Synthesis and characterization of a biocomposite derived from banana plants (Musa cavendish)

Abstract

Over decades synthetic composites have become an indispensable part of our lives with their various applications such as packaging, sporting equipment, agriculture, consumer products, medical applications, building materials, automotive industry, and aerospace materials among others. Although these polymers have the desired properties for the above applications, they are invariably costly. Furthermore, they cannot be easily disposed of at the end of their useful lives and simply pile up and cause significant damage to the environment. However, the dwindling supply of fossil fuel, increased oil prices, together with the growing public concern of greenhouse gas emissions and global warming, has forced scientists to search for new development of sustainable materials from renewable resources. Hence in recent years, there is an increased interest in biocomposite manufacturing with natural resources as environmental issues are addressed. The research work presented in this dissertation is to the best of the author’s knowledge a world-first overall investigation pertaining to the concept of synthesizing a banana sap based bio-resin (BSM) reinforced with banana fibres. In this work the chemical composition of banana sap was determined to investigate the chemical reactions taking place in the resin formulation. BSM was synthesized, characterized and proposed as a potential bio-resin to be used in the biocomposite manufacture for non-functional motor vehicle components. BSM, a hybrid bio-resin was synthesized with equimolar quantities of maleic anhydride and propylene glycol and 50% banana sap. A control resin without the banana sap was also synthesized for comparison purposes. It was proposed that the presence of sugars, esters and pthalates from the sap, determined by HPLC and GC-MS, contributed to the cross-linking of the polymer chain. The acid value and viscosity of BSM were determined and found to be within specification of an industry resin. The molecular weights of the BSM and control resins were 2179 and 2114 units respectively. These were within the required molecular weight of unsaturated polyester resins. The gel and cures times of the BSM were 60% lower than the control resin suggesting that the banana sap behaved as an accelerator for the curing process. The lower cure time meant that using the banana sap in the formulation was cost effective and time saving. The thermal properties of BSM showed improved degradation temperatures and degree of crystallinity compared to the control resin. A parametric study showed that increasing banana sap concentration in the resin formulation led to increased tensile and flexural properties with 50% being the optimum amount of sap to be added to the formulation. The synthesized bio-resin and control resin were applied to biocomposites and characterized in terms of physical, thermal, mechanical, morphological, chemical and biodegradable properties. Mechanical tests indicated a 15 % increase in tensile strength, 12 % improvement in tensile modulus and a 25 % improvement in the flexural modulus, when compared to structures produced without banana sap. Natural fibres present the challenge of poor adhesion to the matrix. Chemical treatment of the banana fibre was done to improve on the compatibility of resin to fibre. Fibre pull-out showed that treated fibres had a better bond than the untreated fibre. Parametric studies were also done to evaluate the effect of fortifying the BSM resin with nanoclay. A 5% clay loading resulted in a 24% increase in tensile strength and 28% increase in flexural properties. Finally biodegradation studies of the BSM bio-resin, BSM biocomposite, control resin and control composite were investigated and compared to a positive reference, cellulose. Results showed that over a period of 55 days the BSM biocomposite showed 17.6% biodegradation compared to 8% with the control composite. No difference in biodegradation between the BSM bio-resin and the control resin was recorded. BSM biocomposite was proposed as a potential replacement to synthetic composites that contribute to the environmental landfill problems. The main contribution of this research is the use of the reinforcement and matrix from the same natural source. An enriched understanding of the synthesis, characterization and performance of the banana sap based bio-resin and biocomposite for the use of non-functional motor vehicle components is the key outcome of this investigation.