Novel sulfonated poly (vinyl alcohol)/carboxy methyl cellulose/acrylamide-based hybrid polyelectrolyte membranes

Atia Mahmoud; Alaa Fahmy; Abdelrahman Naser; Mohamed Abu Saied

doi:10.1038/s41598-022-26489-0

. 2022 Dec 20;12:22017. doi: 10.1038/s41598-022-26489-0

Novel sulfonated poly (vinyl alcohol)/carboxy methyl cellulose/acrylamide-based hybrid polyelectrolyte membranes

Atia Mahmoud ¹, Alaa Fahmy ^1,^✉, Abdelrahman Naser ¹, Mohamed Abu Saied ^2,^✉

PMCID: PMC9767934 PMID: 36539477

Abstract

Novel polyelectrolytic hybrid membranes are prepared by blending carboxy methyl cellulose (CMC)-polyvinyl alcohol (PVA)-acrylamide (AA). Succinic acid and chlorosulfonic acid (CSA) are employed as crosslinkers and modifiers, respectively. Additionally, carboxylated carbon nanotube (CCNT) and sulfonated activated carbon (SAC) as fillers are used to attain appropriate chemical and mechanical stability for use as polyelectrolyte membranes (PEM). CMC, PVA, and AA are mixed and treated with CSA, CCNT, and SAC in different concentrations. First, CMC/PVA/AA solution is modified using CSA to produce a sulfonated polymeric matrix. Second, a different amount of CCNT or SAC was added as a filler to enhance the ion exchange capacity (IEC), ionic conductivity, and chemical stability. Third, the solution is cast as polyelectrolytic membranes. Chemical interactions between CMC, PVA, AA and other membrane components were confirmed using various characterization techniques such as Raman scattering spectroscopy and Fourier Transform Infrared (FTIR). Furthermore, mechanical strength, methanol uptake, gel fraction, ion exchange capacity (IEC), proton conductivity (PC), chemical and thermal stability were determined as functions of varied membrane modification components. Results reveal that the increase of CSA, CCNT and SAC is leading to increase the IEC values reaching 1.54 mmol/g for (CMC/PVA-4% CSA), 1.74 mmol/g for (CMC/PVA-4%CSA-2%CCNT) and 2.31 mmol/g for (CMC/PVA-4% CSA-2% SAC) comparing to 0.11 mmol/g for non-modified CMC/PVA/AA membrane. Sequentially, the proton conductivity value is changed from 1 × 10^–3 S/cm in non-modified CMC/PVA/AA membrane to 0.082 S/cm for (CMC/PVA-4% CSA), 0.0984 S/cm for (CMC/PVA-4%CSA-2%CCNT) and 0.1050 S/cm for (CMC/PVA-4% CSA-2% SAC). Such results enhance the potential feasibility of modified CMC/PVA/AA hybrid as polyelectrolytic membranes.

Subject terms: Chemistry, Energy science and technology, Materials science, Nanoscience and technology

Introduction

Currently, direct methanol fuel cells (DMFC) represent an inventive alternative for current power sources among the other fuel cell (FCs) types. DMFC had significant importance in the recent few years because of its low operating temperature, high-power density, high energy conversion efficiency and become less expensive fuel¹. Rather, DMFC is considered one of the important tools that take a part in turning to carbon–neutral operations².

The electrolytic membrane is the operating heart of the cell, it is responsible for conducting protons (H⁺) from the anode part to the cathode. Some of the important characteristics of the polyelectrolytic membrane are good conductors for protons (H⁺), electrically insulators, very low methanol cross-over chemically stable, and withstand during cell operating conditions³.

However, a major restriction of DMFC is the dropout of methanol through the electrolytic membrane and the production of highly reactive polymeric electrolytes with optimum water management. In addition, fouling is one of the problems that may be affected the polymeric membranes⁴ by decreasing their efficiency by blocking the proton-binding sites. Particularly, the fouling that happened by fuel impurities or other biological and chemical interactions⁵. The fouled polymeric membrane must be subject to recovery process or replaced, this would increase the cost-operating efficiency. Rana et al.⁶ found that, the addition of silver salts to polymeric membrane leading to an improvement of anti-fouling effect.

Nowadays Nafion^® is widely used as an electrolyte in polymer electrolyte membrane fuel cell (PEMFC) but is limited by methanol crossover and water management problems^7,8.

