Exercises: New materials and sustainability

Explain what a smart material is and give an example of one used in an everyday product, indicating what stimulus it reacts to (temperature, light, electricity, etc.).

When selecting a material for a product, several criteria must be evaluated at the same time. Name and explain three selection criteria (for example: mechanical properties, cost, environmental impact, availability, appearance, etc.).

The image shows four numbered samples of engineering materials representative of the four families studied.

Observe their appearance (lustre, texture, visible internal structure) and assign each number to its material family, justifying each assignment with a visual clue.

Explain what a bioplastic is, from what raw materials it can be obtained (maize, sugar cane, plant waste) and an everyday product where it is already used.

Explain what a shape-memory material is and describe how it is used in a known application (spectacle frames that recover their shape, medical stents that expand with body heat).

What is graphene? Describe it in two sentences (a sheet of carbon one atom thick) and name an extraordinary property of its that interests technology.

Name and explain three sustainability criteria that you should review before choosing a material (renewable or recycled origin, recyclability, carbon footprint of its production, toxicity, etc.).

Explain in two sentences what a life-cycle assessment (LCA) of a product is and what designers use it for when comparing two candidate materials.

Explain the difference between a bioplastic and a conventional plastic regarding origin and end-of-life behaviour, and comment on why 'bioplastic' does not always mean 'biodegradable'.

Observe the four numbered samples in the image again.

State which sample you would choose to manufacture (a) the light and strong wing of a drone, (b) a container that withstands oven heat, and (c) a cheap, mouldable remote control casing, reasoning each choice based on the properties of the corresponding family.

A backpack company compares two candidate fabrics based on three criteria scored from 0 to 10, as shown in the figure.

Read the scores of each fabric across the three criteria and explain which fabric you would choose for a school backpack and which for a hiking backpack, justifying each decision with data from the chart.

Aerogel is one of the best known thermal insulators and weighs hardly anything. Explain why it is not currently used on a large scale in house construction (cost, brittleness, limited production) and in which special applications its price is justified (aerospace, critical piping).

Compare carbon fibre and glass fibre as reinforcements in composite materials: mechanical performance, weight, cost and a typical application of each where the choice is clear (racing vs general use).

Explain what a self-healing material is, how it basically works (microcapsules with a healing agent, internal networks that rearrange themselves), and describe two applications where it would save on maintenance (vehicle bodies, screens, pipes).

For the frame of a racing drone (minimum mass, frequent crashes, medium budget), you are hesitating between 3D-printed ABS, carbon fibre and aluminium. Analyse each option (weight, impact resistance, repairability, cost) and justify your final choice.

A dental implant must coexist with the body for decades. List the material requirements (biocompatibility, mechanical and fatigue strength, no degradation or release of substances) and explain why titanium or certain ceramics are the usual choice over standard steel.

For food packaging, the cheapest material is not the most sustainable, and the most sustainable one makes the product more expensive. Propose a multi-criteria decision-making method (criteria, weighting and scoring) that allows a justified choice to be made, and apply it to two real materials of your choice.

Imagine you need a material that does not yet exist for a mobile phone case that self-heals when scratched. Write a brief specification: properties it must meet, how you would test each one and what sustainability criteria you would demand in its manufacture.

A company is designing a domestic hand blender. To reduce costs, the technical team proposes manufacturing the main reduction gear coupled to the motor out of nylon (PA66) without permanent lubrication and heat-sealing the outer ABS casing, preventing it from being opened without breaking it. The assembly has a predicted mean time to failure of 2,5 years under normal domestic use (just as the legal warranty expires). (a) Provide technical justification for why this selection of materials and joining process reflects a pattern of planned obsolescence as opposed to an accidental mechanical failure. (b) Propose two specific technical modifications (one involving a material change or surface treatment for the gear, and another involving the joint design for the casing) that will triple the appliance's lifespan while facilitating its repair, and analyze the trade-off between the increase in initial manufacturing cost and the environmental impact throughout its life cycle.

For a laptop casing, three materials are evaluated using these weighted criteria: weight (40%), cost (30%) and recyclability (30%). The scores (0–10) are: aluminium (weight 6, cost 5, recyclability 9), magnesium (9, 3, 6) and ABS (7, 8, 3). (a) Calculate the weighted score for each material and decide which one you would choose based on the figures. (b) Analyse how the decision changes if cost is weighted at 50%, and comment on what this shows about decision matrices.

