Q 6

1. Q 6 PLASTICS

2. 1862 first synthetic plastic 1866 Celluloid 1891 Rayon 1907 Bakelite 1913 Cellophane 1926 PVC 1933 Polyethylene 1938 Teflon 1939 Nylon stockings 1957 velcro 1967 “The Graduate” Short History of Plastics

3. Any solid substance that can be moulded into a new shape under pressure is said to be plastic. • When referring to plastics we talk about polymers, mainly because plastic is a state, condition, property. e.g. metals when heated to a certain temp are said to be plastic and certain polymers when moulded are no longer plastic after moulding. Plastics can be any colour and can be moulded into complex shapes.

4. Numerous items such as household equipment, toys, building materials, decorative objects, containers, packaging, aircraft parts, motor car parts, safety screens, etc are made form plastics.

5. Plastics can have a wide range of “properties” e.g. plastic grill on front of motor car must be decorative and tough where as a plastic drinking cup must be able to withstand temps up to 100 degrees • Plastics can be hard or soft, transparent or opaque, rigid flexible. They are poor conductors of heat and electricity. Plastics are suitable for insulation

6. TYPES OF PLASTICS Plastics are divided into three main categories – 1.) Natural plastics 2.) Modified Natural Plastics 3.) Synthetic Plastics

7. Natural Plastics • Decorative objects have been made as far back as the 1860’s form natural plastics. Items such as spoons, combs, Knife and tool handles, horn cups etc. The most popular natural plastics are: • AMBER • ANIMAL HORN • SHELLAC • NATURAL RUBBER

8. Amber is a resinous substance which oozes from pine trees and solidifies. It is fairly soft and can be carved into shape and polished. Pine trees that produce amber usually grow in the Baltic region Amber

9. Animal horn is composed completely of keratin. This is a fibrous protein which is found in the outer layers of the skin, finger nails, hair and animal horns. Animal Horn

10. Natural rubber is a cream coloured elastic material extracted from the rubber tree. It is more often referred to as a Natural polymer. Natural Rubber

12. Shellac is a resinous substance. It is produce by the parasitic insects which live on trees, generally in India. Shellac was once important as an adhesive and wood polish. Lact insect Shellac

13. How Plastics are Classified

14. Introduction • We use plastics daily, anything from plastic garbage bags to compact discs to the cars we drive incorporate some type of polymer. • Most common material used is production of polymers is petroleum. (oil) • These materials contain the basic elements that are used in forming polymers...carbon, hydrogen, oxygen, nitrogen, chlorine, and fluorine.

15. CARBON • Considered to be the backbone of polymerization. • A general “model” of a monomer is below: H            H |              | C  ==== C |              |   H          "X"

16. Polymerization • Polymers are macromolecules because smaller molecules are joined together to form polymer chains. • This process is called polymerization. • For a monomer to polymerize, it must be capable of forming at least two covalent bonds,  one on the front, one on the back.

17. Network Structure • Some of these monomers are poly functional, meaning that three or more bonds can be formed, resulting in a network. •   This network structure determines the properties of the material. •   There are two classifications of polymerization: addition and condensation, with addition being the most common. •   During the addition polymerization process atoms add onto one another to form the polymer chains. •   No atomic change takes place, atoms simply connect to the "arms" of their neighbor. 

18. Branched Polymers • Structural branching can be achieved by causing a macromolecule to grow at several locations rather than just at the ends. •   These polymers will not  pack together as tightly as linear polymers. •   An example of a branched polymer is low density polyethylene; however high-density polyethylene remains essentially linear.

19. Thermoplastics • A polymer formed through the addition process is called a thermoplastic material. • Properties of thermoplastics in general are that they become soft when heated and harder when cooled. •   These materials have no strong bonds between individual molecules and can be softened by heat and remolded. •   Thermoplastics are recyclable materials.

20. Cross Linking Thermoplastics may have varying degrees of cross linking ranging from none to heavy.

21. ADDITION POLYMERISATION • Adding together of large number of mers so that they form into long CHAIN-LIKE molecule • Example – Polymerisation of Ethylene • Catalyst added to Ethylene molecule.

22. Weaker Bond is broken down, leaving Carbon atom free to link up with other carbon atoms • Weak Bond is attacked by a Free Radical Element. Chain stopper Free radical • Weak Bond contains two electrons, one which is attacked by radical other is left.

23. New molecule behaves like a radical and the process is repeated continuously. • Several thousand molecules can be joined together this way in a single second until eventually a chain stopper is incorporated which terminates the process

24. The result is that the pot is now full of a large number of interwoven chain molecules, twisted around each other like spaghetti. • Where these chains touch off each other Secondary Bonds are formed. Therefore the Secondary Bonds provide the three dimensional structure. These bonds are much weaker than Primary Bonds, and are susceptible to heat.

