What Are Plastics Definition Classification Polymerization and Everyday Uses
Plastics is essential in chemistry and helps students understand various practical and theoretical applications related to this topic. Plastics are all around us—in bottles, toys, furniture, electronics, and even clothes. Learning about plastics is important for understanding both their chemistry and their impact on our world.
What is Plastics in Chemistry?
A plastic refers to a synthetic or semi-synthetic material made up of long-chain polymers, often derived from petroleum or natural gas. Plastics can be easily molded into different shapes when heated.
This concept appears in chapters related to polymers, polymerization, and the classification of materials, making it a foundational part of your chemistry syllabus.
Molecular Formula and Composition
Plastics do not have a single molecular formula. Each plastic is a polymer with repeating units called monomers. For example, polyethylene has a repeating unit of (–CH2–CH2–)n, where "n" is a large number.
These are organic macromolecules mainly made of carbon and hydrogen atoms, with some plastics also containing oxygen, nitrogen, or chlorine atoms.
Preparation and Synthesis Methods
Plastics are produced by polymerization of monomers. The two main methods are addition polymerization (like in polyethylene and polypropylene) and condensation polymerization (like in nylon and bakelite).
In industry, catalysts, pressure, and temperature are adjusted for efficient production of plastics. Some plastics are made using addition polymerization, while others use condensation polymerization.
Physical Properties of Plastics
Plastics can be hard or soft, transparent or colored, and flexible or rigid. They are generally lightweight, resistant to corrosion and chemicals, poor conductors of electricity, and can be made into films, fibers, or solids.
They have a wide range of melting points depending on their structure. Plastics are typically insoluble in water but soluble in some organic solvents.
Frequent Related Errors
- Confusing plastics with rubbers or natural fibers.
- Mixing up thermoplastics with thermosetting plastics.
- Forgetting plastics are mostly non-biodegradable.
Types of Plastics: Thermoplastics and Thermosetting Plastics
Plastics are mainly classified as thermoplastics and thermosetting plastics:
- Thermoplastics: Soften on heating and can be remolded many times. Examples: Polyethylene, PVC, Teflon, Nylon.
- Thermosetting plastics: Harden permanently after being heated once and cannot be remolded. Examples: Bakelite, melamine, epoxy resin.
What are the 7 Main Types of Plastic?
The 7 main types of plastic are identified by recycling codes 1 to 7. Each type has unique uses and safety levels:
- 1. PET (Polyethylene Terephthalate): Water bottles, soft drink bottles. Widely recycled.
- 2. HDPE (High-Density Polyethylene): Milk jugs, shampoo bottles. Safe and commonly recycled.
- 3. PVC (Polyvinyl Chloride): Pipes, wires, toys. Some forms can release toxins.
- 4. LDPE (Low-Density Polyethylene): Plastic bags, wraps. Flexible, less commonly recycled.
- 5. PP (Polypropylene): Food containers, car parts, ropes. Microwave-safe, strong.
- 6. PS (Polystyrene): Cups, plates, foam packaging. Can leach chemicals if heated.
- 7. Other (Miscellaneous): Polycarbonate, acrylic, nylon, etc. Used for CDs, sports gear, water bottles.
Chemical Properties and Reactions
Plastics are generally not very reactive under normal conditions. They resist most acids and bases but can degrade with UV light or specific chemical exposures. Additives in plastics can affect their chemical stability. Some plastics release toxic gases when burned.
Uses of Plastics in Real Life
Plastics are everywhere! They are used in packaging (bottles, bags), electronics, furniture, textiles, medical devices (syringes, tubes), toys, kitchenware, and even automobiles and planes.
Some plastics, such as nylon and polyester, are used in making clothes and ropes. In modern medicine, plastics save lives by making equipment lighter and safer.
Environmental Impact and Recycling of Plastics
Plastics are non-biodegradable, meaning they do not decompose easily. This leads to major plastic pollution challenges for our environment. Household and industrial waste often ends up in landfills or oceans, harming wildlife. Plastics can take hundreds of years to degrade.
Recycling plastics helps reduce waste and save energy. Steps include collecting, sorting by type, cleaning, shredding, melting, and remolding. New technologies also focus on biodegradable plastics, which break down faster in nature.
Relation with Other Chemistry Concepts
Plastics are strongly related to polymer chemistry, organic chemistry, and environmental science. Understanding plastics helps you learn about properties of polymers, polymer degradation, addition and condensation reactions, and material science.
