Sonication assisted liquid phase exfoliation of graphene using instant coffee : the mechanical and thermal properties of PVA/graphene nanocomposite / Abu Hannifa Abdullah

Faculty of Chemical and Process Engineering Technology

Thesis (Doctor of Philosophy in Chemical Engineering) -- Universiti Malaysia Pahang – 2019

Includes bibliographical references

Graphene is known as a wonder material which can be applied to various valuable application. Sonication assisted liquid phase exfoliation (LPE) is one of the best methods to produce graphene for the polymer filler application. The advantages of this method include defect-free graphene, economically viable and simple processing technique. However, most of the LPE processing method involved the use of highly toxic and costly substance as dispersing solvents such as N-methyl-2-pyrrolidone or Dimethylformamide. This is the biggest drawback for this method and therefore in this thesis, a new water based dispersing agent is introduced to counter the existing problem while utilising green technology. Herein, instant coffee was introduced as a dispersant to replace the mentioned solvents. The reason behind choosing instant coffee as dispersant is due to the Chlorogenic acid (CA) content in the coffee which assist the exfoliation process. Instant coffee-based graphene (GC), was produced by sonication assisted LPE process and the output was confirmed by using Ultraviolet visible spectroscopy, Transmission electron microscopy, Atomic force microscopy and Raman spectroscopy. The features of the GC were evaluated by the thickness and mean length of the graphene which were recorded at the range of ~1.7 nm (4 layers) and ~101-200 nm respectively. Centrifugation was performed to control the lateral size and thickness of graphene and it was found out that higher centrifugation speed lead to lower mean length and layer of graphene as well as the amount of the graphene. As confirmed by Raman spectroscopy, the graphene was found out to have less defect compared to graphene oxide. The GC was also tested for the electronic properties and the result shown the bandgap value of the graphene was 3.1eV as well as the photoluminescence which has shown the broadening and shifts for the florescence peak. The results give potential to the produced graphene to be applied in electronic application such as semiconductor and supercapacitor. The XPS reveal that the GC is a functionalised graphene with about ~30% of functional group attached. To study the scalability of the production method, the effects of the processing parameter for GC were studied and the exponential factor for the concentration of initial graphite, sonication time, sonication power and volume were obtained. The use of Central Composite Design (CCD) to get the highest concentration of graphene solution was also done and was verified. The highest concentration achieved was at about ≈ 0.0412 mg/ml. The produced graphene GC was then used as a filler for PVA nanocomposite and the properties of the nanocomposite were studied. The increase up to ~86% for the tensile strength and 83% for Modulus Young were recorded for the nanocomposite compared to the pristine PVA while 8°C increase in thermal stability and only 1°C increase in melting temperature was recorded. In conclusion, the use of instant coffee to produce graphene (GC) has been verified and extensively studied. Furthermore, the applicability of the GC has also been shown from the improvement of the mechanical and thermal properties of the GC filled PVA nanocomposite. This study will likely contribute to the advancement of the cost-effective graphene production and supporting the development of the PVA/graphene nanocomposite to be widely used for various suitable application.