STUDIES ON THE AGRO BASED FATTY ACIDS EPOXY RESINS AND THEIR COMPOSITES

Abstract

T he increasing environmental regulations generated by disposal of conventional plastics and related polymers from petrochemicals have intensified researches into polymers that have their origin from annually renewable resources such as plant oils, cellulose and lactic acid. As part of the solution to these problems concerted efforts are being made by scientists and researchers in both research and educational institutions to design novel products possessing acceptable qualities. Polymer composites manufactured by using agro based plant/crop oil as matrices and bio-fibers such as flax, hemp, sisal, kenaf and wood, as reinforcements are having the capability of recycling, commercial viability and environmental acceptability with triggered biodegradability defined as “Sustainable” agro based products. The most interesting raw material candidates for bio-based thermosets can be found among the plant oils. The plant oils are triglycerides, composed of glycerol combined with fatty acids into an ester. There are many sources for plant oils, and these can be grown almost all over the world. Soybean, linseed, rape seed, corn, canola, palm or sun flower are some oils. For their use in thermosets the triglyceride compound must be isolated and purified, and also functionalized to obtain reactivity. The plant oil is then cross-linked in a similar manner as crude oil based thermosets. Various chemical modifications for the plant oil are possible; and they utilize the unsaturated double bonds in the fatty acid part of the triglyceride. In this contribution we will describe the use of agro based chemically modified plant oil i.e., epoxidized soybean oil (ESO) via the epoxidation of the unsaturation present in the hydrocarbon chain. The objectives of this research work are to develop new epoxidized soybean oil (ESO) based polymers. The research work is divided in three parts: 1. Optimization of anhydride/epoxy ratio. 2. Modification of ESO by addition of a co-monomer. 3. Preparation of ESO based composites. This will surely increases the demand of epoxidized soybean oil as raw material for industrial applications. Various characterization techniques used to the study of mechanical, thermo-mechanical, thermal and morphological properties of the different systems. The variation in anhydride to epoxy stoichiometric ratios permits the control of thermo-physical properties along with the thermal properties over a wide range. The storage modulus, glass transition temperature, and cross-link density increased with an increase in the hardener content and reaches maximum at stoichiometric equivalence and decreases further. In contrast the izod impact strength and thermal stability shows monotonic behavior. This is further supported by SEM micrographs. All these results concluded that the anhydride/epoxy, ratio R = 1 works best. Our data supports the contention that any deviation from stoichiometry lowers the properties because a negative departure from stoichiometry results in a less improved network. The variation of DGEBA content was used to modify the epoxidized soybean oil (ESO) and the modified system shows the properties corresponding to the amount of modifier (DGEBA).From DMA, FTIR, mechanical properties, SEM and TGA results, it was concluded that properties were enhanced only up to 20phr DGEBA. Thus 10 and 20 phr DGEBA works best and approached to an ideal composition which gives the optimum property. Thus, at lower concentration of modifier, properties characteristic to ESO, which is soft and flexible with higher impact property, were obtained. At higher concentration of modifier, system obey property characteristic to DGEBA, which is inherently brittle. The silane treatment effectively increases the thermo-mechanical properties of the composites. In silane treated fiber, the interpenetration of the coupling agent into the cell wall of fibers through pores and its deposition in the inter-fibrillar region, generating a barrier that hinders the moisture access to fibers and reduces its hydrophilic nature. And finally improves the properties. From DMA, mechanical properties, SEM and TGA, it was observed that with increasing fiber content in ESO-untreated fiber composites gives declined Tg, increasing mechanical properties, poor adhesion and lower thermal stability. In case of ESO-silane treated fiber composites, from DMA, mechanical properties, SEM and TGA, it was observed that with increasing fiber content Tg was increased, mechanical properties were improved, better adhesion and higher thermal stability. All these properties were higher than untreated fiber composites. For both the composite systems, composites at 1.5 wt% fiber loading give the optimum properties and works best. Again from DMA, mechanical properties, SEM and TGA, it was observed that with increasing fiber content in ESO/DGEBA (10)-untreated fiber composites gives declined Tg but improved mechanical properties, poor adhesion and lower thermal stability. From DMA, mechanical properties, SEM and TGA, it was observed that with increasing fiber content ESO/DGEBA (10)-silane treated fiber composites gives increasing Tg, increasing mechanical, better adhesion and higher thermal stability. All these properties were higher than untreated fiber composites. For ESO/DGEBA (10)-untreated fiber system, composites at 1.5 wt% fibers loading gives the optimum properties whereas for ESO-silane treated system, 2.5 wt% composite works best. Thus the developed ESO based polymer systems and composites would be interesting alternative, derived as biomaterials from renewable resources. And the widening of the range of properties is very important for future studies. Therefore it is hoped that the results described will be useful for a state- of-art- designing of suitable ESO based polymers and composites.