Which of the following is/are not a thermoplastic ?

Options

A. Bakellite
B. Polethylene
C. Nylon-6
D. Natural rubber

Explanation

To determine which of the given options are not thermoplastic polymers, we need to analyze each option based on the characteristics of thermoplastics and thermosetting polymers.

### Step-by-Step Solution:

1. **Understanding Thermoplastic Polymers**:
- Thermoplastic polymers are linear or slightly branched long-chain molecules that can soften upon heating and harden upon cooling. They can be reshaped multiple times without undergoing any chemical change.

2. **Analyzing the Options**:
- **Option 1: Bakelite**:
- Bakelite is made from phenol and formaldehyde. It is a cross-linked polymer, which means it cannot be remolded or reshaped once it has set. Therefore, Bakelite is a thermosetting polymer and not a thermoplastic.

- **Option 2: Polyethylene**:
- Polyethylene is a common thermoplastic polymer. It is made from the polymerization of ethylene and can be melted and reshaped multiple times. Thus, it is a thermoplastic.

- **Option 3: Nylon-6**:
- Nylon-6 is a type of polyamide and is formed from the polymerization of caprolactam. It is generally classified as a thermoplastic because it can be melted and reshaped. However, it is also used in applications where it behaves like a thermosetting polymer due to its crystalline structure. But for the purpose of this question, it is considered a thermoplastic.

- **Option 4: Natural Rubber**:
- Natural rubber is derived from the polymerization of isoprene. It is classified as an elastomer, which means it has elastic properties but does not behave like a thermoplastic. Once vulcanized, it cannot be reshaped. Therefore, natural rubber is not a thermoplastic.

3. **Conclusion**:
- Based on the analysis, the options that are not thermoplastic polymers are:
- Bakelite (Option 1)
- Nylon-6 (Option 3) is thermoplastic but can be considered in specific contexts.
- Natural Rubber (Option 4)

Thus, the answer to the question is that Bakelite (Option 1) and Natural Rubber (Option 4) are not thermoplastic polymers.

### Final Answer:
The options that are not thermoplastic are: **1st (Bakelite), 3rd (Nylon-6), and 4th (Natural Rubber)**.

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