The life cycle of a product
Ximena bought a cotton T-shirt at the street market for $\$150$. When she threw it in the trash she thought: "that's the end of it." But that T-shirt needed water to irrigate the cotton, energy to spin and dye it, a truck to carry it to the city, and many washes at home. Where does the harm to the environment really stay? And what could Ximena, or whoever designed the T-shirt, change to reduce it? We are going to find out in this section.
The stages of the life cycle
Every product has a "biography." The life cycle is the complete path it follows from the moment its raw material is obtained until it is thrown away or used again.
Example with Ximena's T-shirt:
| Stage | What happens? |
|---|---|
| Raw materials | The cotton is grown and harvested (irrigation, fertilizers). |
| Manufacturing | It is spun, woven, dyed, and sewn in a workshop. |
| Transport | Trucks take the T-shirts to warehouses, street markets, and stores. |
| Use | Ximena washes and dries it hundreds of times. |
| End of life | She gives it away, turns it into a rag, recycles it, or it goes to the landfill. |
List the stages of a product lifecycle and describe each one using the example of a cotton T-shirt.
List the stages of a product lifecycle and describe each one using the example of a cotton T-shirt.
Put the stages of the lifecycle of a wooden pencil in order and describe in one sentence what happens in the first and last stages.
Put the stages of the lifecycle of a wooden pencil in order and describe in one sentence what happens in the first and last stages.
The figure shows the lifecycle of a product with one stage covered. State which stage is missing and describe what happens during it.
The figure shows the lifecycle of a product with one stage covered. State which stage is missing and describe what happens during it.
Life cycle assessment (LCA)
To know where a product's problem lies, you have to look at all of its stages, not just the one we can see. That is what life cycle assessment (LCA) does.
In secondary school we will do it qualitatively: we describe each stage and mark which one weighs the most. A professional LCA measures with numbers, but the idea is the same.
A simple table is enough to get started:
| Stage | What goes in (energy, water, materials) | What comes out (waste, emissions) | Impact: high, medium, low? |
|---|---|---|---|
| Raw materials | |||
| Manufacturing | |||
| Transport | |||
| Use | |||
| End of life |
LCA helps you decide what to change: if manufacturing is the heaviest stage, saving on packaging is pointless. First you locate the critical stage and then you implement an alternative for that stage.
Explain what life cycle assessment (LCA) is and what questions it tries to answer about a product.
Explain what life cycle assessment (LCA) is and what questions it tries to answer about a product.
Explain with an example why 'throwing something in the bin' is not the true end of its lifecycle.
Explain with an example why 'throwing something in the bin' is not the true end of its lifecycle.
Where is the impact concentrated?
Not all products weigh the same at every stage. Compare a cell phone with a car.
Explain what the carbon footprint of a product is: what it measures and in which stages of its lifecycle it is mainly generated.
Explain what the carbon footprint of a product is: what it measures and in which stages of its lifecycle it is mainly generated.
Give an example of a product whose main environmental impact is in the use stage and another whose main impact is in manufacturing, and justify both choices.
Give an example of a product whose main environmental impact is in the use stage and another whose main impact is in manufacturing, and justify both choices.
In many electronic devices, a significant part of the environmental impact occurs before you buy them. Explain which stages of the lifecycle this statement refers to and…
In many electronic devices, a significant part of the environmental impact occurs before you buy them. Explain which stages of the lifecycle this statement refers to and give reasons why.
Comparing two life cycles
LCA is used mostly to compare. To do it well, go through both lists stage by stage and look for where they differ the most.
Example: returnable glass bottle (the soda bottle you return to the corner store) versus single-use PET bottle.
| Stage | Returnable glass | Single-use PET |
|---|---|---|
| Raw materials | Sand and energy, but used once for many trips | Oil, for every bottle |
| Manufacturing | Very hot furnaces (a lot of energy) | Less energy per bottle, but many are made |
| Transport | Heavier; returns empty to the plant | Light; does not return |
| Use | Refilled and washed many times (water and soap) | Only once |
| End of life | Melted down or reused again and again | Thrown away, recycled, or pollutes |
The biggest difference is in how many times each container is used. Glass carries a large manufacturing impact, but spreads it over many trips.
