**2. Polymers**

Polymers are high molecular weight and long-chain compounds formed by connecting many monomers (small units) through covalent bonding. Small companies' connections could lead, during polymerization, to different arrangements of polymer chains, namely linear, branched or cross-linked. The next subsections include the different types of polymers and how they are prepared and characterized.

#### *2.1. Types of Polymers*

## 2.1.1. Thermoplastic Polymers

These are mostly linear or branched polymers that soften and flow when heated, rapidly shape into complex products while in a melted state, and then hardens (solidify) when cooled. The hardening and softening process as a function of the material temperature is fully reversible [41]. Thus, most thermoplastics can be remolded many times without chemical structure effects, although chemical degradation may limit the number of cycles. The apparent advantage of thermoplastic polymers is that waste thermoplastics can be recycled, and a piece that is broken or rejected after molding can be re-grounded and remolded. The plastics used for drink bottles are typical thermoplastics that are widely recycled [42]. The largest scale volume thermoplastics include polyethylene, polypropylene, polystyrene, poly (vinyl chloride). Other thermoplastics include polyethylene terephthalate, polycarbonate, and polyamide (nylon).

Electricity is essential to our standard of living because it powers almost every aspect of our lives, but electricity is potentially lethal. On the other hand, plastics do not conduct electricity and are therefore used in various applications where their insulating properties are needed. Plastics are especially suited to housings for goods such as hairdryers, electric razors, and food mixers as they protect the user from the risk of electric shock. The thermoplastic polymers used in electric machines as insulators [43] are provided in the following Table 2.


**Table 2.** Application of thermoplastic with electrical system.
