1. Introduction
Polymeric materials play a functional role in every aspect of daily life, from clothing to infrastructure. Polymers differ greatly from other materials, such as ceramics or metals, based upon the types of bonding. Metals bond metallically, creating a sea of electrons, and ceramics generally bond ionically, strongly tying electrons to lattice points. Polymers bond covalently in carbon chains, which (in general) make their properties more variable due to the possibilities of arrangement in bond length, angle, and molecular configuration. Polymers, on average, tend to be more lightweight, have a greater range of colors, lower thermal and electrical conductivity, less brittleness, more resistance to acids, bases, and moisture, and higher dielectric strength than their ceramic or metallic counterparts, but with great range. This variety of properties leads to a variety of classifications, and therefore differing processing methods based on the classification of polymer.
2. Polymer Classifications
Polymer processing differs greatly based on the category of polymer within the system. Polymers can be classified by chemical composition, structure, or testing behavior (thermal or mechanical).
2.1. By Chemical Composition
Most polymers are organic molecules, based upon a repeating carbon skeleton, but can also include other elements within the chain, most often oxygen, nitrogen, or sulfur. The base unit of a polymer chain is known as a monomer, or mer. The composition of the monomer will greatly affect the properties exhibited. Monomers can either be natural or synthetically created. Examples of common monomers can be seen in Figures 1-4. Within the monomer, the electronegativity and bonding properties of the constituent e...
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The first term that I noted during the movie was Conductive Polymers. Conductive polymers are almost always organic meaning a large class of chemical compounds whose molecules contain carbon. These polymers have extended delocalized bonds which are bonds found in a molecule that do not belong to a single atom or covalent bond. They are conjugated systems of double bonds and in a aromatic systems. The conjugated systems are atoms covalently bonded with alternating single and double bonds. When the electrons are removed or added into the valence bands the electrical conductivity increases. The conductive polymer has a low conductivity until the electron is removed from the valence band called (p-doping) or (n-doping) until it becomes more conductive. The movement of the charges is what is responsible for electrical conductivity. These polymers are plastic which are organic polymers and with mechanical properties such as flexibility and elasticity.
Polymer chains are long, individual chains, although they behave as if they are attached to each other. The individual chains are actually held together by ‘Electrostatic Forces’ between molecules, also known as ‘Hydrogen Bonds’. Scientists discovered this, by using a special type of X-ray microscopy called ‘XANES’. This was able to reveal the orientation of molecules in materials. It has also been discovered that the components of Kevlar fiber, have a radial orientation that is in a crystal. The crystal-like regularity is the largest contributing factor in the strength of Kevlar fiber.
Figures 3a-d show the effect of polymerization time on %GY (Fig. 3a) ; %GE (Fig. 3b); %TC (Fig. 3c) and %HP (Fig. 3d) at four different temperatures ( 50 0 ; 60 0 ; 70 0 and to 80 0C ). It is evident that , as the reaction time became longer , all polymer yield , except %GE , increased. The polymerization time corresponds to 180 min. brought about the maximum percentages for the positively dependence of polymer criteria.
Polyethylene (PE) is one of the most commonly used polymers which can be identified into two plastic identification codes: 2 for high-density polyethylene (HDPE) and 4 for low density polyethylene (LDPE). Polyethylene is sometimes called polyethene or polythene and is produced by an addition polymerisation reaction. The chemical formula for polyethylene is –(CH2-CH2)n– for both HDPE and LDPE. The formation of the polyethylene chain is created with the monomer ethylene (CH2=CH2).
spaced –CONH– amide groups. Nylon 6-6, or poly(hexamethylneadipamide), is composed of. two structural monomers (hexamethylendiamine (H2N(CH2)6NH2) and adipic acid. (HOOC(CH2)4COOH), whereas Nylon 6, or poly(6-caprolactam), is composed of a single structural unit (either 6-aminocaproic acid (H2N(CH2)4COOH) or caprolactam). Ultimately, the answer is yes.
Keep it Simple Science. Production of Materials. Port Macquarie: Keep it Simple Science, 2005. 24-27. Print
PU polymers are traditionally and generally formed by reacting di- or polyisocyanate with an apolyol. Both the iso-cyanates and polyols used to make polyurethanes have on average two or more than two functional groups per molecule.
Polymer-Polyethylene is partially crystalline as well as amorphous because it has crystalline and amorphous regions. Also it has linear chains so this is the simplest structure compared to a branched or network chain. This can be of an advantage to it over other types of materials as its good toughness and elongation makes it very significant in the engineering industry as it can be moulded or extruded into shape...
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Polysaccharides Polysaccharides are polymers composed of multiple subunits of monosaccharides (simple sugars). They are formed by condensation reaction, in the same way as disaccharides are formed, the difference stands in the larger number of monomer units which they are composed from . The number of monosacchardies composing the chain is variable, and there are two types of chains that can be formed: branched or unbranched. The chains may be folded, thus making them compact and therefore ideal for storage.
Conductive polymer has been known to have poor process ability due to their physical and mechanical characteristics. In order to overcome this difficulty, it has to be treated with a conductive polymer.Such treatment with a conducting polymer reduces the surface resistivity to (1–104 Ω).”6”
“ Poly means many and mer means parts, so polymer means many parts. Polymers are made from many small molecules held together through covalent bonding ”
There are many different polymers available depending upon the starting raw ingredients. There are several broad categories, each with numerous variations. The most common are known as polyester, vinyl ester, epoxy, phenolic, polyimide, polyamide, polypropylene, polyether ether ketone (PEEK), and others. The reinforcement materials are often fibers but can also be common ground minerals.
Polymers are some of the core factors that enable the continuation of life, which is both the natural and the synthetic ones. Over time since the beginning of life, natural polymers were the main supports to living things. Eventually, in line with human development, synthetic polymers has become a valuable addition to the available and usable polymers.
I have spent so much time learning about design through the paradigm of materials but now I want to connect mechanical aspects to the knowledge I have already gained. I am particularly interested in the research done by Dr. Drew Nelson, Dr. Sheri Sheppard and Dr. Friedrich Prinz whose work most closely fits my interests. I am interested in doing research in mechanical design as influenced by material usage. I am also looking forward to taking courses such as Imperfections in Crystalline Solids, The Magic of Materials and Manufacturing, and Nanomaterials Synthesis and Applications for Mechanical Engineers to explore topics I have already studied, but from a mechanical engineering perspective. Stanford’s combination of rigor and creativity appeal to me. I have always enjoyed a challenge and get great satisfaction from expanding my knowledge. Coming from a Materials Science and Engineering background where I have performed well, both in academics and leadership, I know I can be an asset to and learn from the world-class Mechanical Engineering program at