PSI - Issue 17

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

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its molecular structure coming from plant origin. Viscosity of the resin at 20 °C and 25 °C is 3240 mPa·s and 1780 mPa·s respectively and the viscosity of the hardener at 20 °C and 30 °C is 33 mPa·s and 25 mPa·s respectively. Two parts were recommended to be mixed at a ratio of 100:24 by weight and exposed to thermal curing for 45 minutes at

120 °C as reported in the technical data sheet. 2.1. Multi-walled Carbon Nanotubes Functionalization

Pristine MWCNTs were functionalized in a 3:1 ratio of sulfuric acid to the nitric acid (mixture acid), total volume of the mixture acid used was 100 ml. This mixture acid was heated to a temperature of 90 °C and then this mixture was maintained at this temperature. Subsequently, 1g of pristine MWCNTs was added to the mixture acid and five different synthesis were carried out using time of heating as 15, 30, 45, 60 and 90 minutes in a reflux (Men et al. 2008; Osorio et al. 2008). After the synthesis, mixture was diluted in a deionized water (1L) and then it was filtered by using a 0.22 µm membrane filter paper by using a vacuum filtration. Resultant solid was then washed with deionized water until the pH reaches neutral, generally five washes were enough. Finally, MWCNTs were dried in an oven at 60 °C for 24h and then they were weighed for different time of functionalization. Afterwards, drie d MWCNT’s were added to dimethylformamide (DMF) and the soluble part of MWCNT’s was separated from insoluble part. Hypothesis is that the functionalized part of MWCNT’s is soluble in DMF and pristine part of MWCNT’s that remains insoluble in DMF is unaffected by the chemical synthesis. 3. Material Characterization 3.1 TGA TGA is a technique by which mass of sample is observed with reference to the temperature as it is heated or cooled. Sample was heated from the room temperature to the 900 ºC in a nitrogen atmosphere with a gas flow rate of 200 ml/min and a heating rate of 10 ºC/min. After this step, an isotherm was maintained at 900 ºC for 10 minutes which is followed by cooling to room temperature at a heating rate of 10 ºC/min. Four samples were tested, they are as follows: a) P ristine MWCNT’s b) MWCNT’s functionalized by 60 minutes c) MWCNT’s dissolved in DMF d) MWCNT’s insoluble in DMF. 3.2 Scanning Electron Microscopy (SEM) To observe the microstructure of pristine and functionalized MWCNT’s , scanning electron microscopy is used. Samples were prepared by depositing a thin film of MWCNTs over the Indium Tin Oxide (ITO) coated glass (to make them conductive) using physical vapour deposition (PVD). Pristine MWCNT’s, 45 -minute functionalized MWCNTs and 90-minute functionalized MWCNTs were observed at a length scale of 500 nm. 3.3 Preparation of nanocomposites Fabrication of pristine and functionalized MWCNT’s reinforced epoxy composites was done by the following method. MWCNT’s we re first added to the acetone and sonicated for 30 minutes to make MWCNT’s easy to disperse in the epoxy matrix and reduce the viscosity of the mixture. Then, epoxy was added to this mixture and sonication was carried out for another 30 minutes. It was followed by magnetic stirring for 3h at 80 °C to completely remove the acetone from this mixture. Degassing of the mixture was done for 15 minutes to ensure the removal of any trapped air bubbles due to previous processes. At this point, hardener was added to it and magnetic stirring was carried out for 15 minutes without heating. Subsequently, sonication was done for another 2 minutes followed by degassing for 5 minutes. Lastly, this mixture was poured into tensile test mould and this mould was then put into oven at 120 °C for 45 minutes followed by slow cooling till room temperature (RT). Figure 1 shows the pure epoxy specimens and MWCNT ’s reinforced epoxy composites. Figure 1c) shows the tensile test specimen with the speckle pattern for digital image correlation (DIC). 3.4 Mechanical Characterization Samples for tensile tests were manufactured from neat resin and from both pristine and functionalised MWCNTs according to different wt% of nanofiller/bio-based resin content. They were tested according to the ASTM D638 standard and a Digital Image Correlation (DIC) system was also used for studying the strain field distribution. Examples of neat resin samples and nanocomposite samples are reported in Figure 1 a) and b). The tensile test set-up and the sample, whose surface was prepared for DIC are shown in reported in Figure 1 c).