UGEB2380 The Chemistry of Life 2024-25 Lecture Notes PDF

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Plastics, Pollution, and Sustainability Polymer Discovery First artificial polymers were semi-synthetic, produced by chemical modification of naturally occurring polymers like the cellulose of...

UGEB2380 The Chemistry of Life Academic Year 2024-25 Dr. Sam CK HAU (Department of Chemistry) Plastics, Pollution, and Sustainability Polymer Discovery First artificial polymers were semi-synthetic, produced by chemical modification of naturally occurring polymers like the cellulose of cotton In 1845, Swiss chemist Christian Schoenbein invented guncotton - reaction of cellulose with nitric acid and converting some of the hydroxyl groups (–OH) into nitrate groups (–O–NO2) As a smokeless explosive guncotton 3 Polymer Discovery Celluloid - a substitute for ivory In 1869, John Wesley Hyatt produced celluloid by combining camphor with a lightly nitrated form of nitrocellulose A host of successful products like dentures, photographic film, combs, brush handles, ping pong balls 4 Polymer Discovery GA (from tree) Rubber - highly valued for its elasticity and bounce If heat rubber directly, it becomes soft and soggy and loses its resilience In 1839, the American inventor Charles Goodyear inadvertently dropped a mixture of crude rubber and sulphur onto a hot stove modity Sulphur forms cross-links between the polyisoprene chains of the rubber and keep the rubber resilient, this process is known as vulcanisation Y Sinsrubber 5 Polymer Uses and Structures Plastics are highly versatile- 37 * shape. Exhibit a range of properties from firm and rigid to soft and flexible Relatively light and inexpensive Be formed into a limitless variety of shapes and objects Often quite durable and resistant to decomposition About 300 million tons of various types of plastics are produced each year in worldwide 6 Polymer Uses and Structures Plastic derives from the Greek ‘plastikos’ meaning a material can be moulded and shaped Plastics are polymers - very large molecules or macromolecules, made up of a large number of linked monomers (repeated combination of much smaller molecules) A typical synthetic polymer molecule contains thousands of monomers linked together in a chain and produce a compound with a very high molecular mass 7 Polymer Uses and Structures All commercial plastics are synthetic polymers, produced in the laboratory or factory from one or more different types of monomers Biopolymers are the polymers produced by living organisms, like polysaccharide chains of starch or cellulose, the strands of DNA molecules 8 Polymer Formation Addition Polymers - a No loss of at om polymer in which all atoms originally present in the monomer units are retained An unsaturated monomer containing either a double or triple bond - link with its neighbouring monomers through covalent bonds Polyethylene is formed through addition polymerisation of ethylene or one of its derivatives 9 Polymer Formation Polymerisation … produces … … with the following uses of… H H H H C C C C Milk and juice containers, grocery and produces bags, detergent and motor oil jugs, and toys H H Ethylene H H n Polyethylene (PE) Def H H H H C C Food-storage contains, plastic yogurt cups, bottle C C caps, drinking straws, rope, carpeting, upholstery, CH3 H CH3 H n and plastic automotive parts Propylene Polypropylene (PP) H H H H C C C C Styrofoam cups, utensils, insulated coolers, and Ph H Ph H n packing peanuts Styrene Polystyrene (PS) ka H H H H · C C C C Water and sewer pipes, electrical insulation, Cl H Cl H n outdoor furniture and vinyl siding and flooring Vinyl chloride Polyvinylchloride (PVC) F F F F Nonstick cookware coating, anticracking C C C C components of nail polish, stain-resistant coating F F F F on carpets and upholstery, and coating on n windshield-wiper blades Tetrahydrofluoroethylene Polytetrafluoroethylene (Telfon) ↳ Polymer Formation Condensation polymer - types 2 a the creation of each new link monome in the growing polymer chain < is accompanied by the generation and release of a s small molecule like water or alcohol Polyethylene terephthalate (PET) - a clear plastic widely used to manufacture bottles for water and soft drinks Nylon - a high strength fibres used in fabrics and ropes 11 Polymer Formation Copolymers - consist of A B 1 1AFS) Etern = : = chains produced by two or more different kinds of monomers and exhibits the general pattern of A-B-A-B- A-B… along the chains, where A and B represent ABAB-.. each monomer type ⑮ Homopolymers - consist of chains produced from a single type of monomer X A 4 Branches B 12 Properties of Polymers Physical properties of a given polymer depend on: The structure of monomer The average length of the polymer chains The architecture of the polymer chains, whether linear or branched The presence of additives D like plasticisers that affect properties Eig the flexibility and other Charm) The shape or form into which the plastic is moulded or extruded 13 LD and HD Polyethylene Difference in the physical properties of low density polyethylene (LDPE) and high density polyethylene (HDPE) derive from differences in their molecular structures LDPE is more flexible due to its disorganised and branched strands; uses include plastic food wrap and the plastic squeeze bottles The linear and more organised strands of HDPE produce a more stronger material and be applied on beverage bottles and containers for consumer products like laundry detergent and motor oil Trap air - Plastic Category Categorised based on their response to heat Plastics that soften in response to heat (and harden when cooled) - thermoplastics > - of repeat --E Thermosetting plastics