Outline: Polymeric MaterialsDefinitionClassification of PolymerPolymerizationStructure-Property RelationshipEffect of Temperature on ThermoplasticsPolymer ProcessingStrain-induced CrystallineAdditives

Polymeric Materials in Everyday Life

Polymer Applications Plastics: two types of plastic are thermoplastic and thermosettingElastomers: consist of linear polymer chain that are lightly cross-linked & high degree of elasticity

Polymer ApplicationsFibers: be capable of being drawn into long filament having at least a 100:1 length-to diameter ratio. Ex. PA (nylon), PES (dacron), and PAN (acrylic fibers).Adhesives: used to join together the surfaces of two solid materials

Polymer ApplicationsFoams: containing volume percentage of small poresFilms: having thicknesses between 0.025 0.125 mm and used as packaging product

DefinitionPOLYMER (Greek root) poly= manymeros = part substance containing high-molecular-weight molecules, consisting of repeating unit which are bond to each otherMONOMER mono= onemeros = part

Classification: SourceNatural polymers : wood, rubber, cotton, wool, leather, and silk.Synthetic polymers : PE, PP, PVC, PS, and PET.

Classification: Structure & Physical Property ThermoplasticLinear or branched polymers in which chains of molecules are not interconnected to one another.Polymer can be soften or molten and reformed into new shapes. Process can be reheated.

Classification: Structure & Physical PropertyThermosetting Polymers that are heavily cross-linked to produce a strong three dimensional network structure.Polymer cannot be soften or molten and reshaped.

Classification: Structure & Physical PropertyElastomerThese are polymers that have an elastic deformation > 200%Material resumes its original shape when stretched or compressed and then released.

Differences between Thermoplastic & Elastomer2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.ThermoplasticElastomer

VulcanizationCross-linking elastomer chains by introducing sulfur or other chemicalsPolyisoprene

Properties of Thermoplastic Polymers

Properties of Thermosetting Polymers

Properties of Elastomers

Design/Materials SelectionDesign the type of polymeric material you might select for the following applications: A surgeons gloveA beverage containerA car bumper

Polymerization Polymerization:The process that monomer units are bonded by covalent bonds to generate giant molecules.

Addition PolymerizationProcess by which polymer chains are built up by adding monomers together without creating a byproduct.Unsaturated Bond: the double- or even triple- covalent bond joining together in an organic moleculeFunctionality: the average no. of reactive functional groups (sites) per monomer

Addition Polymerization 1. Initiationor Disproportionation 2. Propagation 3. TerminationCombinationNote:- Addition polymerization is used in the synthesis of PE, PP, PVC, and PS, as well as many of the copolymers.

Addition Polymerization2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.(a) producing free radicals from initiators such as benzoyl peroxide(b) attachment of a polyethylene repeat unit to one of the initiator radicals(c) attachment of additional repeat units to propagate the chain.

Condensation PolymerizationA polymerization mechanism in which a small molecule (e.g., H2O, CH3OH, etc.) is condensed out as a byproduct. The thermosetting polyesters and phenol-formaldehyde, nylons, and PC are produced by condensation polymerization.

Condensation Polymerization

Condensation PolymerizationHexamethylene diamine+Adipic acidWater+H2O

Degree of PolymerizationEx. Calculate the degree of polymerization if polyethylene (PE) has a molecular weight of 56,000 g/mol.

The degree of polymerization refers to the total number of repeat units in the chain.Mrepeat unit = 2(atomic wt. of C) + 4(atomic wt. of H) = 2(12) + 4(1) = 28

Degree of Polymerization = 56,000/28 = 2,000

Ex. Structure-Property Relationship

Solubility

softens and swells in hydrocarbon solvent

Insoluble in most organic solvents

Effect of Temperature on ThermoplasticsGlass Temperature (Tg): the temp. range below which the amorphous polymer assumes a rigid glassy structureMelting Temperature (Tm): the temp. range above which molecules transform form ordered to disordered molecular states.Degradation Temperature: the temp. above which a polymer burns, chars, or decomposes.

Effect of Temperature on Thermoplastics2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

Effect of Temperature on Thermoplastics2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning is a trademark used herein under license.

ProcessingThermoplasticInjection MoldingExtrusionBlow MoldingCompression MoldingThemosettingReaction Injection Molding (RIM)Compression MoldingElastomerExtrusionCompression Molding

FiberSpinning

Injection Molding Injection molding is the most widely used technique for fabricating thermoplastic materials. Probably the most outstanding feature of this technique is the speed with which pieces can be produce due to cycle times are short (commonly within the range of 10 30 s)

Injection Molding Machine Injection Unit - Hopper- Barrel, Heater- Nozzle- Screw Mold Unit- Stationary Mold- Movable Mold Clamping Unit

Reaction Injection Molding (RIM) Thermosetting polymers may also be injection molded; curing takes place while the material is under pressure in a heated mold.

A process likes injection molding. Two or more kinds of fluid plastics are mixed, often without heating, and injected into a mould where the mixture solidifies.

ExtrusionThe extrusion process is simply injection molding of a viscous thermoplastic through an open-ended die, similar to the extrusion of metals. The technique is especially adapted to producing continuous lengths having constant cross-sectional geometries.

Ancillary Equipmenti.e. Bonding, Cutting, Printing,

Extrusion Major type of Extrusion Products Profile Pipe Sheet Film Wire Covering Filament

Blown Film Extrusion This process related to the extruder is fitted with an annular die, pointing (usually) upwards. The tube produced is inflated with air and at the same time is drawn upwards in a continuous process.

Fiber Forming The process by which fibers are formed from bulk polymer material is termed spinning. The strength of fibers is improved by a post forming process called drawing.

Blow MoldingInjection Blow MoldingExtrusion Blow Molding

Compression MoldingCompression molding is almost exclusively used for thermosetting and elastomer.Step1. Place and preheat compound or preform between male & female mold2. The mold is closed, heat & pressure are applied3. The mold is opening

Strain-induced Crystalline when a rubbery polymer is stretched, the molecules become aligned, which leads to crystallization (non-permanent) non-rubbery polymers can be stretched to increase their crystalline proportion permanently stretching in two directions simultaneously induces biaxially oriented crystallization e.g. biaxially stretched PET, PVC, PP: good strength with high clarity (no optical interference)

Strain-induced Crystalline This figure shows a schematic of the blow-stretch process used for fabrication of a standard two-liter PET (polyethylene terephthalate) bottle from a preform. The stress induced crystallization leads to formation of small crystals that help reinforce the remaining amorphous matrix.

Strain-induced Crystalline

AdditivesFillers: to improve mechanical properties and reduce cost.Plasticizers: to improve flexibility, ductility, and toughness of polymers. Their presence also produces reductions in hardness and stiffness.Stabilizers: to protect against atmospheric oxidation or UV radiation.Colorants: to classify application of materials.Flame retardants: may function by interfering with the combustion process through the gas phase, or by initiating a chemical reaction that causes a cooling of the combustion region.