*3.2.3 Proton conductivity, methanol permeability, and selectivity of chitosan-nanosilica membrane with silane addition*

Proton conductivity of chitosan-nanosilica silane addition membrane can be seen in **Figure 4(a)**. The membrane proton conductivity is measured by using EIS to determine impedance of the membrane. **Figure 4(a)** explains that the proton conductivity increases in line with silane addition to a certain point then decreases. Chitosan-nanosilica with the addition of silane membrane nanosilica:silane variation 1:0.50 has the highest proton conductivity value than another variation of silane addition. It shows that silane composition addition is optimal for interacting with amine group on the chitosan matrix and form a polysiloxane network on nanosilica addition of silane. Excess silane addition (>50%) on the variation nanosilica:silane 1:1, 1:1.50 and 1:2 can cause proton conductivity value become low. This is because the hydrogen bonding that occurs between the silane with chitosan matrix and polysiloxane network is already saturated, so the ability to transport proton facilitate is less than optimal. **Figure 4(a)** shows the highest proton conductivity values obtained at chitosan-nanosilica addition of silane membrane variations nanosilica:silane 1:0.50 is 7.89 x 10−4 S/cm. This fact is consistent with the previous fact obtained in the water uptake test. The membrane with the highest

**187**

conductivity.

*permeability, (c) membrane selectivity.*

**Figure 4.**

bigger than 1 × 10−5 S/cm [35].

aggregates which cause mass transport (methanol) [37].

*Characterization of Chitosan Membrane Modified with Silane-Coupled Nanosilica for Polymer…*

water uptake has the highest proton conductivity as well. This is true as water in a proton exchange medium, so the higher the water uptake the higher the proton

*The relationship of silane addition in chitosan-nanosilica membrane to their (a) proton conductivity, (b) methanol* 

The proton conductivity value obtained by chitosan-nanosilica membrane by silane addition of nanosilica:silane 1:0.5 is 7.89 x 10−4 S/cm. This value is smaller than the Nafion 117 proton conductivity membrane which is 5.66 x 10−2 S/cm [8]. According to [35], this is related to the Nafion 117 structure. There are many Fluor atoms (F) which have large electronegativity value so that Nafion 117 can be more easily forming hydrogen bonds with water, so it is more easily to absorb water that is needed as a proton transport medium, so the conductivity of the Nafion 117 proton is greater. Although the proton conductivity value of chitosannanosilica membrane of nanosilica:silane = 1:0.5 in the study is smaller than Nafion 117, but this membrane can still be used as PEM for applications in DMFC. The membrane can still deliver protons even though they are slow. The proton conductivity value obtained is above the minimum requirement, which is must be

**Figure 4(b)** shows that membrane methanol permeability is affected by silane addition. Methanol permeability occurs due to methanol transport in aggregate pores that is further dependent on the pores volume in the membrane. There are two types of pore in the polymer membrane: network pores or ionic clusters and aggregate pores. Proton transport occurs through two types of pore, while the mass transport (methanol, water, and gas) occurs only through the porous aggregate [36]. Network pores is a small cavity between the polymer chains that is responsible for proton conduction. Aggregate pores are large cavities that cover polymer

*DOI: http://dx.doi.org/10.5772/intechopen.95580*

*Characterization of Chitosan Membrane Modified with Silane-Coupled Nanosilica for Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95580*

#### **Figure 4.**

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

is a decrease in the silane variation of 1:1 to 1:2 (excess) that is 8.7, 5.4, and 4.1 MPa respectively. This happens because excess silane causes an imbalance in the interaction between silane and nanosilica. The effect of silane addition to nanosilica gives various levels of elongation at break on the membrane that are 6.07, 13.67, 6.1, 4.1, 7.88, and 2.18% respectively. Membrane elasticity is determined by the magnitude of modulus young. The fact is that silane addition can increase modulus young value of nanosilica:silane variation membrane 1:0.25 to 1:1, and decrease significantly in

*The relationship of silane addition in chitosan-nanosilica membrane to their mechanical properties.*

A membrane is said to be good and has the best mechanical performance seen from the high tensile strength values and low elongation at break values [22, 34], so modulus young values which expected is high. In this research chitosan-nanosilica membrane with nanosilica:silane is 1:0.5 reach optimum mechanical properties. Silane addition to nanosilica increases physical interaction between nanosilica and chitosan. Hydrogen bonds formed between hydroxyl groups in polysiloxane with amine and ether groups in chitosan as described in **Figure 1**. Strong interaction between nanosilica and chitosan causes high physical and mechanical strength