A company markets water bottles made from PLA (polylactic acid) under the claim: "100% biodegradable: vanishes in nature leaving no trace". An independent laboratory tests the container's mass loss over 180 days in three different media: (1) Industrial composting plant at 58 °C and 60% relative humidity: 94,5% degradation; (2) Seawater at 18 °C: 0,6% degradation; (3) Conventional anaerobic landfill at 22 °C: 1,8% degradation with methane generation. (a) Based on the data, technically refute the advertising claim and predict what environmental impact this container will cause if it ends up scattered in the marine environment or if users dispose of it in the yellow recycling bin mixed with traditional PET. (b) Justify why PLA degrades rapidly in industrial composting but remains virtually inert in the sea, linking the process to the polymer's glass transition temperature (Tg ≈ 60 °C).

A racing bicycle manufacturer promotes a new frame with an epoxy matrix reinforced with carbon nanotubes (CNTs) at 1,5% by mass, claiming that "thanks to nanotechnology it is twice as strong as standard carbon and represents an eco-friendly and completely safe material". (a) Justify from materials science why such a small volume fraction of nanomaterial can significantly increase both the elastic modulus and the toughness of the resin (relate the specific surface area of the nanomaterial to stress transfer at the molecular level). (b) Refute with two technical arguments the claim that it is an "eco-friendly and safe" material: identify the specific toxicological risk from inhalation during machining or sanding operations in the workshop, and analyze the actual feasibility of separating and recycling this composite material at the end of its life cycle.

A company claims to have developed an "unbreakable and scratch-resistant" screen protector by replacing tempered glass with a polycarbonate sheet coated with a nanometric silicon film. To validate its commercialization, you must design its technical specifications sheet. (a) Design an approval protocol by defining four standardized or quantitative tests to check: surface hardness against scratching, drop impact resistance, optical transmittance in the visible spectrum, and screen adhesion durability. For each test, describe the experimental method and set a reasonable numerical acceptance criterion with its units. (b) Justify why in materials engineering the concepts of "unbreakable" and "scratch-resistant" represent a contradictory technical compromise (hardness versus toughness), and predict what type of mechanical failure this polymeric protector will undergo when subjected to a severe point impact compared to one made of tempered glass.

Extended Producer Responsibility regulations require home appliance manufacturers to finance the recycling of their products, penalizing economically any waste that cannot be mechanically recovered. The head of a current vacuum cleaner has the following design: an ABS outer casing ultrasonically welded with overmolded TPU (elastomer) trims, a polypropylene rotating brush with bristles glued using epoxy resin, and an internal motor screwed to a concealed metal chassis. (a) Analyze what specific technical problems these three joining systems and material mixtures will cause in a mechanical recycling and shredding plant. (b) Redesign the material selection and fastening systems of the head by applying Design for Disassembly guidelines, ensuring that an operator can separate the pure materials in less than 60 seconds using basic hand tools.

Unit challenge. Is your home sustainable from a materials science perspective? Take on the role of an ecodesign consultant and analyze the impact of the engineering materials around you.

1. Home audit: Select 5 everyday objects in your home. Classify their components into traditional engineering families (metals, polymers, ceramics, or composites) and record their approximate mass with a kitchen scale (in $\text{kg}$, with a precision of $0,01\text{ kg}$).

2. Data extraction and analysis: Go to the INE website (Statistics on waste collection and treatment) and check the actual recycling rate of plastic and metal packaging in Spain. In LibreOffice Calc, create a table and a comparative chart between the total mass inventoried in your sample and the official actual recycling rate.

3. Redesign and innovation: Choose the object in your sample with the poorest life cycle and write a replacement proposal (maximum one page). Propose replacing its original material with a new engineering material (for example, bacterial biopolymers, graphene, or aerogels), justifying the improvement in mechanical and thermal properties as well as its final environmental impact.

Assessment criteria:

• Rigour in technical classification and precision in measuring materials.

• Quality of processing real INE data and representation using LibreOffice Calc.

• Scientific-technical justification and sustainable viability of the selected new material.