PSI - Issue 17

Anurag Singh et al. / Procedia Structural Integrity 17 (2019) 857–864 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

861

5

Figure 3 : Effect on hydrophilicity of MWCNT’s after functionalization

Table 1: Percentage of functionalized MWCNTs soluble in DMF

4.2 Hydrophilic behavior change Pristine MWCNT’s and MWCNT’s functionalized by 30 minutes are checked for hydrophilicity , this behavior was confirmed by putting separately pristine and functionalized MWCNT’s in a bottle containing water and dichloromethane (DCM). Pristine MWCNT’s show ed an affinity towards DCM and settled at the bottom, while MWCNT’s functionalized by 30 minutes show ed a hydrophilic nature and gets attracted towards water at the top. Thus, confirming the change of behaviour from hydrophobic to hydrophilic, this is an indication towards obtaining the functionalized MWCNT’s. Functionalized products were then dissolved in DMF and then functionalized and non-functionalized parts were separated by vacuum filtration. Percentage of filtered products were noted, and no significant change was noticed among the percentages obtained, exception being the 60-minute functionalized product, it is more likely to be an outlier. This leads to a conclusion that with an increase of time of synthesis overall yield decreases but the percentage of functionalized product inside the yield quantity remains the same. Thus, time of reaction consumes more pristine MWCNT’s but does not change the final product of functionalized MWCNT’s , only the quantity gets decreased. Therefore, 30 minutes of functionalization wa s chosen for producing bulk functionalized MWCNT’s as 15 minutes of synthesis was not as consistent. 4.3 TGA TGA results of pristine, functionalized MWCNT’s , MWCNT’s soluble in DMF fraction and MWCNT’s insoluble in DMF fraction are shown in figure 5. Percentage of weight loss in pristine MWCNT’s was noted to be 13.74% whereas the functionalized MWCNT’s weight decreased to 25.41%. Weight loss of MWCNT’s soluble in DMF was the maximum with the decrease going down to 59.16%. This increase in weight loss from pristine to functionalized MWCNT’s can be due to the presence of carboxylic group at the surface of functionalized MWCNT’s. Weight loss of MWCNT’s which were insoluble in DMF was 17.12%, which is close to the pristine MWCNT’s. This led to affirmation of the hypothesis that the MWCNT’s dissolved in DMF were functionalized part and the insoluble part is the one which remain unaffected by the chemical functionalization. 4.4 SEM SEM micrographs of pristine MWCNT’s , DMF soluble functionalized MWCNT’s and DMF insoluble part of functionalized MWCNT’s are shown in figure 4 at 500 nm length scale. In figure 4a) they can be seen in the form of long seamless wires and are entangled together due to the weak Vander wall forces. From the figure 4b), which is fraction of MWCNT’s separated by DMF, MWCNTs seen as well dispersed and distinguished but the length of the MWCNTs is shorter than the pristine MWCNT’s . It is because of the chemical functionalization, which has resulted in the shortening of the length. In figure 4c) the length of MWCNT’s seems to get shortened due to the chemical functionalization and loss of MWCNT’s as compared to pristine MWCNT’s can be easily noticed. 4.5 Energy dispersive X-ray spectroscope (EDS) Table 2 and figure 5 shows the EDS results for pristine and functionalized MWCNT’s. Results of pristine MWCNT’s shows the presence of metal oxide as a catalyst during the production of carbon nanotube. Use of aluminium oxide as a catalyst was verified from the technical data sheet of the pristine multi-walled carbon nanotubes provided by the supplier. Figure 5b) shows that functionalized MWCNT’s has resulted in an increase of oxygen content to 27.23%, and there has been a significant decrease in the aluminium content. This signifies that the aluminium oxide earlier presents in the sample has been diminished by using the strong acid. Thus, oxygen appearing in the results is due to the functionalization.