History of Synthetic Polymers

UGEB2380 - The Chemistry of Life

• Course title: The Chemistry of Life
• Academic year: 2024-25
• Lecturer: Dr. Sam CK HAU (Department of Chemistry)

Plastics, Pollution, and Sustainability

• Subtopic explores plastics, pollution, and sustainability.

Polymer Discovery

• First artificial polymers: Semi-synthetic, produced through chemical modification of naturally occurring polymers (e.g., cellulose in cotton).
• Guncotton (1845): Swiss chemist Christian Schoenbein invented guncotton by reacting cellulose with nitric acid, converting some hydroxyl groups into nitrate groups. Used as a smokeless explosive.
• Celluloid (1869): John Wesley Hyatt created celluloid by combining camphor with a lightly nitrated form of nitrocellulose. A substitute for ivory, used in dentures, photographic film, combs, brush handles, and ping-pong balls.
• Vulcanized rubber (1839): American inventor Charles Goodyear accidentally mixed crude rubber with sulphur on a hot stove. This created cross-links between polymer chains, making the rubber more resilient. This process is known as vulcanization.

Polymer Uses and Structures

• Versatile plastics: Exhibit wide range of properties, from firm/rigid to soft/flexible; relatively light and inexpensive.
• Limitless shapes and objects: Can be molded into a wide variety of shapes and objects.
• Durable and resistant to decomposition: Often quite durable and resistant to breaking down.
• Massive production: About 300 million tons of various plastics are produced globally each year.
• Polymers: Large molecules (macromolecules). Made up of repeated smaller molecules (monomers).
• Polymer structures: Polymer structures can be linear, branched, cross-linked, or networked.

Polymer Uses and Structures (continued)

• Synthetic polymers: Produced in laboratories or factories from monomers.
• Biopolymers: Produced by living organisms (e.g., starch, cellulose, DNA molecules).

Polymer Formation

• Addition polymers: No atoms are lost during polymerization. Monomer units retain their original atoms. Unsaturated monomers (double or triple bonds) link to neighboring monomers via covalent bonds. Examples - Polyethylene; formed by polymerization of ethylene or one of its derivatives.
• Condensation polymers: Creation of a new link in the growing polymer chain is accompanied by the release of a small molecule (e.g., water or alcohol). Examples - Polyethylene terephthalate (PET), Nylon,

Polymer Formation (Polymerisation)

• List of examples of various types of produced polymers (Ethylene, Polyethylene, Propylene, Polypropylene, Styrene, Polystyrene, Vinyl Chloride, Polyvinyl chloride, Tetrahydrofluoroethylene, Polytetrafluoroethylene).

Copolymers and Homopolymers

• Copolymers: Consist of two or more monomers.
• Homopolymers: Consist of one type of monomer

Properties of Polymers

• Properties depend on: Monomer structure, average polymer chain length, chain architecture (linear or branched), and presence of additives (e.g., plasticizers).
• Additives: Can affect flexibility and other properties.

LD and HD Polyethylene

• LDPE: Lower density, more flexible, disorganised branched chains, used for plastic wrap and squeeze bottles
• HDPE: Higher density, stronger, linear chains, used for beverage bottles and other consumer products

Plastic Category

• Thermoplastics: Soften when heated and harden when cooled.
• Thermosets: Soft and moldable initially, but become permanently hard and won't soften when heated further (may decompose at high temperatures)
• Elastomers: Elastic polymers that return to their original shape after stretching or squeezing.

Synthetic Rubber

• Styrene-butadiene copolymer: Common synthetic rubber; used in tires, automotive parts, and other goods
• Neoprene: A homopolymer produced from chloroprene; more resistant to heat and organic solvents; used in wetsuits
• Bakelite: First synthetic polymer widely used; hard and resistant to heat and electricity. Made from phenol and formaldehyde.

Synthetic Rubber (continued)

• In 1935, Wallace Carothers created nylon-6,6 by mixing monomers; used in various applications from clothing, to military supplies.

Plastic and Sustainability

• Environmental costs: Significant environmental costs associated with plastic production and disposal from non-renewable resources
• Waste disposal: Plastic waste does not decompose readily; significant amounts of waste end up in landfills, causing pollution & generating toxic gases during incineration
• Recycling Issues: Only a small percentage of plastic is recycled; confusion about the recycling processes.

Recycling

• Resin codes: Numbers assigned to aid in classifying and recycling plastics
• Sorting and processing: Plastics are sorted by type, cleaned, and shredded, then melted into granules that can be sold

Bioplastic

• PLA (Polylactic Acid): Produced from starch derived from corn or other plants, a thermoplastic; biodegradable in composting facilities.
• Substitution for PET: Can potentially replace PET in certain applications.
• Biodegradation time: Takes several months to biodegrade; only small amounts directed to composting due to processing costs

Pollution and Wastes

• Definition of pollution: An excess of a substance (from human or natural sources) present in the wrong environmental location.

Air Pollution

• Primary pollutants: Substances released directly from a specific activity. Examples - CO, CO2, SO2, NO, and NO2 released by burning fossil fuels
• Secondary pollutants: Pollutants produced from reactions involving primary pollutants. Example - SO3, HNO3, H2SO4 produced from reactions between water, NO_x, or SO₂, O₃.
• Photochemical smog: Complex combination of pollutants resulting from sunlight interacting with nitrogen dioxide (NO₂), ozone (O₃), and volatile organic compounds (VOCs).

Water Pollution

• Biological contamination: Presence of disease-causing microorganisms
• Thermal pollution: Increased temperature of water bodies harming aquatic life
• Sedimentary pollution: Increased accumulation of suspended particles impacting sunlight penetration and carrying chemical and biological pollutants
• Chemical pollution: Release of harmful chemicals
• Eutrophication: Selective stimulation of plant life in water at the expense of animals

Land Pollution

• Municipal solid waste: Solid materials discarded by homes, businesses, and public institutions.
• Sanitary landfills: Large waste disposal sites where garbage is compacted and covered.
• Incineration: Combustion of waste reducing volume but generating hazardous waste (ash) that needs disposal.
• Material composition of MSW: Breakdown of waste into various materials (plastics, metals, paper, food scraps, etc.)

Hazardous Waste

• Chemical waste: Waste materials that may endanger public health or wildlife.
• Persistent organic pollutants (POPs): Organic compounds resistant to degradation, and can accumulate in the environment, causing issues in bioaccumulation (accumulation in living tissues)
• DDT (dichlorodiphenyltrichloroethane): A synthetic insecticide that resists degradation and poses threats to wildlife like birds, fish, and other animals. It is a chlorinated organic compound, and highly soluble in fats.

Test your knowledge about the significant developments in synthetic polymers, focusing on the contributions of Christian Schoenbein and the creation of celluloid. This quiz covers key applications, characteristics, and the processes that influence polymer resilience. Dive into the fascinating history of material science!