The Science of Plastics: Composition, Production, and Properties

Understanding Plastics: Composition and Origin

Plastics consist of long chains of molecules, made of carbon, that are called polymers. Polymers are composed of smaller molecules called monomers.

Types of Plastics Based on Origin

There are two main types of plastics according to their origin:

• Natural Plastics: These are obtained directly from vegetable or animal sources. Examples include latex and cellulose (produced by plants), as well as casein (from milk).
• Synthetic Plastics: These are made with compounds derived from petroleum, natural gas, and coal (carbon). Most plastics used today are synthetic.

Industrial Production: Polymerization and Processing

The industrial process for producing plastic from raw materials is called polymerization.

Manufacturing Stages and Additives

During the subsequent manufacturing process, various additives are incorporated to modify the material's properties and reduce costs. This process involves two main stages:

• Fillers: Fillers may be added to reduce the cost of production and enhance certain properties of the raw materials. Some typical fillers include fiberglass, paper, mineral powder, and others.
• Chemical Additives: Chemical additives can also be used, such as plasticizers, which increase the flexibility and resistance of the final product. Pigments may also be added to give the plastic a specific color.

Key Properties and Environmental Impact of Plastics

Physical Characteristics

The general properties of plastics include:

• Mechanical Resistance: Physically resistant to stretching, bending, twisting, and compression.
• Insulation: Good electrical, thermal, and acoustic insulators.
• Ductility: They can be pulled to make threads.
• Malleability: They can be pressed into thin sheets.
• Lightweight: They have a typical density of 0.9 to 1.3 grams per cubic centimeter.
• Impermeability: They are impermeable to liquids.

Recycling Methods

Plastics are recyclable in many ways, including:

1. Chemical Recycling: This process breaks plastic down into its chemical components.
2. Mechanical Recycling: This breaks plastic into small pieces that can be melted and made into tiny pellets.
3. Energy Recovery: This involves burning plastic to produce heat, electricity, or energy for other industrial processes.

Biodegradability

• Non-Biodegradable Plastic: This type is typically made from petroleum. Most of the plastics that we use today are non-biodegradable.
• Biodegradable Plastic: This type is becoming more common. Some biodegradable plastics are broken down by bacteria and other biological agents. For example, Biopol is used to make bottles and moldings.