Scientists develop recyclable pollen-based paper for repeat printing

Scientists at Nanyang Technological University, Singapore (NTU Singapore) have developed a pollen-based “paper” which, after being printed on, can be “erased” and reused multiple times without damaging the paper. could.

In a research paper published online advanced Materials On 5 April, scientists at NTU Singapore demonstrated how high-resolution color images could be printed on non-allergenic pollen paper with a laser printer, and then “unprinted” – completely removing the toner without damaging the paper. By removing – with an alkaline solution . They demonstrated that this process could be repeated at least eight times.

The NTU team, led by Professors Subra Suresh and Cho Nam-joon, said this innovative, printer-ready pollen paper could become an eco-friendly alternative to conventional paper, thanks to a multi-step process with a significant negative environmental impact. is created through

It can also help reduce the carbon emissions and energy use associated with traditional paper recycling, including repulsing, de-toning (removing printer toner) and repackaging.

Other members of this all-NTU research team are research fellow Dr. Zi Zhao, graduate students Jingyu Deng and Hyunhuk Tae, and former graduate student Mohammad Shahrudin Ibrahim.

Prof Subra Suresh, President of NTU and senior author of the paper, said: “Through this study, we demonstrated that we can print high-resolution color images on paper produced from a natural, plant-based material, which is a The medium was non-allergenic. Process that we recently developed. We demonstrated the feasibility of doing this repeatedly without destroying the paper, making this material a viable environmentally friendly alternative to traditional wood-based paper. It’s a new approach to paper recycling – not only by making paper a more sustainable way, but also by increasing the lifespan of the paper so that we can get the most value out of each piece of paper we produce. With further development in scalable manufacturing the concepts established here can be adapted and extended to produce other ‘directly printable’ paper-based products such as storage and shipping cartons and containers.”

Professor Cho Nam-joon, senior author of the paper, said: “In addition to being easily reusable, our pollen-based paper is also highly versatile. Unlike wood-based traditional paper, pollen is produced in large quantities and naturally is renewable, making it potentially an attractive raw material in terms of scalability, economics and environmental sustainability.In addition, by integrating conductive materials with pollen paper, we can potentially achieve enhanced functions and properties The material could be used in soft electronics, green sensors and generators.”

This innovation adds to a series of pioneering discoveries and technological advances by NTU researchers from multiple disciplines, whose cutting-edge scholarly research has translated NTU’s commitment to practices benefiting industry and society, which was released in the University’s Sustainability Declaration. In line with the vision mentioned in in 2021 and NTU 2025 strategic plan.

A patent application has been filed based on this NTU innovation.

More sustainable way of papermaking

Traditional paper is made from the cellulose fibers found in wood, and the papermaking process involves energy-intensive steps that include logging, debarking, and chipping. The pulp and paper industry accounts for 33 to 40 percent of all industrial timber traded globally[1]This form of papermaking adds to the global problem of deforestation and rising carbon emissions.

In contrast, pollen grains are produced regularly and in large quantities as a carrier of genetic material in plant reproduction. The process of making pollen-based paper is similar to that of traditional soap making, which is much simpler and less energy-intensive.

Using potassium hydroxide, the scientists first removed the cellular components contained in hard sunflower pollen grains and turned them into soft microgel particles. This step also removes the ingredient in pollen that causes allergies.

The scientists then used deionized water to remove unwanted particles from the resulting pollen microgel, before pouring it into a 22 cm x 22 cm mold to air-dry. This makes a piece of paper about 0.03 mm thick, or about half the thickness of a human hair.

Earlier research by the same NTU team showed that pollen paper can bend and curl in response to moisture in the air. To “stabilize” the paper and make it insensitive to moisture, scientists immersed it in acetic acid—an active ingredient in vinegar.

Print, rinse and repeat

To demonstrate the printability of their sunflower pollen sheet, scientists at NTU printed a painting from Vincent van Gogh’s Sunflower series using a laser printer. He found that the paper passed through the printer without any tears or damage.

When the tape was affixed to the printed image and removed, none of the toner powder particles came off, suggesting that the toner layer was well deposited on the pollen paper surface.

While the colors of an image printed on pollen paper differed slightly from the same image printed on conventional paper (partly due to differences in subsequent treatments), image resolution and clarity were comparable on both types of paper.

The scientists also found that subsequent immersion in water did not damage or soften the printed pollen sheet—a result essential to the material used for printing.

After this the team of NTU showed that the pollen sheet can be unprinted. “Unprinting” is a concept that has emerged in recent years as an environmentally friendly alternative to traditional methods of removing toner from used paper before it is recycled. This unprinting involves weakening the bond between the toner powder and the paper for laser printing.

The scientists did this by immersing the paper and gently rubbing it in a common laboratory reagent that is alkaline for two minutes. The pollen paper swells when immersed in an alkaline solution, causing the toner layer to mechanically disintegrate and separate from the paper.

Swelled by the unprinting process, the paper was then left to shrink in ethanol for five minutes, and air-dried. After being treated with acetic acid, the paper was ready for reprinting.

This process of treating the pollen paper with acid, printing, then washing the printed image can be repeated up to eight times without any loss of the structural integrity of the paper or the quality of the printed images.

This is in contrast to unprinting techniques used for traditional paper, in which chemicals (such as chloroform or acetone) are used to weaken the bond between the toner and the paper, or to separate the toner from the printed paper. High-intensity light is used for this. Both of these steps can damage the physical integrity of the paper, making it unsuitable for reprinting. In addition, the use of chemicals can pose environmental and health risks, the scientists said.

In addition to sunflower pollen, NTU scientists found that camellia and lotus pollen could also be used to make paper-like materials similar to sunflower pollen. Their work thus suggests that more than one type of pollen can be used to create a pollen-based alternative to traditional paper.

This study builds on the team’s body of research on pollen conducted at NTU over the years. Professors Cho and Suresh and their research team previously demonstrated that pollen paper can bend, twist and even crawl like a caterpillar in response to changing levels of humidity in the air, causing The material becomes a potential candidate for applications in soft robotics.

The same team also showed that they could get pollen paper to fold itself into different 3D configurations by printing different patterns on the paper.