Plastic is a polymer material made from carbon and hydrogen that can be molded into shapes when heat and pressure are applied. Early plastics like celluloid and Bakelite were developed in the 1800s-1900s, but plastic use expanded in the 20th century. Plastics can be thermoplastics, which can be remelted and reshaped, or thermosets, which set permanently after initial molding. Common plastics are made through polymerization of monomers into chains or networks and have properties like strength, durability, and electrical insulation. Plastics are widely used for their processability, low cost, and ability to be formed into complex shapes.

1. CHAPTER 6 : PLASTIC6.0 PlasticPlastic : An organic polymer material (with carbon and hydrogen base) with the ability to flow into a desired shape when heat and pressure are applied to it and retain the shape when they are withdrawn

2. Polymer : A material consisting of long molecular chains or networks of low-weight elements to form a single compound

3. 6.1 The History of Plastic1. Regnault (1835)a France chemical scientist

4. introduce a chemical material called vinyl chloride monomer transformed in white powder (polyvinyl chloride - PVC)

5. but not popular because of not enough raw materials at that moment2. John Wesley Hyatt (1866)an American, finally came upon the solution with celluloid

6. produced billiard balls using celluloid as a substitute3. Alexander Parkes (1855)origin from Birmingham, England

7. won a bronze medal at the 1862 Great International Exhibition in London

8. produced a hard but flexible transparent material, which he called Parkesine from an organic material derived from cellulose

9. claimed that this new material could do anything rubber was capable of, but at a lower price

10. Parkesinesoon lost its luster due to the high cost of the raw materials needed in its production4. Leo Hendrik Baekeland (1907)a Belgian-born American living in New York state

11. developed a liquid resin that he named Bakelite6.2 Properties of Plastic1. The general properties : i. light ii. processable iii. durable iv. resist corrosion v. colour stay vi. translucent vii. transparent viii. good electric insulator ix. good thermal insulator x. wear resistance

12. 6.3 Polimer1. Polymera chemical substance made up of a lot of mer or repeating units or molecules to form a long flexible chain

13. a material consisting of long molecular chains or networks of low-weight elements to form a single compound2. Polymerizationa process of linking the monomers together to form a polymer

14. a chemical reaction in which high-molecular-mass molecules are formed from monomers3. Monomer : a single molecule or a small molecule that may become chemically bonded to other monomers to form a polymer.4. Homopolymer : polymeric materials which consist of polymer chains made up of single repeating units.

15. 5. Copolymer : consist of polymer chains made up of two or more chemically different repeating units which can be in different sequences.Linear polymer M – M – M – MAlternating copolymer M – O – M – O – M – ORandom copolymer O – M – O – O – M – O – MBlock copolymer M – M – M – O – O – O – M6. Amorphous (non-crystalline)a substance having no specific space lattice, the molecules being distributed at random

16. a structure not having the long range repetitive pattern of atoms arrangement6.4 Polymer StructureIt is a long linkage structure.

17. The chains of molecules bonded by a weak force and flexible causes the carbon bondage to move and rotating in the chains.

18. Polymer exists in two structures : amorphous (non-crystalline) and semi-crystalline.6.4.1 Amorphous Structure (non-crystalline)At a high temperature, the polymer became a viscous liquid where the chains moved and glide into one another in tangled state.

19. The chains arrangement are randomize and not in certain geometry pattern.

20. When the temperatures are reduced, the flexibility of molecule properties is blocked and it is similar to the glassy state.6.4.2 Semi-Crystalline StructureWith slow cooling, the molecules will have the certain structure.

21. Causing the molecule to packed together and increased the forces between them, with higher strength, rigid and brittle.

