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Chemistry for Engineering Logistics

POLYMERS AND POLYMER MATERIALS

1.Basic Terms in Polymer Chemistry

2.Manufacture of Polymer Products

Department “ORGANIC CHEMISRTY AND TECHNOLOGY”

Assoc. Prof. V. Grozev

1. Basic Terms in Polymer Chemistry

The word "polymer" derives from the ancient Greek word πολύς (polus, meaning "many, much") and μέρος (meros, meaning "parts").

The term “polymer” refers to a molecule whose structure is composed of multiple repeating covalently bonded units:

[ CH2 CH ] [ CH2 CH ] [ CH2 CH ] Cl Cl Cl unit covalent bonds unit

Polymer macromolecule

From this structure originates a characteristic of high molecular mass and attendant properties of all polymer substances.

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1. Basic Terms in Polymer Chemistry

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A HDPE macromolecule is composed of “n” number of units, where n = 10,000 ÷ 100,000. The molecular weight ranges from 2*105 to 3 *106.

“Monomer” is molecule of low molecular weight capable of reacting with identical or different molecules of low molecular weight to form a polymer.

For example a large number (Y) of ethylene molecules (monomer) react and Z macromolecules of polyethylene are formed (HDPE – high density polyethylene) .

1. Basic Terms in Polymer Chemistry

Polymerazation - the process of converting a monomer or a mixture of

monomers into a polymer.

An example of reaction is the union of thousands of ethylene molecules

that gives polyethylene: nH2C=CH2 → [−CH2CH2−]n

Other addition polymers include polypropylene (made by polymerizing H2C=CHCH3), polystyrene (from H2C=CHC6H5), and polyvinyl chloride (from

H2C=CHCl).

A condensation reaction is a chemical reaction in which two

molecules or moieties (functional groups) combine to form a larger

molecule together with the loss of a small molecule:

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1. Basic Terms in Polymer Chemistry

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Other monomers and polymers are: poly styrene, polyvinyl chloride, poly methyl methacrylate etc.:

CH2 CH

CH3

PP - polypropylene

CH2 CH

C6H5

PST - polystyrene

n

n

2. Manufacture of Polymer Products

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2.1. Polymer products

The polymer products:p folios; fibers;elastomers (rubber);industrial and domestic articles made of polymer materials – tubes, fittings, construction materials;adhesives, paints, sealants.

2. Manufacture of Polymer Products

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2.2. Thermoplastics and thermosetsA thermoplastic is a polymer which becomes soft and even turns

into a liquid when heated and turns into a solid or hardens when cooled. Thermoplastics can be heated and cooled many times because their is no links between the polymer chains:

Thermoplastics can be formed when hot and turned into a solid after cooling. That is the basic principle of processing of thermoplastics into polymer products.

2. Manufacture of Polymer Products

2.3. Thermoplastics and thermosets

Thermosets are materials that undergo a chemical reaction (cure) and transform from a liquid to a solid. In its uncured form the material has two components A (monomer) and B (other monomer or catalyst/heat).

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BA chemical reaction

macromolecules

macromolecules with cross-linking between them (solid state):

+

Solid state

liquid

cross-linking

2. Manufacture of Polymer Products 9

2.4. Polymer processing

There are many methods for manufacture of polymer products. Some of them are compression molding, injection molding, melt spinning , reaction injection molding.

1. Compression molding – technological apparatus and work

2. Manufacture of Polymer Products

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2. Injection molding - technological apparatus and work

Injection molding is used extensively for the manufacture of polymeric items. A reciprocating/rotating screw both melts polymer pellets and provides the pressure required to quickly inject the melt into a cold mold. The polymer cools in the mold and the part is ejected.

112. Manufacture of Polymer Products

3. Extrusion molding

Polymer tubes can be manufactured by extrusion molding. The screw plasticates the heated polymer and injects it into a die. The polymer mass takes the form of the die and then solidifies in a cool water.

2. Manufacture of Polymer Products

4. Reaction injection molding

This method is a processing technique for the formation of polymer parts by direct polymerization in the mold through a mixing activated reaction. A simplified process schematic is shown at right.

Two reactive monomeric liquids A and B, are mixed together by impingement and injected into the mold. The components A and B polymerize and solidify in the mold. The last technology operation is ejection of the obtained polymer product from the mold..

Primary uses for reaction injection molding products include automotive parts, business machine housings and furniture.

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2. Manufacture of Polymer Products

5. Melt spinning

Melt spinning is the preferred method of manufacture for polymeric fibers.

The polymer is melted and pumped through a spinneret (die) with numerous holes (one to thousands). The molten fibers are cooled, solidified, and collected on a take-up wheel.

The next operation is stretching of the fibers in order to provide orientation of the polymer chains along the fiber axis.

Polymers such as poly(ethylene terephthalate) and nylon 6,6 are melt spun in high volumes.

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rocess Schematic

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