Epoxidized soybean oil is a type of organic matter that is a light yellow viscous oily liquid at room temperature. It is non-toxic, soluble in most organic solvents and hydrocarbons, and insoluble in water. It has excellent heat resistance, light resistance and compatibility. It is often used as a plasticizer in PVC products, especially in transparent PVC products, food packaging products and other non-toxic products.
Recently, some researchers published a paper, drawing on the adhesion mechanism of classic commercial epoxy resin glue and marine mussels, to develop a sustainable and strong adhesive whose components are all derived from biomass: epoxy soybean oil (produced by the epoxidation reaction of soybean oil), malic acid (found in apples, grapes, hawthorn and other fruits), tannic acid (commonly found in trees, red wine and black tea). This adhesive is suitable for almost any substrate surface, is easy to use (it cures in 5 minutes with a household hair dryer), is environmentally friendly, cheap and practical, and has adhesion properties comparable to the strongest classic epoxy adhesives on the market today. It is also easy to produce on a large scale and has good commercialization prospects.
As a classic adhesive, epoxy resin is obtained by the reaction of epoxy compounds and polyamine compounds, where the latter serves as a curing agent and can undergo nucleophilic reactions with epoxy functional groups. Both compounds are petrochemical products and are non-renewable products. The researchers drew on the adhesion mechanism of marine mussels, in which the catechol group helps the cross-linking reaction occur, so they hypothesized that three components: epoxy compounds, nucleophiles and mixtures of compounds with a catechol structure should also have good adhesion properties.
The researchers then selected among common natural compounds: epoxidized soybean oil is currently the most commonly used bio-based plasticizer and can be used as the first component; nucleophiles are mainly selected from acids and alcohols, such as fumaric acid, malic acid and succinic acid can be used as alternatives; tannic acid, catechol, and gallic acid are also expected to be third components. After comparison, both fumaric acid and succinic acid had solubility problems, and the formula containing catechol and gallic acid did not produce solids after the reaction stopped. Only when epoxidized soybean oil, malic acid and tannic acid are combined, it has good results. Subsequently, the researchers determined that the optimal ratio of simple mixing of the three components was 1:0.4:0.5 (mass ratio), and the strongest adhesion performance could be achieved by reacting at 70 °C for 24 hours.
This adhesive works on a variety of surfaces. The researchers applied it to sandblasted steel, polished aluminum, Teflon, polished steel, sandblasted aluminum, PVC plastic and wood surfaces to test the bonding strength and compare it with commercial products. This adhesive exhibits excellent adhesion properties on all of these surfaces. Surprisingly, the bond strength of this adhesive to polished aluminum was 13 ± 1 MPa, surpassing all control commercial adhesives.
This adhesive also has good water resistance. After being soaked in water for 24 hours, it still maintains about 75~100% of the initial bonding strength. Even after being soaked in water for 1 week, it still maintains about 26~78% of its performance. Similar experiments were conducted in artificial seawater with similar results, indicating that the adhesive can resist corrosion from salts. In addition, the cost of this glue is not high. The cost of bisphenol A and amines used to make classic epoxy resin is about US$3,880 per ton. According to the three-component ratio described by the researchers, the cost is about US$5,150 per ton, which shows commercial promotion potential.
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Reference
- Sustainably sourced components to generate high-strength adhesives
Nature, 2023, 621, 306-311.
