A Korean research team has developed an innovative closed-loop 4D printing technology that enables the creation of self-actuating and fully recyclable structures using sulfur waste generated from petroleum refining processes. The breakthrough demonstrates how industrial by-products can be transformed into high-value smart materials with applications in advanced manufacturing and robotics.
The research was conducted by a joint team led by Dong-Gyun Kim of the Korea Research Institute of Chemical Technology (KRICT), Jeong Jae Wie of Hanyang University, and Yong Seok Kim of Sejong University. Their work introduces the world’s first 4D printing technology based on sulfur-rich polymers that can respond to heat, light, and magnetic fields.
Large quantities of elemental sulfur are produced as by-products 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. Finding ways to convert this abundant industrial waste into valuable materials has therefore become increasingly important for sustainable manufacturing.
One promising solution is the development of sulfur plastics—advanced materials capable of transforming waste sulfur into high-value products. Sulfur plastics possess unique properties, including the ability to transmit infrared light that conventional plastics cannot, making them suitable for applications such as infrared camera lenses. They can also capture heavy metals, enabling potential use in water purification systems. These characteristics position sulfur plastics as environmentally friendly materials that support circular resource use while advancing industrial innovation.
Despite their advantages, sulfur plastics have traditionally been difficult to use in 3D printing because of their densely cross-linked internal structures, which limit flowability during the printing process. To address this challenge, the research team engineered a loosely cross-linked sulfur polymer network that can be easily extruded and printed into complex three-dimensional forms.
By precisely controlling the sulfur content and cross-linking structure, the researchers successfully created 4D printed materials with shape-memory properties. These structures can autonomously transform their shape when exposed to heat or light, eliminating the need for additional mechanical systems.
The team also introduced a novel chemical welding method. When exposed to a near-infrared laser for just eight seconds, the printed structures undergo a temporary bond breakage and reconnection process that allows separate components to fuse together without adhesives. This approach enables the assembly of complex 4D structures in a modular manner similar to building with interlocking blocks.
In another advancement, the researchers incorporated 20 percent magnetic particles into the polymer, enabling the development of soft robots measuring less than one centimeter. These miniature robots can move autonomously by responding to external magnetic fields, combining magnetic responsiveness with the shape-memory characteristics of the sulfur polymer.
A key feature of the technology is its closed-loop manufacturing capability. After use, the printed structures can be melted and reused entirely as new printing feedstock, allowing the material to be recycled repeatedly. This enables a fully circular manufacturing process with 100 percent recyclability.
According to Dong-Gyun Kim, the innovation demonstrates how industrial sulfur waste can be transformed into advanced functional materials. He noted that smart materials capable of autonomous movement and full recyclability could become essential components in the future development of soft robotics and automation technologies.
The study detailing this breakthrough has been published in the scientific journal Advanced Materials.
