(409e) Fabrication and Thermal Degradation Studies of Exfoliated Graphene Reinforced Poly (lactic acid) Nanocomposite

As a biodegradable thermoplastic derived from sustainable resources, polylactide (PLA) has received considerable attention for potential applications. As a result, PLA production and consumption is expected to increase exponentially in the near future. Although PLA is explored as a promising material in the field of eco-friendly biocomposites, it has limited crystallinity and higher brittleness, leading to its poor mechanical properties¹ and therefore slower utilization of PLA at industrial level.² To alleviate this issue, several nano-scale fillers are reported as reinforcing agents to strengthen the green polymer. Further, graphene, the new generation carbonaceous layered material is regarded as potential reinforcing material in polymer matrix to improve mechanical properties and fasten the crystallization rate.³ In addition to this, graphene can acts as a barrier to reduce gas permeability of the PLA matrix due to its inherently higher aspect ratio.

In the present work, an attempt has been made to fabricate exfoliated graphene via thermal exfoliation of expandable graphite followed by bath sonication technique. We have reinforced exfoliated graphene in PLA matrix via solution casting method. X-ray diffraction pattern of expandable graphite exhibited a sharp intense peak corresponding graphitic carbon structure at 2θ=26.5º. After thermal exfoliation of expandable graphite, intensity of its characteristic peak 2θ=26.5º diminished drastically due to the increase in inter-layer distance of graphene layers which is also pictoriated by Field-emission scanning electron microscopy. The disappearance of this peak in all the PLA composites clearly indicated the completely exfoliated state of graphene layers in the PLA matrix, when subjected to sonication process. Enhancement in the thermal stability for PLA composites by 4ºC in comparison with neat PLA was observed by thermo gravimetric analysis. The activation energy for PLA composites is estimated from the thermal degradation kinetic analysis of PLA composites using Coats-Redfern method which is based on integral approach. Increase in activation energy of the PLA composites by 21 kJ/mol, also corroborated the enhancement in thermal stability. In addition to this, the reinforcement acted as an efficient nucleating agent by enhancing the rate of crystallization and is confirmed by polarized optical microscopy studies. Increase in the degree of crystallinity of the PLA composites is also observed after the incorporation of graphene in the PLA matrix by X-ray diffraction analysis. The enhancement in the properties is due to the completely exfoliated state of graphene in the PLA matrix as depicted by scanning electron microscopy images.

AUTHOR INFORMATION

*Corresponding author.

Email: pugal@iitg.ernet.in & vkatiyar@iitg.ernet.in

References

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 2. Zhou, S.; Zheng, X.; Yu, X.; Wang, J.; Weng, J.; Li, X.; Feng, B.; Yin, M. Hydrogen bonding interation of poly(D,L-Lactide)/hydroxyapatite nanocomposites, Chem. Mater , 2007, 19, 247-253.

3. Shen, C.; Jing, T.; Ren, W.; Zhang, J.; Jiang, Z. Chemical and thermal reduction of graphene oxide and its electrically conductive polylactic acid nanocomposites, Composites Science and Technology, 2012, 72, 1430–1435.