or thermosets are soft and mouldable when first prepared but on heating they harden permanently; won’t soft again but decompose if exposed to high enough temperatures Elastomers - elastic polymer that returns to its original shape after stretching or squeezing 15 Synthetic Rubber Styrene-butadiene copolymer is the most common synthetic rubber, and serves as a good substitute for natural rubber in the manufacture of various consumer goods Highly durable and widely used in tire treads and automotive belts and hoses FOJET -B Copolymerisation of butadiene -- and styrene in a 3:1 ratio produces styrene-butadiene copolymer addition polymer Synthetic Rubber Neoprene, a homopolymer produced from chloroprene and it was invented in 1931 by the American chemist Wallace Carothers, who also invented nylon a few years later Much more resistant to heat and exposure to organic solvent, also provides good thermal insulation and is used in wetsuits TY Polymerisation of chloroprene Cl Cl Cl Cl Cl Cl Cl Cl produces polychloroprene, also known as Neoprene addition  Synthetic Rubber Bakelite - the first synthetic polymer to be prepared but no longer widely used Maintains its hardness even on heating and resistance to heat and electricity; it is a condensation polymer formed from the combination of phenol and formaldehyde, with loss of water Copolymer OH OH OH H H O H H O H H OH OH OH C C H H H H H H H H C O CH2 H H H H OH OH 18 Synthetic Rubber In 1935, Wallace Carothers and co-workers at DuPont Corporation created the condensation polymer nylon-6,6 by mixing two monomers ↓E Toothbrush bristles, replacement for the silk of stockings and other clothings, making parachutes, ropes, and other military supplies 6C 6a COOH NH2 HOOC H 2N Adipic acid 1,6-Diaminohexane Adipic acid unit Adipic acid unit O O O O H H H H N (CH2)6 N (CH2)4 N (CH2)6 N (CH2)4 Diamionhexane unit Diamionhexane unit 19  Plastic and Sustainability High mechanical strength and low density or light weight But… Carries significant environmental costs Produced from nonrenewable resources and the manufacture is not sustainable Plastic waste does not decompose readily Only about 10% was recycled and about 80% ends up in landfills -(incineration produce irritating or toxic gases) > 7 million tons of the plastic wastes ends up in the ocean each year (micro plastics) ↳ - * 20 Recycling Recyclable plastics are assigned a “resin code number” to aid consumers in classifying them for recycling Numbers 1 to 6 correspond to the most common recyclable plastics and number 7 includes all other types of plastics ✓ The plastics are first sorted by type, cleaned and shredded ✓ Then melted and formed into granules for sold Rules for the types of plastics for recycling can vary from one community to another; confusion remains; plastic products not recyclable owing to their mixed composition Recycling X 22 Bioplastic Polylactic acid (PLA) produced from the starch derived from corn or other plants Thermoplastic and used to make food containers, cups, plates, utensils… Biodegradable and can replace PET in certain application To decompose, PLA is sent to industrial scale compositing facilities at high temperature (>60℃), high humidity and adequate exposure to oxygen Take several months for PLA to biodegrade and only very small amounts are directed to such facilities F 23 Pollution and Wastes Pollution is defined as an excess of a substance generated either by human activity (anthropogenic - human generated) or by nature is present in the wrong environmental location Air pollution Water pollution Land pollution 24 Air Pollution Primary air pollutant - an air pollutant generated as the direct result of a specific activity E.g CO, CO2, SO2, NO and NO2 generated from burning coal, gasoline and similar fuels Secondary air pollutant - a pollutant formed by the further reaction of a primary air pollutant E.g. SO3 from the oxidation of SO2 by O2; also HNO2, HNO3, H2SO4 from the reaction between water and NOx or SO2; O3 25 Air Pollution L Photochemical smog - a E complex combination of pollutants resulting from the T interaction of sunlight with Sche nitrogen dioxide (NO2), ozone (O3) and subsequent reactions involving atmospheric oxygen and hydrocarbon pollutants Volatile organic Eq compounds (VOCs) - organic (carbon-based) compounds with relatively low boiling points (< 250℃) and a propensity to evaporate 26  Water Pollution Biological contamination - the presence of disease-causing and life- threatening microorganisms SEEHrY Thermal pollution - raise the temperature of water bodies Sedimentary pollution - the accumulation of suspended particles within a body EST of water (block sunlight and carry chemical and biological pollutants) Chemical pollution - the release of harmful or undesirable chemicals Eutrophication - selective stimulation of plant life at the expense of animals 27 Land Pollution Municipal solid waste - solid materials discarded by homes, businesses and public institutions Sanitary landfills - large disposal sites in which garbage is compacted and covered each day by a thin layer of soil Incineration - reduces the volume of solid waste by about 90% through combustion and generate electricity but need to dispose the resulted ash which is hazardous waste 28  Hazardous Waste Chemical waste that may endanger public health or wildlife Persistent organic pollutants (POPs) - organic compounds that resist degradation in the environment and can undergo bioaccumulation in the food chain HE ** chlorine DDT - a synthetic insecticide cheap ➡ Resistance to degradation ➡ Existence as a chlorinated organic compound ➡ High solubility in fat like milk F ➡ Interference with the reproduction of birds, fish and other animals