Vegetable oil-based epoxies

Key words vegetable oil-based epoxy, preparation of epoxy, curing of epoxy, structure-property relationships of epoxy, application of epoxy. 

The preparation of epoxy resins from a large number of vegetable oils such as sunflower, cotton-seed, linseed, vernonia, soybean, castor and Mesua ferrea has been reported. However, most of these epoxy resins exhibit poor mechanical properties which limit their applications. Vegetable oil-based epoxy resins rather than epoxidised vegetable oils are also used as reactive diluents. These are low viscosity materials used in conjunction with industrial epoxy resins to reduce viscosity and to increase the molecular mass of the latter. As a reactive diluent can also act as a solvent for the resin system, it enables the production of high-solid and low VOC (volatile organic compound) coatings. 

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SEM micrograph of (a) a vegetable oil-based epoxy resin and (b) a commercial PVC blend. 

Compounds such as vegetable oils, fatty acids, di/polyhydroxy compounds, epichlorohydrin and catalysts are required for the preparation of vegetable oil-based epoxies. The resinification or epoxy formation methods are similar to those of conventional petrochemical-based epoxy resins. 

A variety of poly/dihydric oils are used for the preparation of glyddyl ether-type epoxy resins. These include bisphenols, namely bisphenol-A (BPA), bisphenol-F (BPF), bisphenol-S (BPS) and bisphenol-H (BPH) and so on. Other aromatic diols and polyols such as phenolic resin, MF resins and hyperbranched polyol may also be used in the preparation of vegetable oil-based epoxy resins. Bisphenol-A (2,2-bis(4-hydroxyphenyl)propane) is one of the most widely used aromatic diols for the synthesis of epoxy resin. The resins are commonly used as lacquers for coated metal products such as food cans, bottle tops and water pipes. There are also reports on the use of bisphenol-S (BPS) (bis(4-hydroxyphenyl) sulphone), in the synthesis of epoxy resin. The advantages of resistance to deformation by heat and improvement of thermal stability were observed for such epoxy resins. The presence of sulphone group (BPS-based epoxy resin) in the epoxy resin exhibits better gel time than BPA-based epoxy. Another important diol, namely bis(4-hydroxydiphenyl)methane or bisphenol-F (BPF) is used for the synthesis of low viscosity epoxy resins. BPF generally comprises several isomers such as bis(2-hydroxylphenyl)methane (i.e. ortho-ortho isomer), bis(4-hydroxylphenyl)methane (i.e. para-para isomer) and... 

The other important diol which finds wide application in synthesis of flame retardant epoxy thermosets is 4,4 -isopropylidene bis(2,6-dibromo-phenol) (tetrabromobisphenol-A,TBPA).The primary use of TBPA is as a reactive flame retardant in epoxy resin-based circuit boards and in electronic enclosures made of polycarbonate-acrylonitrile, butadiene-styrene, etc. Hexafluorobisphenol-A (bisphenol-AF, hexafluoroisopropylidene diphenol) has also been used for the synthesis of fluorinated epoxy resin aiming at the anticorrosion coatings market for industrial vessels and pipes. The key disadvantages of fluorinated epoxies are their relatively high costs and low Tg, which limit their commercialisation. Thus utilisation of such diols in vegetable oil-based epoxy resins may result in similar performance. 

As with other polymers and resins, the modification of epoxy resins eliminates a number of disadvantages including brittleness, low thermal stability and high flammability to give the required properties for end applications. Considerable effort has therefore been made to improve the thermal and mechanical properties of vegetable oil-based epoxy resins. These may be grafted or blended with other flexible resins such as polyester, polyacrylate and polyurethane to improve their flexibility and other performance characteristics. 

Table 7.1 Physical properties of vegetable oil-based epoxy resins...

Table 7.2 Average values of properties of vegetable oil-based epoxies...

Epoxidised vegetable oils are flammable as hydrocarbon is their major constituent. However, vegetable oil-based epoxy resin can be made flame... 

What are the important parameters to be determined in confirming the suitability of vegetable oil-based epoxy resins for industrial applications ... 

Are vegetable oil-based epoxy resins cured by a conventional peroxide curing system in the same manner as polyesters ... 

Is it possible to confirm the curing characteristics of vegetable oil-based epoxy resins by instrumental techniques such as FTIR, rheometer or DSC Explain your answer. 

The flame retardancy of petroleum-based epoxy is higher than that of vegetable oil-based epoxy resins. Give reasons for this statement. How is vegetable oil-based epoxy resin modified to improve its toughness and thermal properties ... 

Why is the alkali resistance of vegetable oil-based epoxy cured films... 

Researchers are exploring the feasibility of manufacturing epoxidised vegetable oil-based polymer composites. Composite materials have been manufactured utilising vegetable oil-based epoxy resins and a range of... 

The incorporation of bio-based epoxy into clay nanoplatelets is one of the best combinations for developing environmentally benign high performance materials. High performance nanocomposites of vegetable oil-based epoxy resins and alkylammonium modified montomorillonite (MMT) have been already reported by many researchers. 

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