Scientists at an IBM research laboratory may have stumbled on a new type of useful thermoset polymer.
IBM researchers and other scientists have reported finding a recyclable, strong thermoset by reacting paraformaldehyde with certain diamines. In the May 16 issue of the major, peer-reviewed journal Science, the researchers state the thermoset polymer has very high tensile strength, excellent solvent resistance and high resistance to stress cracking, making it suited to high performance uses.
High performance thermosets such as polyimides and polybenzimidazoles are used in such applications as aerospace, electronics and automotive. However, all known thermosets are difficult to recycle because they cannot by remolded once cured, and decompose when heated in attempts to form new parts, the Science paper authors explain. They state in the article that the new thermosets can be treated with acidic solution to recover the monomers.
Lead author of the Science paper is Jeannette M. Garcia of IBM's Almaden Research Center in San Jose, Calif. Co-workers included other IBM personnel and scientists with Eindhoven University of Technology in Holland, and King Abdulaziz City for Science and Technology in Saudi Arabia.
A composites expert indicates in an accompanying Science piece that the reported research is a milestone.
The authors “report a crucial step towards recyclable thermosets,” stated Timothy E. Long, a scientist with Virginia Polytechnic Institute & State University's Department of Chemistry, Macromolecules and Interfaces Institute. “The goal is to create reversible thermosets that combine the desirable thermal and chemical stability of conventional thermosets with recyclability and reprocessability.”
Long said the work showed the thermosets' raw materials could be recovered with sufficient purity to convert to a new product.
The research team said a low temperature reaction between paraformaldehyde and 4,4-oxydianiline created networks that can polymerize at higher temperature to make polyhexahydrotriazine.
“The use of a multifunctional amine for making triazine polymeric networks is unprecedented,” Long wrote. “The tensile properties of these triazine thermosets exceed conventional polyimide benchmarks,” he added.
The researchers reported the new untreated thermoset had tensile strength of about 2 million pounds per square inch. When reinforced with carbon nanotubes, tensile strength — or Young's modulus — shot up to 2.9 million psi. The reinforced tensile modulus is in the neighborhood of values for reinforced epoxies, unsaturated polyesters and nylons, the researchers pointed out.
High performance thermosets could “enable longer product lifetimes and may require less plastic to achieve similar performance,” Long concluded. The researchers stated such new thermosets could lead to cost savings through the reworking of defective parts made from expensive materials.
IBM personnel and other scientists helped their research through computational modeling analysis to understand what the molecules were doing during the reactions.
Different diamine monomers could create a variety of new thermosets. Organogels are other kinds of polymers possible with the new reactions. Organogels can exhibit self-healing properties.
Formaldehyde and some amine-like monomers have long been reacted to create low-tech, unrecyclable thermosets. Melamine-formaldehyde and urea-formaldehyde polymers, for example, have been used to mold items like dishware.