Pollen-based paper that can be printed and then 'unprinted' developed by NTU scientists

(From left) NTU's Professor Cho Nam-Joon, Professor Subra Suresh and research fellow Zhao Ze with the paper-like material made from pollen grains. PHOTO: NANYANG TECHNOLOGICAL UNIVERSITY

SINGAPORE - Your photographs could in future be printed and "unprinted" on a new type of paper made, not with wood pulp, but from plant pollen.

The paper is developed by researchers from the Nanyang Technological University (NTU) and can undergo up to eight cycles of printing and unprinting, according to Professor Subra Suresh and Professor Cho Nam-Joon, the project's leaders.

The paper is touted by Prof Suresh as 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," he said.

The paper is made using pollen grains, which are generated regularly for the reproductive cycle of plants.

Sunflower pollen grains were used in the paper's development process. They were harvested and then put into a potassium hydroxide solution to extract their cellular components to turn them into soft microgel particles.

This process has the additional benefit of removing the allergy-causing components of the pollen.

Using deionised water to remove unwanted particles, the microgel is then set in a mould to air-dry and form the pollen paper, a similar process used to turn wood pulp into conventional paper.

The NTU scientists demonstrated the printability of the paper by using a laser printer to print an image of a painting from Vincent van Gogh's Sunflowers series.

They found that immersing the printed pollen paper in water did not damage or soften material.

To "unprint" the image, the paper was soaked in an alkaline solution, causing the surface to swell and dislodge the ink particles, removing the image.

It was then left to shrink back to its normal size in an ethanol solution and treated with acetic acid before being rendered ready for printing again.

According to Prof Cho, this process can be repeated another eight times without any loss of the paper's structural integrity or the quality of the printed images.

He said: "Aside from being easily recyclable, our pollen-based paper is also highly versatile.

"Unlike wood-based conventional paper, pollen is generated in large amounts and is naturally renewable, making it potentially an attractive raw material in terms of scalability, economics and environmental sustainability."

An earlier version of the pollen paper by the same NTU team showed that it can bend and curl in response to moisture in the air.

Prof Suresh said that through a more sustainable means of production and by extending the lifespan of each piece of paper, its value can be maximised.

An image printed on paper, made using sunflower pollen, is "unprinted" after being immersed in ethanol. PHOTO: NTU

He added that the paper can be used for products such as storage and shipping cartons and containers.

Besides this, the paper also can contribute to wider sustainability efforts, according to Prof Cho, such as replacing the plastic substrates currently used in semi-conductors.

He said: "By integrating conductive materials with the pollen paper, we could potentially use the material in soft electronics, green sensors and generators to achieve advanced functions and properties."

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