**4. Conclusions**

*Chitin and Chitosan - Physicochemical Properties and Industrial Applications*

**Temperature range on an oblique curve (°C)**

*The area of change (stages) in mass percentage reduction on TGA thermogram of membrane samples.*

Nanosilica:silane = 1:0 38.92 371.98 Nanosilica:silane 1 = 1:0.5 44.15 452.94 Nanosilica:silane 1 = 1:2.0 40.74 387.96

**Mass residue (%) at 450°C**

Nanosilica:silane = 1:0 35–120 120–220 220–430 12.72 9.96 36.02 41.58 Nanosilica:silane 1 = 1:0.5 40–150 150–330 330–450 13.72 34.06 7.79 44.09 Nanosilica:silane 1 = 1:2.0 35–140 140–335 335–450 14.35 36.16 8.78 37.93

**Mass reduction on an oblique curve (%)**

**Temperature (°C) when sample is degraded and remaining 44%**

**(%) at III <sup>I</sup> II III <sup>I</sup> II III**

**Mass residue** 

**Chitosan-nanosilica Membranes**

**Chitosan-nanosilica Membranes**

**Table 2.**

**Table 3.**

not significant indicates that the water content in samples are not significantly different. Mass reduction in chitosan-nanosilica membrane samples with silane coupling agent is higher when compared to sample without silane. This shows that

The second weight-loss in **Table 2** appearing at around 150–335°C indicates the decomposition of chitosan polymer chain in hybrid membrane [10]. This chain decomposition is related to the loss of side groups as acetyl groups (as shown in **Figure 1**) in chitosan because the acetyl groups has a weak phi bond so it breaks easily first. The temperature range and the percentage of sample weight-loss is significantly different. The temperature range and the percentage of mass reduction in two samples with silane as coupling agent shows a large range. The second stage temperature range in the sample with silane shows a widened temperature region. This is due to the presence of the silane as coupling agent interact with the acetyl groups thus preventing the release of the acetyl groups. As a result, a large number

The third weight-loss stage is observed near 335–450°C is due to unstable parts of the polymeric matrix whereas it is occurring due to complete decomposition of the backbone of polymeric matrix [48] and residual organic groups [8]. The temperature range and the percentage of sample weight-loss in this stage is significantly different. The temperature range in third stage in two samples with silane as coupling agent shows a large range while the percentage of mass reduction is a small range. The incorporation of silane has improved the interaction of nanosilica and chitosan by introducing more functional groups with hydrogen bond formation as **Figure 1** and FTIR results. Hydrogen bond between hydroxyl groups (–OH) in silane-coupled nanosilica interacts with the amine group (–NH2) ether group (C–O–C) of chitosan that could form a good interface interaction [32]. This all makes it difficult for chitosan chain to degrade so that the degradation temperature range is greater and the remaining mass is less. In addition, chitosan membrane samples with silane-coupled nanosilica have higher component heterogeneity than chitosan-nanosilica without silane. High heterogeneity of polymer components causing a longer range of degradation and decomposition temperature. Therefore, it can be understood that **Table 3** shows that nanosilica:silane 1 = 1:0.5 have the

chitosan-nanosilica with silane is more hygroscopic.

*Chitosan-nanosilica:silane membrane thermal degradation.*

of these groups release at higher temperatures.

**194**

The influence of silane as coupling agent on the chitosan-nanosilica membrane causes homogeneity and prevents agglomeration between nanosilica and chitosan. The higher silane compositions added, it decrease the water uptake, increases proton conductivity, decreases methanol permeability, and increases selectivity of the membrane. The best membrane performance is on the variation of nanosilica: silane 1:0.50 which has water uptake of 37.52%, tensile strength of 11.8 MPa, proton conductivity of 7.8988 x 10−4 S/cm at 25°C, methanol permeability of 5.8434 x 10−7 cm2 /s, and membrane selectivity of 13.5174 x 102 S s/cm3 . This membrane has high thermal stability of 452.94°C with mass residue 44%. Based on the results of membrane selectivity analysis, the best and most suitable chitosan membrane for electrolyte polymer applications is the chitosan membrane with the addition of nanosilica:silane = 1:0.5; 1:0.25; 1:1; 1:0; 1:1.5 and 1:2.0 (w/w). This is based on the order of membrane selectivity values from the highest to the lowest. The results of FT-IR, SEM and AFM analysis on membranes show that optimum silane addition provides the best interaction between chitosan matrix and silane-coupled nanosilica so that they have higher thermal resistance. When compared to Nafion 117 membrane, this membrane has lower proton conductivity value, but the advantages are it more environmentally friendly, has lower methanol permeability, higher temperatures stability and of course more economical in terms of cost. Further efforts are needed to increase the proton conductivity of this chitosan membrane for DMFC applications.
