New insights into 3D printing membranes

To address the controversies on the feasibility of 3D printing for membranes, researchers from the Singapore University of Technology and Design (SUTD) and Nanyang Technological University (NTU) have coined a new term 'hybrid additive manufacturing' for the water treatment industry.

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Overview of the relationship between 3D printing and membrane-based water treatment industry.
Source: SUTD

3D printing has seen great advancements in various aspects over the past few decades, and many industries have seen innovative breakthroughs in their respective fields. Amongst them, the water treatment industry has also reaped benefits off the prospects of 3D printing. High performance spacers and membranes can be fabricated by 3D printing, and they help increase permeate production while minimising energy consumption in purification processes.

Researchers from NTU and SUTD reviewed the recent efforts, shortcomings as well as the conflicting reports of 3D printing in membrane-based water treatment (refer to figure). Their research paper has been published in Water Research.

In the paper, they showed the potential of 3D printed spacers. The great freedom of design in 3D printing enables the fabrication of complex and innovative spacers, which was previously impossible with conventional heat extrusion methods. These spacers were able to reduce the number of dead zones within the flow channel, and help mitigate detrimental membrane fouling problems. Some spacer designs such as the helical spacer, turbospacer, and column spacer were even able to reduce energy consumption.

An interesting perspective was also presented in the paper regarding the feasibility of 3D printed membranes. Microfiltration membranes (MF) with pore sizes < 1 μm were previously fabricated by conventional processes such as sintering or phase inversion. However, for 3D printing, the Two-Photon Polymerization printing technique is said to have the finest printing resolution of about 1 μm up to date. Theoretically, it should be impossible to fabricate microfiltration (MF) membranes with 3D printing. It has thus sparked much confusion in the water treatment industry when an increasing number of publications reported the successful fabrication of 3D printed MF membranes over the past decade.

In an attempt to resolve this confusion, the paper critically analyses these 3D printed membranes, especially on 3D printing's role in the overall fabrication process. Hybrid additive manufacturing, a process where 3D printing is used in conjunction with other established fabrication methods, is also introduced in the paper. It shows how 3D printing can still be a powerful tool in the fabrication of membranes when used together with other established processes despite its inadequate printing resolution.

"3D printing is gradually evolving from a single-standalone process to a multi-integrated process. The application continues to grow in the water treatment industry, especially the membrane-based technologies. Future focus is expected to shift from lab scale prototyping to large scale manufacturing," said principal investigator Associate Professor Chong Tzyy Haur from NTU.

"It will not be an easy challenge to overcome upscaling and material limitations, but consistent research efforts are already evident today. Potentially, 4D printing can even be a possibility in the future to fabricate smart spacers and membranes that adapt to its surrounding environment," explained co-author Professor Chua Chee Kai from SUTD.

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