Polymer Processing 1

8/2/2019 Polymer Processing 1

1/26

Polymer Processing


2/26

Polymer Processing Preshaping steps:

Solids handling and conveying: most processes usually involvefeed in particulate form

Plastication: The creation of a polymer melt from a solid feed.

Mixing: often required to achieve uniform melt temperature

or uniform composition in compounds Pumping : The plasticated melt must be pressurized and

pumped to a shaping device

Shaping:

The polymer melt is forced through the shaping devices tocreate the desired shape.

Shape stabilization:

Involves the solidification of the polymer melt in the desiredshape, through heat transfer


3/26

3

Extrusion

Extrusion is a process in which solid thermoplastic material is melted

and forced through an orifice (Die) of desired shape and then cooled.

Extruded products:

Sheet Film

Tube

Profile (e.g. PVC window frames)

Cable coating

Process based upon screw extrusion:

Injection moulding

Injection blow moulding

Extrusion blow moulding


4/26

4

This section covers the basics of extrusion. There are many products

made via extrusion and most of them involve machinery for melting

the plastic (an extruder) and the means to shape the plastic melt (a

die).

So the processing steps involved in extrusion are :

Feeding (Add the resin).

Melting ( add heat to the polymer).

Pumping (transport of the melt).

This can be accomplished by generating melt at a high pressure or by

using an actual pump (like a gear pump)

Forming ( shaping the melt ).

Cooling (remove excess heat so that the material becomes rigid and

retains its shape ).


5/26

5

Sketch of Extrusion Line

Thus the function of the extruder is to :- melt the plastic

- pump the plastic


6/26

The Single Screw Plasticating Extruder

Pellets, powders or flakes are drawn by gravity from a hopper tothe gap between a rotating screw and a heated barrel. They aretransported forward, compacted, melted and pumped through adie where the melt is shaped prior to solidification by cooling .


7/26

Blown, or tubular, film extrusion is one of the major processes used

for manufacturing plastic films. In this process, plastic pellets are

fed into the hopper and melted in the extruder. After exiting the

extruder barrel, the molten resin enters an annular die. The resin is

forced around a mandrel inside the die, shaped into a sleeve, and

extruded through the round die opening in the form of a rather

thick-walled tube. The molten tube is then expanded into a

bubble of the desired diameter.

Film Blowing


8/26

Film Blowing

Extrude a tube upwards through vertical die

Inflate tube till it becomes a film

Collect film and process as needed


9/26

Film Blowing

Extruder

Die/Blower

Assembly

Sizing Basket

Nip Rollers

Windup

Frost Line


10/26

Injection molding is a versatile process that can produce small

parts that weight in fraction as well as large parts that weight in kg.

During this process, molten plastic is forced (injected) into a mold

and cooled until the melt solidifies.

When the part is cooled sufficiently, the mold is opened, the part

is ejected from the mold, and the mold is closed again to repeat the

cycle.

Injection Molding Process


11/26

Products Market Sectors

Automotive.

Computers, telecoms & optical disks.

Construction.

Medical.

Packaging.

Appliances.

Home & Leisure.


12/26

Products Telecoms and Computers


13/26


14/26

Injection Molding Machine


15/26

Single Stage Reciprocation Screw


16/26


17/26


18/26


19/26


20/26


21/26


22/26

The reaction injection molding is quiet different from

conventional thermoplastic molding.

RIM involves two or more liquid reactants flowing into a

mixing chamber and begin to polymerize as they flow into the

mold.

The basic difference from thermoplastic processing is that the

RIM process involves polymerization in the mold rather than

cooling a molten polymer to form a part.

Because the reactant, typically isocynate and polyol, are low

viscosity , so low pressure is required to fill the mould.

Reaction Injection Molding (RIM)


23/26

Reaction Injection Molding (RIM)


24/26

PRODUTION AND PROPERTIES POLYETHYLENE TEREPHTHALATE

Commonly abbreviated PET, PETE

It is a thermoplastic polymer resin of the polyester family and is used in synthetic

fibers, beverage bottles, food and other liquid Container, thermoforming

applications; and engineering resins often in combination with glass fiber..

Depending on its processing and thermal history, polyethylene terephthalate may

exist both as an amorphous (transparent) and as a semi-crsytalline polymer.

The semi-crystalline material might appear transparent or opaque and white

(particle size up to a few microns) depending on its crystal structure and particle

size.

Its monomer can be synthesized by the esterification reaction between

terephthalic acid and ethylene glycol with water as a byproduct.

Polymerization is through a Polycondensation reaction of the monomers (done

immediately after esterification) with water as the byproduct.

Commercially Important Polymer


25/26

Terephthalic Acid Process

In the Terephthalic acid process, esterification of ethylene glycol and Terephthalic acid is

conducted directly at moderate pressure (2.75.5 bar) and high temperature (220260 C).

Water is eliminated in the reaction, and it is also continuously removed by distillation

n C6H4(CO2CH3)2 + n HOCH2CH2OH *(CO)C6H4(CO2CH2CH2O)]n + 2n H2O

(PTA) (Ethylene Glycol) (PET) (Water)


26/26

PET in its natural state is a colorless, semi-crystalline resin.

PET can be semi-rigid to rigid, and it is very lightweight.

About 60% crystallization is the upper limit for commercial products, with theexception of polyester fibers. Besides, about 60% crystalline polymer about 40%

of the polymer chains remaining amorphous.

Clear products can be produced by rapidly cooling molten polymer to form an

amorphous solid.

Amorphous PET forms when its molecules are not given enough time to arrange

themselves in an orderly, crystalline fashion as the melt is cooled. When allowed

to cool slowly, the molten polymer forms a more crystalline material.

Its excellent wear resistance, high flexural modulus, and superior dimensional

stability make it a versatile material for designing mechanical and parts.

Polymer Processing 1

Documents

Transcript of Polymer Processing 1