4. SELECTION OF POLYMER
The performance requirement of
the intended end use.
The economic factors.
The availability of suitable and
processing equipment.
5. Selection of compounding
ingredients
REQUIREMENT:-
•Their degree of effectiveness.
•The efficiency of processing
ingredients.
•The condition of processing
•The requirement of the end use
•The environmental exposure to which
the product will be subjected.
6. FACTORS THAT INFLUENCE
COMPOUNDING
• Physical form & melting characteristics of the
polymer considered .
•Degree of dispersion or solubilisation of the
additive in the final mixture.
•Physical form of the plastics raw material or
compound to be produced.
7. METHODS OF INCOPORATING
ADDITIVES
• Added to the monomer ie before or during the
production of the polymer.
•Added during the working up of the polymer.
•Added in a separate manufacturing step.
•Incorporated directly before or during molding of
a plastic to a semifinished product or finished
article.
8. Addition of additives before or
during a polymerisation process
•Additives should be inert.
•Used by the producer of the base resins.
Examples-
Stabilization of impact resistant PS and pre
stabilasation of PVC produced by suspention
polymerisation.(in both cases antioxidants are
added to the monomers)
9. Addition of additives during the
working up of the polymer
•Used by polymer manufacturer.
•Additives used must satisfy specific requirements
determined by the process such as emulsifiability
, solubility in certain solvents , low volatility or
stability to hydrolysis.
•Polymer must be in dispersed form.
Example- In modification of styrene polymer,such
as ABS.
10. Methods of Compounding
There are four basic methods
– Dry mixing,
– Batch mixing,
– Continuous mixing,
– Compounding by Screw extruder.
The selection of the method determined by
–Condition of the material,
–The volume of end product required,
–The sensitivity of the material to breakdown during
shear.
11. Dry Mixing
Dry mixing the plastic with its additives in a
500 pound capacity paddle mixer.
The paddles are turned at 30 to 90 seconds or
until the mix is homogeneous.
If the mix is too long, it will develop lumps of
glass, while too short a mix will produce an
unequal dispersion of glass fibres.
Dry mixer are preferred for powders, plastic
pellets with fibers and also for mixing
plasticizers with PVC.
12. Types of Dry mixers
There are four types of dry mixers:
– High speed impellers,
– Ribbon mixers,
– Paddle mixers and
– Drum tumblers.
13. Dry mixer
The mixer consists of an enclosed container with
a higher speed impeller mounted at the bottom.
An impeller is similar to the rotating blades of a
helicopter.
The impeller is capable of 80 to 3600 revolutions
per minute (RPM). Mixing is fast with materials
blended within 2-4 minute cycles.
Heat generated during the mixing process must
be drawn off through a cooling jacket to retard
decomposition of the material and to block the
development of lumps.
14. drum tumbler
Drum tumblers are popular with molding
operation for the dispersion of powdered
colorants with the plastic pellets.
In a drum tumbler, plastic pellets (with
approximately 1 to 2% colorant) are placed in a
250 gallon drum and tumbled dry for
approximately 30 minutes.
Drum tumblers are used when the additives
disperse easily throughout the mixture without
tending to lump or cluster together.
16. Continue……
High speed mixture is widely used for PVC dry
blending and for the dispersion of colorants,
pigments etc….
And also it is using for mixing polymer powder with
pellets.
HSM is made of impellers mounted in the bottom of
stationary vessel.
Rotational speed of impellers is upto-1000rpm.
The motors are using for rotating impellers.
18. Continue……
Two roll mills are used mostly for mixing materials
with coarse particles.
In roll mills, the size reduction takes place between
two rolls can have either a smooth or a profiled
surface.
It is reducing the particles size from 1mm˃ to ˃
0.010mm.
Rolls are rotating as counter-rotating only.
Toll roll mill are mainly using in calendering process
of PVC sheet.
20. Banbury mixers :
The Banbury mixer is a brand of internal batch mixer, named for
inventor Fernley H. Banbury.
