COMPOUNDINGCOMPOUNDING

DefinitionDefinition

The Process by which ingredients are intimately mixed together into as nearly a homogeneous mass is known as compounding.

CRITERIA FOR CRITERIA FOR COMPOUNDINGCOMPOUNDING

• Selection of polymer.Selection of polymer.• Selection of Selection of compoundingcompounding

ingredients.ingredients.

SELECTION OF POLYMERSELECTION OF POLYMER

The performance requirement The performance requirement of the intended end use.of the intended end use.

The economic factors.The economic factors. The availability of suitable and The availability of suitable and

processing equipment.processing equipment.

Selection of compounding Selection of compounding ingredientsingredients

REQUIREMENT:-REQUIREMENT:-•Their degree of effectiveness. Their degree of effectiveness. •The efficiency of processing The efficiency of processing ingredients.ingredients.•The condition of processing The condition of processing •The requirement of the end useThe requirement of the end use•The environmental exposure to The environmental exposure to which the product will be which the product will be subjected.subjected.

FACTORS THAT INFLUENCE FACTORS THAT INFLUENCE COMPOUNDINGCOMPOUNDING

• Physical form & melting characteristics of Physical form & melting characteristics of the polymer considered .the polymer considered .•Degree of dispersion or solubilisation of the Degree of dispersion or solubilisation of the additive in the final mixture.additive in the final mixture.•Physical form of the plastics raw material or Physical form of the plastics raw material or compound to be produced.compound to be produced.

METHODS OF INCOPORATING METHODS OF INCOPORATING ADDITIVESADDITIVES

• Added to the monomer ie before or during Added to the monomer ie before or during the production of the polymer.the production of the polymer.•Added during the working up of the Added during the working up of the polymer.polymer.•Added in a separate manufacturing step.Added in a separate manufacturing step.•Incorporated directly before or during Incorporated directly before or during molding of a plastic to a semifinished molding of a plastic to a semifinished product or finished article.product or finished article.

Addition of additives before or Addition of additives before or during a polymerisation processduring a polymerisation process

•Additives should be inert.Additives should be inert.•Used by the producer of the base resins.Used by the producer of the base resins.

Examples-Examples-

Stabilization of impact resistant PS and pre Stabilization of impact resistant PS and pre stabilasation of PVC produced by suspention stabilasation of PVC produced by suspention polymerisation.(in both cases antioxidants polymerisation.(in both cases antioxidants are added to the monomers)are added to the monomers)

Addition of additives during the Addition of additives during the working up of the polymerworking up of the polymer

•Used by polymer manufacturer.Used by polymer manufacturer.•Additives used must satisfy specific Additives used must satisfy specific requirements determined by the process requirements determined by the process such as emulsifiability , solubility in certain such as emulsifiability , solubility in certain solvents , low volatility or stability to solvents , low volatility or stability to hydrolysis.hydrolysis.•Polymer must be in dispersed form.Polymer must be in dispersed form.

Example- In modification of styrene Example- In modification of styrene polymer,such as ABS.polymer,such as ABS.

Methods of CompoundingMethods of Compounding

There are four basic methodsThere are four basic methods– Dry mixing, Dry mixing, – Batch mixing,Batch mixing,– Continuous mixing,Continuous mixing,– Compounding by Screw extruder. Compounding by Screw extruder.

The selection of the method determined by The selection of the method determined by –Condition of the material,Condition of the material,–The volume of end product required, The volume of end product required, –The sensitivity of the material to breakdown during The sensitivity of the material to breakdown during shear. shear.

Dry MixingDry Mixing Dry mixing the plastic with its additives in a Dry mixing the plastic with its additives in a

500 pound capacity paddle mixer. 500 pound capacity paddle mixer. The paddles are turned at 30 to 90 seconds or The paddles are turned at 30 to 90 seconds or

until the mix is homogeneous.until the mix is homogeneous. If the mix is too long, it will develop lumps of If the mix is too long, it will develop lumps of

glass, while too short a mix will produce an glass, while too short a mix will produce an unequal dispersion of glass fibres. unequal dispersion of glass fibres.

Dry mixer are preferred for powders, plastic Dry mixer are preferred for powders, plastic pellets with fibers and also for mixing pellets with fibers and also for mixing plasticizers with PVC.plasticizers with PVC.