The polyelectrolytic membrane can be produced using different types of polymers after the modification process to enhance the desired character and improves their ionic conductivity. Modification can be done through blending and/or chemical treatment⁹. Introducing inorganic materials such as HAP¹⁰, CNT¹¹ or GO¹² with polyelectrolytic membranes leads to improving protonic conductivity and mechanical stability in addition to enhancing barrier effect which is the important property of preventing fuel cross-over¹³.

For more effectiveness, functionalization of the inorganic blend is the key factor to producing a filler with high surface active (interfacial area), good compatibility and prevented sedimentation or agglomeration during the polyelectrolytic membrane production process¹⁴. CNTs are one of the most attractive materials as inorganic membrane fillers owing to their high aspect ratio and surface area with low density. It has a limited dispersion in the polymeric membrane owing to its low functional groups. The polymeric blend can be improved by the addition of CNTs or modified CNTs through the functionalization of CNTs with –COOH, –OH, or –SO₃H groups^15,16. Not only mechanical or thermal stability improved but also ionic conductivity growing as a result of micro-channels provided by polymer blend around CNTs. Rambabu et al.¹⁷ discussed modifying CNTs by introducing –SO₃H groups using polystyrene sulfuric acid to prepare the SPEEK nanocomposite membrane. The protonic conductivity and mechanical stability were improved particularly with increasing sulfonation process rather than overall performance¹³.

Another attractive filler is the activated carbon (AC) molecular sheet. The advantage of AC is attributed to its excellent thermal¹², mechanical¹⁸ and transport properties. However, AC is difficult to exfoliate in a polymer matrix due to its high cohesive force between them. Thus, AC is functionalized with other groups such as (–SO₃H) to impart specific features and interactions¹⁹.

Rahul et al.²⁰ stated that, the salt incorporation in polymeric membrane produces relatively higher proton conductivity (~ 10^–5 to ~ 10^–3 S/cm), flexible geometry and electrochemical stability. The benefit of protonic conducting components is their advanced dynamics for the proton association. The protonic conducting blends as (NH₄⁺) are good proton conducting sources in the development of some types of polymeric membranes²¹. Leena et al.²² provided that NH₄SCN can increase the (H⁺) transferred across cell parts through the polymeric membrane. several studies explained that²³ the transportation based on polymeric ammonium complexes system is mainly due to NH₃–H⁺.

PVA-ZnO-based polyelectrolyte DMFC membrane was prepared by Diyan Ul Imaan²⁴ through impregnating zinc oxide nanoparticles in a cross-linked PVA matrix. The obtained membrane possesses high water uptake (105%), IEC (0.78 meq/g) and low ionic conductivity (3.9 mS/cm). In the same way, Tripathi and Shahi¹⁶ prepared N-p-carboxy benzyl chitosan-silica-PVA proton exchange membrane for DMFC by sol–gel method. The obtained membrane exhibits low ionic conductivity as a result of weak proton conducting carboxylic groups. The conductivity and stability improved through the introduction of high charge density (–SO₃H) groups. Asnag et al.²⁵ successfully prepared PVA-CMC based nanocomposite film via a solution casting technique for electrical and optical properties. Polyacrylamide/Nafion electrolyte membrane⁷ shows an increase in water and methanol uptake with raising the amount of Polyacrylamide in the membrane. In contrast, the IEC shows decreasing by inserting Polyacrylamide into Nafion^®.

Therefore, in this work, the research was conducted to find an alternative membrane for DMFC based on sulfonated CMC and PVA. Due to the non-toxicity, cheapness, biodegradability, and good matrix forming of CMC and PVA, they are selected for this study. Acrylamide (AA) blend is added to improve the ionic conductivity and facilitate proton transportation across the membrane through the formation of positively charged ammonium (NH₄⁺) ions^7,26. The blending of CMC with PVA and AA followed by sulfonation using chlorosulfonic acid (CSA) with the addition of carboxylated carbon nanotube (CCNT) or sulfonated activated carbon (SAC) as fillers to improve the blocking methanol crossover and enhance the IEC and proton transportation property of the membrane with enhanced electrochemical performance.

Modification of CMC/PVA/AA based membranes through introducing of CCNT and SAC are providing reinforcement and will give a winding path for methanol cross-over through the membrane in addition maintain water swell-ability which may be overcome the methanol-crossover and water management fuel cell problems²⁷. Furthermore, the introducing of CCNT and SAC can improve the mechanical and thermal stability in addition to its involvement to enhance ionic conductivity by providing a large interfacial area and ionic channels.

