POLYMER

GROUP MEMBERS - FARHANA BT AHMAD NURSYAMIMI RAIDAH BT AYOB FATIHATUL HUSNA BT RUSMAN ASMA AFIFAH BT MOHD ROSLI AMAL MADIHA BT MOHD ROSLAN NUR FARHANA BT MOHAMED ZAKI

STRUCTURES

 Natural polymers - derived from plants and animals - e.g: wood,rubber,cotton,proteins,enzymes,cellulose  Synthetic polymers - synthesized from small organic molecules. - e.g: plastics, rubbers, fiber materials  Polymers formed from hydrocarbon molecules  A saturated hydrocarbon is one where all bonds are single, that is, the number of atoms is maximum (or saturated).  non-saturated hydrocarbons contain some double and triple bonds  Isomers are molecules that contain the same molecules but in a different arrangement. An example is butane and isobutene. Single bond Double bond Triple bond

 Polymer molecules are huge and often referred as macromolecules that have internal covalent bonds.  For most polymers, these molecules form very long chains. The backbone is a string of carbon atoms, often single bonded.  Polymers are composed of basic structures called mer units. A molecule with just one mer is a monomer.

 Examples of polymers are polyvinyl chloride (PVC), poly-tetra- chloro-ethylene (PTFE or Teflon), polypropylene, nylon and polystyrene.  Chains are represented straight but in practice they have a three- dimensional, zig-zag structure.  Homopolymer - all the mers are the same  Copolymer - more than one type of mer present - arrangements: random, alternating, block, and graft.

 The mass of a polymer is not fixed, but is distributed around a mean value, since polymer molecules have different lengths.  The average molecular weight can be obtained by averaging the masses with the fraction of times they appear (number-average) or with the mass fraction of the molecules (called, improperly, a weight fraction).  The degree of polymerization is the average number of mer units, and is obtained by dividing the average mass of the polymer by the mass of a mer unit.  Polymers of low mass are liquid or gases, those of very high mass (called high-polymers, are solid). Waxes, paraffins and resins have intermediate masses.  Polymers are usually not linear; bending and rotations can occur around single C-C bonds (double and triple bonds are very rigid).Random kings and coils lead to entanglement, like in the spaghetti structure.

MOLECULAR STRUCTURE (a) Linear Polymers *the repeat units are joined together in single chains (b) Branched Polymers *side-branch chains are connected to the main ones © Cross linked Polymers *adjacent linear chains are joined together one to another at various positions by covalent bonds (d) Network Polymers *Multifunctional monomers forming 3 or more active covalent bonds (d) Network Polymers *Multifunctional monomers forming 3 or more active covalent bonds

 Polymer Crystallinity – the packing of molecular chains to produce an ordered atomic array.  Polymer molecules are often partially crystalline (semi crystalline), with crystalline regions dispersed within amorphous material.  Chain disorder or misalignment, which is common, leads to amorphous material since twisting, kinking and coiling prevent strict ordering required in the crystalline state.  Linear polymers with small side groups, which are not too long form crystalline regions easier than branched, network, atactic polymers, random copolymers, or polymers with bulky side groups.  Crystalline polymers are denser than amorphous polymers, so the degree of crystallinity can be obtained from the measurement of density.  Polymer Crystals - In the fringed-micelle model, the crystallites (micelles) are embedded in an amorphous matrix.  Polymer single crystals grown are shaped in regular platelets (lamellae) Spherulites are chain-folded crystallites in an amorphous matrix that grow radially in spherical shape “grains”.

MECHANICAL PROPERTIES

STRESS-STRAIN BEHAVIOR The Stress/Strain behavior of solid polymers can be categorized into several classes of behavior: 1) Brittle Fracture- characterized by no yield point, a region of Hookean behavior at low strains and failure characterized by chonchoidal lines such as seen in inorganic glasses. 2) Yield Behavior- characterized by a maximum in the stress/strain curve followed by yielding deformation which is usually associated with crazing or shear banding and usually ductile failure. Ductile failure exhibits a high extent of deformation on the failure surface. Yield behavior can result in necking which exhibits a close to constant load regime and a terminal increase in the stress. 3) Rubber-Like Behavior- characterized by the absence of a yield point maximum but exhibiting a plateau in an engineering stress/strain curve. Often rubber-like behavior exhibits a terminal increase in the stress followed by failure which results in a tear with little permanent deformation exhibited in the failure surface, e.g. Jell-O

FRACTURE OF POLYMERS During the fracture process, cracks form at regions where there is a localized stress concentration (i.e. : scratches, notches and sharp flaws) As with metals, the stress is amplified at the tips of these cracks, leading to crack propagation and fracture. Covalent bonds in the network or cross-linked structure are severed during fracture. For thermoplastic polymers, both ductile and brittle modes are possible, and many of these materials are capable of experiencing a ductile-to- brittle transition. One phenomenon that frequently precedes fracture in some thermoplastic polymers is crazing. Associated with the crazes are region of very localized plastic deformation, which lead to the formation of small and interconnected microvoids.

MISCELLANEOUS MECHANICAL CHARACTERISTICS  Impact strength  Fatigue  Tear strength and hardness

The application in polymer

Polystyrene Characteristic  Excellent electrical properties and optical clarity; good thermal and dimensional stability; relatively inexpensive Uses  Wall tile, battery cases, toys, indoor lighting panels, appliance housings.

Fibers Natural fibers : cotton, wool, and silk Modern fiber: Nylon, polyester, rayon, and acrylic Nylon: used for parachutes. Property: Elastic and electrical resistance

Elastomers Elastomers – rubber The high elongation and flexibility or elasticity of these materials, against its breaking or cracking. Depending on the distribution and degree of the chemical bonds of the polymers, elastomeric materials can have properties or characteristics similar to thermosets or thermoplastics, so elastomeric materials can be classified into: Thermoset Elastomers - are those elastomer materials which do not melt when heated. Thermoplastic Elastomers - are those elastomers which melt when heated.

Properties of elastomer materials :  Can not melt, before melting they pass into a gaseous state  Swell in the presence of certain solvents  Are generally insoluble.  Are flexible and elastic.  Lower creep resistance than the thermoplastic materials Examples and applications of elastomer plastic materials:  Natural rubber - material used in the manufacture of gaskets, shoe heels...  Polyurethanes - Polyurethanes are used in the textile industry for the manufacture of elastic clothing such as lycra, also used as foam, wheels, etc...  Polybutadiene - elastomer material used on the wheels or tires of vehicles, given the extraordinary wear resistance.  Neoprene - Material used primarily in the manufacture of wetsuits is also used as wire insulation, industrial belts, etc...  Silicone - Material used in a wide range of materials and areas due their excellent thermal and chemical resistance, silicones are used in the manufacture of pacifiers, medical prostheses, lubricants, mold, etc...