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.).

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).

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).

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 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'.

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).

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.

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).

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.

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.).

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.

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.