Materials and methods

Materials

CMC (average Mw = 90,000 g/mol, DS = 0.7) was obtained from Acros Organics, Fisher Scientific, UK. PVA (typically average Mw = 124,000 g/mol, 95–96.5% hydrolyzed) was obtained from Fisher Scientific, UK. Chlorosulfonic acid (M = 116.52 g/mol, purity 99%, density 1.753 g/mL at 25 °C) was purchased from Merck, Germany. Multi-wall CCNT (density 2.1 g/cm³, diameter 10–20 nm, length 10–30 nm, –COOH content 2 wt%) was achieved from XFNANO, Jiangsu, China. Activated carbon (Mw = 12.01 g/mol, sulfur content 0.15%, acid solubility 2.0%) bought from Uni-CHEM chemical reagents, Korea.

Preparation of CMC/PVA/AA based hybrid polyelectrolytic membranes

Specified solutions of 10 wt% CMC, 10 wt% PVA, 10 wt% AA, and 2 wt% succinic acid solutions were prepared by dissolving the pre-weighed amount of each in de-ionized water at room temperature with stirring for 2, 8, 2 h, and 30 min, respectively till the solutions become homogenous. All solutions of CMC, PVA, AA, and succinic acid were stored at room temperature. The suggested reaction that takes place between membrane components was illustrated in (Scheme 1).

Scheme 1 — Illustrate the reaction route for CMC, PVA, and AA in addition (H⁺) hopping mechanism in the membrane.

Sulfonated activated carbon (SAC) was prepared according to the method that was reported by Bermejo et al.²⁸ with modification²⁹ by mixing 10 g pure activated carbon with 100 mL of sulfuric acid, the mixture was stirred at 160 °C for 8 h. Then the mixture was washed several times with deionized water and allowed to dry at 60 °C for 6 h. Finally, SAC was packed and stored at room temperate for the next use.

The membrane was prepared by mixing 3 mL of CMC, 4 mL of PVA, 2 mL of AA, and 1 mL of succinic acid solutions then the mixture was vigorously stirred at 40 °C for 4 h. The previous steps were repeated to prepare 13 samples for use in the next steps. First, the various amounts (v/v %) of chlorosulfonic acid (CSA) (1, 2, 3, and 4%) were step-wise added to 4 samples during the stirring process, where the temperature was raised to 65 °C for 4 h. Second, 4% of CSA was added slowly to 4 samples under stirring conditions and temperature within 65 °C for 4 h. Then various amounts (w/v %) of CCNT (0.5, 1, 1.5, and 2%) were added under the previous condition for extra 2 h. Third, 4% of CSA was added slowly to 4 samples under stirring conditions and temperature within 65 °C for 4 h, then various amounts (w/v %) of SAC (0.5, 1, 1.5, and 2%) were added under the previous condition for extra 2 h. The remine sample is still without any additives. All mixtures were cast onto a polypropylene sheet. The solvent was removed by evaporation at room temperature for 12 h and then the casted membranes were allowed to dry at 70 °C for 6 h. Finally, the dried membranes were subjected to different characterization methods.

Characterization

Spectral analysis

The chemical bonding and functional groups within the CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes were evaluated using (Shimadzu FTIR-8400 S, Japan) with a resolution of 4 cm⁻¹ and a wavenumber range of 400–4000 cm⁻¹¹. Additionally, a laser Raman scattering spectrometer (SENTERRA-Bruker, Germany) equipped with a Leica microscope was also employed to investigate the chemical bonding and possible interactions inside the prepared polymeric membranes³⁰.

Morphological features and microstructure

Morphological features and microstructure of CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes were investigated using scanning electron microscopic (SEM), (JEOL JSM-6360LA, Japan). SEM was in operation at an acceleration voltage of 15 kV. Magnification power varied from 500 to 5000^31,32.

Mechanical properties

Tensile strength and the elongation at break of CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes have been conducted at ambient temperature using a universal testing machine (Shimadzu UTM, Japan) and the test was repeated three times for each membrane. Tensile and elongation measurements were carried out with cross-head movement at a constant speed of 3 mm/min for specimens of 30 × 10 mm³².