Banbury batch mixer consists of cylindrical chamber or shell with
in which materials to be mixed are deformed by rotating blades or
rotors .
The blade motion causes the mixture to be shear between blade
and tip and shell and creating shuffling of material Cycle time 2-4
min Size 50-75 kg Producing large shapeless lumps.
Internal batch mixers such as the Banbury mixer are used for
mixing or compounding rubber and plastics. Its invention resulted in
major labor and capital savings in the tire industry.
It is also used for reinforcing fillers in a resin system.
22. Continue……
Ribbon Blender is useful for convective mixing.
In most of convective mixers, a mixing rotor within
a static housing, moving groups of particles from
one region to another.
Ribbon mixtures are available both as batch mixture
as well as continuous mixture.
The rotational speed in ribbon blender is typically in
the range of 10 to 60 rpm.
Many different ribbon geometries are available.
24. Planetary Mixture
The mixing blade is set off center and is carried on a rotating
arm. It therefore travels round the circumference of the
mixing bowl while simultaneously rotating around its own
axis.
This is therefore a double rotation similar to that of a spinning
planet rotating around the sun, hence the name.
Planetary Mixers are used for dry mixing and dough mixing.
The homogenous mixing if various lngredients of different
densities in different proportions for solid/solid, liquid/solid,
and liquld/Iiquid is achieved effectively by the use of
Planetary Mixer.
25. Continue…
Planetary Mixers for the preparation of ointment, toothpaste,
creams.
The blades each rotate on their own axes, and at the same
time on a common axis, thereby providing complete mixing in
a very short timeframe.
26. Extruders
Screw extruders are the process tool used in
compounding, injection molding, injection blow
molding, extrusion, and extrusion blow molding.
Screw extrusion technology is used as the plastic
mixing and melting device.
GF are efficiently compounded with plastic
using screw extruders.
Two Types
– Single Screw Extruder
– Twin Screw Extruder
27. A single screw extruders
It classified by the ratio of the length of the
screw to the inside diameter of the screw.
Standard extruders have 30 to 1 ratios.
The size of extruders range from small
laboratory models with 1/2 inch diameters to
large production extruders with 8" diameter
barrels.
Consist of long steel screw which rotates steel tube
called barrel
Extruder outputs range from a few pounds an
hour up to 1,000 pounds per hour.
28. Continue…
Barrel, is wrapped with heating elements
to maintain the barrel at the melt
temperature of the plastic.
The plastic is pumped from one end of the
screw to the other by rotating the screw.
The rate at which the plastic moves from
one end of the extruder to the other is
controlled by the speed of the screw.
29. Zones of Extruder & its Functions:
Feed Zone - Transport the material from hopper
to compression zone.
Compression Zone - Compacts, eliminates air gap
- Transport the material from
compression to metering zone.
Softens the material
Metering zone - Melts, Mixes, the material pressurizes
and pumps the melt.
30.
31. Twin Screw Extruder
The efficiency of the mixing action of the single screw extruder
compounder depends on maintaining higher friction between the wall
of the barrel and the material than between the materials and the
screw surface.
If the friction is higher on the screw surface, plastic will stick to the
screw surface, decompose and clog the mixing process.
In a single screw, extruder's plastic pastes, flakes. Sometimes low
bulk density materials tend to stick to the screw surface.
To overcome these restrictions, the twin screw extruder was
developed.
The twin screw extruder has two screws that are arranged side by
side and intermesh.
The intermeshing action of the two screws constantly self-wipes the
screw flights.
32. Continue
It is impossible for plastics to stick to the screw surface.The
positive pumping action of the intermeshing screws allows for
the compounding of all forms of plastic materials not possible
with a single two stage extruder.
33. Continue…
There are two type of rotating
1. Co-rotating.
2. Counter –rotating.
Co-rotating:
When two screws rotates along same side in a barrel then
the phenomena is called co-rotating
