Material Choice and Recycling

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1Summary 重點摘要

In Secondary 3, material choice looks beyond function and cost to the whole life cycle: designing with wood, metal, plastic and fabric, reading recycling symbols and codes, and reusing or recycling to cut the impact of disposal.

2Vocabulary cards Vocabulary

3Step by step Steps

1. From function to life-cycle material choiceSecondary 1 and 2 taught us to choose materials by hardness, strength and other properties. In Secondary 3 designers look further, to a product's whole life cycle: where the material comes from, how much energy making it consumes, and where it goes after use. Extraction, manufacture, transport, use and disposal all consume resources and affect the environment, and only by counting all of them is a design responsible. For example, disposable plastic cutlery carries the heaviest life-cycle burden for a picnic; washable bamboo or stainless steel cutlery costs a little more to make but can be reused hundreds of times — greener in the long run. That is life-cycle thinking.
2. Designing with four classes of materialThis year asks you to apply wood, metal, plastic and fabric in real designs, matched by function, environment and appearance: wood is warm and easy to work, good for structure and surfaces; metal is strong and durable where loads must be carried; plastic is light, waterproof and can be moulded into complex shapes; fabric is soft and breathable next to the body. For example, a folding camping chair might use aluminium tube for a light, strong frame, hard-wearing breathable canvas for the seat, and moulded plastic joints that resist rust and slipping — three materials each doing what they do best.
3. How use and disposal affect the environmentEvery material consumes energy and water during extraction, refining and manufacture, and may pollute: felling trees affects forest ecology, refining metals uses vast electricity and produces waste water, plastics come from oil and may release harmful gases when burned. For disposal, Hong Kong's three strategic landfills are filling up, non-degrading plastics persist underground for centuries, and broken-down microplastics enter the sea and the food chain. For example, a discarded bottle at sea shatters into countless specks under sunlight and waves; fish eat them, we eat the fish — the pollution returns to us, so design and use must both cut single-use plastic.
4. Why reuse and recycling matterThere are two main routes to lighten the load: reuse means cleaning or simply repairing an item and using it again, such as refilling glass bottles or passing on old clothes, with the least extra resource; recycling breaks waste down and melts it into raw material for new products, like recasting aluminium cans or remaking paper. Both extend the life of resources and underpin sustainable development — and when reuse is possible it comes first, because recycling itself consumes energy. For example, Hong Kong's community recycling network takes paper, metals, plastics, glass and small appliances, and encourages residents to pass on good-condition items through second-hand shops — reuse and recycling running side by side.
5. Reading recycling symbols and plastic codesProper recycling starts with identification: the triangle of three chasing arrows is the international recycling symbol showing a material can be reprocessed; most plastic items carry a code from one to seven inside a small triangle on the base — code 1 is PET used for drink bottles, 2 is HDPE for detergent bottles, 5 is PP for food boxes, 6 is foam polystyrene, and 7 means other plastics. Different codes must be collected separately for effective reprocessing. For example, before recycling a bottle, read the base code, separate the body from the cap, empty and rinse it — one contaminated batch can send the whole load to landfill.
6. Hong Kong's recycling practice and lawHong Kong promotes sorting with three-coloured recycling bins: blue for paper, yellow for metal cans and brown for plastics, plus glass collection points and the producer responsibility scheme for waste electrical equipment — air conditioners, refrigerators, washing machines, televisions and computers collected by registered recyclers. In law, each plastic shopping bag must cost at least fifty cents, and the government has begun regulating disposable plastic tableware, pushing waste reduction at source through legislation. For example, when you buy a new refrigerator, the shop must arrange for the old one to go to a registered recycler rather than ordinary waste — producer responsibility in daily life.
7. Practising green principles in designBringing sustainability into design can start from several moves: use less material and prefer a single material so the product sorts easily; join with screws instead of glue so it can be taken apart, repaired and given new parts; choose recycled stock and mark products with the recycling symbol to guide users; leave service points to extend life. Such decisions cost least at the sketch stage yet matter most. For example, a portable speaker with a single-plastic shell, screw assembly, a base printed with its plastic code and a replaceable battery needs only a new battery after five years — beside a glue-sealed rival that must be thrown away whole, its design clearly follows the circular economy.

5Worked example Example

6Common mistakes Mistakes

7Quick check Quick check

8Recap Recap

• Material choice must consider the whole life cycle, from source to disposal
• Wood, metal, plastic and fabric are combined by their properties in good design
• The recycling symbol and the 1 to 7 plastic codes are the basis of sorting
• Reduce first, then reuse, then recycle — the order that extends resource life
• Mono-materials, screw assembly and replaceable parts are practical green design rules