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Why Study Polymer Science and Processing? Employment Opportunities: 135,000,000 tons of plastics alone are produced annually an estimated one in three research dollars in North America is invested in polymer science. Scientific Interest: structure-property relationships of polymers and polymer compounds chemical modification of polymers for advanced applications polymer blending and compatiblization techniques Engineering Design Challenges: life-cycle analyses polymer compound development design/optimization of polymer processing methodologies polymer synthesis Introduction CHEE 490 1.1 U.S. Polymer Production (billions of pounds) 1993 1992 1993 1992 PLASTICS FIBERS Thermosetting Resins Cellulosics Phenol resins 3.08 2.92 Rayon 0.28 0.28 Urea resins 1.74 1.55 Acetate 0.23 0.22 Polyesters (unsaturated) 1.26 1.18 Epoxies 0.51 0.46 Noncellulosics Melamine resins 0.27 0.23 Polyester 3.56 3.58 Nylon 2.66 2.56 Thermoplastic Resins Olefin 2.14 2.00 Low-density polyethylene 12.04 11.92 Acrylic 0.43 0.44 PVC and copolymers 10.26 9.99 Total 9.30 9.07 High-density polyethylene 9.91 9.81 Polystyrene 5.37 5.10 SYNTHETIC RUBBER Polypropylene 8.61 8.42 Styrene-butadiene rubber 1.89 1.92 Polybutadiene 1.03 1.02 Total 53.06 51.57 Ethylene-propylene rubber 0.58 0.58 Nitrile rubber (NBR) 0.14 0.13 Other 1.37 1.42 Total 5.00 5.07 Chemical and Engineering News, April 11, 1994. TOTAL PRODUCTION 67.35 65.71 Introduction CHEE 490 1.2 Polymer Science and Processing Technology Successful product design requires a knowledge of: the requirements of the final product the behaviour of polymeric materials commercial polymer processing technology relevant cost and market factors. At the heart of polymer science and technology is molecular structure. It dictates not only final product properties, but polymer synthesis and processing methods. Introduction CHEE 490 1.3 Classification of Polymer Applications 1. Elastomers static uses: gaskets, hoses dynamic uses: tires, sports equipment 2. Adhesives structural: epoxy resins non-structural: pressure-sensitive tapes, hot-melt adhesives 3. Coatings lacquers, paints 4. Plastics semi-crystalline: automobile exterior amorphous: packaging films, plexi-glass 5. Fibres natural/modified: cotton, rayon synthetic: carpeting, apparel Introduction CHEE 490 1.4 Emphasis of Course Material (Weeks 1-6) Each of the five applications will be examined from the following perspectives: Industrial requirements for end-use and processing Basic testing methods Polymer compound formulations » essential polymer properties » compound additives Relevant engineering science » Elastomers: origin of elasticity, crosslinking, reinforcement » Adhesives: surface energy » Coatings: viscosity » Plastics: mechanical properties, polymer composites » Fibres: crystallization Introduction CHEE 490 1.5 Emphasis of Course Material (Weeks 7-12) Each of the five applications will be examined from the following perspectives: Industrial polymer processing techniques » extrusion » injection molding » fibre spinning » compression molding » polymer/additive blending Key processing variables » polymer compound rheology » fluid mechanics Assessment of processing variables Introduction CHEE 490 1.6 Design Project Develop a polymer compound and processing method for a component of your choice. 1. Define engineering and aesthetic qualities. 2. Propose a compounding recipe that will satisfy these requirements. 3. Recommend appropriate processing techniques for manufacturing the product. Examples? Contact lens, medical catheter, biodegradable packaging, artificial joint, high-performance tire tread... Introduction CHEE 490 1.7 Basics of Polymer Structure What distinguishes polymers from other organic compounds is molecular weight and dimension. Differences in composition, architecture and molecular weight give rise to differences in mechanical properties (strength, elasticity, toughness) and chemical properties (solubility, aging). Introduction CHEE 490 1.8 Polymer Classification: Terminology While we have chosen an applications perspective on polymer classification, many alternate schemes are widely used. These are usually composition/property specific, as opposed to applications oriented. Introduction CHEE 490 1.9 Polymer Classification: Thermoplastic/Thermoset One of the most practical and useful classification of polymer compounds is based on their ability to be refabricated. Thermoplastic: polymers that can be heat-softened in order to process into a desired form. Polystyrene, polyethylene recyclable food containers Thermoset: polymers whose individual chains have been chemically crosslinked by covalent bonds and therefore resist heat softening, creep and solvent attack. Phenol-formaldehyde resins, melamine paints permanent adhesives, coatings