New Approaches to Polymers and Composites from Plant Oils
Almost all commercially successful polymers and plastics are now synthesized from petroleum based raw materials. Manufacture of useful polymers from plant oils would present a number of advantages such as the renewability of the raw materials, fast biodegradability of the polymers and cheaper prices. Synthesis of polymers from plant oils is not new: ancient Egyptians used flax oil to protect the wood in their ships. However synthesis of rigid, load bearing polymers that are suitable for fiber reinforcement is a new and very active research field.
When an organic chemist looks at a triglyceride the double bonds, the allylic positions, the carbonyl group and the alfa position to the carbonyl group are noticed as the only useful positions for derivatization. So the task of the polymer chemist is to synthesize new monomers from plant oils using these functional groups. The following are some examples from our efforts in this field.
Epoxidation of the soybean oil double bonds followed by opening of the epoxy ring with acrylic acid gave acrylated epoxidized soybean oil (AESO) which is a plant oil based analog of vinyl ester resins. When this monomer is mixed with styrene reactive diluent, a liquid molding resin is obtained which can be reinforced with glass fiber and can be cured free radically to give laminates with a tensile strength of 450Mpa (1)
Plant oils can be brominated at the allylic positions easily . Reaction of allylic bromide with silver isocyanate gives the isocyanate substituted triglyceride. This molecule can be easily converted to polyurethanes with various diols and polyols and particularly, with hydroxyl bearing oils such as castor oil. Thus the first example of a polyurethane where both of the monomers are plant oil based are obtained. The polymer is suitable for the production of flexible foams. (2)
Acrylated epoxidized soybean oil can be reacted with furylamine in a Michael reaction. When the amine is the limiting reagent a desired fraction of the acrylate groups can be preserved for future manipulations. The resulting amine can be easily quaternized with methyl iodide and the product turns out to be an excellent exfoliating agent for montmorillonite clay. XRD analysis indicated an increase in intergallery distance from 12 A to 26 A. When a sample of exfoliated clay is mixed with AESO and free radically cured one observes a 30 % increase in modulus with a 2 % clay loading. This constitutes the first nanoclay reinforced material whose matrix polymer and exfoliating agent are plant oil based. (3)
Our work in this exciting field has so far produced approximately 140 new plant oil based polymers among which 12 are promising in terms of mechanical properties and ease of synthesis. Newer strategies wherby the oil based monomer is grafted onto an existing high molecular weight polymer are now being persued with the hope of increasing fracture toughness of the products.
1. US Pat. 6.121.398 S.Kusefoglu, R.Wool
2. S.Kusefoglu, G.Caylı, J.Applied Pol. Sci., 109, 2948 (2008)
3. E.Altuntas, G.Çaylı, N.Nugay, S.Kusefoglu, Designed Mon.and Poly. ,11, 371 (2008)