Manufacturing with PlasticsCompetenciesSlide 3Chemistry of PolymerizationSlide 5Slide 6Slide 7Slide 8Slide 9PolymersThermoplasticSlide 12Slide 13POLYMER STRUCTURES AND COPOLYMERSSlide 15Slide 16Slide 17Slide 18Slide 19CrystallinitySlide 21Slide 22Thermal & Mechanical PropertiesManufacturing With PlasticsSlide 25Molding ProcessExtruder barrel and screwSlide 28Defects in ExtrusionSlide 30Injection MoldingSlide 32Slide 33Slide 34Reaction Injection MoldingCompression moldingTransfer MoldingSlide 38Slide 39Slide 40IT 208 Chapter 18 1Manufacturing with PlasticsChapter 18IT 208Chapter 182CompetenciesDefine key terms associated with polymers and plastics and describe the difference between the two.Differentiate between thermoplastics and thermosets, and identify the use for each.Identify the correct plastics process used to make uniquely different productsDefine the two processes of polymerizationDifferentiate between linear, branched, and cross-linked polymersIT 208Chapter 183IT 208Chapter 184Chemistry of PolymerizationThe carbon atom must always have four covalent bonds. The four noted carbon compounds are•Methane – has one carbon atom bonded to four hydrogen atoms•Ethane – two carbon atoms with six hydrogen atoms•Propane – three carbon atoms with eight hydrogen atoms•Butane – four carbon atoms with 10 hydrogen atomsIT 208Chapter 185Chemistry of PolymerizationEvery carbon atom must have four bonds, but it is possible for two or three of the bonds to be between the same two carbon atoms. •If two of the hydrogens are removed from the ethane molecule, the bonds that went to the hydrogen will simply form a new double bond between the carbons. (p.340)When double bonds are formed •the once “ane” suffix is changed to “ene”•triple bond is formed the “yne” suffix is used.So we have the progression of: Etha ne to Ethene to Ethy ne (Acetylene)IT 208Chapter 186IT 208Chapter 187Chemistry of PolymerizationAn unsaturated molecule is any compound having double or triple bonds. This unsaturated state enables the compound to be reacted with itself, which is the key to polymerization.IT 208Chapter 188Chemistry of PolymerizationA molecule will polymerize if •it has at least two reaction points•maintains at least two reaction points after each joining of the compound. Polymerization is when these bonds are opened, they can react with another ethane molecule and continue reacting to form chains containing thousands of carbon atoms.IT 208Chapter 189Chemistry of PolymerizationThis type of polymerization is called addition, chain-growth or chain reaction polymerization. Condensation polymerization also known as step-growth or step-reaction. •One characteristic of this reaction is that reaction by-products such as water are condensed out.IT 208Chapter 1810PolymersThe reactions form what is know as polymers. Polymers are grouped into 3 categoriesThermoplastic polymers (TP) •represents 70% of the tonnage of all synthetic polymers produced. •Can be easily and economically shaped into products•Can be subjected to this heating and cooling cycle repeatedly without significant degradation of the polymer. Common TP polyethylene, polyvinylchloride, polypropylene, polystyrene, and nylonIT 208Chapter 1811Thermoplastic(linear) - Soften repeatedly when heated (straight chains)PET•Polyethylene Terphalate (Beverage Containers)HDPE •High Density Polyethylene (Milk bottles, detergent bottles)PVC•Polyvinyl Chloride (Food wrap, vegetable oil bottles)LDPE•Low Density Polyethelene (Shrink wrap, plastic bottles)PP•Polypropylene (Margerine and yogurt containers)PS•Polystyrene (Egg cartons, fast food trays)IT 208Chapter 1812PolymersThermosets polymers (TS)•cannot tolerate repeated heating cycles, when initially heated, they soften and flow for molding but the elevated temperatures also produce a chemical reaction that hardens the material into an infusible solid.•toaster parts, automotive engine parts, electrical outlet parts, handles on pots and pans, ash traysElastomers (rubbers) •exhibit extreme elastic extensibility when subjected to low mechanical stress.IT 208Chapter 1813PolymersPlastics •Polymers compounded with various additives.Additives•Agents that enter the molecular structure and are designed to change its properties (Antioxidants, flame retardants, lubricants, etc.)Fillers •Incorporated to improve mechanical properties, often called reinforcing agents. (Increase bulk, stiffness, etc.)IT 208Chapter 1814POLYMER STRUCTURES AND COPOLYMERSThere are structural differences among polymer molecules. There are three aspects of molecular structure 1. Stereoregularity 2. Branching and cross-linking 3. Copolymers. We will discuss only #2 and 3IT 208Chapter 1815POLYMER STRUCTURES AND COPOLYMERSStereoregularity •Concerned with the spatial arrangement of the atoms and groups of atoms in the repeating units of the polymer moleculeBranching and cross-linking (see overhead)Linear polymers •Because their structure is linear. Generally, a polymer consists of more than one type of structure. •Thus a linear polymer may contain some branched and cross-linked chains. (This is the characteristic of a thermoplastic polymer)IT 208Chapter 1816POLYMER STRUCTURES AND COPOLYMERSBranched polymer •side branches chains are attached to the main chain during the synthesis of the polymer. •Branching interferes with the relative movement of the molecular chain. As a result, resistance to deformation and stress-crack resistance are affected. •Branched polymers are like a pile of tree branches compared to straight logs of linear chainsIT 208Chapter 1817POLYMER STRUCTURES AND COPOLYMERSCross-linked polymers•when primary bonding occurs between branches and other molecules at certain connection points. •Lightly cross-linked structures are characteristic of elastomers. •When the polymer is highly cross-linked it considered thermoset.IT 208Chapter 1818POLYMER STRUCTURES AND COPOLYMERSIT 208Chapter 1819POLYMER STRUCTURES AND COPOLYMERSCopolymers •Polymers whose molecules are made of repeating units of two different types. •Also possible are terpolymers , which consist of mers of three different types. (ex. ABS or acrylonitrile-butadiene-styrene)IT 208Chapter 1820CrystallinityAmorphous and crystalline structures are possible with polymers, although the tendency to crystallize is