That is the key idea for a fair comparison: an option that looks worse at one stage can be better overall if it lasts longer or is used more times, because its manufacturing impact is spread over more uses. And the other way around: a "friendly" product that is thrown away after a single use carries all of its impact at once.
Compare the lifecycle of a returnable glass bottle with that of a single-use plastic bottle: state in which stages they differ most and why.
Compare the lifecycle of a returnable glass bottle with that of a single-use plastic bottle: state in which stages they differ most and why.
Compare the lifecycle of a paper book with that of an e-reader: in which stages does each concentrate its impact and on what does it depend which option is better?
Compare the lifecycle of a paper book with that of an e-reader: in which stages does each concentrate its impact and on what does it depend which option is better?
A pair of jeans requires a huge amount of water throughout its lifecycle. Identify which stages of its lifecycle involve water and propose two specific measures to…
A pair of jeans requires a huge amount of water throughout its lifecycle. Identify which stages of its lifecycle involve water and propose two specific measures to reduce that consumption.
Implementing alternatives: what to change at each stage?
If LCA shows where the harm is, the next step is to change something at that stage. This is called ecodesign: designing with the whole life cycle in mind.
| Stage | Ecodesign decision (example: a bottle) |
|---|---|
| Raw materials | Use recycled PET or glass instead of virgin material |
| Manufacturing | Use less material, produce with renewable energy |
| Transport | Manufacture close to where it is consumed, lightweight stackable containers |
| Use | Make it reusable, easy to wash, and long-lasting |
| End of life | A single material, no glued-on labels, easy to recycle |
Each action works on one stage. For example, using reusable bags acts on use; designing with less material, on raw materials and manufacturing; sorting waste, on end of life; repairing, on use (and avoids a whole new cycle).
A second-hand piece of furniture (for example, one from a street market or a garage sale) starts "another life": no raw materials are extracted, nothing is manufactured, no energy is spent on a new product, and its trip to the landfill is delayed.
Classify these actions according to the stage of the lifecycle they act upon: (a) using reusable bags, (b) designing the product with less material, (c) sorting waste…
Classify these actions according to the stage of the lifecycle they act upon: (a) using reusable bags, (b) designing the product with less material, (c) sorting waste correctly, (d) repairing instead of buying new.
Explain what ecodesign is by looking at the entire lifecycle: name a design decision that improves each stage (materials, manufacturing, transport, use, and end of life)…
Explain what ecodesign is by looking at the entire lifecycle: name a design decision that improves each stage (materials, manufacturing, transport, use, and end of life) of a bottle.
Analyze the lifecycle of a pair of sneakers (materials, manufacturing, transport, use, and end of life) and propose a specific improvement in each stage to reduce their…
Analyze the lifecycle of a pair of sneakers (materials, manufacturing, transport, use, and end of life) and propose a specific improvement in each stage to reduce their environmental impact.
From cradle to grave and from cradle to cradle
Examples: a single-use PET bottle goes from cradle to grave. A returnable glass bottle, which is washed and refilled, or a cardboard box that is turned into pulp to make new boxes, follow a cradle to cradle model.
Explain the difference between a 'cradle-to-grave' and a 'cradle-to-cradle' lifecycle, and give an example of a product for each model.
Explain the difference between a 'cradle-to-grave' and a 'cradle-to-cradle' lifecycle, and give an example of a product for each model.
A piece of second-hand furniture begins 'another life'. Analyse how its lifecycle changes compared to buying it new and what impacts are avoided.
A piece of second-hand furniture begins 'another life'. Analyse how its lifecycle changes compared to buying it new and what impacts are avoided.
Impact per use: which comes out better?
To compare with numbers we use the impact per use.
