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

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During a typical creep cycle, the amorphous phase uncoiled first followed by rotation and separation of crystalline region as explained by Papanicolaou et al. (2011). This is attributed to large plastic deformation and development of Non linearity dominance during tensile loading mainly at high stress levels. 2. Materials

2.1. Sample preparation

Carbon nanotubes of diameter 10-20 nm and length 3-8 µm as per Nanoshel certification and isotactic polypropylene (iPP, melt temperature 150°C) supplied by Otto chemicals private Limited (properties in Table 1. and Table 2.), were employed in this study. Dispersion of MWCNT in to polypropylene matrix is still an ongoing research. In this study, we opted solution casting method proposed by Khare et al. (2017) for material development. PP pellets

Table 1. MWCNT specifications and properties. (Pristine and – COOH functionalized) Description Value Units Length 3-8 µm Diameter 10-20 nm Carbon purity 99.9 (Pristine) 98 (Functional) % %

Table 2. Polypropylene specifications and properties. Description

Value

Units

Melting point

135-140

°C

Form

Pellet

- -

Configuration

isotactic

were dried in vacuum oven for 24 hours at 80°C to eliminate moisture effects from the material. Ultrasonic bath of water was employed to sonicate MWCNTs in to xylene for four slots of 15 minutes each and simultaneously PP pellets were mixed with xylene in a magnetic stirrer for 15 minutes at 120° C. Both the solutions were mixed and heated again in the stirrer at 134°C, 120 rpm for 22 minutes. The mixture thus obtained was then poured in a petri dish (kept at 180°C in the oven) for 3 hours of curing (2 Hours at 180°C and one hour at 140°C). Developed material was a nanocomposite film with varying MWCNT weight %. 3. Experimental Details

3.1. TGA analysis

Weight change in material with respect to temperature was investigated by TGA analysis using SDT Q 600 for both polymer and nanocomposites. The method incorporates consecutive heating and cooling at ramp rate of 10°C/ min from 20°C to 200°C and vice versa with isothermal stage of 10 minutes. TGA analysis ensures no considerable loss in weight of the material for room temperature and 50°C.

3.2. Static characterization

Quasi static uniaxial tensile tests of flat specimens (80 x 10 x 0.35 mm 3 , length x width x thickness) were carried out at strain rates of 0.1/min at room temperature with end condition of fracture in Tinius-olsen universal testing machine according to ASTM D-882 (Tensile testing of thin plastic sheeting) to obtain the stress levels under and beyond the linear viscoelastic region. Creep tests were performed for stress levels of 0.1, 0.2, 0.5, 1, 2, 5, 7, 10 and 15 MPa on virgin PP, MWCNT(pristine)-PP and MWCNT(-COOH)-PP samples to observe the effect of