A Solution for Thermosetting Plastic Waste?
Created By RISC | 14 hours ago
Last modified date : 14 hours ago
The environmental challenge of plastic waste involves not only conventional recycling but complex plastics that are far harder to manage.
Water bottles, food containers, plastic packaging, and plastic bags are typically made of thermoplastics. These items can therefore be melted and reshaped when heated. But another category of plastic is an increasing environmental concern—thermosetting plastics.
Thermosets are known for their strength and chemical resistance. Once cured by heat, they cannot be melted or reshaped. Instead, they harden permanently and will burn rather than soften. These properties make them ideal for heavy-duty applications such as car tires, polyurethane foams used in sofas and car seats, shoe soles, adhesives, epoxy coatings, or melamine dishware. Their durability, however, also makes thermosets extremely difficult to recycle. Most thermoset waste ends up in landfills or incinerators, contributing to long-term environmental damage.
So how can we deal with thermosetting plastics?
Vitrimerization turns thermosetting plastics into plastics with dynamic structures. These structures allow them to break and reform bonds through a chemical reaction known as transesterification under specific conditions. Plastics that undergo vitrimerization gain a combination of thermoplastic and thermoset properties. They can be melted and reshaped, while still retaining mechanical strength and resistance to heat, sunlight, and chemicals. These materials also possess self-healing capabilities because their bonds can break and reform under appropriate heating, allowing them to be reshaped, repaired, or reused multiple times (typically 3–5 times) without loss of performance. This makes vitrimerization a promising method to address the issue of thermoset plastic waste.
Recycling athletic shoe soles or running shoes made from crosslinked ethylene-vinyl acetate (EVA) foam is a notable example. This type of foam is highly flexible, impact-resistant, durable, and non-compressible. Research shows that EVA thermosets can be converted into EVA vitrimer by grinding EVA scraps into micron-sized particles (<200 µm) and mixing them with catalysts such as zinc acetate (Zn acetate) and materials with hydroxyl groups (-OH), like polyvinyl alcohol (PVOH). When this mixture is hot-pressed, a transesterification reaction occurs, transforming some of the crosslinks into dynamic bonds. Upon further molding, the plastic can be reshaped without adding more chemicals and retains its original properties. Unlike mechanical recycling, which typically degrades material quality, vitrimerized EVA maintains its mechanical integrity. The dynamic bonds can break and reform under heat, making it possible to recycle previously unrecyclable thermoset plastics into high-quality, high-value products.
But vitrimerization still faces challenges. One significant hurdle is reducing thermoset plastic waste into micron-sized particles, especially with rubber materials that are tough and elastic. At room temperature, this grinding is difficult. Therefore, the rubber must be turned into a glass-like state—hard and brittle—making it easier to break down. This process requires extremely low temperatures, increasing production costs.
Advancing this technology could pave the way for recycling more complex waste streams, such as electronic circuit boards, wind turbine blades, automotive and aerospace components, or insulation materials in solar panels. This would significantly reduce industrial and hazardous waste and promote sustainable end-of-life management for these products.
Content by: Suphunphang Raksawong, Sustainable Building Material Researcher
References:
Amin Jamei Oskouei et al. (2024). Vitrimerization of crosslinked poly(ethylene-vinyl acetate): the effect of catalysts. RSC Appl. Polym., 2024, 2, 905.
Alireza Bandegi et al. (2023). Vitrimerization of crosslinked elastomers: a mechanochemical approach for recycling thermoset polymers. Mater. Adv., 2023, 4, 2648–2658.