25. CONDENSATION POLYMERISATION • Used to produce Thermosetting Plastics • It forms a Strong Primary Bond with cross-linking between chains • Two monomers react chemically to form a new molecule with water eliminated as a by-product • The polymer produced cannot be re-softened, has high tensile strength and high melting point

26. Phenol Formaldehyde is an example Phenol Phenol Formaldehyde

27. Phenol Formaldehyde • Each of the Phenol molecules give up a Hydrogen atom, and the Formaldehyde molecule gives up an Oxygen atom, and these join to form water. WATER

28. CO-POLYMERISATION • This type of polymerisation involves adding together different types of Mers. • This allows many different polymers to be manufactured • Example – Polyvinylchloride, this is a combination of PVC and POLYETHYLENE

29. CO-POLYMERISATION

32. Thermosetting Plastics • Primary covalent bonding giving 3-D structure. • Internal structure is cross-linked. • They are rigid, strong, inflexible and cannot be remoulded. High melting point.

33. Thermo Plastics • Bonded by weak van-der-waals forces between adjacent chains. • Internal structure can be linear or branched. • They are soft,

34. Polyethylene terephthalate (PET) used in bottles, carpets and food packaging • Polypropylene (PP) used in food containers, battery cases, bottle crates, automotive parts and fibres; • Polystyrene (PS) used in dairy product containers, tape cassettes, cups and plates • Polyvinyl chloride (PVC) used in window frames, flooring, bottles, packaging film, cable insulation, credit cards and medical products.

35. Compare Thermoplastic Thermoset Elastomer (Rubber)

36. Additives • Catalysts plus the application of heat and pressure are used to accelerate reactions between substances. • Other agents are added to achieve desired properties of the material. • Some of those include plasticizers, fillers, reinforcing agents, and stabilizers.

37. COMMON TERMINOLOGY • LINEAR STRUCTURE – this type of chain results from the process of Addition Polymerisation. • The chain molecules are bonded together along their length by weak Vander walls Forces • Bonds are so weak heat and high pressure can overcome them • Polymer material with Linear structures have a low melting point and tensile stength. ie Elastomers

38. BRANCHED CHAINS– this type of chain results from addition ploymerisation. • Weak Van Der Walls forces bond the molecular chains together along their length • Side Branching means each chain has greater surface area and More Van der Walls forces • The cumulative effect of these Van der Wall forces gives a stiffer, stronger chain structure with a higher melting point. I.e. Polyethylene

39. CROSSLINKING- In condensation, a strong rigid 3-D network is formed by primary covalent bonds between adjacent chains. • These bond and are called crosslinks and give the polymer higher tensile strength, rigidity and resistance to heat. • Thermosetting plastics are formed due to crosslinking.

40. FILLER – These are materials that are added to polymers to increase their volume and strength • GRP – Glass reinforced plastic known as Fibre glass consists of a polymer mixed with glass fibres. This increases the tensile strength of the material • PIGMENTS – have the function of giving colour to the polymer

41. LUBRICANTS – make a polymer easier to mould. Various types of waxes are used in small amounts for this purpose • PLASTICISERS – are added to polymers to improve their flexibility. They achieve this by altering the forces of attraction between molecules of the polymer • NATURAL RUBBER – have linear chain molecules which are folded in nature. They are both plastic and elastic

42. NATURAL RUBBER • This is the sap from the rubber tree. Its polymer chains are of a folded nature and are bonded by weak Van-der-Walls forces. • Natural rubber is both plastic and elastic.

43. SYNTHETIC RUBBER • These are natural rubbers which are processed with sulphur. This is called VULCANISATION. • Vulcanised rubber have folded chains, which are cross-linked. This causes the chains to be permanently bonded. • They are more durable and less flexible than natural rubbers

44. AMORRPHOUS POLYMER • These structures are random and disorganised. They have a low tensile strength and melting point. • Example - Thermoplastics

45. CRYSTALLINE POLYMER • This structure is arranged in a regular geometric pattern. This gives a strong rigid structure with high tensile strength

46. VAN DER WALLS FORCES • These are bonding forces between polymer chains as a result of addition polymerisation. • They are weak secondary bonds and are easily broken by heat and pressure.

47. ELASTOMERS • A group of polymers consisting of linear chains that are coiled, entangled and are subject to minimal cross-linking. • This irregular internal structure and bonding arrangement allows these materials to be very elastic at room temperature.

48. ELASTIC MEMORY – This is the ability of a thermoplastic to return to its original shape when heated • MONOMER - This is a single polymer unit. Polymers are made from many mers. • CATALYST – a substance that speeds up a chemical reaction. ie salt in boiling water • STABILISER – helps to prevent the degrading effects of heat, ultraviolet light on the polymer • PROMOTERS – are similar to catalysts in that they speed up a chemical reaction • INHIBITOR – prohibits a reaction from occur

49. CO-POLYMER • This is a polymer formed when two different mers are linked together in the same polymer chain. • This new polymer may have a mixture of new improve properties, it is similar to alloying in metals.

50. PARISON • In BLOW MOULDING, a tube called a parison is extruded between the two halves of a split mould. The mould closes around the parison and air is blown into it at either end, forcing it out against the wall of the mould.The component is allowed to cool before being removed from the mould. Using this process, thermoplastic materials can be moulded into bottles and drums.