Scientists at Nanyang Technological University, Singapore developed a pollen-based paper that can be printed on and erased multiple times without damaging the paper.
In a research paper published online in Advanced Materials on 5 April, the NTU Singapore scientists demonstrated how high-resolution colour images could be printed on the non-allergenic pollen paper with a laser printer, and then ‘unprinted’. The process could be repeated up to at least eight times.
This novel, printer-ready pollen paper could become an eco-friendly alternative to conventional paper, which has a significant negative environmental impact, said the NTU team led by Professors Subra Suresh and Cho Nam-Joon. It could also help to reduce the carbon emissions and energy usage of conventional paper recycling, which involves repulping, de-toning and reconstructing. A patent application has been filed based on this NTU innovation.
Prof Subra Suresh, NTU President and senior author of the paper, said: “Through this study, we showed that we could print high-resolution colour 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 Cho Nam-Joon, senior author of the paper, 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. In addition, 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.”
The conventional paper industry is responsible for 33 to 40% of all industrial wood traded globally, and adds to the global problem of deforestation and rising carbon emissions.
Meanwhile, pollen grains are generated regularly and in large amounts for plant reproduction. Using potassium hydroxide, the scientists first removed the cellular components encapsulated in sunflower pollen grains and turned them into soft microgel particles. This step also removes the component in pollen that causes allergies.
The scientists proceeded to use deionised water to remove unwanted particles from the resulting pollen microgel, later casting it into a 22 cm x 22 cm mould for air-drying. This results in a piece of paper that is about 0.03 mm in thickness or about half the thickness of the human hair. Earlier research showed that pollen paper can bend and curl in response to moisture in the air. To make the paper insensitive to moisture, the scientists immersed it in acetic acid.
To test their sunflower pollen paper, the NTU scientists printed a painting from Vincent Van Gogh’s Sunflowers series using a laser printer. The paper passed through the printer without damage, and the toner layer was well-deposited on the pollen paper surface.
According to the report in Science Daily, “the colours of the image printed on pollen paper differed slightly from the same image printed on conventional paper, the image resolution and clarity on both types of paper were comparable. The scientists also found that subsequent immersion in water did not damage or soften the printed pollen paper — an outcome essential for materials used for printing”.
The NTU team next showed that the pollen paper could be unprinted by immersing the paper and rubbing it gently in a common lab reagent that is alkaline for two minutes. The pollen paper swelled when immersed in the alkaline solution, causing the toner layer to mechanically disintegrate and break away from the paper. The paper was later left to shrink in ethanol for five minutes, and air-dried. After treating it with acetic acid, the paper was ready for printing again.
This entire process of printing and unprinting pollen paper could be repeated another eight times without any loss of the paper’s structural integrity or the quality of the printed images.
The NTU scientists also found that pollen grains from camellia and lotus could also be used to make a paper-like material.