Types of Dry mixersTypes of Dry mixers

There are four types of dry mixers:There are four types of dry mixers:

– High speed impellers,High speed impellers,

– Ribbon mixers,Ribbon mixers,

– Paddle mixers and Paddle mixers and – Drum tumblersDrum tumblers..

Dry mixerDry mixer

The mixer consists of an enclosed container with The mixer consists of an enclosed container with a higher speed impeller mounted at the bottom. a higher speed impeller mounted at the bottom.

An impeller is similar to the rotating blades of a An impeller is similar to the rotating blades of a helicopter. helicopter.

The impeller is capable of 80 to 3600 revolutions The impeller is capable of 80 to 3600 revolutions per minute (RPM). Mixing is fast with materials per minute (RPM). Mixing is fast with materials blended within 2-4 minute cycles.blended within 2-4 minute cycles.

Heat generated during the mixing process must Heat generated during the mixing process must be drawn off through a cooling jacket to retard be drawn off through a cooling jacket to retard decomposition of the material and to block the decomposition of the material and to block the development of lumps.development of lumps.

drum tumblerdrum tumbler

Drum tumblers are popular with molding Drum tumblers are popular with molding operation for the dispersion of powdered operation for the dispersion of powdered colorants with the plastic pellets. colorants with the plastic pellets.

In a drum tumbler, plastic pellets (with In a drum tumbler, plastic pellets (with approximately 1 to 2% colorant) are placed in a approximately 1 to 2% colorant) are placed in a 250 gallon drum and tumbled dry for 250 gallon drum and tumbled dry for approximately 30 minutes. approximately 30 minutes.

Drum tumblers are used when the additives Drum tumblers are used when the additives disperse easily throughout the mixture without disperse easily throughout the mixture without tending to lump or cluster together.tending to lump or cluster together.  

High Speed MixtureHigh Speed Mixture

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High speed mixture is widely used for PVC High speed mixture is widely used for PVC dry blending and for the dispersion of dry blending and for the dispersion of colorants, pigments etc….colorants, pigments etc….

And also it is using for mixing polymer And also it is using for mixing polymer powder with pellets.powder with pellets.

HSM is made of impellers mounted in the HSM is made of impellers mounted in the bottom of stationary vessel.bottom of stationary vessel.

Rotational speed of impellers is upto-Rotational speed of impellers is upto-1000rpm.1000rpm.

The motors are using for rotating impellers.The motors are using for rotating impellers.

Two Roll MillTwo Roll Mill

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Two roll mills are used mostly for mixing Two roll mills are used mostly for mixing materials with coarse particles.materials with coarse particles.

In roll mills, the size reduction takes place In roll mills, the size reduction takes place between two rolls can have either a smooth between two rolls can have either a smooth or a profiled surface.or a profiled surface.

It is reducing the particles size from 1mm˃ to It is reducing the particles size from 1mm˃ to ˃ 0.010mm. ˃ 0.010mm.

Rolls are rotating as counter-rotating only.Rolls are rotating as counter-rotating only. Toll roll mill are mainly using in calendering Toll roll mill are mainly using in calendering

process of PVC sheet.process of PVC sheet.

Banbury mixers :

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.

Ribbon BlenderRibbon Blender

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Ribbon Blender is useful for convective mixing.Ribbon Blender is useful for convective mixing. In most of convective mixers, a mixing rotor In most of convective mixers, a mixing rotor

within a static housing, moving groups of within a static housing, moving groups of particles from one region to another.particles from one region to another.

Ribbon mixtures are available both as batch Ribbon mixtures are available both as batch mixture as well as continuous mixture.mixture as well as continuous mixture.

The rotational speed in ribbon blender is The rotational speed in ribbon blender is typically in the range of 10 to 60 rpm.typically in the range of 10 to 60 rpm.

Many different ribbon geometries are Many different ribbon geometries are available.available.

Planetary MixturePlanetary Mixture

Planetary MixturePlanetary Mixture

The mixing blade is set off center and is carried on a The mixing blade is set off center and is carried on a rotating arm. It therefore travels round the rotating arm. It therefore travels round the circumference of the mixing bowl while circumference of the mixing bowl while simultaneously rotating around its own axis.simultaneously rotating around its own axis.

This is therefore a double rotation similar to that of a This is therefore a double rotation similar to that of a spinning planet rotating around the sun, hence the spinning planet rotating around the sun, hence the name.name.

Planetary Mixers are used for dry mixing and dough Planetary Mixers are used for dry mixing and dough mixing.mixing.