Methanol uptake

Methanol uptake of CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes are usually defined in weight percent with respect to the weight of the dried membrane. To determine the swelling ability specimens of these membranes were obtained by cutting specified membrane samples into 3 × 3 cm pieces, then the specimens were dried for 6 h at 90 °C, the dried sample weight is assigned as W_dry. The dried samples were soaked in methanol for 12 h (equilibrium swelling) at room temperature to determine the methanol uptake ratio. Afterward, swelled samples were leached from methanol and weighted again (W_wet). The swelling degree was determined by Eq. (1)^32,33

S w e l l i n g d e g r e e (%) = \frac{w_{wet} {- w}_{dry}}{w_{dry}} \times 100

Gel fraction

The membranes were dried at room temperature to avoid any surface shrinking for 12 h and weighed (W₁), then immersed in distilled water for another 24 h, up to an equilibrium swelling weight, to remove the leachable or soluble components. The polyelectrolytic membranes are then dried and weighed again (W₂). The gel fraction (GF %) was carried out according to the method reported by Fahmy et al.³⁴ and calculated by Eq. (2)

G e l F r a c t i o n (G F %) = \frac{w_{2}}{w_{1}} \times 100

Ion exchange capacity

Ion exchange capacity (IEC) represents the total of active sites or functional groups responsible for ion exchange in CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes. In most cases, the IEC is determined using a standard acid–base titration technique. Weighed samples were immersed in 20 cm³ of a 2 M (NaCl) solution for 12 h at 25 °C. The solution was then titrated with a known concentration of NaOH. IEC (in mmol/g) is determined by using Eq. (3)^8,35:

I E C (mmol / g) = \frac{N (m m o l / {cm}^{3}) \times V ({cm}^{3})}{W (g m)}

where N, V, and W are the concentration of the NaOH solution, the volume of the NaOH solution, and the weight of the sample, respectively.

Proton conductivity

The proton conductivity of the membranes was analyzed using impedance spectroscopy (Solartron 1260 gain phase analyzer, interfaced to a Solartron 1480 multistate). The test was conducted at a temperature of 60 °C. The Protonic conductivity (σ) of the membranes was calculated using Eq. (4) from impedance data³⁶

σ (s / cm) = \frac{L}{RWD}

where, (L) is the distance between electrodes, (R) is the membrane resistance, (D and W) are the thickness and width of the membranes, respectively.

Chemical stability analysis

The obtained CMC/PVA/AA-based membranes were investigated for oxidation stability through Fenton test³⁷. The dried membranes specimen (1 × 4 cm²) was soaked in (2 ppm FeSO₄ in 3% H₂O₂) for 1 h at ambient temperature. The weight in grams before and after immersing was determined as W_o and W_f, respectively. The oxidation stability was calculated through Eq. (5):

O x i d a t i o n s t a b i l i t y = \frac{w_{\circ} {- w}_{f}}{w_{f}} \times 100

Fuel cell performance

The performance of the cell membrane was employed using an 890B commercial fuel cell system. The electrocatalysts Pt Ru/C (2 Pt: 1 Ru ratio) were coated into a different side of the CMC/PVA/AA-4%CSA-2%SAC membrane. The diffusion layer was assembled using two carbon paper sheets. The fuel cell unit was operated at 2 mL/min of 2 M methanol at the anode and 250 mL/min of oxygen at the cathode³⁷.

Results and discussion

Investigation of the chemical composition of the membranes

FT-IR spectra

Figure 1 evidence FT-IR spectra of CMC/PVA/AA membrane and modified CMC/PVA/AA-based hybrid polyelectrolytic membrane using CSA, SAC and CCNT. The segments of IR peaks are reported in Table 1. The IR spectra of pristine CMC/PVA/AA membrane (Fig. 1-a) exhibit general peaks of –NH₂, –OH, and C–H functional groups at 3411, 3302 and 2917 cm⁻¹, respectively that found in polymeric blend backbone^38–40.

Table 1.

The main FT-IR transmitted wavelength assignment of (A) virginal CMC/PVA/AA membrane.

Positions				Assignment
A	B	C	D	Assignment
3411	3443	3438	3436	–NH₂ of acrylamide
3302	3224	3234	3239	O–H bending and H-bonding
2917	2922	2920	2921	C–H and symmetric CH₂ stretching of the polymeric backbone
1663	1701	1677	1680	C–O and C=O of CCNT
1414	1423	1410	1410	COO– of SU and C–N of AA
–	1282	1298	1297	O=S=O⁴⁵
	1161	1184	1183	C–C bond
1034	1033	1041	1037	C–O of pyranose ring of CMC
836	867	885	882	O–H bending
–	–	797	796	C–H deformation
–	620	628	627	SO₃^–2 group
–	572	576	573	N–C=O bond

Open in a new tab

(B) CMC/PVA/AA-(4%) CSA. (C) CMC/PVA/AA-(4%) CSA-(2%) CCNT. (D) CMC/PVA/AA-(4%) CSA-(2%) SAC.