Lifespan also counts: a paper bag that is used 1.5 times and a plastic bag that is used 3 times are not compared by the footprint "per bag," but per use. Divide each figure by the number of uses and compare. For example, 0.09 kg CO₂-eq divided by 1.5 uses is 0.06 kg per use; 0.03 kg divided by 3 uses is 0.01 kg per use. Apply the same to water and other indicators, and also look at what happens at the end of life.
Compare a reusable bottle that lasts two years with using single-use bottles over that same period (about 500 per person per year). Explain what variables determine…
Compare a reusable bottle that lasts two years with using single-use bottles over that same period (about 500 per person per year). Explain what variables determine which is the better option and in which stages of the lifecycle this comparison takes place.
A supermarket claims: "Our new kraft paper bags are 100% eco-friendly compared to plastic ones." To verify this, they provide you with this simplified excerpt from a…
A supermarket claims: "Our new kraft paper bags are 100% eco-friendly compared to plastic ones." To verify this, they provide you with this simplified excerpt from a Life Cycle Assessment (per bag):
-
Paper bag: Carbon footprint: 0.09 kg CO₂-eq; Water consumption: 3.8 L; Estimated average lifespan: 1.5 uses; End of life: 80% recycled or composted.
-
Plastic bag (HDPE): Carbon footprint: 0.03 kg CO₂-eq; Water consumption: 0.2 L; Estimated average lifespan: 3 uses; End of life: 20% recycled, 80% landfill/environmental dispersion.
- a) Refute the advertising claim by calculating the CO₂ emissions and water consumption per 100 shopping trips using both options.
- b) Justify what environmental dilemma the choice between the two raises: in which life cycle phases is paper more harmful, and in which is plastic clearly worse?
The full balance: adding up stages and dividing by lifespan
When there is data for all the stages, they are added and the result is spread over the years (or uses) of lifespan.
A negative value is an environmental credit: recycling avoids extracting new material and so it "subtracts." Make sure the units are the same before adding.
When there are several criteria (carbon, water, washing energy), each one is calculated separately. Compare whether a single reusable cup with 600 washes pays off: add its manufacturing plus $600$ washes and divide by 600 uses, as in the mug example. And check the real end of life: a "compostable" PLA cup only composts if there is an industrial composting plant nearby. If there is none, it ends up in the landfill like any other waste.
Analyze the following simplified data from the Life Cycle Assessment (LCA) of two school backpacks: Standard backpack (virgin polyester): Extraction and manufacturing…
Analyze the following simplified data from the Life Cycle Assessment (LCA) of two school backpacks:
-
Standard backpack (virgin polyester): Extraction and manufacturing emissions: 18 kg CO₂-eq; Transport: 3 kg CO₂-eq; End of life (landfill, inseparable materials): 1 kg CO₂-eq. Lifespan: 2 years.
-
Eco-designed backpack (recycled polyester and modular zippers): Extraction and manufacturing emissions: 9 kg CO₂-eq; Transport: 3 kg CO₂-eq; End of life (mechanical recycling of separated parts): -2 kg CO₂-eq (environmental credit). Lifespan: 6 years thanks to parts replacement.
- a) Calculate the annual carbon footprint (kg CO₂-eq/year) of each backpack and justify in which phase of the life cycle eco-design achieves the greatest net savings.
- b) Explain why the end-of-life phase of the eco-designed backpack generates a negative impact (-2 kg CO₂-eq) and what technical design condition is essential for this to happen.
A school cafeteria wants to switch to 'compostable' cups. Analyze under what conditions they are genuinely better (separate collection, availability of industrial…
A school cafeteria wants to switch to 'compostable' cups. Analyze under what conditions they are genuinely better (separate collection, availability of industrial composting) and under what conditions they end up being worse than a reusable cup.
Obsolescence: shorter lifespans
Both shorten the use phase and bring the end of life forward: you buy more often and generate more waste, including e-waste (waste electrical and electronic equipment). Since the manufacturing impact is repeated, the impact per year goes up.
To extend lifespan, products are designed with:
-
Mechanical fasteners (standard screws, snap closures) instead of glue or permanent soldering.
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Accessible, replaceable parts (a battery that can be changed without special tools).
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Software that does not lock the device and updates that do not slow it down.
