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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have a lot of untapped potential as reported on several occasions, they are promising candidates as being with the properties of high strength, having low density, high conductivity, chemical inertness, and low dimensionality, thus their use is open to diverse practical applications (GRADY 2011). Nevertheless, to utilize this untapped potential in the area of polymer composite application, these MWCNT’s must have an ade quate and uniform dispersion. To increase their dispersion in the polymer composites, proposal of making them functionalized with the adequate modality is proposed according to the polymer for which it is to be applied (Kathi, Rhee, and Lee 2009; Ma et al. 2010; Singh 2014). In order to use them for aerospace application, the prime requirement is to have a light weight, high temperature resistant, high strength to weight ratio, resistant to corrosion, flexibility associated with their design, these are few examples associated with the use of composite materials. The most popular technique that has been employed for functionalization of carbon nanotubes is chemical oxidation by using the sulfuric acid and the nitric acid (mixture acid) as the reagents (Hirsch and Vostrowsky 2005; Maxim N. Tchoul et al. 2007; Osorio et al. 2008). Using highly acidic media, carbon nanotubes get oxidized and the surface of carbon nanotubes increases the exfoliation of CNT’s and hence in turn upsurge is seen in the solubility of these carbon nanotubes in the polymer matrix. This also purifies and promotes the dispersion by improving the surface activation. Overall, by doing the chemical functionalization, it will promote the interfacial bonding and the dispersion of the carbon nanotube inside the polymer matrix (Sahoo et al. 2010). During the entire process of chemical functionalization, it must be ensured that the length of the carbon nanotubes should not reduce to an extent to affect their overall individual properties. The chemical functionalization of the carbon nanotubes is well documented in the literature, commonly followed route is by heating them up to the temperature of 90 °C in the presence of mixture acid and keeping the time of reaction limited to 30 minutes has been widely used (Singh 2014). However, due to lack of standards for the processing of carbon nanotubes, different batches of MWCNT’s have different properties and no two batches are the same. Therefore, the method that works for one case does not necessarily work for others. Thus, the need of optimizing the parameters for an individual need arises. In this work, the chemical functionalization of the multi-walled carbon nanotubes is tailored according to the industrial grade MWCNT’s that were available at our disposal. Different time of heating is experimented, and material characterization is carried out to confirm the grafting of carboxylic and alcoholic group on to the walls of carbon nanotubes. After confirming the successful functionalization by the carboxylic and the alcoholic group, these functionalized MWCNT’ s and the pristine MWCNT’s were used as a nano -filler to prepare different specimens at different concentrations. Prepared samples were of pure epoxy and pristine MWCNTs epoxy nanocomposites and the functionalized MWCNTs epoxy nanocomposites at different concentrations. Recently, bio-based thermoset resin systems have attracted significant attention given their environmental benefits related to the wide variety of available natural resources, as well as the resulting reduction in the use of petroleum feedstocks. During the last two decades, considerable improvement on the properties of bio-sourced resins has been achieved to obtain performances comparable to petroleum-based systems (Ramon, Sguazzo, and Moreira 2018). The matrix system considered to produce the nanocomposites, was a bio-based resin system investigated during the ECO-COMPASS project, where new bio-sourced epoxy matrixes for green composites were studied. Further, the mechanical characterization tests were performed along with digital image correlation (DIC) to gather information regarding the stress-strain field. Correspondingly, electrical tests were done to check the electrical conductivity of these specimens and the effect induced by the carbon nanotubes and functionalization to the original properties of the epoxy resin. 2. Materials and Reagents NC7000™ Pristine multi-walled carbon nanotubes (MWCNTs) synthesized by Catalytic Chemical Vapor Deposition (CCVD) technique were used in this work, they were purchased from Nanocyl (Belgium). MWCNTs received with a purity of 90 wt.%, average diameter of 9.5 nm and the average length of 1.5 µm. For studying the effect of chemical functionalization, MWCNTs were functionalized by the sulfuric acid (H 2 SO 4 ) having a concentration of 98 wt.% and nitric acid (HNO 3 ) with a concentration of 69-72 wt.%. All the reagents used in the chemical functionalization were kindly made available at the “ Centro de Investigação em Química da Universidade do Porto (CIQUP) ” . For filtering MWCNT’s after the chemical functionalization, filter paper made of poly tetra flouro ethylene (PTFE) having a pore size of 0.22 µm and diameter of 47 mm was purchased along with a filter assembly from “ Normax, Portugal ” . Polymer matrix used in this work - SR GreenPoxy® 33/SZ 8525 - is an epoxy/hardener resin system, it was supplied by the Sicomin - France. According to the supplier, SR GreenPoxy® 33 has a bio-based carbon content with 35% of