Development strong, stable plant-based thermoset looks promising


Airplanes, electronics and solar cells are all in demand, but the materials holding these items together — epoxy thermosets — are not environmentally friendly. Now, a group reports in ACS' journal Macromolecules that they have created a plant-based thermoset that could make devices "greener."

rThermosets are resins that, when cured, undergo a change that makes them strong and stable. Once thermosets are molded into a shape, they typically are set and cannot be reworked. These materials are frequently used as adhesives and coatings in electronics, appliances and aircraft. But most epoxy thermosets are made with nonrenewable materials, and some contain substances that can potentially harm the environment. And because of their structures, they cannot break down or be recycled. Plant-based thermosets are commercially available but they are usually weak and easily break. Jian-Bing Zeng and colleagues wanted to create a safe and strong plant-based thermoset.

The team developed a new plant-based curing agent – NYL - that was made from castor oil derived monomers, i.e., sebacic acid and decamethylene diamine. They then used this to cure epoxidized soybean oil (ESO) to fabricate all plant oil derived epoxy thermoset through a catalyst-free curing method. 
The researchers found that the curing rate decreased with increasing NYL chain length. “The cross-link density of the epoxy thermoset decreases while the crystallization enhances with increasing NYL chain length, which results in drastic enhancement in tensile strength, Young’s modulus, and elongation at break of the resultant thermosets, enabling those parameters to enhance by up to 59, 145, and 18 times, respectively, compared to sebacic acid cured ESO thermoset,” they wrote.
The crystalline material was not only stronger, and more durable and heat-resistant than before, in addition, light passed through the soybean-based thermoset, potentially making it ideal for applications such as solar cells.

The authors acknowledge funding from the National Science Foundation of China, the Basic and frontier research project of Chongqing, and the Fundamental Research Funds for the Central Universities.