PSI - Issue 14

Vivek Khare et al. / Procedia Structural Integrity 14 (2019) 215–225 Vivek Khare, Shubham srivastava, Sudhir kamle, G.M.Kamath / Structural Integrity Procedia 00 (2018) 000 – 000

217

3

1.1. Multiwall Carbon nanotubes structure and functionalization

Fig. 1. (a) MWCNT-Pristine; (b) MWCNT-COOH Functionalized

Carbon nanotubes used in this study are rolled sheet structures as shown in Figure. 1 with multiple layers (>100) of varying outside diameter ranging from 3-8 µm and length approximately 10-20 nm made up of C-C bonds, strengthen by strong vander-waal potential. Jia et al. (2011), Ganß et al. (2007) and Khare et al. (2017 and 2018), found this strong covalent bonding as a major source of agglomeration and large spherulites formation that hinders the strength and lowers the deformation resistance of nanotubes. To control this drawback, – COOH functionalized nanotubes were proposed. MWCNT-COOH are generally obtained by the chemical reaction of HNO 3 and H 2 S0 4 in the ratio of 1:3 resulting in MWCNT surface modified by – COOH group as suggested by Sadegh et al. (2016). Several studies have been made to characterize the effect of this functionalization and prove to be better replacement for pristine MWCNT in terms of strength, ease of reinforcement and stress transfer efficiency from matrix to fiber. Composites developed from PP matrix exhibits semi crystalline state (both amorphous and crystalline region) as shown in Figure. 2. Viscoelasticity in these polymers is the result of the diffusion of atoms or molecules inside an amorphous phase of the material in which elasticity is usually due to the bond stretching in crystallographic planes in an ordered solid as studied by Papanicolaou et al. (2011). Incorporation of nanofibers like carbon nanotubes increase their resistance to deformation. Deformation at microscale strongly rely on temperature, strain rate and rheology of the deforming material where rate of deformation varies with the applied stresses. One of the best way to characterize rheological behavior of viscoelastic material, is to monitor slow and progressive increase in strain under constant applied stress called as creep. Thermoplastics undergo creep even at room temperature. Although the creep behavior of reinforced nanocomposites depends on many factors like individual creep behavior of matrix, fracture behavior of reinforcement and stress transfer efficiency from fiber to matrix, but this study limits the analysis particularly for nanotubes reinforced nanocomposite materials. 1.2. Microscale deformation of PNCs

Fig. 2. Semi crystalline state of Polypropylene Nanocomposites