Polyethylene 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). The synthesis of polymers starts with ethylene, (or ethene). Ethylene is obtained as a by-product of petrol refining from crude oil or by dehydration of ethanol. Ethylene molecules compose of two methylene units (CH2) linked together by a double carbon …show more content…
This maximises the intermolecular forces between the chains as they are able to pack closely together. However, this reduces the flexibility and is therefore quite rigid and strong. This isotactic polyvinyl chloride structure occurs very little. Another structure that is produced very little is the syndiotactic PVC. The syndiotactic PVC has a regular arrangement and has similar properties of flexibility, rigidity and strength to the isotactic PVC as shown in Figure #. The most commonly produced PVC structure by addition polymerisation is the atactic PVC. As seen in Figure #, the chlorine atoms are branched randomly and asymmetrically along the carbon backbone. Unlike the other two structures, the random orientation prevents the polymers from packing closely together and is described to be ‘amorphous’. Despite the orientation, atactic PVC is quite rigid due to the more electronegative chlorine atoms. This also provides the strength and rigidity for suitable uses in pipes, window and door frames and even credit cards. PVC is classified as a thermoplastic, which can be re-shaped in the presence of heat. Situations where temperatures reach up to 160 degrees Celsius (melting point) would cause deformation to the PVC; this would be considered a
Have you ever wondered why the plastic bag that you left on the porch during winter cracks or breaks more easily than when you left it during summer time but a piece of wood which was left just like the plastic bag has no effect whatsoever? This is because of a phenomenon, which only happens to polymers, known as the glass transition. For each polymer, there is a certain temperature at which the amorphous polymers undergo a second order phase transition from a rubbery and viscous amorphous solid to a brittle and glassy amorphous solid called the glass transition temperature, Tg.1 When the polymer, or in this case, the plastic bag, is cooled below their glass transition temperature, it becomes hard and brittle like a glass but when it is used above their glass transition temperatures, it might have a different effect than when used at room temperature or below the glass transition temperature as normally, different types of polymers like clothes, food packaging, insulations for wires, etc. are either used above their glass transition temperatures or
Polymer creatures are very fascinating, because they can grow when put in liquids, and experiments are going to be conducted relating to this growing. A polymer is a very long chain of molecules strung together (What). Polymers are very versatile, and can have almost limitless colors and characteristics (Definition). One of these qualities is absorbency, and some can absorb as much as five hundred times their weight in water (Growing). It is hypothesized that if the polymer creatures are submerged in water for a day it will at least double in size, while it will not grow as much when put in Sprite.
Spinning is a process that involves forcing the liquefied polymer solution through a ‘die’ (small hole). The crystallinity of Kevlar Polymer strands, contributes to the unique strength and stiffness of the material. Kevlar is very similar to other common synthetic polymers, including Nylon, Teflon and Lycra. In all polated to strength. Aromatic refers to the Carbon atoms attached to a ring, and Amides refers to a group of Carbon, Nitrogen and Hydrogen atoms.
First step to produce polyethylene is to obtain the ethane from the ground. Ethane can be obtained either by extraction from natural gas or from crude oil using a process called fractional distillation (AUS-e-TUTE n.d.; University of Washington). Fractional distillation is a process that separates the various components of crude oil, in this case, to obtain ethane.
The plastic obtained from polyethylene can be pressed into varying shapes, ranging from the simplest to the most complicated. The ethylene market is indirectly driven by the increased polyethylene consumption for the production of several plastic components. In 2011, the global propylene market is valued at more than $ 90 billion and significant growth is anticipated in the coming years. Acrylic fibers and coatings, PVC plasticizers and coatings, polyurethane resins, epoxy resins and propylene polymers are applied on polycarbonates and solvents, that are used in the production of propylene. The automotive industry is the biggest end-user of polypropylene. The enormous expansion of ethylene and propylene production will contribute to the growth of the ethylene and propylene market, along with the rising demand for downstream products from India, China, and the Middle East. Tight environmental regulations, fluctuations in raw material prices and political uncertainties in crude oil producing regions are the main factors limiting the ethylene and propylene market [9].
Monomers that are combined by condensation polymerization have two functional groups. A carboxylic acid and an amine can form an amide linkage, and a carboxylic acid and an alcohol can construct an ester linkage. So as each monomer has two reactive sites, they can form long chain polymers by making multiple amide or ester links and releasing a small molecule. Examples of the mentioned mechanism are illustrated below.
Ever since I began studying science and mathematics at all levels of educations I have always had an interest in the production of useful materials. In the growing turmoil of today; a world full of global warming and diminishing resources, questions often arise in my mind such as, "can we make a more efficient, more durable and a renewable resource that will overshadow fossil fuels? and have less of an impact on our environment?" Up to now, I have not found a solution to these questions and answering these questions is a personal aspiration of mine which I aim to fulfil by achieving a degree in Chemical engineering and eventually I will contribute to the field in my own unique way. The debate surrounding sustainable energy fascinates me, having recently learned from personal research I have understood what an authoritative role chemists and chemical engineers play in the industry at the present time and how, by working as a team, they contribute to an improved future for the whole world. However, one of the main reasons that has single-mindedly driven me this far to want to study chemical engineering is a book I have read, “Beyond the Molecular Frontier: Challenges for Chemistry and Chemical Engineering” While reading this book, I had solidified my understandings of what chemical engineering is all about. Also, one of the main processes mentioned was polymerisation and is something I already study in A-level chemistry, it is something that not only interests me, but is a personal career aspiration of mine. Reading this book gave me a determination to be the person who helps improve the future of the industry and provide an answer to the questions I always ask myself by studying this degree.
While highly branched PEP result in rigid PU with good heat and chemical resistance, less branched PEP gives PU with good flexibility and low chemical resistance.
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...
Determines crystalline to amorphous transition temperatures in polymers and plastics and the energy associated with the
Polymers are made from relatively small molecular fragments known as monomers that are joined together. Synthetic polymers which include the large group known as plastics are divided into three groups: commodity thermoplastic, engineering thermoplastics (ETP), and advanced engineering thermoplastics (AETP). The engineering thermoplastics (ETP) have heat resistance, strong mechanical properties, lightness, self-lubrication, and easy manufacturing. This plastic category has been lately used to replace wood and metal applications.
Clive Maier, Theresa Calafut. 1998. ‘Polypropylene: The Definitive User's Guide and Databook’. USA: William Andrew Inc.
Polymer means any of various chemical compounds made of smaller identical molecules called monomers linked together. Some polymers, like cellulose, occur naturally. Polymers have extremely high molecular weights, and made-up of many of the tissues of organisms, and have various uses in industries. The process by which molecules are linked together to form polymers is called polymerization (The American Heritage Science Dictionary, 2005). Polymeric compound is a compound made of many smaller molecules such as cellulose, chitin, soy protein, casein and many more. Polymeric is an organic giant molecule and most of the compound is non-crystalline.
Therefore, plastic packages are coded to indicate the type of resin used to make them. The
First, understanding the basics of polymers. Polymers are very large molecules formed by combining many smaller molecules together chemically. The starting molecules of polymers is called monomer which on combination forms random co-polymers. Co-polymers like SBR are widely used as a modifier in asphalt mix. They are very widely used for preventive pavement maintenance technique in cold weather like in chip seals, slurry seal, cold recycled mix and micro-cracking.