22. The polymer formed with 90% in crystalline chains and the remain in amorphous state.6.5 Types of Polymer ChainsThere are 4 types of molecule chains by polymerization process as shown in the figure below : i. Linear chain polymers a. in the form of a long molecular chains ii. Branched chain polymers b. the linear chain with a series of branched iii. Cross-linked chain polymers c. with short links which connected the closer chains together iv. Network chain polymers d. molecular structure in 3 dimension networks

23. 6.6 Polymerization Processes1. Polymerization : a chemical reaction in which high-molecular-massmolecules are formed from monomers.2. Two types of polymerization process :a. Addition Polymerizationchain reaction involves the straight-forward addition of monomers of the same kind or of different kinds

24. it is occurs between molecules or monomers contains carbon bonding when temperature, pressure and certain catalyst are given

25. examples : i. Polyester are formed from ethylene polymerization ii. Polyvinyl Chloride (PVC)b. Condensation Polymerization step reaction involves between two monomers with the elimination of a simple by product, such as water, hydrogen chloride, etc it is occurs when two monomer substances react together to produce polymer and small molecules (usually water) will be expelled

26. 6.7 Differences between Thermoplastic and ThermosettingThe plastic are divided into 2 large groups : a. Thermoplastics - group of plastics that can be softened every time they are heated - with no curing (chemical change) takes place during the moulding operations - they then can be reshaped - e.g. Polyethylene, Nylon, PVC (Polyvinyl Chloride) b. Thermosetting plastics - group of plastics that only can be heated and formed only once - undergo chemical change (curing) during moulding - can never again be softened by heating - e.g. Epoxy, Polyesters

27. 6.8 ThermoplasticThermoplastic materials belong to the linear and branched chain polymers that are obtained by addition or condensation polymerization of monomers.

28. They can be softened, hardened or resoftened repeatedly by application of heat.

29. Thermoplastics are solids at room temperature , melted or softened by heating, placed into a mold and then cooled to give the desired shape.

30. The monomer linear chains structure of thermoplastics :M – M – M – M – M – MM – M – M – M – M – MM – M – M – M – M – M M is molecule or monomerWhen heated, the chains will move separately and took place to a new position and maintain to that position after the heat and pressure removed The additives of thermoplastics :1. Filleri. wood flour, calcium carbonate, glass fiber, asbestos, aluminium powder, mica granulesii. to improve the impact strength and reduce shrinkage during moulding2. Plasticizersi. to make plastics softer and more flexibleii. to improve flow propertiesiii. to reduce rigidity and brittleness3. Lubricantsi. substance that reduces friction when applied as a surface coating to moving parts to fix the processing and flowability4. Colourantsi. subdivided into dyestuffs, organic and inorganic pigmentsii. pigments more able to resist the temperature and lights5. Antioxidantsi. prevent oxidation, the polymer reacting with oxygenii. oxidation can cause loss of impact strength, elongation, surface cracks and discolourationiii. antioxidants help prevent thermal oxidation reactions when plastics are processed at high temperatures and light-assisted oxidation when plastics are exposed to UV lightiv. stabilizers

31. 6.8.1 Properties of Thermoplasticscan be softened and hardened repeatedly by applying the appropriate thermal and pressure

32. can be attached/ jointed using heat and pressure

33. not liquidify but flow at appropriate pressure and heat for injection moulding

34. when blowed, acts like glasses, can be shape as bottles and round by using pressure or vacuum technique

35. are linear chain polymers form by a long carbon chains through covalent bonding6.9 Thermosetting PlasticThermosetting materials belong to the three-dimensional cross-linked or network polymers.

36. Once they have been set and hardened, they cannot be remelted and returned to their original state (cannot be recycled or reused)

37. The three-dimensional cross-linked structure :

38. Stronger material and insoluble to the solvents because impossible for the solvents to enter and breaks the chains.6.9.1 General Properties of Thermosetsmelted material when the first time heated and then settled or preserved into hard and rigid shape at that temperature

39. after the first formation, no changes will happen eventhough heat and pressure applied

40. usually harder, stronger and more brittle than thermoplastic6.10 The Advantages Of Plastics1. Excellent electrical insulation properties.2. Good insulation properties.3. Certain plastics has good chemical resistance.4. Good resistance to shock and vibration.5. Transparent and translucent.6. Easily coloured.7. Easily assembled or jointed.8. Repairing the self lubricating.9. Good wear and scratch resistance.6.11 The Disadvantages Of Plastics1. Measurement dimension changed by humidity and high thermal extension.2. Low temperature duration for operation (150 - 600˚F).3. Brittle at low temperature.4. Softer and less elastic than metal.5. Certain plastics are easily affected by ultra-violet.6. Creeps occurs at any temperature.7. Easily burnt.