The homogenous mixing if various lngredients of The homogenous mixing if various lngredients of different densities in different proportions for different densities in different proportions for solid/solid, liquid/solid, and liquld/Iiquid is achieved solid/solid, liquid/solid, and liquld/Iiquid is achieved effectively by the use of Planetary Mixer.effectively by the use of Planetary Mixer.

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Planetary Mixers for the preparation of ointment, Planetary Mixers for the preparation of ointment, toothpaste, creams.toothpaste, creams.

The blades each rotate on their own axes, and at the The blades each rotate on their own axes, and at the same time on a common axis, thereby providing same time on a common axis, thereby providing complete mixing in a very short timeframe.complete mixing in a very short timeframe.

ExtrudersExtruders

Screw extruders are the process tool used in Screw extruders are the process tool used in compounding, injection molding, injection blow compounding, injection molding, injection blow molding, extrusion, and extrusion blow molding. molding, extrusion, and extrusion blow molding.

Screw extrusion technology is used as the plastic Screw extrusion technology is used as the plastic mixing and melting device.mixing and melting device.

GF are efficiently compounded with plastic GF are efficiently compounded with plastic using screw extruders.using screw extruders.

Two TypesTwo Types– Single Screw Extruder Single Screw Extruder – Twin Screw Extruder Twin Screw Extruder

A single screw A single screw extrudersextruders It classified by the ratio of the length of the It classified by the ratio of the length of the

screw to the inside diameter of the screw. screw to the inside diameter of the screw. Standard extruders have 30 to 1 ratios. Standard extruders have 30 to 1 ratios.

The size of extruders range from small laboratory The size of extruders range from small laboratory models with 1/2 inch diameters to large models with 1/2 inch diameters to large production extruders with 8" diameter barrels. production extruders with 8" diameter barrels.

Consist of long steel screw which rotates Consist of long steel screw which rotates steel tube called barrelsteel tube called barrel

Extruder outputs range from a few pounds an Extruder outputs range from a few pounds an hour up to 1,000 pounds per hour.hour up to 1,000 pounds per hour.

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Barrel, is wrapped with heating elements Barrel, is wrapped with heating elements to maintain the barrel at the melt to maintain the barrel at the melt temperature of the plastictemperature of the plastic..

The plastic is pumped from one end of the The plastic is pumped from one end of the screw to the other by rotating the screw. screw to the other by rotating the screw.

The rate at which the plastic moves from The rate at which the plastic moves from one end of the extruder to the other is one end of the extruder to the other is controlled by the speed of the screw.controlled by the speed of the screw.

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.

Twin Screw ExtruderTwin Screw Extruder

The efficiency of the mixing action of the single screw The efficiency of the mixing action of the single screw extruder compounder depends on maintaining higher friction extruder compounder depends on maintaining higher friction between the wall of the barrel and the material than between between the wall of the barrel and the material than between the materials and the screw surface.the materials and the screw surface.

If the friction is higher on the screw surface, plastic will stick If the friction is higher on the screw surface, plastic will stick to the screw surface, decompose and clog the mixing process. to the screw surface, decompose and clog the mixing process.

In a single screw, extruder's plastic pastes, flakes. Sometimes In a single screw, extruder's plastic pastes, flakes. Sometimes low bulk density materials tend to stick to the screw surface. low bulk density materials tend to stick to the screw surface.

To overcome these restrictions, the twin screw extruder was To overcome these restrictions, the twin screw extruder was developed. developed.

The twin screw extruder has two screws that are arranged The twin screw extruder has two screws that are arranged side by side and intermesh. side by side and intermesh.

The intermeshing action of the two screws constantly self-The intermeshing action of the two screws constantly self-wipes the screw flights. wipes the screw flights.

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It is impossible for plastics to stick to the screw It is impossible for plastics to stick to the screw surface.The positive pumping action of the surface.The positive pumping action of the intermeshing screws allows for the compounding of all intermeshing screws allows for the compounding of all forms of plastic materials not possible with a single forms of plastic materials not possible with a single two stage extruder.two stage extruder.

Continue…Continue…There are two type of rotatingThere are two type of rotating

1.1. Co-rotating.Co-rotating.

2.2. Counter –rotatingCounter –rotating..

Co-rotating:Co-rotating: When two screws rotates along same side in a barrel

then the phenomena is called co-rotating

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Counter-Rotating:Counter-Rotating: When the two screws rotates the different side in a

barrel, then the phenomena is called counter-rotating.

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