Step-by-Step Reaction Example
1. Formation of Polyethylene by Addition Polymerization2. Start with the monomer ethylene (CH2=CH2).
3. Under high pressure and with a catalyst, ethylene molecules join to form a long chain:
(CH2=CH2)n → (–CH2–CH2–)n
4. Polyethylene plastic is the final product.
Lab or Experimental Tips
Always identify the type of plastic before conducting chemical experiments—thermoplastics soften with heat, while thermosets do not. Vedantu educators suggest using simple physical tests or recycling codes to distinguish between them quickly.
Try This Yourself
- List the main monomer used in making PVC.
- Identify which plastics are safe for hot food storage.
- Give two environmental problems caused by plastic waste.
Final Wrap-Up
We explored plastics—their types, properties, uses, chemical structure, and environmental impact. For more explanations, live sessions, and study help, check out expert-led classes and materials at Vedantu.
FAQs on Plastics in Chemistry Structure Types and Properties
1. What are plastics in chemistry?
Plastics are synthetic or semi-synthetic polymers made of long chains of repeating units called monomers. In chemistry, plastics are formed through polymerization reactions where small molecules such as ethene (C2H4) join together to form large macromolecules like polyethene (–CH2–CH2–)n.
- They consist mainly of carbon-based covalent chains.
- They can be molded when soft and retain shape when cooled.
- They are widely used in packaging, construction, and household products.
2. What is polymerization in plastics?
Polymerization is the chemical reaction in which small monomer molecules join to form a large polymer chain. In plastics, polymerization commonly occurs by:
- Addition polymerization: Monomers with double bonds combine without losing atoms, e.g., nCH2=CH2 → (–CH2–CH2–)n.
- Condensation polymerization: Monomers join with elimination of small molecules like H2O, e.g., formation of nylon.
3. What are the main types of plastics?
The main types of plastics are thermoplastics and thermosetting plastics.
- Thermoplastics: Soften on heating and can be reshaped multiple times (e.g., polyethene, PVC).
- Thermosetting plastics: Harden permanently after heating due to cross-linking and cannot be remelted (e.g., Bakelite).
4. What is the difference between thermoplastics and thermosetting plastics?
The key difference is that thermoplastics can be remelted and reshaped, while thermosetting plastics cannot be remelted after curing.
- Thermoplastics have mostly linear or branched chains with weak intermolecular forces.
- Thermosets have extensive covalent cross-links forming a rigid 3D network.
- Example thermoplastic: polyethene (–CH2–CH2–)n.
- Example thermoset: Bakelite (phenol-formaldehyde resin).
5. What are plastics made of at the molecular level?
At the molecular level, plastics are made of long covalently bonded carbon chains formed from repeating organic monomers.
- Most plastics are hydrocarbons derived from petroleum or natural gas.
- The backbone usually contains C–C bonds, sometimes with atoms like Cl, O, or N.
- Example: PVC contains repeating units of –CH2–CHCl–.
6. What is polyethylene and how is it formed?
Polyethylene (polyethene) is a thermoplastic polymer formed by addition polymerization of ethene. The reaction is:
- nCH2=CH2 → (–CH2–CH2–)n
- Ethene monomers open their C=C double bond.
- The monomers link into a long saturated chain.
- It is used in plastic bags, bottles, and containers.
7. Why are plastics non-biodegradable?
Plastics are generally non-biodegradable because their strong C–C covalent bonds resist breakdown by microorganisms.
- Most microbes cannot produce enzymes that degrade synthetic polymers.
- The long hydrophobic chains are chemically stable and inert.
- This leads to slow decomposition in the environment.
8. What is PVC and what is its chemical structure?
PVC (polyvinyl chloride) is a thermoplastic polymer made from vinyl chloride monomers. It has the repeating unit:
- (–CH2–CHCl–)n
- nCH2=CHCl → (–CH2–CHCl–)n
9. What are biodegradable plastics?
Biodegradable plastics are polymers that can be broken down by microorganisms into simpler substances like CO2, H2O, and biomass.
- They often contain ester or amide linkages that microbes can hydrolyze.
- Example: polylactic acid (PLA).
- They reduce long-term environmental impact compared to conventional plastics.
10. What are the uses of plastics in everyday life?
Plastics are used in everyday life because they are lightweight, durable, chemically resistant, and easily moldable.
- Packaging materials (polyethene, PET).
- Pipes and fittings (PVC).
- Electrical insulation (PVC, Bakelite).
- Medical devices and laboratory equipment.
