7 hours ago
Newswise — A Korean research team has developed a closed-loop 4D printing technology that enables self-actuating and recyclable structures using sulfur waste generated from petroleum refining processes.
A joint research team led by Dr. Dong-Gyun Kim of the Korea Research Institute of Chemical Technology (KRICT), Professor Jeong Jae Wie of Hanyang University, and Professor Yong Seok Kim of Sejong University reported the world’s first 4D printing technology based on sulfur-rich polymers that respond to heat, light, and magnetic fields.
Large amounts of elemental sulfur by-products are generated during petroleum refining. According to the Mineral Commodity Summaries 2025 published by the United States Geological Survey (USGS), global sulfur production reached approximately 85 million tons in 2024. Developing technologies that convert this abundant material from a simple industrial by-product into a valuable resource has therefore become increasingly important.
One promising solution is “sulfur plastics,” which are attracting attention as a representative circular material capable of converting waste sulfur into high-value resources.
Sulfur plastics possess several advantageous properties. They can transmit infrared light that conventional plastics cannot, making them suitable for infrared camera lenses, and they can also capture heavy metals, enabling applications in water purification systems. As a result, sulfur plastics are regarded as environmentally friendly, resource-circulating materials that can simultaneously contribute to environmental protection and the development of advanced industries.
Despite these advantages, sulfur plastics have been difficult to apply in 3D printing technologies for complex structures. Their densely cross-linked internal network structures, have made them difficult to use in 3D printing due to low flowability.
To overcome this limitation, the research team engineered a loosely cross-linked sulfur polymer network, enabling the material to be easily extruded and printed into complex 3D structures.
By precisely controlling the sulfur content and cross-linked network structure of the polymer, the researchers realized 4D printing with shape-memory properties. These structures can autonomously transform their shapes in response to heat or light without additional mechanical systems.
In addition, applying a near-infrared (NIR) laser for just eight seconds triggers a chemical welding process, where internal bonds temporarily break and reconnect. This allows printed components to be firmly joined together without adhesives, enabling the fabrication of complex 4D structures similar to assembling LEGO blocks.
Furthermore, by incorporating 20% magnetic particles, the team developed soft robots smaller than 1 cm that move autonomously without external power sources. By combining the shape-memory properties of the polymer with magnetic responsiveness, the robots can perform sophisticated motions by following external magnetic fields.
Another key feature of this technology is its closed-loop manufacturing capability. After use, the printed 4D structures can be melted and fully reused as printing feedstock, enabling 100% recycling of the material and establishing a complete resource-circulating manufacturing system.
Dr. Dong-Gyun Kim of KRICT stated,
“This study represents the first example of upcycling industrial sulfur waste into advanced robotic materials. Smart materials that can move autonomously and be recycled are expected to become key drivers of future soft robotics and automation technologies.”
The study was published in Advanced Materials.
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KRICT is a non-profit research institute funded by the Korean government. Since its foundation in 1976, KRICT has played a leading role in advancing national chemical technologies in the fields of chemistry, material science, environmental science, and chemical engineering. Now, KRICT is moving forward to become a globally leading research institute tackling the most challenging issues in the field of Chemistry and Engineering and will continue to fulfill its role in developing chemical technologies that benefit the entire world and contribute to maintaining a healthy planet. More detailed information on KRICT can be found at https://www.krict.re.kr/eng/
The research was supported by the KRICT core research program, the Ministry of Science and ICT of Korea, and the U.S. Army International Technology Center.