Proton conductivity of chitosan-nanosilica silane addition membrane can be seen in **Figure 4(a)**. The membrane proton conductivity is measured by using EIS to determine impedance of the membrane. **Figure 4(a)** explains that the proton conductivity increases in line with silane addition to a certain point then decreases. Chitosan-nanosilica with the addition of silane membrane nanosilica:silane variation 1:0.50 has the highest proton conductivity value than another variation of silane addition. It shows that silane composition addition is optimal for interacting with amine group on the chitosan matrix and form a polysiloxane network on nanosilica addition of silane. Excess silane addition (>50%) on the variation nanosilica:silane 1:1, 1:1.50 and 1:2 can cause proton conductivity value become low. This is because the hydrogen bonding that occurs between the silane with chitosan matrix and polysiloxane network is already saturated, so the ability to transport proton facilitate is less than optimal. **Figure 4(a)** shows the highest proton conductivity values obtained at chitosan-nanosilica addition of silane membrane variations nanosilica:silane 1:0.50 is 7.89 x 10−4 S/cm. This fact is consistent with the previous fact obtained in the water uptake test. The membrane with the highest

1:1.5, then increase again in silane addition variation 1:2.

including tensile strength, elongation and modulus young.

*3.2.3 Proton conductivity, methanol permeability, and selectivity of chitosan-nanosilica membrane with silane addition*

**186**

**Figure 3.**

*The relationship of silane addition in chitosan-nanosilica membrane to their (a) proton conductivity, (b) methanol permeability, (c) membrane selectivity.*

water uptake has the highest proton conductivity as well. This is true as water in a proton exchange medium, so the higher the water uptake the higher the proton conductivity.

The proton conductivity value obtained by chitosan-nanosilica membrane by silane addition of nanosilica:silane 1:0.5 is 7.89 x 10−4 S/cm. This value is smaller than the Nafion 117 proton conductivity membrane which is 5.66 x 10−2 S/cm [8]. According to [35], this is related to the Nafion 117 structure. There are many Fluor atoms (F) which have large electronegativity value so that Nafion 117 can be more easily forming hydrogen bonds with water, so it is more easily to absorb water that is needed as a proton transport medium, so the conductivity of the Nafion 117 proton is greater. Although the proton conductivity value of chitosannanosilica membrane of nanosilica:silane = 1:0.5 in the study is smaller than Nafion 117, but this membrane can still be used as PEM for applications in DMFC. The membrane can still deliver protons even though they are slow. The proton conductivity value obtained is above the minimum requirement, which is must be bigger than 1 × 10−5 S/cm [35].

**Figure 4(b)** shows that membrane methanol permeability is affected by silane addition. Methanol permeability occurs due to methanol transport in aggregate pores that is further dependent on the pores volume in the membrane. There are two types of pore in the polymer membrane: network pores or ionic clusters and aggregate pores. Proton transport occurs through two types of pore, while the mass transport (methanol, water, and gas) occurs only through the porous aggregate [36]. Network pores is a small cavity between the polymer chains that is responsible for proton conduction. Aggregate pores are large cavities that cover polymer aggregates which cause mass transport (methanol) [37].

The decrease in methanol membrane permeability as shown in **Figure 4(b)** from the composition of nanosilica:silane 1:0 to 1:1 is caused by properties adhesion and interface interaction (hydrogen bonds) of chitosan-nanosilica with the silane addition is stronger [15] than chitosan-nanosilica membranes without silane addition (1:0). According to [29], the decrease in hydrophilicity in this case is due to the silane nature which is able to balance the hydrophilic and hydrophobic nature of an organic or inorganic material. The addition of nanosilica which has been carried out by silane can close pores on the chitosan membrane through strong interactions between amines in chitosan with polysiloxane in nanosilica so that most of the methanol does not pass through the membrane.

Chitosan-nanosilica membrane with silane addition in nanosilica:silane variation 1:1.5 and 1:2 there is an increase in methanol permeability value that is 5.8887 × 10−7 cm2 /s and 5.9341 × 10−7 cm2 /s respectively. This is due to the composition of silane addition cannot interact perfectly with chitosan matrix so the adhesion force decreases and the chitosan matrix interaction with silane nanosilica addition is weak. The highest methanol permeability value was obtained on the chitosan-nanosilica membrane without silane is equal to 6.5229 × 10−7 cm2 /s. The addition of silane chitosan nanosilica membrane that has good performance in methanol permeability value followed by high proton conductivity value is the chitosan-nanosilica membrane addition of nanosilica:silane 1:0.5 variation which is 5.8434 × 10−7 cm2 /s. This is also supported by the proton conductivity value obtained by 7.8988 × 10−4 S/cm. Chitosan-nanosilica membrane with silane addition nanosilica variation: silane 1:0.5 has the lowest methanol permeability value when compared to Nafion 117 membrane that is 1.01 × 10−6 S/cm [16]. For DMFC applications, it is expected that membranes with small methanol permeability. Small permeability prevents leaks and avoids methanol cross over.