Introduction CHEE 490 1.10 Polymer Classification: Chain Architecture Linear: A linear polymer chain is one without branches. Its actual conformation may not be “line-like”, but varies with chain stiffness, crystallinity and applied stresses. Branched: Chains with an appreciable number of side-chains are classified as branched. These side chains may differ in composition from the polymer backbone. Crosslinked: A continuous network of polymer chains is a crosslinked condition. In effect, there is just one polymer chain of infinite molecular weight. Chain architecture has a dramatic effect on properties such as viscosity, elasticity and temperature stability. Introduction CHEE 490 1.11 Polymer Classification: Chemical Microstructure Homopolymers: polymers derived from a single monomer (can be linear, branched or crosslinked). poly(ethylene), poly(butadiene). Random copolymers: two monomers randomly distributed in chain. AABAAABBABAABBA poly(acrylonitrile-ran-butadiene) Alternating copolymers: two monomers incorporated sequentially ABABABABABABABAB poly(styrene-alt-maleic anhydride) Block copolymers: linear arrangement of blocks of high mol weight AAAAAAAAAAABBBBBBBBBBBBBBBAAAAAAAA polystyrene-block-polybutadiene-block-polystyrene or poly(styrene-b-butadiene-b-styrene) Graft copolymers: differing backbone and side-chain monomers poly(isobutylene-graft-butadiene) Introduction CHEE 490 1.12 Polymer Classification: Chemical Class A popular classification scheme amongst chemists is based on polymer functionality. Polyesters: O poly(ethylene terephthalate) - Dacron C O Polyamides: H O poly(caprolactam) - nylon 6 N C Urethanes: carbamate linkages through reaction H O of diisocyanates and diols. N C O Another (!) classification scheme, again favoured by chemists is based on differences between the polymer and constituent monomer(s). Condensation polymers: synthesis involves elimination of some small molecule (H2O in the preparation of nylon) Addition polymer: formed without loss of a small molecule i.e. ethylene polymerization to generate poly(ethylene) Introduction CHEE 490 1.13 Additive Classification: Terminology It is relatively rare for an article to be made from polymer alone. Most are polymer compounds, consisting of a mixture of polymer and various additives. These include: Fillers: solid additives used to modify physical properties. Dilution - talc Reinforcing - carbon black in tires Toughening - rubber in ABS plastic Plasticizers: non-volatile solvents added to improve flexibility Dialkyl phthalates in poly(vinylchloride) Colourants: additives used to change product aesthetics Pigments - soluble colourants Dyestuffs - insoluble additives Antioxidants: compounds that reduce polymer degradation through intervention in free radical reactions Introduction CHEE 490 1.14 Chain-A linear polymer formed by covalent linking of monomeric units. Backbone-Used in graft copolymer nomenclature to describe the chain onto which the graft is formed. Side chain-The grafted chain in a graft copolymer. Cross-link-A structure bonding two or more chains together. Network-A three-dimensional polymer structure, where (ideally) all of the chains are connected through cross-links. Multicomponent polymer, multipolymer, and multicomponent molecule-General terms describing intimate solutions, blends, or bonded combinations of two or more polymers. Copolymer-Polymers that are derived from more than one species of monomer. Block-A portion of a polymer molecule in which the monomeric units have at least one constitutional or configurational feature absent from the adjacent portions. Block copolymer-A combination of two or more chains of constitutionally or configurationally different features linked in a linear fashion. Graft copolymer-A combination of two or more chains of constitutionally or configurationally different features, one of which serves as a backbone main chain, and at least one of which is bonded at some point(s) along the backbone and constitutes a side chain. Polymer blend-An intimate combination of two or more polymer chains of constitutionally or configurationally different features which are not bonded to each other. Interpenetrating polymer network-An intimate combination of two polymers both in network form, at least one of which is synthesized and/or cross-linked in the immediate presence of the other. Semi-interpenetrating polymer network -A combination of two polymers, one crosslinked and one linear, at least one of which was synthesized and/or cross-linked in the immediate presence of the other. Star polymer-Three or more chains linked at one end through a central moiety. Star block copolymer-Three or more chains of different constitutional or configurational features linked at one end through a central moiety.
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