41. 6.12 Factors For Plastics Usages1. Processable and assembleability compared to metalse.g. plastic moulding production- do not need any finishing or tidying process2. Plastics materials are cheaper than metalse.g. nylon replacing zinc3. Plastic propertiese.g. insulation, self lubrication, etc4. Plastic-metal composites can be produced to achieve better propertiese.g. plastic-metal reinforcement are good electrical conductors, lightness and easily produced5. Multiple functions in the same timee.g. housing or covers, insulators and self lubricating bearing6.13 Plastic Manufacturing ProcessIn plastic products manufacturing process, varies of machines used depends upon the shape products and types of resins used.

42. Such as :1. Injection Moulding Process2. Extrusion Moulding Process3. Blow Moulding Process4. Transfer Moulding Process5. Compression Moulding Process6. Rotational Moulding Process7. Thermoforming Process9. Calendaring Process10.Casting Process

43. Injection Moulding Process1. The basic concept of injection moulding machine is a heat-softened thermoplastic material is forced by a screw-drive cylinder into a relatively cool mould cavity that gives the plastic the desired shape.2. The mould usually made from tool steels or beryllium cuprum and can be multiple cavities so that more than one component can be injected in every cycle of process.3. It was the fastest process and widely used.4. Figure 5 shows the typical components of injection moulding machine.

44. 5. Work principles :i. the raw material (resins or pellets) are inserted into the hopperii. under gravity manipulating, the resins enter the injection channel which surrounded by heateriii. certain temperature applied depends upon types of material used, usually around 75˚C - 95˚C for smaller products and 120˚C - 260 ˚C for larger productsiv. when the resins becomes softer, it will be injected using weither the reciprocating-screw or torpedo plungerv. the softened plastics will be enter directly to the nozzle and enters the mould cavityvi. to ensure the mould was fully injected, pressure between 35MPa to 40 MPa are used

45. vii. the product will be solidify in the mould cavity under water cooling cycle through the mouldviii. after that, the injector will be pulled back, the mould then opened and the products will be retrieved from the mouldix. the connecting opener will retrieved the product where the ejector pins will ejected the product from the mould

46. 6. The advantages :the injector mould usage are faster than pressure mould(torpedo plunger)ii. mould cost are lower because of the simplicityiii. various shape, intricate or thinner products can be producediv. high quality parts can be produced at a high production ratev. the process has relatively low labour costsvi. good surface finishes can be produced on the mouldedpartvii. the process can be highly automated.

47. 7. The disadvantages:sink = caused by moulding temperature or the pressure are higherii. flashing = caused by unfitted mouldiii. bubble = caused by cold mould or the pressure are too lowiv. uncompleted moulding = the material did not enter the mould fully, example : small gatesweld line = caused by cold mould, low moulding temperature and time for injection are too fastvi. not economical for small productionvii. certain mould only for certain productviii. high cost of machine means that a large volume of parts must be made to pay for the machineix. the process must be closely controlled to produce a quality products.

48. Extrusion Moulding Process1. A process that supplies a continuous stream of thermoplastic material/ products with equally cross-section where it is directly produced through a shaping tool or to some other subsequent shaping process (dies) placed directly on the end of the extrusion machine.

49. 2. Work principles :i. the pellets or resins are inserted into the hopperii. the material then fed into the heated cylinder by rotating screwiii. when the material become softer, it will be forced continuously by the rotating the screw ramiv. the products or outcomes are formed into continuous shapev. after the product exiting from the die, it will be cooled by air (air-blast system), water (water-bath system) or become cold by interact will cold roll surface where then it will be solidifies while rollingvi. extruded products such as pipe, rod, etc, extrude this way because it can be curved or bended after extruded with hot water by sinking it in it