**3.4 Preparation of Ch/CD films**

In this work, we prepared Ch/CD films by solvent evaporation method. When the film forming solution is placed in an oven (see experimental section), the solvent is evaporated and semi-transparent film with dark brown appearance is obtained. The crosslinking of chitosan chains by carbon dots may be described as follows: In the film forming solution, chitosan exists in dissolved state with protonated –NH3 + groups along the macromolecular chains. The final pH of the solution was found to be 6.2. At this pH, -COOH groups present on the surface of the carbon dots, ionize to give negatively charged –COO− groups, thus rendering negative charges on the surface of CDs. These negative charges bind electrostatically to the protonated amino groups of chitosan chains and a crosslinked network is formed.

**Figure 3.** *(a) A survey scan, ranging from 0 to 1200 eV; XPS spectra of (b) C 1S and (c) O 1S.*

The plain Ch film appeared to be semi-transparent with pale yellow appearance while the Ch/CD film was dark brownish. An optical photograph of the plain Ch/ CD(0) and the Ch/CD(2) films and mode of crosslinking is shown in **Figure 4(a)**.

It is well known that carbon dots emit fluorescence on exposure to UV radiations of suitable Wavelength [27]. This makes them a potential candidate for imaging and other related applications [28]. The optical image of the sample Ch/CD(2), exposed to UV radiations, is shown in **Figure 4(b)**. It can be noticed that the film appears green, due to the fluorescence exhibited by carbon dots present within the film matrix.

#### **3.5 XRD analysis of films**

The crystalline nature of the plain and CDs loaded films was investigated by XRD analysis. The XRD patterns of plain film Ch/CD(0) and carbon dots loaded film Ch/ CD(2) are shown in **Figure 5(a)** and **(b)** respectively. It can be seen that both of the samples, namely plain sample Ch/CD(0) and CDs-loaded sample Ch/CD(2) exhibit two peaks at 2θ values of 14.6 and 18.1, indicating presence of crystalline region within

**103**

composite film.

**Figure 4.**

**3.6 Film expansion study**

*Wound Dressing Application of Ch/CD Nanocomposite Film*

the film matrix. These values are very close to those reported elsewhere [29, 30]. In addition, a scattered broad pattern is also visible, suggesting amorphous region too. The XRD pattern of the nano-composite film Ch/CD(2), as shown in **Figure 5(b)**, also shows similar pattern with the two peaks, occupying almost the same positions. However, the difference lies in the fact that in the case of CD/Ch(2) film the intensities of the two peakes have decreased remarkably, probably due to presence of amorphous carbon dots within the film matrix. It is also noticable that the amorphous scattered bump is much more pronounced in the XRD pattern of composite film.In this way, it may be concluded that presence of carbon dots within the chitosan film has resulted in increase in the amorphous nature of the

*(b) optical image of the sample Ch/CD(2) when exposed to UV radiations.*

*(a) Optical photographs of the samples Ch/CD(0) and Ch/CreD(2) and mode of crosslinking by carbon dots;* 

The use of a polymeric film for wound dressing requires fair structural integrity in the presence of exudate coming out from wound. The reason is that when a film is placed over the wound, it comes in contact with the exudate and begins to undergo expansion in its size. If the film expands appreciably, then it may lose its integrity, become soft and sticky, and ultimately may cause inconvenience to the patient. It

*DOI: http://dx.doi.org/10.5772/intechopen.95107*

#### **Figure 4.**

*(a) Optical photographs of the samples Ch/CD(0) and Ch/CreD(2) and mode of crosslinking by carbon dots; (b) optical image of the sample Ch/CD(2) when exposed to UV radiations.*

the film matrix. These values are very close to those reported elsewhere [29, 30]. In addition, a scattered broad pattern is also visible, suggesting amorphous region too.

The XRD pattern of the nano-composite film Ch/CD(2), as shown in **Figure 5(b)**, also shows similar pattern with the two peaks, occupying almost the same positions. However, the difference lies in the fact that in the case of CD/Ch(2) film the intensities of the two peakes have decreased remarkably, probably due to presence of amorphous carbon dots within the film matrix. It is also noticable that the amorphous scattered bump is much more pronounced in the XRD pattern of composite film.In this way, it may be concluded that presence of carbon dots within the chitosan film has resulted in increase in the amorphous nature of the composite film.

#### **3.6 Film expansion study**

The use of a polymeric film for wound dressing requires fair structural integrity in the presence of exudate coming out from wound. The reason is that when a film is placed over the wound, it comes in contact with the exudate and begins to undergo expansion in its size. If the film expands appreciably, then it may lose its integrity, become soft and sticky, and ultimately may cause inconvenience to the patient. It

**Figure 5.** *X-ray diffraction of film samples (a) Ch/CD(0) and (b) Ch/CD(2) .*

may also be torn and leave the wound surface. Hence, it becomes essential to test its expansion limit and structural integrity. The results of expansion study are shown in **Figure 6**.

It is noticeable that the plain Ch/CD(0) film undergoes 2.8. Fold expansion in its diameter in duration of 60 min, while in the same time frame, the Ch/CD(2) film expands to only 1.3 times and it maintains its structural integrity throughout. It is also worth mentioning here that the plain film sample Ch/CD(0) gets hydrated, slippery and becomes difficult to handle properly Thus it may be concluded from this study that addition of pre-calculated quantity of carbon dots in to chitosan film can render it enough mechanical strength and control its water absorption capacity as per requirement.
