(4)Polymeric Materials

Polymeric Materials:

Polymeric Materials 2 nd semester 2006

Outline: Polymeric Materials:

Dept of Mat Eng 117 Outline: Polymeric Materials Definition Classification of Polymer Polymerization Structure-Property Relationship Effect of Temperature on Thermoplastics Polymer Processing Strain-induced Crystalline Additives

Polymeric Materials in Everyday Life:

Dept of Mat Eng 118 Polymeric Materials in Everyday Life

Polymer Applications:

Dept of Mat Eng 119 Polymer Applications Plastics : two types of plastic are thermoplastic and thermosetting Elastomers : consist of linear polymer chain that are lightly cross-linked & high degree of elasticity

Polymer Applications:

Dept of Mat Eng 120 Polymer Applications Fibers : 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 Applications:

Dept of Mat Eng 121 Polymer Applications Foams: containing volume percentage of small pores Films: having thicknesses between 0.025 – 0.125 mm and used as packaging product

Definition:

Dept of Mat Eng 122 Definition POLYMER (Greek root) poly = many meros = part “substance containing high-molecular-weight molecules, consisting of repeating unit which are bond to each other” MONOMER mono = one meros = part

Classification: Source:

Dept of Mat Eng 123 Classification: Source Natural polymers : wood, rubber, cotton, wool, leather, and silk. Synthetic polymers : PE, PP, PVC, PS, and PET.

Classification: Structure & Physical Property:

Dept of Mat Eng 124 Classification: Structure & Physical Property Thermoplastic Linear 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 Property:

Dept of Mat Eng 125 Classification: Structure & Physical Property Thermosetting 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 Property:

Dept of Mat Eng 126 Classification: Structure & Physical Property Elastomer These are polymers that have an elastic deformation > 200% “Material resumes its original shape when stretched or compressed and then released.”

Differences between Thermoplastic & Elastomer:

Dept of Mat Eng 127 Differences between Thermoplastic & Elastomer ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license. Thermoplastic Elastomer

Vulcanization:

Dept of Mat Eng 128 Vulcanization Cross-linking elastomer chains by introducing sulfur or other chemicals Polyisoprene

Properties of Thermoplastic Polymers:

Dept of Mat Eng 129 Properties of Thermoplastic Polymers

Properties of Thermosetting Polymers:

Dept of Mat Eng 130 Properties of Thermosetting Polymers

Properties of Elastomers:

Dept of Mat Eng 131 Properties of Elastomers

Design/Materials Selection:

Dept of Mat Eng 132 Design/Materials Selection Design the type of polymeric material you might select for the following applications: A surgeon’s glove A beverage container A car bumper

Polymerization:

Dept of Mat Eng 133 Polymerization Polymerization: The process that monomer units are bonded by covalent bonds to generate giant molecules. Polymerization Monomer Polymer Polymer Petroleum Products Monomer Crude Oil or Natural Gas

Addition Polymerization:

Dept of Mat Eng 134 Addition Polymerization Process 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 molecule Functionality: the average no. of reactive functional groups (sites) per monomer

Addition Polymerization:

Dept of Mat Eng 135 Addition Polymerization 1. Initiation or Disproportionation 2. Propagation 3. Termination Combination Note:- Addition polymerization is used in the synthesis of PE, PP, PVC, and PS, as well as many of the copolymers.

Addition Polymerization:

Dept of Mat Eng 136 Addition Polymerization ©2003 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 Polymerization:

Dept of Mat Eng 137 Condensation Polymerization A polymerization mechanism in which a small molecule (e.g., H 2 O, CH 3 OH, etc.) is condensed out as a byproduct. The thermosetting polyesters and phenol-formaldehyde, nylons, and PC are produced by condensation polymerization.

Condensation Polymerization:

Dept of Mat Eng 138 Condensation Polymerization ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

Condensation Polymerization:

Dept of Mat Eng 139 Condensation Polymerization Hexamethylene diamine + Adipic acid Water + H 2 O 6,6-Nylon

Degree of Polymerization:

Dept of Mat Eng 140 Degree of Polymerization Ex . Calculate the degree of polymerization if polyethylene (PE) has a molecular weight of 56,000 g/mol. Degree of Polymerization = Average molecular weight of the polymer Molecular weight of the repeating unit The degree of polymerization refers to the total number of repeat units in the chain. Polyethylene (PE) M repeat 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:

Dept of Mat Eng 141 Ex. Structure-Property Relationship Property Low Density Polyethylene High Density Polyethylene Branches many few Density 0.195 - 0.925 g/cm 3 0.945 - 0.965 g / cm 3 Crystallinity 55% - 75% 80% - 95% Hardness, Flexibility soft, pliable harder, stiff Glass transition temp. Melting Point about 75 o C about 110 o C about 100 o C about 130 o C Typical Uses food wrapping, film, flexible bottles, garbage bags milk jugs, bleach bottles, pipes, an excellent electrical insulator Solubility softens and swells in hydrocarbon solvent Insoluble in most organic solvents

Slide 142:

Dept of Mat Eng 142

Effect of Temperature on Thermoplastics:

Dept of Mat Eng 143 Effect of Temperature on Thermoplastics Glass Temperature (Tg): the temp. range below which the amorphous polymer assumes a rigid glassy structure Melting 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 Thermoplastics:

Dept of Mat Eng 144 Effect of Temperature on Thermoplastics ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

Effect of Temperature on Thermoplastics:

Dept of Mat Eng 145 Effect of Temperature on Thermoplastics ©2003 Brooks/Cole, a division of Thomson Learning, Inc. Thomson Learning ™ is a trademark used herein under license.

Processing:

Dept of Mat Eng 146 Processing Thermoplastic Injection Molding Extrusion Blow Molding Compression Molding Themosetting Reaction Injection Molding (RIM) Compression Molding Elastomer Extrusion Compression Molding Fiber Spinning

Injection Molding:

Dept of Mat Eng 147 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:

Dept of Mat Eng 148 Injection Molding Machine Injection Unit - Hopper - Barrel, Heater - Nozzle - Screw Mold Unit - Stationary Mold - Movable Mold Clamping Unit

Reaction Injection Molding (RIM):

Dept of Mat Eng 149 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.

Extrusion:

Dept of Mat Eng 150 Extrusion The 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 Equipment i.e. Bonding, Cutting, Printing,…

Extrusion:

Dept of Mat Eng 151 Extrusion Major type of Extrusion Products Profile Pipe Sheet Film Wire Covering Filament

Blown Film Extrusion:

Dept of Mat Eng 152 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:

Dept of Mat Eng 153 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 Molding:

Dept of Mat Eng 154 Blow Molding Injection Blow Molding Extrusion Blow Molding

Compression Molding:

Dept of Mat Eng 155 Compression Molding Compression molding is almost exclusively used for thermosetting and elastomer. Step 1. Place and preheat compound or preform between male & female mold 2. The mold is closed, heat & pressure are applied 3. The mold is opening

Strain-induced Crystalline:

Dept of Mat Eng 156 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:

Dept of Mat Eng 157 Strain-induced Crystalline (c) 2003 Brooks/Cole Publishing / Thomson Learning™ 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:

Dept of Mat Eng 158 Strain-induced Crystalline

Additives:

Dept of Mat Eng 159 Additives Fillers: 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.