Grade 8 Chapter 17: Man-made Materials

Introduction

For centuries, humans relied on natural materials like wood, stone, and animal fibers for their needs. However, with advancements in science and technology, we have learned to modify natural materials or synthesize entirely new ones to create 'man-made materials' with properties superior to their natural counterparts. These materials have revolutionized various aspects of our lives, from clothing and construction to electronics and medicine. This chapter will explore some important man-made materials, including plastics, synthetic fibers, glass, ceramics, and concrete, focusing on their properties, uses, and environmental considerations.

Man-made Materials

Man-made materials (or synthetic materials) are substances that are processed or manufactured by humans using natural resources or chemical reactions to achieve desired properties. They are designed to meet specific needs that natural materials cannot fulfill or to improve upon existing materials.

Plastics

Plastics are synthetic materials derived from petroleum (crude oil) and natural gas. They are polymers, meaning they are made up of long chains of repeating molecular units called monomers. Plastics are versatile, lightweight, durable, and resistant to corrosion, making them widely used.

Types of Plastics

• Thermoplastics:
  • Can be softened repeatedly by heating and hardened by cooling.
  • Can be reshaped and recycled.
  • Examples: Polythene, PVC (Polyvinyl Chloride), Polystyrene.
  • Polythene (Polyethylene): Used for plastic bags, bottles, toys.
  • PVC (Polyvinyl Chloride): Used for pipes, electrical insulation, raincoats, flooring.
  • Polystyrene: Used for disposable cups, packaging foam, insulation.
• Thermosetting Plastics:
  • Once molded and hardened by heating, they cannot be softened or reshaped again.
  • Cannot be recycled.
  • Examples: Bakelite, Melamine.
  • Bakelite: Used for electrical switches, handles of cooking utensils (heat resistant).
  • Melamine: Used for making dinnerware, floor tiles, fire-resistant fabrics (heat and fire resistant).

Environmental Impact of Plastics

Most plastics are non-biodegradable, meaning they do not decompose naturally over time. This leads to:

• Landfill accumulation: Plastics persist in the environment for hundreds of years, filling up landfills.
• Pollution: Plastic waste pollutes land and oceans, harming wildlife.
• Burning issues: Burning plastics releases toxic gases.

Recycling: Recycling plastics is crucial to reduce waste and conserve resources. The 'Reduce, Reuse, Recycle' (3R's) principle is important for plastic management.

Fibers

Fibers are thread-like structures used to make fabrics. They can be natural or man-made.

• Natural Fibers: Obtained from plants (e.g., cotton, jute) or animals (e.g., wool, silk).
• Synthetic Fibers (Man-made Fibers): Manufactured from chemical substances. They are generally stronger, more durable, wrinkle-resistant, and quick-drying compared to natural fibers.

Types of Synthetic Fibers

• Rayon: (Artificial Silk) - Made from chemically treated wood pulp. Properties similar to silk, absorbs moisture, can be dyed. Used for clothing, carpets.
• Nylon: First fully synthetic fiber. Strong, elastic, lightweight, wrinkle-resistant, easy to wash. Used for ropes, fishing nets, parachutes, stockings, toothbrushes.
• Polyester: Strong, wrinkle-resistant, easy to wash, quick-drying. Used for fabrics (terylene, terrycot), bottles (PET), films.
• Acrylic: (Artificial Wool) - Lightweight, soft, warm, wool-like feel, resistant to moths and chemicals. Used for sweaters, blankets, shawls.

Glass

Glass is an amorphous (non-crystalline) solid, usually transparent or translucent, primarily made from sand (silica), soda ash (sodium carbonate), and limestone (calcium carbonate).

• Properties: Transparent, hard, brittle, resistant to chemicals, poor conductor of heat and electricity.
• Types of Glass:
  • Soda-lime glass (Soft glass): Most common type. Used for window panes, bottles, ordinary glassware. Low melting point.
  • Borosilicate glass (Hard glass/Pyrex): Contains boron oxide. Highly resistant to heat and thermal shock. Used for laboratory glassware, bakeware, pharmaceutical bottles.
• Uses: Windows, mirrors, bottles, laboratory equipment, optical lenses, decorative items.

Ceramics

Ceramics are inorganic, non-metallic materials processed by heating at high temperatures. They are typically hard, brittle, and resistant to heat and corrosion.

• Examples: Pottery, bricks, tiles, porcelain, cement, concrete.
• Properties: Hard, brittle, high melting points, resistant to corrosion, good insulators.
• Uses: Building materials (bricks, tiles), pottery, sanitary ware, electrical insulators, dental fillings, advanced engineering applications.

Concrete

Concrete is a composite construction material made from a mixture of cement, aggregate (sand and gravel), and water. It hardens over time to form a strong, durable material.

• Composition: Cement (binding agent), sand (fine aggregate), gravel/crushed stone (coarse aggregate), water.
• Properties: High compressive strength, durable, fire-resistant, can be molded into various shapes.
• Uses: Widely used in construction for buildings, bridges, roads, dams, foundations, etc. Reinforced concrete (with steel bars) is particularly strong.

Summary

• Man-made materials: Synthesized by humans to achieve specific properties.
• Plastics: Polymers from petroleum.
  • Thermoplastics: Can be reshaped/recycled (Polythene, PVC, Polystyrene).
  • Thermosetting Plastics: Cannot be reshaped/recycled (Bakelite, Melamine).
  • Most are non-biodegradable, requiring 'Reduce, Reuse, Recycle'.
• Synthetic Fibers: Strong, durable, wrinkle-resistant.
  • Rayon (artificial silk), Nylon (ropes, parachutes), Polyester (fabrics, PET bottles), Acrylic (artificial wool).
• Glass: Amorphous solid from sand, soda ash, limestone.
  • Soda-lime glass (common), Borosilicate glass (heat resistant, labware).
• Ceramics: Inorganic, non-metallic, high-temperature processed. Hard, brittle, heat/corrosion resistant (bricks, tiles, pottery).
• Concrete: Mixture of cement, aggregate, water. High compressive strength, durable, used in construction.

References

1. Maharashtra State Board Science and Technology Standard Eight Textbook (Specific Edition/Year) - Chapter 17: Man-made Materials.
2. Maharashtra State Board 8th Standard Science Syllabus.
3. Balbharati Science and Technology Textbook.