Dixie currently produces two lines of bioresins; MAESO, derived from soybean oil, and MAELO, from linseed oil feedstocks. Like typical unsaturated polyester resins, they contain a reactive diluent such as styrene or vinyl toluene. However, Dixie also makes a methacrylated fatty acid (MFA) derived from palm, coconut and soybean oils, which can be used to replace all or some of the styrene or vinyl toluene. Using MFA reduces emissions and odors in the manufacturing process, and the MFA resins are tougher and less brittle than those made with styrene.
“We’re also working on a toughener made with soybean oil, which can be used for epoxies, vinyl ester and polyester resins. When we’ve compared it to products that are currently available in the market, it appears to have similar properties. This could have a really big impact,” says Campanella.
In most cases the processes for manufacturing bio-based composites are no different than those for oil-based composites. “You may have to optimize your formulation, but that also happens if you’re using a resin made from oil,” says Campanella. Dixie generally sticks with palm oil, soybean oil and linseed oil or their fatty acids because of their pricing and availability.
Much of the interest in bio-based composites comes from the transportation industry, says Campanella. Ford, BMW, Mercedes Benz and Jaguar all have interior products made with biocomposites, ranging from seat backs and door panels to carpeting and insulation. There are biocomposites in many sporting goods, including tennis rackets, snowboards and bicycles. In the construction industry, windows, doors, insulation and other building products have all been made with bioresins and/or natural fibers.
Megan Robertson, associate professor in the department of chemical and biomolecular engineering at the University of Houston, is researching several aspects of bio-based resins. Her research group initially tried replacing Bisphenol A (BPA) in epoxy resins with readily-available vegetable oils, but the resulting composites did not have the necessary strength or thermal properties.
They then tried bio-based phenolic acids derived from fruits and vegetables. “They have very similar functionality and similar chemical structures to BPA, which can impart desirable physical properties to the resin,” says Robertson. The problem is that bio-based phenolic acids aren’t currently obtainable in large volumes. More recently the researchers have focused on epoxies made from the more widely available lignin-based feedstocks. Resins made with lignin-derived molecules could have commercial potential in the shorter term.