Introduction: What Happens When We’re Done?
Have you ever wondered what happens to your smartphone or your favorite pair of trainers once they are broken or worn out? In the past, most products followed a "linear" path: we made them, used them, and then threw them in the bin. Today, designers have a much bigger responsibility. They have to think about the End of Life (EoL) of a product before they even start building it.
In these notes, we will explore how products are handled at the end of their useful lives, how materials are recovered, and why sending things to the landfill is the very last resort. This is a vital part of Topic 9: Designing for maintenance and the cleaner environment.
1. Designing for Disassembly (DfD)
If you want to recycle a product, you first have to be able to take it apart! Design for Disassembly is a strategy where designers ensure that a product can be easily and quickly dismantled at the end of its life.
How do designers do this?
• Reducing the number of parts: The fewer pieces there are, the faster it is to take apart.
• Using fewer types of materials: If a product is made entirely of one type of polymer (like polypropylene), it is much easier to recycle than a product made of five different plastics mixed together.
• Using standard fittings: Instead of using permanent adhesives (glues) or welds, designers use mechanical fixings like screws, nuts, and bolts. This allows the product to be "unbolted" rather than smashed.
• Easy-to-access joints: Making sure a technician (or a robot) can reach the screws easily without damaging the components inside.
Note: For more on how products are kept running before they reach this stage, see the chapter on "Designing for maintenance, repair and disassembly".
2. Recovered Material Collection and Sorting
Once a product is taken apart, the materials need to be collected and sorted. This is a massive logistical challenge. Think about how many different materials are in a single laptop!
Sorting Materials
Materials must be separated into categories so they don't contaminate each other. For example:
• Metals: Ferrous metals (like mild steel) can be separated using large magnets, while non-ferrous metals (like aluminium) require different techniques.
• Polymers: Plastics are often sorted using infrared sensors that identify the specific chemical signature of PET, PVC, or ABS.
• Papers and Boards: Different grades of paper need to be kept separate to maintain the quality of the recycled pulp.
Quick Tip: Look for the little recycling symbols on plastic bottles. These are "Identification Codes" that help sorting facilities know exactly which polymer they are dealing with.
3. Re-processing Materials
Re-processing is the stage where "waste" is turned back into "raw material."
• Polymers: Thermoplastics like LDPE or PP can be shredded into small pellets, melted down, and injection moulded into brand-new products. (Note: Thermosetting plastics like epoxy resins cannot be remelted, which makes them much harder to re-process!)
• Metals: Metals can be melted down and cast into new shapes almost indefinitely without losing their properties. This uses significantly less energy than mining new ore.
• Woods: While solid timber isn't usually "melted," waste wood can be chipped and turned into manufactured boards like chipboard or MDF.
Calculating Recycling Efficiency
In your exam, you might be asked to look at material waste. A common formula to remember is the Percentage Waste formula:
\( \text{Percentage Waste} = \left( \frac{\text{Weight of Waste Material}}{\text{Total Weight of Material Used}} \right) \times 100 \)
Example: If a manufacturing process uses 50kg of steel but 5kg is cut off as scrap, the waste percentage is \( (\frac{5}{50}) \times 100 = 10\% \). Designers aim to keep this number as low as possible!
4. Energy Recovery
Sometimes, a material cannot be recycled. Maybe it is contaminated, or it’s a composite material that is too difficult to separate (like some GFRP). In this case, we use Energy Recovery.
This usually involves incineration (burning the waste). The heat generated from burning the rubbish is used to boil water, create steam, and turn turbines to generate electricity.
Is this "good" for the environment?
It is better than landfill because it produces useful energy and reduces the volume of waste. However, it is not as good as recycling because the original material is "lost" forever and cannot be used to make new products.
5. The Implications of Landfill Disposal
Landfill is the bottom of the pile. This is where waste is buried in the ground. Designers try to avoid this at all costs due to several major issues:
• Environmental Damage: As materials break down, they can release toxic chemicals (leachate) into the soil and groundwater.
• Methane Emissions: Organic waste in landfills produces methane, a powerful greenhouse gas.
• Space: We are simply running out of places to put our rubbish!
• Wasted Resources: Every item in a landfill represents "lost" energy and raw materials that could have been reused or recycled.
Biodegradability: Some materials, like natural fibres (cotton, wool) or certain papers, will naturally break down in a landfill. However, most synthetic polymers and metals will stay there for hundreds of years.
Quick Review: Key Takeaways
1. Design for Disassembly: Making products easy to take apart using screws instead of glue.
2. Sorting: Essential for high-quality recycling (e.g., separating ferrous and non-ferrous metals).
3. Re-processing: Turning waste back into raw materials (pellets for plastics, ingots for metal).
4. Energy Recovery: Burning non-recyclable waste to create electricity.
5. Landfill: The least sustainable option; causes pollution and wastes valuable resources.
Common Mistake to Avoid: Don't confuse recyclable with biodegradable. A plastic bottle might be 100% recyclable (it can be melted and reused), but it is 0% biodegradable (it won't rot away in the ground naturally).
Did you know? Using recycled aluminium to make a new soda can uses \( 95\% \) less energy than making a can from "virgin" aluminium ore! This is why recovered material collection is so important for the environment.