Polymer Science and Engineering

http://www.londonmet.ac.uk/pgprospectus/courses/polymer-science-and-engineering.cfm




My master course is Polymer Science and Engineering(plastics and rubbers). This link is about my course. After I know course structure, I find textbook that is SPECIFICALLY connected to my subject. 'Textbook of Polymer Science' (FRED W.BILLMEYER,JR.) suit for me. I read chapter thirteen (Hydrocarbon Plastics and Elastomers) and write summary.

Polyethylene

- Low-Density(Branched) Polyethylene

Ethylene polymer was branched polyethylene.

Polymerization>>Ethylene (b.p., -104 ˚C) is made from the thermal (steam) and catalytic cracking of a variety of hydrocarbons, ranging from ethane derived from natural gas to fuel oil.

Ethylene polymerization can be carried out with benzene or chlorobenzene as solvent. At the temperatures and pressures used, both polymer and monomer dissolve in these compounds so that the reactions are true solution polymerizations. Water or other liquids may be added to dissipate the heat of reaction.

Structure>> Low-density polyethylene is a partially (50-60%) crystalline solid melting at about 115 ˚C, with density in the range 0.91-0.94. It is soluble in many solvents at temperatures above 100 ˚C, but only a few solvent mixtures provide borderline solubility at or near room temperature.
Properties>> The physical properties of low-density polyethylene are functions of three independent structural variables: molecular weight, molecular-weight distribution or long-chain branching, and short-chain branching.
Applications>> Almost two-thirds of the low- and medium-density branched polyethylene produced has gone into film and sheeting.


- High-Density (Linear) Polyethylene


Linear polyethylene can be produced in several ways, including radical polymerization of ethylene at extremely high pressures, coordination polymerization of ethylene, and polymerization of ethylene with supported metal-oxide catalysts.
Polymerization>> The coordination polymerization of ethylene utilizes a catalyst prepared as a colloidal dispersion by reacting, typically, an aluminum alkyl and TiCl4 in a solvent such as heptane. Ethylene is added to the reaction vessel under slight pressure, at a temperature of 50-75 ˚C. Heat of polymerization is removed by cooling. Polymer forms as a powder or granules, insoluble in the reaction mixture. Heat of polymerization is removed by cooling. At the completion of the reaction, the catalyst is destroyed by the admission of water or alcohol, and the polymer is filtered or centrifuged off, washed, and dried.
Properties>> Most of the differences in properties between branched and linear polyethylenes can be attributed to the higher crystallinity of the latter polymers, Linear polyethylenes are decidedly stiffer than the branched material (modulus of 100,000 versus 20,000 psi), and have a higher crystalline melting point and greater tensile strength and hardness.
Application>> The production of bottles and other containers by blow molding.

Crosslinked Polyethylene
There has been considerable interest in converting polyethylene to a thermosetting material, in order to combine its low cost, easy processing, and good mechanical properties with the enhanced form stability at elevated temperatures, resistance to stress crack, and tensile strength expected in a crosslinked polymer.

My opinion about this chapter
This is the basic of Polymer Science. I am interested in properties of Polyethylene because it has many structures, so it 's many applications. It 's produced thin film by low density polyethylene or hard container by high density polyethylene. It 's very fantastic products. I think that I can understand this chapter because it's many technical words. I studied Bachelor degree in chemistry, so I have known the meaning of technical words in my field. But some words I don't understand for instance ;

• crack ; I cracked an egg into the pan.


• dissipate ; Bad smell dissipated in the air.


• elevate ; Smoking often elevates blood pressure.


• carry out (phrasal verb) ; Our soldiers carried out a successful attack last night.


• to dissolve in


• to dissipate the heat


• to remove by
• catalytic cracking of a variety of hydrocarbons
• to dissipate the heat of reaction