**Figure 4(c)** explains that the highest membrane selectivity is obtained on the chitosan-nanosilica membrane with silane addition in nanosilica:silane variation 1:0.5. Membrane selectivity is a parameter that connects proton conductivity with methanol permeability. For DMFC applications, the desired membrane is a membrane with high conductivity and low methanol permeability, so the determination of membrane selectivity uses Eq. (7) [8]. Through this membrane selectivity determination, the facts show that the chitosan-nanosilica membrane with 1:0.5 silane addition is the membrane with the best performance as PEM for DMFC applications. Membrane selectivity aims to evaluate membrane performance capability based on high proton conductivity values and low methanol permeability values. The membrane selectivity is influenced by modulus young value as mechanical properties of the membrane. It can be explained that the higher membrane selectivity, the higher modulus young so that the membrane physical properties are in harmony with the membrane chemical properties as polymer electrolyte membrane (PEM). The results of membrane synthesis in this study are supported by high modulus young values, high proton conductivity values and low methanol permeability.

When compared to Nafion 117, chitosan-nanosilica membrane with silane addition in nanosilica:silane variation 1:0.5 has lower membrane selectivity value. It shows that chitosan-nanosilica membrane with silane nanosilica variation: silane 1:0.5 addition has the ability under Nafion 117, but this membrane can still be used as PEM for DMFC applications, it means that the membrane can deliver protons even though it runs slowly but it can reduce the entry of methanol fuel through the membrane supported by methanol permeability obtained that is smaller than Nafion 117 membrane.

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**Figure 5.**

*Characterization of Chitosan Membrane Modified with Silane-Coupled Nanosilica for Polymer…*

**Figure 5** shows FT-IR spectra of nanosilica and chitosan-nanosilica membrane with silane addition. The FT-IR spectrum of chitosan on the membrane is characterized by the presence of ─CN groups (amide groups) in all variations of the chitosan-nanosilica membrane with the addition of silane at the wavenumbers 1627.92 cm−1 and 1635.64 cm−1 [38]. The wavenumbers shift in the FTIR spectrum of chitosan indicates an interaction between the amide group in the chitosan matrix and the polysiloxane network in the nanosilica addition of silane through hydrogen bonds. The absorption around the wave number 1060–1084 cm−1 indicates the ─CO group (ketone group) [38]. The ─CO group (ketone group) which is a characteristic of the polysaccharide appears at the wave number 1080.14 cm−1. The -CH bonds in -NHCOCH3 appear at wave numbers 2854.65 cm−1 and 1404.18 cm−1 [39, 40]. This

In FT-IR spectrum of nanoslilca in **Figure 5**, the main functional group analysis results is the emergence of Si–O–Si groups on nanosilica and chitosannanosilica membrane with silane addition. Absorption around wave numbers 1100–1200 cm−1 and 460–480 cm−1 indicates the presence of the Si–O–Si group (siloxane group) [39]. This absorption band (Si-O-Si groups) did not appear in the chitosan membrane spectra but appear in chitosan-nanosilica membrane. This sharp increase in absorption band intensity indicates the presence of stretching vibrations of Si–O–Si (siloxane group) which is getting stronger. According to [24], it indicates that some of the siloxane groups (Si–O–Si) of polysiloxane network in silane addition and nanosilica have interacted strongly with chitosan matrix. Absorption band at wave number 894.97 cm−1 indicates the presence of the Si–OH groups (silanol groups) [38]. The Si–OH groups (silanol groups) show hydrogen bonds existence between silanol groups in nanosilica-silane with amide groups in the chitosan matrix. It is also seen in **Figure 5** that there are absorption bands around wave number 3400–3500 cm−1 which indicate the –OH (hydroxyl)

*FT-IR spectra of chitosan-nanosilica membranes with variation of silane addition. (a) Chitosan; (b)Nanosilica;* 

*(c) chitosan membrane with nanosilica:silane = 1:0; (d) 1:0,25; (e) 1:0,05; (f) 1:1; (g) 1:1,5; (h) 1:2.*

N–H bonds, indicating that the chitosan could be

*3.2.4 Functional groups analysis of chitosan-nanosilica membrane with silane* 

*DOI: http://dx.doi.org/10.5772/intechopen.95580*

*addition*

absorption in assigned to the –+

interacting with another groups by coulombic forces [40].

*Characterization of Chitosan Membrane Modified with Silane-Coupled Nanosilica for Polymer… DOI: http://dx.doi.org/10.5772/intechopen.95580*
