Fig 2 shows a children's outdoor climbing frame. Several components are made from different polymers. The main hand-grip bars are made from nylon and the slide surface is made from high-density polyethylene (HDPE).
(a) Name one property of nylon that makes it suitable for hand-grip bars on outdoor play equipment. [1]
(b)(i) The slide surface is made from HDPE using rotational moulding. Describe the process of rotational moulding. [4]
(b)(ii) Give two advantages of rotational moulding for producing a large hollow product such as a slide section. [2]
(c) The table below shows four polymers. Complete the table by writing whether each polymer is a thermoplastic or a thermosetting plastic, and state one typical product made from each.
| Polymer | Thermoplastic or thermosetting | Typical product |
|---|
| Polypropylene (PP) | | |
| Melamine formaldehyde | | |
| Polyethylene terephthalate (PET) | | |
| Epoxy resin | | |
[4]
(d) The climbing frame connectors are made from ABS (acrylonitrile butadiene styrene) using injection moulding.
(d)(i) Describe the process of injection moulding. [4]
(d)(ii) Explain why injection moulding is suitable for producing large quantities of identical connectors. [2]
(e) A flame retardant additive is used in the polymer for the climbing frame connectors. Explain why a flame retardant is necessary for this product. [2]
(f) Some components of the climbing frame have faded in colour after being outdoors for several years. Name the type of additive that could prevent this fading and explain how it works. [2]
(g) The manufacturer carries out a burn test to identify an unknown polymer sample. Describe how a burn test is used to identify polymers. [4]
(a) One property of nylon suitable for hand-grip bars on outdoor play equipment: hard-wearing / resistant to abrasion. [1] Nylon withstands repeated gripping, friction from hands, and exposure to grit without its surface deteriorating. Other valid properties include its toughness (impact resistance), self-lubricating nature (low friction), and resistance to chemicals and weathering.
(b)(i) The rotational moulding process used to produce the HDPE slide surface:
- A measured quantity of HDPE powder or granules is placed inside a hollow metal mould. [1]
- The mould is closed, placed in an oven, and heated while being rotated slowly on two perpendicular axes simultaneously (biaxial rotation). [1]
- As the mould rotates and heats, the polymer powder melts and coats the entire inside surface of the mould evenly, building up a uniform wall thickness. [1]
- The mould is transferred to a cooling station while still rotating. Once the polymer has solidified, the mould is opened and the finished hollow product is removed. [1]
The simultaneous rotation on two axes ensures that molten polymer distributes uniformly over all internal surfaces.
(b)(ii) Two advantages of rotational moulding for producing a large hollow product such as a slide section:
- It can produce large, seamless hollow shapes in a single piece without joints or weld lines, which is important for structural integrity and safety on play equipment. [1]
- It produces a uniform, even wall thickness throughout the product, ensuring consistent strength. [1]
Other valid advantages include relatively low tooling costs compared to injection moulding for products of this size, and minimal material waste.
(c) Completed polymer classification table:
| Polymer | Classification | Typical product |
|---|
| Polypropylene (PP) | Thermoplastic [0.5] | Food container / bottle cap / rope / medical syringe [0.5] |
| Melamine formaldehyde | Thermosetting [0.5] | Kitchen worktop surface / tableware / electrical insulation [0.5] |
| Polyethylene terephthalate (PET) | Thermoplastic [0.5] | Drinks bottle / food packaging / polyester fibre [0.5] |
| Epoxy resin | Thermosetting [0.5] | Adhesive / circuit board / surface coating / composite matrix [0.5] |
[4 marks total, 0.5 per correct cell]
The key distinction: thermoplastics (PP, PET) soften when reheated and can be reshaped, while thermosetting plastics (melamine formaldehyde, epoxy resin) undergo permanent cross-linking during curing and cannot be reshaped.
(d)(i) The injection moulding process for producing ABS connectors:
- ABS granules are fed from a hopper into a heated barrel. [1]
- Inside the barrel, a rotating Archimedean screw pushes the granules forward where heater bands melt them into a viscous liquid. [1]
- The screw then acts as a ram, injecting the molten ABS under high pressure (typically 100-150 MPa) into a closed, cooled steel mould cavity shaped to form the connector. [1]
- The polymer cools and solidifies rapidly in the water-cooled mould. The mould halves then separate and ejector pins push the finished connector out. [1]
(d)(ii) Two reasons why injection moulding is suitable for large quantities of identical connectors:
- Injection moulding has a very fast cycle time (typically seconds per part), enabling thousands of identical connectors to be produced per day. [1]
- The steel mould produces parts with high dimensional accuracy and repeatability, so every connector is identical. [1]
(e) Why a flame retardant additive is necessary for climbing frame connectors:
- Children's play equipment must comply with safety standards for fire resistance, as the equipment is used by vulnerable users who may not react quickly to a fire. [1]
- A flame retardant slows the spread of fire and can make the polymer self-extinguishing if exposed to a flame source, giving more time for evacuation and reducing the severity of potential injury. [1]
(f) The additive that prevents colour fading:
- UV stabiliser [1]
- It works by absorbing or blocking ultraviolet radiation from sunlight. Without a UV stabiliser, UV energy breaks the covalent bonds in the polymer chains, causing chain scission. This degradation leads to colour fading, surface chalking, and eventual brittleness. The stabiliser absorbs the UV energy and dissipates it as heat, protecting the polymer structure. [1]
(g) How a burn test is used to identify polymers:
- A small sample of the unknown polymer is held with metal tongs or pliers and brought into contact with a controlled flame (e.g. a Bunsen burner). [1]
- Observe the burning behaviour: whether the polymer continues to burn, self-extinguishes when removed from the flame, or does not ignite. This first observation narrows down the polymer family. [1]
- Note the colour of the flame produced (e.g. yellow for polyethylene, blue-yellow for nylon, green tinge for PVC). [1]
- Note the smell of the smoke: for example, polyethylene smells of candle wax, polystyrene has a sweet/aromatic smell, PVC produces an acrid/hydrochloric acid smell, and nylon smells of celery or burning hair. These observations are compared against reference data to identify the polymer. [1]
