The handle of pressure cookers is made of plastic because it should be made non-conductor of heat. The plastic used here is the first man-made plastic, which is:
Bakelite
Understanding Pressure Cooker Handle Materials
Pressure cookers operate at high temperatures, and their handles are designed to be held safely without transferring heat to the user's hands. This requires the handle material to be a good thermal insulator, meaning it should be a non-conductor of heat.
Identifying the First Man-Made Plastic
The question specifically asks for the first man-made plastic used for this purpose, which must also be a non-conductor of heat. Let's examine the options provided:
- Polythene: This is a common plastic used in bags, films, and containers. While it is a plastic, it's not known for high-temperature resistance or being the very first man-made plastic.
- Terylene: This is a type of polyester fiber, primarily used in textiles and bottles. It is not a plastic suitable for molding sturdy, heat-resistant handles.
- Nylon: Nylon is a versatile plastic used in fibers and molded parts. It has good properties, but it was developed later than the plastic specifically mentioned as the first man-made plastic often used for electrical and heat-resistant parts.
- Bakelite: This is a thermosetting plastic made from phenol and formaldehyde. It was synthesized by Leo Baekeland in 1907 and was the first synthetic plastic. Bakelite is known for its excellent electrical insulation and thermal resistance, making it ideal for applications requiring heat stability, such as electrical switches, appliance handles, and cookware handles like those on pressure cookers. Its properties make it a superb non-conductor of heat.
Why Bakelite is Suitable for Pressure Cooker Handles
Based on the properties and historical context, Bakelite fits the description perfectly. It is:
- The first truly synthetic, man-made plastic.
- A strong, rigid material when molded.
- An excellent thermal insulator (non-conductor of heat).
- Durable and resistant to high temperatures encountered during cooking.
These characteristics ensure that the handle remains cool enough to touch while the pressure cooker is hot, providing a safe grip.
| Material | Type | Thermal Conductivity | Historical Significance (First Man-Made Plastic) |
|---|---|---|---|
| Polythene | Thermoplastic | Insulator (but softens at lower temps) | No |
| Terylene | Polyester Fiber | Moderate Insulator (not a rigid plastic) | No |
| Nylon | Thermoplastic/Fiber | Insulator (better heat resistance than Polythene, but melts) | No |
| Bakelite | Thermosetting Plastic | Excellent Insulator (high heat resistance, doesn't melt) | Yes |
Considering the requirements for a non-conductor of heat and being the first man-made plastic, Bakelite is the correct answer.
Revision Table: Key Concepts
| Term | Definition/Significance |
|---|---|
| Thermal Insulator | A material that does not conduct heat easily, preventing heat transfer. |
| Bakelite | The first synthetic plastic (phenol formaldehyde resin), known for heat resistance and electrical insulation. |
| Thermosetting Plastic | A plastic that hardens irreversibly when heated, maintaining shape at high temperatures. |
| Pressure Cooker Handle | Part requiring a heat-resistant, non-conductive material for safe handling. |
Additional Information: Properties of Bakelite
Bakelite belongs to a class of polymers called thermosets. Unlike thermoplastics which can be repeatedly melted and reshaped, thermosets undergo a chemical change during molding (curing) that makes them rigid and heat-resistant. This is why Bakelite objects retain their shape even when exposed to high temperatures. This property is crucial for applications like handles on hot appliances. Besides heat resistance, Bakelite is also resistant to electricity, chemicals, and impacts, making it a very durable material for various industrial and household items developed in the early 20th century.
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