POLYSULFONE COMPOSITE MEMBRANE CONTAINING ACID–BASE COMPLEX PARTICLES OF CARBOXYMETHYL CELLULOSE BENZOATE–BENZYL CHITOSAN AS THE PROTON EXCHANGE MEMBRANE

• Main Author: Maria Gunita, Anggi
• Format: Theses
• Language: Indonesia
• Subjects: Kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/34864
• Institution: Institut Teknologi Bandung

The depletion of fossil fuels and global warming issues have triggered many studies in the field of environmentally friendly renewable energies. Among of them are the hydrogen and methanol fuel that can be synthesized and released harmless gas emissions. This kind of fuels uses fuel cell, an electrochemical cell that converts chemical energy to electrical energy. One type of fuels cell is the Direct Methanol Fuel Cell (DMFC) which is widely used for portable device application. The heart of the DMFC is the a polyelectrolyte membrane which has the function to deliver protons from anode to cathode of the cell. The good quality commercial membrane, Nafion®, is still fairly expensive in the market, due to high production cost. Inspite of the high price of Nafion®, it is still shown a drawback, high methanol crossover in DMFC application. Therefore, further researches are required to synthesize polyelectrolite membranes with a good quality but low production cost. In the previous research, acid base complex polyelectrolyte membrane containing nanoparticles carboxymethyl cellulose (CMC)-chitosan embedded on polysufone (PSf) matrix was successfully synthesized. This membrane shows the conductivity in the same order of magnitude as the comercial membrane Nafion® as the state art for DMFC application. Unfortunatelly, this membrane shows the decline in conductivity when the composition of nanoparticles increases. This is suspected due to the low dispersion of nanoparticles in the hydrophobic polysulfone matrix. Therefore, in this research, the CMC-chitosan particles were modified through benzoylation of CMC and benzylation of chitosan in order to increase the hydrophobicity the particles. The particle synthesis is carried out in several steps : synthesis of carboxymethyl cellulose (CMC) from cotton cellulose, synthesis of carboxymethyl cellulose benzoate (CMCB) from CMC, synthesis of benzyl chitosan (BC) from chitosan, and synthesis of acid-base complex particles CMCB–BC with the formation of the electrostatic interaction among acid-base groups. All of the particles were characterized using FTIR (Fourier Transform Infra Red) for functional groups identification and X-ray diffraction for the crystalinity determination. The membranes with acid-base complex particles (CMCB–BC) then synthesized by dispersing the particles into PSf/DMAc solution at various composition of 1,45; 3,03; 4,75; 6,64; 10,36; dan 15,33 (w/w)% , which then cast into films using phase invertion method, and named as A to F membranes, respectively. The membrane morphologies were then characterized using SEM (Scanning Electron Microscopy). Special treatment was carried to characterize the hydrophilicity and the proton conductivity of the membrane. This characterization was conducted by comparing the refluxed membranes which aims to activate the particles in the membrane, and the untreated membranes. Characterization of hydrophylicity of the membrane was carried out by measuring the contact angle and water uptake, while the proton conductivity was delivered by determinating of the Ion Exchange Capacity (IEC) and the impedance of the membrane. Other properties such as mechanical strength and methanol affinity were also observed by tensile test method and methanol uptake, respectively. The SEM images shows the aggregation of particles on hydrophilic cluster growing in line with the addition of particle composition. As the results, the membrane hydrophilicity was increased with the increase of hydrophilic particles concentration. On the order hand, the conductivity of protons shows declines from membrane A to D and then increases significantly on the membrane E and F. The refluxed membranes show the same tendencies in terms of hydrophilicity and conductivity but with higher value. Meanwhile, the mechanical strength of membrane in the dry state is found to decreased with the decrease of PSf concentration. The optimum membrane among these variation is the membrane A with 1,45% particles concentration. The membrane have the following properties : water uptake of 7,45%; IEC of 0,3351 meq g-1; proton conductivity of 5,99 x 10-2 S/cm; and tensile strength of 27,93 MPa properties. Here we suggest that membrane A can be applied for proton conducting membranes in DMFC based on the properties mention above. In addition, the membrane was synthesize using a source that avalaible abundantly in Indonesia, therefore the production cost is possible to be reduce than of Nafion®.