939-960kg/m 3 Price1.3-1.45US $/kg Mechanical Properties Young's Modulus0.6-0.9GPa Elastic Limit17.9-29MPa Tensile Strength20-45MPa Elongation200-800% Hardness - Vickers5.4-8.7 HV Fracture Toughness1.4-1.7MPa.m 1/2 Thermal Properties Max Service Temp100- 120C Thermal Expansion126- 19810 -6 /K Specific Heat1810- 1880J/kg.K Thermal Conductivity0.4- 0.44W/m.K Electrical Properties Resistivity3 x 10 22 -3 x 10 24 .cm Dielectric constant2.2-2.4 Polyethylene terephthalate (PET) Thermo-mechanical design Energy/CO 2 efficient design Eco-properties: production Production energy77-85 MJ/kg Carbon dioxide1.9 -2.2 kg/kg Recycle ? Eco-properties: manufacture Injection / blow moulding 12 - 15 MJ/kg Polymer extrusion 3 - 5 MJ/kg Environmental notes. PE is FDA compliant - it is so non-toxic that it can be embedded in the human body (heart valves, hip-joint cups, artificial artery).

18. © MFA and DC 2007 Energy breakdown for PET bottle Material

19. © MFA and DC 2007 Applying the strategy Production Manufacture Use Disposal Assess energy use over life Energy 1. Analysis Minimize: embodied energy CO 2 / kg Material 2. Strategy Minimize: weight heat loss electrical loss system Use Disposal Select: recyclable non- toxic materials Minimize: process energy CO 2 /kg Manufacture

20. © MFA and DC 2007 Embodied energy of materials per kg CES Edu Level 2 DB Hybrids

21. © MFA and DC 2007 Embodied energy of materials per m 3 CES Edu Level 2 DB Hybrids

22. © MFA and DC 2007 Embodied energy per unit of function Mass 325 38 25 20 45 g Mass/litre 433 38 62 45 102 g/litre Emb. energy 14 80 84 200 23 MJ/kg Energy/litre 8.2 3.2 5.4 9.0 2.4 MJ/litre Glass PE PET Aluminum Steel Function: contain 1 litre of fluid Steel wins on material embodied energy Processing? Recycling? Toxicity? Steel wins on material embodied energy Processing? Recycling? Toxicity?

23. © MFA and DC 2007 Material choice depends on function and system Static barrierMobile barrier Bending strength per unit mass Criterion Bending strength per unit material energy Function Absorb impact, transmit load to energy-absorbing units or supports CFRP, Ti-alloy, Al-alloy Selected materials Cast iron, steel M Mf U D Dominant phase of life Energy M Mf U D

24. © MFA and DC 2007 Concept, embodiment, detail PetrolDieselSupercarsHybrid

25. © MFA and DC 2007 The main points Scoping LCA gives quick, approximate “portrait” of energy / CO 2 burden of products. A practical tool for assessing eco-burden and guiding (re)-design. Consider system dependence  Optimise within one concept  Explore alternative concepts Separate the life-phases  Material  Manufacture  Use  Disposal Base material choice on relative contributions to stress The CES EduPack provides data to help with this

26. © MFA and DC 2007 Demo

27. © MFA and DC 2007 Exercises: Eco-comparisons (1) 8.1 Rank the commodity materials Low carbon steel Age hardeing aluminum alloys Polyethylene by embodied energy/kg and embodied energy/m 3. Use the means of the ranges given in the database. (Energy per unit volume is that per unit weight multiplied by the density) Polyethylene Density 939 – 960 kg/m 3 Embodied energy 76.9 – 85 MJ/kg Answer The Al alloy has the highest energy content, by far, by both measures. Per kg, steel has the lowest energy content; by volume, it is polyethylene.

28. © MFA and DC 2007 Exercises: Eco-comparisons (2) 8.2. Plot a bar chart for the embodied energies of metals and compare it with one for polymers, on a a “per unit yield strength” basis. Use the “Advanced” facility to make the function Which materials are attractive by this measure? The most attractive, from an embodied energy per unit strength perspective are carbon steels and cast irons. Among polymers, biopolymers like Polylactide (PLA) and starch based polymers perform well. Answer.

29. © MFA and DC 2007 Exercise: the nature of embodied energy 8.3 Iron is made by the reduction of iron oxide, Fe 2 O 3, with carbon, aluminum by the electro-chemical reduction of Bauxite, basically Al 2 O 3. The enthalpy of oxidation of iron to its oxide is 5.5 MJ/kg, that of aluminum to its oxide is 16.5 MJ/kg. Compare these with the embodied energies of cast iron, of carbon steel, and of aluminum, retrieved from the CES database (use means of the ranges given there). What conclusions do you draw? Cast iron, grey Embodied energy 16.4 – 18.2 MJ/kg The embodied energies are between 3 and 12 times larger than the thermodynamically necessary to reduce the oxide to the metal. There are several reasons. The largest is that industrial processes, at best, achieve an energy-efficiency of around 33% (the blast furnace, used to make iron, is remarkably efficient). Then there is transport, the energy to run, heat, light and maintain the plant in which the metal is made, and many other small contributions to the total energy input per unit of output. Aluminum alloys Embodied energy 184 – 203 MJ/kg

30. © MFA and DC 2007 End of Unit 8