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Extraction of Polystyrene micro
beads from EPS with OptimumSolvent Recovery
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Purpose Of the Project
EPS- Expanded Polystyrene popularly known as
Thermocol
It consists mostly of voids filled with gas and are
considered as Use-Throw materials
Polystyrene micro beads are of more economic value
This project is to obtain a more economic valued
beads from Thermocol waste with an optimumsolvent recovery
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Stages Of Project
1) Extraction Of Micro beads
Dissolution of EPS in a solvent Phase
Preparation Of Emulsion
Separation Of Micro beads from Solvent Phase
2)Solvent Recovery Process
Need for most economical way with optimum recovery
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Solvent Selection
D-Limonene is preferred as it is obtained from a renewable
source (citrus oil) and is environment friendly solvent
Initial stage of experiments are carried with toluene as solvent
as it is cheaper than D-limonene and it readily dissolves poly
styrene
These results can be extended to d-limonene as solvent
Solubility parameter values should be studied to select a
suitable solvent for a dissolving polymer
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Solubility Parameter
Dissolution of an amorphous polymer in a solvent is governedby the free energy of mixing
Gm = Hm - TSmwhere Gm is the Gibbs free energy change on mixing, Hm is the
enthalpy change on mixing, T is the absolute temperature, and Smis the entropy change on mixing.
The heat of mixing must be smaller than the entropic term forpolymersolvent miscibility
Gm < 0 The cohesive energy, CED; of a material is the increase in the
internal energy per mole of the material if all of theintermolecular forces are eliminated
Cohesive energy density = CED = (Hvap - RT)/V
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Hildebrand Solubility parameters
Solubility Parameter is given by square root of CED
d = (CED)1/2= ((Hvap - RT)/V)1/2
Hmix = Vmix[(E1/V1)1/2-(E2/V2)
1/2]*(12)
Hmix = Vmix[d1 - d2 ]*(12)12 are mole fractions of solute and solvent
Vmix is Volume of mixture
E1 is energy of vaporization of specie 1
V1 is molar volume of specie 1
Therefore, [d1 - d2] should be small for dissolution.
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Solubility Parameter Values
Solubility parameters for some common
polymers
Solubility parameters for some common
Solvents
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Experiment
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Prepared samples of different wt% of EPS in toluene (1%,
2% and 4% of EPS in toluene). Solvents used are water, methanol, 1:1mixture of water and
methanol.
Take EPS- Toluene sample of known concentration in a test
tube which forms the oil phase. To this sample (oil phase) add the solvent, drop by drop until
the inversion phase occurs.
Now shake the test tube to ensure proper and uniform
dispersion and observe the formation of beads and observetheir behaviour (i.e. stability, coagulation etc.).
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Observations
For water as solvent, no beads are formed (irrespective of
concentration of EPS-toluene sample), but the mixture sample
is retained at the top surface of water. Shaking resulted in
dispersion of EPS sample into polystyrene beads which
immediately settled at the surface of water.
For EPS-Toluene in methanol we got thread like structured
fibers after immediate drying
For EPS-toluene in 1:1 methanol/water emulsion, milky
solution is formed, and slowly beads coalesce to form threadlike structures.
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Effect Of Concentration
These results are similar for 1%,2%,5% EPS in toluene
So as far as concentration change is concerned no significant
change is observed
Also for all these concentrations, there was immediateseparation of phases (oil phase at the top and water at the
bottom)
So in all the cases of experiments above, we stirred rigorously
& within no time poured onto flat plate and dried it
So we need to obtain stability of emulsion to prevent the
separation of phases
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Density effects
When tested with increased concentration of EPS in
toluene(20%), the results ( Polystyrene Spheres Formation)
were better with water than the remaining two solvents.
This could be because of difference of densities of oil phasewith that of solvent phase
Increasing to 20% w/w of EPS (in toluene) will make the
density of oil phase approximate to that of water
Hence the possible dispersion occurs instead of immediatephase separation
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Take away
Hence concentration of EPS in Toluene should
be optimal considering the density and
viscosity effects
If possible a third component should be added
to oil phase which doesnt increase viscosity
but increases density
Also for stability of emulsion, addition of
emulsifier is must
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What are Emulsifiers
When there is a problem of making an
emulsion, emulsifying agent can be used to
stabilize the emulsion
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Selection Of Emulsifier- The HLB System
There are hundreds of emulsifiers which are available in
industry
But only the appropriate emulsifiers can serve the
purpose efficiently The selection of emulsifier can be done on the basis of
HLB system
HLB stands for Hydrophile-Lipophile Balance
All emulsifiers consist of a molecule that combines both
hydrophilic and lipophilic groups
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HLB System
Hydrophile-Lipophile Balance is the balance ofthe size and strength of the hydrophilic (water-loving or polar) and the lipophilic (oil loving ornon-polar) groups of the emulsifier.
The HLB System enables you to assign a number
to the ingredient or combination of ingredientsyou want to emulsify, and then to choose anemulsifier or blend of emulsifiers having thissame number
An emulsifier that is lipophilic in character is
assigned a low HLB number (below 9.0), and onethat is hydrophilic is assigned a high HLB number(above 11.0). Those in the range of 9-11 areintermediate.
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Available emulsifiers in lab:
SLS
Tween 80 (HLB Value = 15)
Span 80 (HLB Value = 4.3)
The emulsifier we
selected is Tween 80
Because the HLB
number matches with
that of ingredient
Toluene
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Taken Ingredients:
Solvent: Water and Methanol
Oil phase: Eps in Toluene of different concentrations
Emulsifier: 4:1 blend of Tween 80 and Span 80
HLB Value of Blend of two emulsifiers:
HLB Value of E1 = HLB1
HLB Value of E2 = HLB2 Volume fraction of E1 = x1 Volume fraction of E2 = x2 HLB Value of Blend = x1 * HLB1 + x2 * HLB2
For Tween 80 : Span 80 = 4:1
HLB Value of Blend = 0.8*15 + 0.2*4.3 = 12.86
Result
No convincing change
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Contd..
Emulsifier: Sodium Lauryl Sulphate
Result:
Addition of SLS to water phase:
Mixed SLS in water and then added the oil phase drop by drop.
After stirring and drying, we got fibrous structured polystyrene
Addition of SLS to Oil phase:
Taken SLS in oil phase and added water drop by drop to the oilphase
We were able to get relatively good results in this case
But after the stirring is done, in about 5-10 min and when theemulsion is poured in a flat plate we obtain small beads separatedbut after some time they coalesce
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