Strong and durable like thermosets, yet moldable and recyclable like thermoplastics, vitrimers are ‘malleable thermosets’ which are challenging the status quo in the composites industry. Mallinda, a startup company founded by some of the pioneering inventors of the technology, is developing malleable CFRPs for rapid (∼30 s) production cycle times.
For over 50 years, synthetic polymers have been divided into two general categories: thermosets which have excellent mechanical properties, but must be irreversibly cured; and thermoplastics, which can be melted down and reprocessed, but have inferior thermal and mechanical properties (Figure. 1) . This characteristic allows thermoplastics to be molded relatively quickly for high volume manufacturing, using techniques such as injection molding. Futhermore, these materials can be recycled by melt-processing. On the down side however, the majority of thermoplastics are susceptible to mechanical deformations and creep at elevated temperatures; therefore, they do not have a sufficiently robust dimensional stability at high temperature. In addition, commercial thermoplastics are typically of higher cost in comparison to analogous thermoset resins. Thermosets are the resins of choice for structural composites applications, such as aerospace composite part fabrication where stiffness and durability are critical. While thermoset resins offer significant performance benefits compared to their thermoplastic counterparts, significant cure times for thermoset resins make them unsuitable for high volume applications such as automotive. Furthermore, due to the inability to reprocess thermoset resins after they have been cured, these materials are refractory to repair and remolding. Recently, this paradigm has been challenged by the arrival of malleable thermoset materials, also known as vitrimers.
This article appeared in the May–June 2018 issue of Reinforced Plastics.