Synthesis of Polyelectrolyte Pani Membrane

SYNTHESIS OF POLYELECTROLYTE PAni MEMBRANE BY PHASE INVERSION AND ITS CHARACTERIZATIONS

• NURUL IZZATI IZNI BT MAT YUSOFF

1. INTRODUCTION

During the last few decades, the application of membrane based separation is the leading technology as one of the alternatives used in separating and removal of organic solvents. Moreover, it holds a significant commercial impact in several areas including water and wastewater treatment, chemical, food industries, pharmaceuticals, petrochemical related industries and bioseparation areas (Javed Alam et al., 2012). However, membrane-based separation processes are comparatively new in the field of separation which makes current membranes have limitations that hinder their wide used in aggressive solvents. The situation has led many studies in order to develop this membrane-based technology.

Amongst the new generation of intrinsically conducting polymer, polyaniline (PAni) membranes have captured the intense attention of scientific community and one of the promising candidates. PAni is a polymer which poorly soluble in almost all solvents and has been widely known due to its conductive properties. Most important, it is easy to synthesize this polymer and it has an interesting doping and dedoping characteristics. However, the high yield of PAni demands several essential conditions. In order to obtain a higher quality polymer product, highly pured monomers, chemicals and solvents are needed. Besides, a strict control on polymerization conditions are needed since the small variation in the polymerization conditions might alter the nature of the product (Sadia Ameen et al., 2011).

From the previous study, there are many research have been done in order to produce a stable and useful PAni membrane in nanofiltration. Most of the researches focused on synthesize, membrane fabrication and doping/dedoping of PAni membrane. However, the study on PAni membrane can be expand more instead of those previous research. The stability and performance of PAni membrane on polyelectrolyte coating should be done to further this study. Polyelectrolyte is a macromolecular species that upon being placed in water or any other ionizing solvent dissociates into a highly charged polymeric molecule (Reza Derakhshandeh et al., 2010). One of the methods of polyelectrolyte coating is layer by layer (LBL) coating. LBL is the simplest process being used by most of the researcher. There are numerous advantages of this method compared to other methods for thin film fabrication. The unique advantages of the method are that, both organic and inorganic can be incorporated into LBL thin films besides offers easier preparation and durable (unknown, yr).

2. PROBLEM STATEMENTS

There are numerous number of membranes have been develop by researchers. However, membranes nowadays have fixed physical-chemical properties which make separation by membranes very limited to the fixed selectivity of their constituent. Therefore, new membrane materials must be explored to cope with these limiting factors. Next generation of filtration membranes must be more selective and robust which requires low chemical and energy input (Sajjad Sedaghat, 2014). These properties must be considered to meet goals in applications since current membranes often problematic in cost.

Membranes basically can be prepared from ceramic and polymeric materials. There are many studies shown that ceramic materials have several advantages over polymeric materials. As example, membrane from ceramic materials is highly stable in terms of chemical and thermal stability. Unfortunately, the market share of polymeric membranes is far greater than ceramic membranes as the polymeric materials are easier to process and less expensive (Khulbe et al., 2008). Instead of those materials, there are also membranes from inorganic materials that have been successfully applied in dehydration of tetrahydrofuran (THF). However, to produce an inorganic membrane requires a high cost rather than polymeric membrane beside their system design is more complex (Chapman et al., 2007). Therefore, membrane from polymeric material is a suitable candidate for the research since it meets the desired criteria.

PAni as a polymeric material has been widely researched due to its conductive properties. To date, although PAni has been applied to a number of applications but there are still some deficiency. For instance, PAni membranes which applied to chemically crosslinked swell in THF although it retained their structure while too much thermal crosslinking gave membranes with no fluxes in any solvents at all. Furthermore, unsupported PAni membranes shrank during the process of thermal crosslinking which causing some trouble for large scale membrane productions where certain amount of bending or curling is required (Loh et al., 2008). An alternative to thermal or chemical crosslinking would be polyelectrolyte coating to make them more stable.

3. OBJECTIVES

The objectives of this study are:

1. To produce phase inversion PAni membrane from chemical polymerization of PAni in APS solution.
2. To introduce polyelectrolyte onto the synthesized membrane.
3. To characterize the membrane morphological, physical, chemical, electrical and filtration properties.

