Effect of Surface Chemistry of the Nano - Reinforcement Matrix on the Mechanical and Electrical Properties of FRPs

Killi, Krushnamurty and Ch, Subrahmanyam (2017) Effect of Surface Chemistry of the Nano - Reinforcement Matrix on the Mechanical and Electrical Properties of FRPs. PhD thesis, Indian Institute of Technology Hyderabad.

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Abstract

The present study has been devoted to achieve the optimum surface chemistry of the nano reinforcement ma trix for achieving the best mechanical properties . Two kinds of Fibre Reinfored Plastics (FRPs) were studied in the present work. They are glass fiber reinforced epoxy (glass - epoxy) composites and Carbon fiber reinforced epoxy (C - epoxy) composites. The fo rmer were studied for their impact and mechanical properties when reinforced with nanoclay and the later for their mechanical and electrical properties when reinforced with carbon nanotubes/carbon nanofibers or graphene oxide. For the E - glass - epoxy composi tes, studies were carried out to understand how does amine modified nanoclay influence the crosslink density and toughness of the epoxy matrix. Based on the toughness changes that were observed with the amino modified nanoclay addition to epoxy, new mecha nism was proposed on the mechanical property improvements for glass - epoxy reinforced with nanoclay. Typical results highlighted the role of nanoclay in toughening the fiber - matrix interface and thereby improvig the mechanical properties of glass - epoxy co mposites upto an optimium nanoclay addition, whereas, at higher loadings , the matrix embrittlement is found to be beneficial in increasing the impact resistance. Besides, nanoclay reinforced E - glass - epoxy composites, nanoclay reinforced glass - epoxy composites were also made with different fiber volume fractions and tested for their mechanical properties. Results show that nanoclay addition can increase the mechanical properties of the GFRPs having a lower fiber volume fraction. As the fiber volume fr action of the GFRPs increases, the reinforcement ability of nanoclay has diminished. For improving mechanical properties of the C - epoxy composites, functionalized MWCNTs and CNFs are used as the additional reinforcements. Carbon nanofibers (CNFs) and multi walled c arbon nanotubes (MWCNTs) were functionalized under helium/air plasma and the surface characteristics were compared with that of chemical functionalization. Changes in the surface functional groups on CNFs/MWCNTs due to plasma/chemical treatment wer e estimated by using a temperature programmed decomposition (TPD) technique, elemental analysis, Raman spectroscopy and BET surface area analysis. Raman spectroscopic studies highlighted that vi chemical functionalization increases the degree of disorder for CNFs/MWCNTs when compared to plasma treatment. TPD also confirmed that air plasma treatment leads to the highest number of acidic groups on the surface that decomposes to evolve carbon dioxide. The modified CNFs/MWCNTs were used as additional reinforcement s to fabricate carbon fiber reinforced plastics (CFRPs). It has been observed that air plasma treated CNFs/MWCNTs improved the tensile and flexural strength of a C - epoxy composites significantly as compared to conventional chemical functionalization, where as the best performance of air plasma treated CNFs/MWCNTs is due to higher acid functional groups on the surface, which improves the interface compatibility between the CNFs/MWCNTs to the epoxy matrix. Enhanced electrical conductivities were achieved in C - epoxy composites by integrating them with conducting polymers (CPs), namely polypyrrole (PPY), poly (3,4 - ethylene dioxythiophene) (PEDOT) and graphene oxide (GO) enwrapped by CPs. This was achieved by in - situ polymerization of pyrrole or 3,4 - ethylenedioxyt hiophene (EDOT) in the presence of the GO (template), sodium bis(2 - ethylhexyl) sulfosuccinate (structure directing agent:), ferric chloride (oxidant), the electrically conductive sheets of GO enwrapped CPs were obtained. The formation of CP coating on GO w as confirmed by Raman spectroscopy, scanning electron microscopy and thermo gravimetric analysis studies. Different wt% of CP and CP coated GO were added to the epoxy resin and was used to prepare the 2D laminated C - epoxy composites by hand layup method. The DC electrical conductivity of the prepared C - epoxy composites was analyzed by using current - voltage (I - V) characteristics and AC impedance measurements. Typical results showed that CP coated GO, at 0.5wt% addition to epoxy imparted the highest DC elect rical conductivity to C - epoxy composite.

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