Understanding Thermoplastics and Thermosets

Understanding Plastics

Plastics are corrosion-resistant, lightweight, and have low electrical conductivity. They possess good insulation properties but often have low tensile strength and are not suitable for use at high temperatures. While some are made with natural materials, most are obtained from petroleum and coal products. They derive their name from their ability to deform under pressure.

Thermoplastics

Thermoplastics soften when heated, can be molded into various forms, and harden again upon cooling. They are generally recyclable.

Polyethylene (Polythene)

Low-Density Polyethylene (LDPE)

• Weak, soft, and flexible.
• Softens at 85°C.
• Good insulation.
• Used for: bags, raincoats.

High-Density Polyethylene (HDPE)

• Rigid, strong, and resistant.
• Softens at 125°C and resists chemical attack.
• Used for: plumbing, showers.

Polypropylene

• More resistant and rigid than polyethylene.
• Softens at 150°C.
• Possesses high resilience.
• Used for: chairs, toys, helmets.

Polyvinyl Chloride (PVC)

• Low density and high resistance.
• Rigid PVC is used for durable applications like gutters and furniture.
• Flexible PVC (with plasticizer) becomes soft and flexible, used for hoses and bags.
• Notable brands include: Vinyl, Glasspack, Kautex.

Acrylics (Plexiglass)

• May crack and scratch easily.
• Softens at 170°C.
• It is a fragile, lightweight material.
• Used for: banners, glazing.

Nylon

• Used as a fiber for clothing, socks, and other wear-resistant applications.
• It is hard and resistant to chemical attack.
• Very compact and hard, with a high friction coefficient and high melting point.
• Used for: small combs, rails.

Polystyrene

Found in various forms. Easily printable and suitable for signage. Offers high impact strength and is cost-effective. Two main types:

• Extruded Polystyrene: Used for glazing, jars, etc.
• Expanded Polystyrene (EPS): Used for insulation, protective packaging, etc.

Polycarbonate

Unbreakable, with maximum impact resistance. Transparent, lightweight, portable, and economical. Available in three main forms:

• Mobile: Glazing
• Corrugated: Roofs
• Compact: Glazing for banks

Thermosets (Thermostable Plastics)

When heated, these polymers soften, can be shaped, and then become permanently rigid, with no way of softening again.

Phenol-Formaldehyde (Bakelite)

• Hard and brittle.
• Heat-resistant, and a good thermal and electrical insulator.
• Decomposes at high temperatures.
• Used for: casserole handles.

Urea-Formaldehyde

• Colorless and can be stained.
• Harder than Bakelite, with no taste or smell.
• A good insulator.
• Used for: drawer handles.

Melamine-Formaldehyde

Similar to urea-formaldehyde. Its qualities make it suitable for:

• Kitchen countertops
• Unbreakable vessels

Polyester Resin

Polymerized at room temperature by combining resin and a chemical hardener. This increases its strength and fiber volume, often known as Fiberglass Reinforced Plastic (FRP). Used for: bodywork, tanks.