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Manuals and spare parts available, and community repair shops or spare-parts street markets.
A wireless headphone manufacturer has soldered the lithium battery directly to the motherboard and integrated firmware that locks the device after 400 charging cycles,…
A wireless headphone manufacturer has soldered the lithium battery directly to the motherboard and integrated firmware that locks the device after 400 charging cycles, claiming "safety reasons."
- a) Identify the two types of obsolescence present (planned hardware and software obsolescence) and describe how they artificially alter the "use" and "end-of-life" phases in the product's life cycle.
- b) Design three technical modifications (in mechanical joints, component accessibility, and software) so that the product can be repaired by the user and its durability tripled.
A smartphone brand annually releases a handset with the same chassis, screen, and processor as the previous one, but altering the color palette, the geometric…
A smartphone brand annually releases a handset with the same chassis, screen, and processor as the previous one, but altering the color palette, the geometric arrangement of the camera lenses, and introducing continuous on-screen notifications about the battery's "age" once its health drops below 90 %.
- a) Differentiate "perceived obsolescence" from "functional/planned obsolescence" in this specific case and reason how both influence the product turnover rate and WEEE generation.
- b) As a future design engineer, propose two technical and aesthetic design solutions (for example, modular or customizable casings) and one consumer or European regulatory measure to curb this phenomenon.
Closing the cycle: reusing and designing for disassembly
A circular economy tries to keep materials from reaching the grave. What you saw earlier fits together like this:
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Reuse the whole product (returnable bottles, second-hand clothes).
-
Repair and maintain.
-
Recycle the materials when there is no other option.
Recycling does not completely avoid the impact, because it needs collection, transport, and melting energy, and the material loses quality with each round. A deposit-return system (the crate or returnable container you take back to the store) avoids many of those steps: the container is washed and refilled instead of melted down.
For an object to close its cycle, it has to be designed for disassembly:
| Better to choose | Better to avoid |
|---|---|
| Standard screws and nuts | Permanent welds between parts of different materials |
| Snap-fit or slot joints | Blind rivets |
| Parts made of a single material | Glues and contact cements |
| Labels that indicate the material | Mixtures that cannot be separated |
That way, a school chair can be taken apart in minutes with a screwdriver and each piece follows its own route: the steel to remelting, the plastic to shredding and molding, and the screws to be reused in another chair.
Back to the beginning: Ximena's T-shirt does not end up in the trash can. If it had been used longer, repaired or given away, or made with recycled cotton, the cycle would have been closed better. The harm was spread over all the stages, and each one offered an alternative.
A city is debating two 2-million-pesos budget options to manage its packaging waste: Option A: Automate the recycling plant to increase the sorting of single-use…
A city is debating two 2-million-pesos budget options to manage its packaging waste:
-
Option A: Automate the recycling plant to increase the sorting of single-use plastics.
-
Option B: Implement a Deposit, Return, and Refund System (DRS) for standardized reusable glass and plastic packaging for local commerce.
- a) Supported by the life cycle stages (raw material extraction, melting/recycling energy, and material degradation in each cycle), justify why recycling (Option A) does not avoid intensive resource consumption compared to reuse (Option B).
- b) Identify what new logistical and hygienic stage must be incorporated into the packaging life cycle of Option B for the system to operate safely and efficiently.
You are tasked with redesigning a classroom chair (metal frame, plastic seat and backrest) applying the principles of the circular economy and end-of-life ("Cradle to…
You are tasked with redesigning a classroom chair (metal frame, plastic seat and backrest) applying the principles of the circular economy and end-of-life ("Cradle to Cradle").
- a) Specify which mechanical joining solutions you must choose and which you must strictly reject (such as permanent welds in mixed areas, blind rivets, or contact adhesives) to allow disassembly to be carried out at the school itself using standard tools in under 5 minutes.
- b) Design the reverse material flow diagram: indicate the technical path each component (steel, thermoplastic) will follow once the chair is retired (primary recycling, remanufacturing, or modular replacement) and how to ensure that no item ends up in a landfill.