Effect of Cellulose and Titanium Dioxide on the properties of Chitosan film

Chitosan film has attracted attention due to its advantages; it is easily modified due to numerous active sites. However, the use of chitosan film alone has limited applications. Therefore, it is necessary to modify chitosan film. In this study, chitosan was modified through addition of titanium dioxide and cellulose, extracted from grass (imperata cylindrica). Chitosan-cellulose-titanium dioxide composite film was prepared with different compositions of chitosan, cellulose and titanium dioxide. The result of the tensile test showed the addition of cellulose and titanium oxide improved tensile strength of the chitosan film. FTIR and XRD analysis confirmed the formation of chitosan-cellulose-TiO2 composite film.


Introduction
Several industries have begun developing composite materials, especially environmentally friendly composites. A composite is a combination of two or more macroscopically different materials with better properties than the initial materials. Composites consist of a matrix as a binding element and filler as reinforcement. The addition of fillers to the composite matrix aims to improve its mechanical properties, such as tensile strength. In this way, its properties can be designed for certain applications.
The adsorbent properties of chitosan composite are of primary concern. Used alone as an adsorbent, chitosan is easily damaged due to its weak mechanical properties. Some researchers have modified chitosan to form composites with other materials [1]. In this study, chitosan was modified by addition of cellulose and titanium dioxide (TiO2) particles. Cellulose is a natural polymer formed by linear chains of glucose units with β-(1,4)-glycosidic bonds [2]. Cellulose was chosen as a filler in the chitosan matrix because its chemical structure is similar to chitosan. The similarity in chemical structure contributes to strong adhesion force and a compact material. TiO2 particles were also added to the chitosan matrix in order to improve chitosan's ability to remove dye from water, as TiO2 can decompose dye into harmless molecules.
This study investigates the effect of cellulose and TiO2 addition on chitosan film, especially its mechanical properties. Chitosan-cellulose-TiO2 composite films were prepared with different compositions and then characterized by tensile test, FTIR, and XRD.

Materials
Chitosan (deacetylation degree: 75-85%) was purchased from Tokyo Chemical Industry Co., Ltd. Japan. Cellulose was isolated from grass following the same procedure described in our previous work [3].

Methods
Preparation of chitosan-cellulose-TiO2 composite film was conducted by dissolving chitosan with acetic acid (20 mL, 2%) for 2 hours at room temperature. This was followed by the addition of cellulose extracted from grass and colloidal TiO2 particles (dispersed in distilled water) at varied concentrations, as shown in Table 1. The solution was then poured into a glass plate and dried in an oven at 40°C. The obtained composite films were characterized with tensile test, FTIR, and XRD.

Results and Discussion
This study compared only two films, namely, chitosan film and chitosan-cellulose-TiO2 composite film , in order to observe the difference between chitosan films with and without cellulose and TiO2. Chitosan and chitosan-cellulose-TiO2 composite films show slightly different appearances. Chitosan film is more transparent than chitosan-cellulose-TiO2 composite film. Cellulose is visible in the chitosan-cellulose-TiO2 composite film, while TiO2 is not visible ( Figure 1).
a. b.  FTIR spectrum of chitosan-cellulose-titanium dioxide composite film ( Figure 2b) shows changes in absorption bands for -OH and -NH in chitosan film. The absorption band widened and shifted to a larger wave number, 3452.00 cm -1 . The widening of the band occurs due to the addition of the -OH groups, due to the addition of cellulose. The shift in wave numbers occurs due to the presence of hydrogen bonds and electrostatic forces between the three components: chitosan, cellulose and TiO2. Absorption band of amide I also shifted to a lower wave number. Absorption bands for Ti-OH and Ti-O appear at wave numbers 1637.58 cm -1 and 669.79 cm -1 , respectively. These results are in accordance with the studies reported by Oliveira (2017) [12] and Saravanan (2018) [13] and confirm the formation of chitosancellulose-TiO2 composite film.
Tensile test was conducted for all compositions shown in Table 1, using ASTM (American Standard Testing Material) D638 TYPE IV. Results are shown in Figure 3. The study prepared films of varying compositions: chitosan-cellulose-TiO2, chitosan, chitosan-cellulose and chitosan-TiO2 The aim was to investigate the effects of each filler on the mechanical properties of chitosan. Figure 3 shows the addition of cellulose can increase the tensile strength of chitosan film. A similar result was also found by addition of TiO2 particles, which increased tensile strength of chitosan composite more than cellulose particles. One probable cause is that TiO2 particles are smaller than cellulose particles, resulting in better adhesion force and producing more compact material. The tensile strength of chitosan film was 12.33 kgf/mm 2 . The tensile strengths of chitosan-cellulose film and chitosan-TiO2 film were 14.00 kgf/mm 2 and 15.42 kgf/mm 2 , respectively. The highest tensile strength (16.17 kgf/mm 2 ) was obtained by chitosan-cellulose-TiO2 film containing 0.9 g chitosan, 0.05 g 4 cellulose and 0.05 g TiO2, where the weight of both fillers are the same. Hydrogen bonding between chitosan, cellulose and TiO2 increases the tensile strength of the film. However, when the weight of one of the fillers is higher than 0.05 g, the composite's tensile strength decreases because fillers tend to interact with themselves, reducing adhesion force and thus decreasing tensile strength [14].

Figure 3. Tensile strength of composite films with different compositions
XRD analysis was also performed to study the effect of cellulose and titanium dioxide on chitosan crystallinity (Figure 4). A broad peak with high intensity at 2=20° is typical of chitosan, illustrating its crystalline and amorphous phases (Figure 4a) [15]. After forming a composite film with cellulose and titanium dioxide, the crystallinity of chitosan reduces, wherein the typical peak intensity of chitosan decreases and results in a new amorphous material. A new peak was observed at 2=24.78°, which is typical of titanium dioxide. These results confirm the formation of chitosan-cellulose-TiO2 composite film. The obtained amorphous material offers several applications, such as an adsorbent.

Conclusions
Chitosan was successfully modified using grass-derived cellulose and titanium dioxide. The addition of cellulose and titanium dioxide improved the mechanical properties of the chitosan film. FTIR and XRD analysis confirmed the formation of chitosan-cellulose-titanium dioxide film. The addition of cellulose and titanium dioxide reduced the crystallinity of chitosan film.