Typical symmetrical stretching of –COO– bands of SU was observed at 1414 cm⁻¹ (Fig. 1-a) which demonstrates the formation of crosslinked network and formation of ester covalent bond between CCNT and CMC/PVA polymeric blend (Fig. 1D)⁴¹. Moreover, the spectrum of –OH and –NH₂ exhibits intensity decreases (Fig. 1B–D) which is assigned to the reaction of these groups with others during the sulfonation process or network formation⁴². The absorbance peaks at 1282, 1298 and 1297 cm⁻¹ (Fig. 1B–D) resulting from CSA addition confirming the introduction of –SO₃H groups to the CMC/PVA/AA polymeric matrix⁴³.

Further confirmation, the stretching vibrational absorbed peaks at 620, 628 and 627 cm⁻¹ also confirmed the presence of SO₃^–2 within the polymeric matrix⁴³. Furthermore, the FT-IR spectrum of modified CMC/PVA/AA (Fig. 1B–D) possesses new bands at 572, 576 and 573 cm⁻¹ which are assigned to carbonyl amide (–N–C=O) that confirm the covalent bond between nitrogen from AA and carboxylic group of CCNT and SU. These results verify the presence of –SO₃H, –OH, –COO⁻, –NH, and –NCO⁻ groups within CMC/PVA/AA polymeric matrix^41,44.

Raman spectroscopy

To find out more about the membrane microstructure, the nondestructive Raman spectroscopy technique was used as shown in Fig. 2. The absorbed peak at 605 cm⁻¹ that appeared in all Raman curves except the curve (A) is related to the C–S covalent bond and this band increases in intensity (Fig. 2I-A) with the increase of CSA molar ratio resulting in increases of –SO₃H groups⁴⁶. The other strong vibrational peak that appeared around 900 cm⁻¹ was attributed to the C–C of the polymeric chain. Other signals that have emerged at 1099 cm⁻¹ due to the asymmetric vibration of C–O–C bonds confirm the cross-linking reactions⁴⁷. In addition, a strong valance band at 1634 cm⁻¹ owing to the C=O group and the intensity of this band decreases with the functionalization process of CMCC/PVA/AA with CSA, CCNT and SAC⁴⁸.

(I) Raman spectra of (A) CMC/PVA/AA, (B) CMC/PVA/AA-(1%) CSA, (C) CMC/PVA/AA-(2%) CSA, (D) CMC/PVA/AA-(3%) CSA, (E) CMC/PVA/AA-(4%) CSA. (II) Raman spectra of (E) CMC/PVA/AA-(4%) CSA, (F) CMC/PVA/AA-(4%) CSA-(0.5%) CCNT. (G) CMC/PVA/AA-(4%) CSA-(1%) CCNT. (H) CMC/PVA/AA-(4%) CSA-(1.5%) CCNT. (J) CMC/PVA/AA-(4%) CSA-(2%) CCNT. (**III**) Raman spectra of (E) CMC/PVA/AA-(4%) CSA. (K) CMC/PVA/AA-(4%) CSA-(0.5%) SAC. (L) CMC/PVA/AA-(4%) CSA-(1%) SAC. (M) CMC/PVA/AA-(4%) CSA-(1.5%) SAC. (N) CMC/PVA/AA-(4%) CSA-(2%) SAC.

It is worth recalling that all spectra of Fig. 2II,III are quite similar with the same pattern, as a result of the structure of CCNT and SAC does not undergo major damage during the preparation and modification process⁴⁹.

