- The reversible physical crosslinking and de-crosslinking of the polymer through the salting-out effect demonstrate the recyclability of the polymeric ink.
- Revolutionary method has the potential to redefine the landscape of 3D printing, paving the path towards a more sustainable and responsible future.
The world of 3D printing is experiencing a paradigm shift, transitioning from energy-intensive and environmentally taxing methods to a more sustainable and eco-conscious approach.
However, traditional 3D printing techniques often face criticism for their reliance on energy-intensive processes and the use of harsh chemicals, which can impose substantial environmental costs.
At the forefront of this revolution are researchers at the University of California San Diego, who have developed a groundbreaking technique utilising the simple interaction of polymer ink and salt water to create solid structures.
This innovative method revolves around a unique polymer solution known as poly(N-isopropylacrylamide) or PNIPAM. When this liquid ink is extruded through a needle into a calcium chloride salt solution, an instantaneous solidification occurs upon contact with the saline environment.
Salting-out effect
The phenomenon, dubbed the “salting-out effect,” is the driving force behind this novel 3D printing technique.
The “salting-out effect” is a well-established phenomenon in chemistry. The introduction of aqueous salt solutions significantly lowers the phase transition temperature of PNIPAM solutions, bringing it below 10°C.
The reduction in temperature enables the spontaneous formation of physical crosslinks within the PNIPAM chains at room temperature, effectively solidifying the solution upon contact with the salt solution.
The beauty of this process lies in its simplicity and efficiency. The PNIPAM solutions, readily extrudable through needles, solidify instantly upon encountering salt ions, preserving the printed structures without the need for additional steps, specialized equipment, or harsh chemical additives.
Reversible nature
The elimination of complex post-processing steps and reliance on toxic substances marks a significant stride towards environmentally responsible manufacturing.
Furthermore, the reversible nature of the salting-out effect underscores the inherent recyclability of this 3D printing method. The physical crosslinking and de-crosslinking of the polymer, induced by the salt solution, allow for easy dissolution of the solid structures in fresh water, reverting them back to their liquid form.
The characteristic opens up a new avenue for sustainable polymer material utilisation, minimising waste and maximising resource efficiency.
The researchers, led by Professor Jinhye Bae  in the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering at the UC San Diego Jacobs School of Engineering,  envision their simple and reversible 3D printing technique as a key contributor to the development of environmentally friendly polymer manufacturing technologies.
Beyond its inherent sustainability, the  technique demonstrates remarkable versatility, enabling the production of complex structures with integrated functionality.
The researchers have successfully printed electrical circuits using PNIPAM ink mixed with carbon nanotubes, which successfully powered a light bulb.
The ability to dissolve these printed circuits in fresh water highlights the potential for creating water-soluble and recyclable electronic components, further pushing the boundaries of sustainable technological innovation.
The implications of this breakthrough are far-reaching. By eliminating the need for energy-intensive steps, toxic chemicals, and specialized equipment, this new 3D printing technique paves the way for a more environmentally friendly and cost-effective approach to polymer manufacturing.