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Scientists create pollen-based paper that can be reused for printing and unprinting.

Scientists at Nanyang Technological University in Singapore (NTU Singapore) have created a pollen-based “paper” that can be “erased” and reused several times without causing damage to the paper after it has been written on.

In a research paper published online on April 5, 2019, NTU Singapore scientists demonstrated how high-resolution color images could be printed on non-allergenic pollen paper with a laser printer and then “unprinted” (by completely removing the toner without damaging the paper) with an alkaline solution. They showed that this technique could be repeated up to eight times in total.

According to the NTU team led by professors, this new, printer-ready pollen paper could become an eco-friendly alternative to traditional paper, which is created through a multi-step process with a major negative environmental impact.

It could also help cut down on the carbon emissions and energy consumption connected with traditional paper recycling, which includes repulping, de-toning (removing printer toner), and rebuilding.

Dr. Ze Zhao, graduate students Jingyu Deng and Hyunhyuk Tae, and former graduate student Mohammed Shahrudin Ibrahim are the other members of this all-NTU research team.

Through this work, we demonstrated that we could print high-resolution color images on paper made from a natural, plant-based material that was rendered non-allergenic through a technology we recently invented,” stated Prof. Subra Suresh, NTU president and senior author of the publication. We also showed that this could be done multiple times without degrading the paper, making this a viable eco-friendly alternative to traditional wood-based paper. This is a novel method of paper recycling in which we not only make paper in a more sustainable way, but also extend its lifespan so that we get the most value out of each piece of paper we generate. With further advances in scalable manufacturing, the concepts described here could be used and extended to make other “directly printable” paper-based products such as storage and shipping boxes and containers. “

Prof. Cho Nam-Joon, the report’s principal author, said: “Our pollen-based paper is highly adaptable in addition to being easily recyclable. Pollen, unlike traditional wood-based paper, is produced in huge quantities and is naturally renewable, making it an appealing raw material in terms of scalability, economics, and environmental sustainability. Furthermore, by combining conductive materials with pollen paper, we might employ the material to create enhanced functionalities and features in soft electronics, green sensors, and generators. “

“Through this study, we showed that we could print high-resolution color images on paper produced from a natural, plant-based material that was rendered non-allergenic through a process we recently developed. We further demonstrated the feasibility of doing so repeatedly without destroying the paper, making this material a viable eco-friendly alternative to conventional wood-based paper. This is a new approach to paper recycling—not just by making paper in a more sustainable way, but also by extending the lifespan of the paper so that we get the maximum value out of each piece of paper we produce. The concepts established here, with further developments in scalable manufacturing, could be adapted and extended to produce other ‘directly printable’ paper-based products such as storage and shipping cartons and containers.”

Prof Subra Suresh, NTU president

This is the latest in a long line of discoveries and technological advances made by NTU researchers across a wide range of disciplines, whose cutting-edge scholarly research translates NTU’s commitment to sustainability into practices that benefit industry and society, as outlined in the university’s Sustainability Manifesto released in 2021 and the NTU 2025 strategic plan.

This NTU innovation has been the subject of a patent application.

A more environmentally friendly method of papermaking

Traditional paper is created from wood cellulose fibers, and the papermaking process includes energy-intensive activities such as logging, debarking, and chipping. The pulp and paper sector contributes to the global problem of deforestation and rising carbon emissions, accounting for 33 to 40% of all industrial wood sold globally [1].

Pollen grains, on the other hand, are produced in vast quantities and on a regular basis as genetic material carriers in plant reproduction. Pollen-based paper is made in a similar way to traditional soapmaking, although it is considerably easier and less energy-intensive.

Credit: Nanyang Technological University

The scientists used potassium hydroxide to dissolve the biological components enclosed in stiff sunflower pollen grains, resulting in soft microgel particles. This procedure also eliminates the allergen-causing component in pollen.

The scientists then filtered the pollen microgel with deionized water to remove any remaining particles before casting it into a 22 cm 22 cm mold to air dry. This produces a piece of paper with a thickness of 0.03 mm, or about half the thickness of a human hair.

An earlier study by the same NTU team demonstrated that pollen paper can bend and curl in reaction to moisture in the air. The scientists submerged the paper in acetic acid—an active component in vinegar—to “stabilize” it and make it resistant to moisture.

Print, rinse, and repeat as necessary.

To show the printability of their sunflower pollen paper, the NTU scientists used a laser printer to print a painting from Vincent Van Gogh’s Sunflowers series. They discovered that the paper went through the printer without tearing or being damaged.

When tape was applied to the printed picture and removed, none of the toner powder particles came off, implying that the toner layer was well-deposited on the pollen paper surface.

While the colors of the image printed on pollen paper vary slightly from the same image printed on normal paper (due to differences in subsequent treatments), the image quality and clarity were equivalent on both types of paper.

The scientists also discovered that further immersion in water did not harm or soften the printed pollen paper, which is critical for printing materials.

The NTU team next demonstrated how the pollen paper could be unprinted. “Unprinting” is a notion that has evolved in recent years as an environmentally beneficial alternative to traditional methods of removing toner from used paper before recycling it. For laser printing, this unprinting entails loosening the link between the toner powder and the paper.

In contrast, typical paper unprinting processes involve the use of chemicals (e.g., chloroform or acetone) to weaken the connection between the toner and paper or the use of high-intensity light to ablate the toner off the printed paper. Both of these methods may cause the paper’s physical integrity to be compromised, rendering it unfit for reproducing. Furthermore, the use of chemicals may pose environmental and health dangers, according to the scientists.

In addition to sunflower pollen, the NTU researchers discovered that pollen grains from camellia and lotus could be used to create a paper-like material similar to sunflower pollen paper. Thus, their findings demonstrate that more than one type of pollen could be employed to develop pollen-based alternatives to traditional fertilizers.

This study adds to the team’s body of pollen research at NTU over the last five years. Profs. Cho and Suresh and their research team previously proved that pollen paper could bend, coil, and even crawl like a caterpillar in reaction to changes in moisture levels in the air, making the material a possible contender for soft robotics applications.

The same researchers demonstrated that by printing different patterns on pollen paper, they could induce it to fold itself up into diverse 3D forms.

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