Topography of the membranes

Surface and cross-section SEM images of the membranes were presented in Fig. 3. As a result membrane has smooth and glossy-like surface morphology and good blend compatibility without any phase separation or cracking passed across the membrane as a result of using SU as a cross-linker agreeing well with previous works⁵⁰. A part of the membrane exhibits an erratic surface as a result of some side reaction between the CMC/PVA/AA polymeric blend. As shown in Fig. 3B, no observed defects in the membrane surface and cross-section during the sulfonation process. The membrane possesses some irregularity as a result of sliding of polymeric chains and large CMC/PVA/AA matrix deformation during the production process⁴⁹ and strong intramolecular bonding between polymeric ionic groups as –SO₃H, OH, and NH⁵⁰. This irregularity also extended to CMC/PVA/AA-(4.0%)-(2.0%) CCNT (Fig. 3C) and CMC/PVA/AA-(4.0%)-(2.0%) SAC (Fig. 3D) membranes. This is an advantage property that can protect CCNT and SAC structures from great damages that can decrease their reinforcement action in the membrane⁴⁹.

SEM micrographs of surface and cross-section of CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes. (A) pristine CMC/PVA/AA membrane. (B) CMC/PVA/AA-(4%) CSA. (C) CMC/PVA/AA-(4%) CSA-(2%) CCNT. (D) CMC/PVA/AA-(4%) CSA-(2%) SAC.

Consequently, this gained property improves the protonic conductivity of membranes through forming of micro-channels around CCNT and SAC blends for water and hydrogen ions¹³. It is worth mentioning that the membranes exhibit good CCNT and SAC dispersibility as a result of the pre-functionalization of the blend before being used in a membrane preparation. Some of the changes in membrane surface and gathered of the blend are due to the creation amendment in matrix molecular arrangement after CCNT and SAC addition that also improves crosslinking behaviour⁴⁹.

Elemental analysis

The elemental composition of CMC/PVA/AA and modified CMC/PVA/AA based hybrid polyelectrolytic membranes were determined through a Carbon, hydrogen, nitrogen, and sulfur (CHNS) analyzer and the obtained results were presented in (Table 2. With the different concentrations of CSA in CMC/PVA/AA (Table 2I), the sulfur content is increased with increasing the molar ratio of CAS in the membrane suggesting an increase of –SO₃H groups attached to the polymeric backbone. Adversely, carbon and hydrogen content exhibit slight loss with the CSA addition. The obtained behaviour confirmed the modification of CMC/PVA/AA by sulfonation which takes place without any undesired degradation or fragmentation which is also assured by the C/N and C/H ratio^51,52. The amount of carbon is increased with increasing the amount of CCNT in CMC/PVA/AA membrane and the hydrogen percent shows a slight change (Table 2II). This can be explained through the reaction of –COOH group of CCNT with –OH group of PVA to form an ester bond through the elimination of H₂O molecule causing the decrease of hydrogen ratios.

Table 2.

Elemental composition of CMC/PVA/AA-based hybrid polyelectrolytic membranes with different concentrations of CSA, CCNT and SAC.

	Sample	Elemental Content %
	Sample	N	C	H	S	C/N	C/H
I	0% CSA	2.2	43.46	7.005	0.104	19.712	6.204
	1% CSA	2.82	38.50	6.394	3.025	13.646	6.021
	2% CSA	2.84	33.19	6.258	5.816	11.696	5.303
	3% CSA	2.38	29.94	5.936	7.577	12.576	5.044
	4% CSA	1.89	25.02	6.192	9.010	13.216	4.041
II	4% CSA-0.5% CCNT	2.32	26.29	5.464	8.715	11.331	4.811
	4% CSA-1% CCNT	2.27	29.05	5.752	8.717	12.798	5.050
	4% CSA-1.5% CCNT	2.24	25.36	5.629	9.587	11.321	4.506
	4% CSA-2.0% CCNT	2.09	31.43	5.532	7.685	15.065	5.682
III	4% CSA-0.5% SAC	2.61	26.16	5.441	9.307	10.022	4.807
	4% CSA-1.0% SAC	2.7	27.86	5.648	9.61	10.318	4.9328
	4% CSA-1.5% SAC	2.54	28.1	5.704	9.682	11.063	4.926
	4% CSA-2.0% SAC	2.31	29.53	5.456	9.944	12.688	5.412

Open in a new tab

The amount of sulfur (that related to –SO₃H groups) content was not greatly affected during the addition of CCNT indicating good stability of –SO₃H groups. The influence of SAC addition to CMC/PVA/AA-(4%) CSA has been presented in (Table 2III). It was noted that an increase in the amount of carbon and sulfur percent with the addition of SAC resulting more –SO₃H groups attached to the membrane that will improve the ionic conductivity. Therefore, the slight variations in C/H and C/N% ratios give a positive snapshot of no major change in the membrane structure and agree well with previous work⁵³.