effect of silica on the properties of cellulose acetatepolyethylene glycol membranes for reverse...

8/10/2019 Effect of Silica on the Properties of Cellulose Acetatepolyethylene Glycol Membranes for Reverse Osmosis

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EFFECT OF SILICA ON THE PROPERTIES OFCELLULOSE ACETATE/POLYETHYLENE GLYCOL

MEMBRANES FOR REVERSE OSMOSIS

By: I MADE PENDI ADI MERTA

(2311100033)

DEFFRY DANIUS DWI PUTRA

(2311100088)


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2.1 MATERIALS

MATERIAL SUPPLIED BY

Cellulose acetate (CA, Mw

30,000 and acetyl content39%), BDH laboratories supplies,

Poole, England.acetone

Polyethylene glycol-600 (PEG)

Silica (SiO2)

Sigma Aldrich


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2.2 Preparation of doped solutions

1. 10 g of CA was dissolved in 80 mL of acetone withconstant stirring at 80 C for 2 h.

2. 10 g of PEG was added with regular stirring at 80 Cfor 6 h.

3. The viscous and clear solution was obtained, whichwas termed as a blended doped Solution, CA/PEG-1[26].

4. The different ratios of CA/PEG (12/8, 14/6 and 16/4g/g) were used to prepare three additional dopedsolutions, labeled as CA/PEG-2, CA/PEG-3 andCA/PEG-4 respectively.

5. The casting solutions were allowed to cool down toroom temperature (25 C) and were kept for 24 h in asealed flaskto remove micro bubbles formed in thesolution.


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2.3 Membrane physical

Characterization

1. The doped solution was spread slowly on glass plate bymaintaining uniform thickness with the help of micrometer

adjustable filmapplicator (Ref: 1117/300 Sheen instruments).

2. The temperature of casted membranes was lowered

immediately to 0 C for 15 min to induce (TIPS). The TIPScauses the formation of dense and asymmetric structure.

3. It was followed by precipitation under controlled evaporation

by increasing temperature up to 60 C [27].

4. The skinned membranes, thus formed [28] were carefully

removed from the glass plates by using a sharp knife. The

thickness of the resulting membranes was measured and

was found in the range of 50200 microns.


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2.4 Modification of doped solutions

1. Silica (15%, w/v) was dispersed in alkaline solution (10 mL)before adding to the CA/PEG-4 blended dope solution with

constant stirring for 2 h at 80 C.

2. The membranes (CPS-1CPS-5) were casted and dried

following the same procedure as mentioned in Section 2.3


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3. Characterization

3.1. Membrane performance3.1.1. Experimental set up of RO rig

3.1.2. Water content

3.1.3. Permeate flux(J)

3.1.4. Salt rejection3.2. Membrane permeability

3.3. Contact angle measurement

3.4. Fourier Transform infrared spectroscopy (FTIR)

3.5. Thermal analysis

3.6. Mechanical stability

3.7. Scanning electron microscopy (SEM)


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4. Results and discussions

4.1. Membrane performance

Table 1. CA/PEG-1 membrane showed a maximum fluxof 0.87 L/h m2 while it

exhibited minimum salt rejection capacity of52%. CA/PEG-4 membrane had

81.5% salt rejection and its flux was0.35 L/h m2.


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Results and discussions It was observed that with the increased content of cellulose

acetate, the water content, flux and membrane permeabilitywas decreased while the salt rejection capacity was increased

remarkably.

PEG is hydrophilic in nature and acts as pore former [38].

CA/PEG-1 membrane, with maximum quantity of PEG, showedincrease in water flux, but at the same time salt rejection was

compromised. This might be attributed to the formation of

macro voids [39] on membrane which allowed the passage of

salt along with water. Moreover, the diffusion rate of water was

accelerated by the presence of PEG due to its hydrophilic

nature. PEG increased the tendency of pore formation and as

a consequence fluxwas increased.


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Result

Similarly, the flux of all modified membranes also increased with theincrease in silica content. CPS-5 membrane has highest fluxof 2.46 L/h

m2

The salt rejection increased from 81.5% to 92% for CPS-4 membrane as

a result of incorporation of silica particles [42]


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Fig. 3 shows tthe flux

increased remarkably with the

increase of SiO2 content.

The increase in permeationfluxwas due to the increase in

surface hydrophilicity which

was rendered by SiO2

particles.

4.1.1. Analysis of membrane fouling during permeation


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4.2. Contact angle

In general, a smaller contactangle corresponds to a more

hydrophilic material

Fig. 4 represents digital

image of a liquid droplet on adry surface of all membranes

in which the contact angle

() is measured according to

the sessile drop method


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4.3. Contact angle

Fig. 5 that there isdecrease in contact angle

by increasing silica particle

concentration.

These resultsdemonstrated that silica

particle can improve

hydrophilicity of membrane

The less hydrophilicsurface shows larger

contact angle with the

surface and vice versa.


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4.4. Mechanical stability

Fig. 10. It was noteworthythat the elongation-at-break, tensile stress andYoung's modulus initiallyincreased with the

addition of SiO2 particlesand reached at peakwhen the SiO2 particleconcentration was 4%(w/v) and then declinedas the SiO2 particleconcentration was furtherincreased. Yan et al.


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4.5. SEM analysis

Fig. 12 (af) represents theimages of modifiedmembranes with differentsilica loadings.

The top surface morphology

is shown on Fig. 12(a). Itwas observed that micro-size silica particle (0.51m) were distributed in themembrane.

The interaction of silica

particles with polymerdisrupts the mobility ofpolymeric chains resulting inthe formation ofmacroscopic defects [29].But as concentration


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CONCLUSION

The modifiedmembranes resulted into an improved trend in thesalt rejection and permeation properties. CPS-4 had 92% saltrejection which provided almost 11% increase in salt rejectioncapacity compared with the control membrane (81.5%).

The mechanical stability of the modifiedmembranes, increasedfrom 1 to 4% (w/v) of silica loading. Further increase in SiO2

particles in the casting solution resulted in the decrease of tensilestrength and elongation at break.

The SEM images revealed incorporation of silica particles withinthe asymmetric composite membrane, that improved hydrophilicityof the composite membrane also enhanced fouling resistance.

This study showed a critical need for optimizing the silica particle

loading, as overloading of silica may not be advantageous for ROperformance and has negative impact on the RO membraneproperties.

effect of silica on the properties of cellulose acetatepolyethylene glycol membranes for reverse...

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