4. LITERATURE REVIEW

5. METHODOLOGY

1. Chemicals

All chemicals and reagents will be used are analytical grade. AnalaR aniline, ammonium persulfate (APS), N-methyl-2-pyrrolidone (NMP), 4-methylpiperidine (4MP), poly(acrylic acid) (PAA) poly(allylamine hydrochloric) (PAH), hydrochloride acid (HCL) and lithium chloride (LiCl)

2. PAni synthesis by chemical polymerization

To produce an Aniline solution, 37.25 g of 0.4 mol Aniline will be added into a beaker containing 400 mL of 1.0 M HCl. The mixture is well mix. In another beaker, APS solution will be prepared by adding 91.26 g of 0.4 mol APS into 256 mL of 1.0 M HCL. To prevent the mixture from freezing at -15 ^oC, add 66.8 g and 39.68 g of LiCl into both beakers respectively. After finish the preparation of both solutions, mix them in a conical flask. The conical flask then will be put in an incubator shaker at temperature -15 ^oC and continuously shake for 48 h. During this period, a reaction occur which polymer filter cake will be produced. After 48 h, filter and wash with 1.5 L DI water to remove any left-over reactants. To deprotonate the emaraldine salt to its base form, the filter cake then is being place in a beaker contain 250 mL ammonia solution (33% w/v) in a beaker and will be mix by using incubator shaker for 12 h at room temperature. Next, the filter cake will be filter and will be wash with 1 L DI water. To remove any low weight PAni oligomers and decrease time drying, the filter cake will be wash again with 500 mL methanol before being dry under vacuum for 24 h. After drying, the dry Emeralidine Base (EB) powder will be pass through a 160 µm mesh sieve to remove remaining clusters. Then, the EB powder will be stored under argon at 4 ^oC until required (Chapman et al., 2007).

3. Membrane production by phase inversion

PAni membrane will be produce by wet phase inversion method. First of all, 4MP and NMP will be mix in a beaker to make up the solvent. Then EB powder will be add using a funnel and mix at speed 300 rpm for 12 h. After 12 h mixing, dope the solution by adding maleic acids and mix at speed 150 rpm for 12 h. The solution will turn from dark blue to dark green to indicate that acid doping is taken place. The solution is then left to stand for 4 h to remove air bubble. Next, cast the solution on a nonwoven polyester support fabric and immediately immersed in DI water at room temperature for 24 h. During the 24 h, DI water will be change once after 12 h (Loh et al., 2008).

4. Polyelectrolyte coating

Polyelectrolyte coating of PAni membrane will be done by dipping the membrane into an anionic and cationic solution. Anionic solution will be used in this research is PAA while PAH is for cationic solution. To prepare anionic solution, PAA will be dissolve in DI water and 5 M HCl will be used to adjust the pH to 3.5. For cationic solution, PAH also will be dissolve in DI water but to adjust the pH solution to 3.5, 5 M NaOH will be used. Next, PAni membrane will be immerse in PAA solution for 10 min followed by two DI water rinses for 2 and 1 min respectively. The PAni membrane then will be immerse in PAH solution for 10 min followed by two DI water rinses for 2 and 1 min respectively. These complete the first bilayer of polyelectrolyte coating. For the next layer, the steps before will be repeated again which is starting from immersing in anionic solution and then cationic solution. After finish the process, the membrane need to be wash with ammonia and let it to fully dry before being proceed with characterization (Jinhua Dai et al., 2005 & unknown, yr).

5. Characterization of PAni membrane

6. Flow chart

Stock and reagent

solutions preparation

PAni synthesis by chemical polymerization

Characterization of EB powder by using GPC

Membrane production and casting

Polyelectrolyte coating

Characterization

Analysis

6. GANTT CHART

7. MILESTONE

Table 7.1 : Milestone

8. EXPECTED OUTCOMES/COMMERCIALIZATIONS

9. REFERENCES

Chapman, P., Loh, X.X., Livingston, A.G., Li, K., & Oliveira, T.A.C. (2007). Polyaniline

Membranes for The Dehydration of Tetrahydrofuran by Pervaporation. Journal of Membrane Science, 309 (2008), pp. 102-111.

Loh, X.X., Sairam, M., Bismarck, A., Steinke, J.H.G., Livingston, A.G., & Li, K. (2008)

Crosslinked Integrally Skinned Asymmetric Polyaniline Membranes for Use in Organic Solvents. Journal of Membrane Science, 326 (2009), pp. 635-642.