Moisture adsorption-desorption behaviour in poly (vinyl alcohol-co-acrylic acid)/graphene oxide nanocomposite copolymer films / Farah Aqilah Md Zulkiflie

Farah Aqilah , Md Zulkiflie (2023) Moisture adsorption-desorption behaviour in poly (vinyl alcohol-co-acrylic acid)/graphene oxide nanocomposite copolymer films / Farah Aqilah Md Zulkiflie. Masters thesis, Universiti Malaya.

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Abstract

The widely employed technique for dehumidifying air through refrigerant cooling method consumes an immense amount of energy. To improve energy efficiency, independent humidity control system using desiccant has been introduced. This study focuses on finding an alternative to the commonly used solid desiccant, silica gel, to improve the mechanical properties, sorption capacity and recyclability. This study reports on the synthesis of poly(vinyl alcohol-co-acrylic acid) (P(VA-AA)) via solution polymerisation from the hydrolysis of poly(vinyl acetate-co-acrylic acid) (P(VAc-AA)). To enhance both the mechanical and sorption properties of the copolymer, graphene oxide (GO) was incorporated as a filler at different concentrations ranging from 0.5% to 5%. The prepared samples were characterised by various techniques, including Fourier transform infra-red spectroscopy (FTIR), field emission scanning electron microscope (FESEM), X-ray diffraction analysis (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results demonstrate that the added filler was uniformly distributed within the polymer matrix, leading to enhanced thermal properties. It was also observed that the nanocomposite film containing 2% GO, denoted as P(VA-AA)/GO2, showed improved mechanical characteristics with values of 4.780 MPa for tensile strength, and 7.831 GPa for Young's modulus. The samples were also tested for their ability to adsorb moisture from the surroundings at different relative humidity (RH) levels and their capability to maintain optimum sorption capacity for 10 repeated cycles. Experimental results show that P(VA-AA)/GO2 exhibited notable improvement in sorption capacity for all RH levels. The P(VA-AA)/GO2 can adsorb 0.245 g/g water vapour at 25 °C and 90% RH, compared to the P(VA-AA) without filler, which could only adsorb 0.015 g/g water vapour at the same conditions. This vast difference is attributed to the larger proportion of hydrophilic functional groups in GO. This result is also supported by the contact angle measurements, in which P(VA-AA)/GO2 has reduced contact angles by 31% compared to its pristine copolymer that indicates its hydrophilicity. The composite desiccant is also able to maintain its adsorption capacity at every cycle (10 cycles).

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