PSI - Issue 5

L. ALEXANDRESCU et al. / Procedia Structural Integrity 5 (2017) 675–682 Laurentia Alexandrescu/ Structural Integrity Procedia 00 (2017) 000 – 000

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increasing surface polarity, or treated with an acid, thus improving the mechanical anchoring effect due to increased surface roughness (Hyunwoo Kim and all, 2010; Bunch, J.S. and all 2008). Oxidation of graphite nanoparticle surface in order to activate it is a method of improving wettability and chemical bonding of graphite/polymer matrix. Graphene oxide has been an extensively studied material in the past 20 years particularly due to its special characteristics and potential applications.

EXPERIMENTAL

Materials. All composites contain the same two polymer components: the polyamide elastomer PA6 (POLIMID B AV NATURALE – Poliblend Engineering Polymers Italy), with the following characteristics: specific weight, 1.40g/cm 3 ; impact resistance, 1.4 KJ/m 2 ; melt flow index (230°C /2.16 kg), 14g/10 min; melt temperature, 215-230°C, and polypropylene PP (Triplen 949- impact copolymer for injection moulding - MOL Petrochemicals Group), with the following characteristics: imapact resistance-4 KJ/m2, flex module-1.2 Mpa, melt flow index (180°C /2.16 kg) - 30 g/10min, specific weight -0.89-0.91 g/cm3 and melting point Mp 160-1850°C. Other components: compatibilizer: maleic anhydride grafted polypropylene PP-g-MA in the form of a honey-yellow granules, viscosity of 330000 cps and an acidity index of 43.1 mg KOH/g, manufactured by Sigma Aldrich and the graphite powders (C) 0520BX- Skyspring Nanomaterials USA with average particle size 3-4 nm and concentration of 99.5%. Synthesis of graphene oxide. There are several established methods for graphene oxide synthesis, the most frequently used reported by Kovtyukhova (Kovtyukhova et all 1999), derived from the well-known Hummers method. The procedure for obtaining graphene oxide is as follows: 20 g graphite is mixed with a concentrated H 2 SO 4 (60mL), K 2 S 2 O 8 (10g) and P 2 O 5 (10g) solution at 80°C. The mixture is cooled at room temperature and diluted with a large amount of water. The final stage consists in filtrating and washing the filtrate until neutral pH and drying it at 80°C for 24 hours. Subsequently, 20 g preoxidized graphite (the above method) is added to 460mL concentrated H 2 SO 4 and mixed in a Berzelius flask in ice cold water (t<5°C). To this mixture 60 g KMnO 4 are gradually and slowly added. After a few minutes, the Berzelius flask (in which a dark green solution had formed) was taken out of the ice cold water and placed on a hot plate with magnetic stirring at the temperature of 35°C inside the flask for 2 hours. After heating, 920 mL distilled H 2 O is added to the mixture, and 15 minutes later, the reaction is stopped by adding a large amount of distilled H 2 O (2.8 L) and H 2 O 2 of 30% concentration (50mL). The obtained mixture is decanted, vacuum filtered and washed with HCl 5% and distilled water until reaching a neutral pH. The obtained powder was air dried at the temperature of 60°C for 24 h. Procedure Preparation of various types of thermoplastic elastomers Polyamide, polypropylene, polypropylene graft with maleic anhydride and oxidized graphite were mechanically mixed in a Brabender Plasti-Corder PLE-360 at 10-120 rotations/min, for 3 min. at 230 0 C to melt the plastomer, mixed for 5 min. at 240 0 C and 2 min. at 200 0 C for homogenisation. The total time was 10 minutes. Table 1 shows tested formulations. Table 1: Control – GPP0 and PA/PP-gMA/PP/GO polymer nanocomposite formulations with varying GO amounts (GPP6-0,1%; GPP7-0,3%; GPP8-1%; GPP9-2,5%; GPP10-5%)

Compound

GPP0

GPP6

GPP7

GPP8

GPP9

GPP10

Polyamide sebamid

270

270

270

270

270

270

Polypropilene

30

30

30

30

30

30

Polypropylene graft methylmetacrylat Oxidized graphite

9

9

9

9

9

9

-

0,3

1,5

3

7,5

15

309

309,3

310,5

312

316,5

324

Total

The Brabender mixing diagrams, figures 1 and 2, show that the temperature in the chamber drops from 220 to 213 at higher percentages of oxidized graphite (starts at 260 0 C, decreases to about 220 0 C with a peak of 216 0 C at the end in the case of the 0.15 GO percentage and a lower one at 240 0 C in the case of 5% GO percentage), and there