Researchers from Nanyang Technological University, Singapore (NTU Singapore) have developed a pollen-based paper that can be ‘erased’ and reused multiple times without damage.
Published in Advanced materialsThe team’s research showed how high-resolution color images could be laser-printed onto the non-allergenic pollen paper and then ‘unprinted’ by removing the toner completely without damaging the paper, using an alkaline solution.
Findings showed that the process can be repeated up to at least eight times, making the pollen-based paper a potentially eco-friendly alternative to conventional paper made through a multi-step process with a significant negative impact on the environment, the team said.
Led by professors Subra Suresh and Cho Nam-Joon, the team also believes it can reduce carbon emissions and energy consumption associated with conventional paper recycling, which involves repulping, detonation and reconstruction.
“This is a new approach to paper recycling – not only by making paper in a more sustainable way, but also by extending the life of the paper so that we get the maximum value out of every piece of paper we produce,” says Prof. Suresh , NTU president and senior author of the article.
“The concepts developed here, with further advancements in scalable manufacturing, can be adapted and expanded to produce other ‘printable’ paper-based products such as storage and shipping boxes and containers.”
Co-senior author Prof Cho Nam-Joon added that unlike conventional wood-based paper, pollen is generated in large quantities and is naturally renewable. Making conventional paper, made from cellulosic fibers found in wood, involves energy-intensive steps, including logging, sand debarking. This contributes to deforestation and rising CO2 emissions.
“In addition, by integrating conductive materials with the pollen paper, we may be able to use the material in soft electronics, green sensors and generators to achieve advanced functions and properties,” Nam-Joon said.
According to the team, they used potassium hydroxide to first remove the cellular components encapsulated in tough sunflower pollen grains, turning them into soft microgel particles. This step removes the component in pollen that causes allergies.
They then used deionized water to remove unwanted particles from the resulting pollen microgel, before pouring it into a 22 x 22 cm mold to air dry. This forms a piece of paper that is about 0.3 mm thick.
Previous research by the team showed that pollen paper can bend and curl in response to moisture in the air. To “stabilize” the paper and make it impervious to moisture, scientists said they submerged it in acetic acid.
To demonstrate printability, the NTU scientists printed a painting with a laser printer and found that the paper passed through the printer without damage.
Although the colors of the image on the pollen paper differed slightly from the same image on conventional paper, in part due to differences in subsequent treatments, scientists said the image resolution and brightness were similar on both types of paper. They also found that immersion in water did not damage or soften the printed pollen paper.
‘Unprinting’, a concept of removing toner from used paper before recycling, was also achieved by immersing the paper and rubbing it in a common alkaline lab reagent for two minutes.
The pollen-based paper swelled upon immersion, mechanically disintegrating the toner layer. The swollen paper was then shrinked in ethanol for five minutes and air dried. After treatment with acetic acid, the team said it was ready to print again.
Conventional non-printing methods use chemicals that may pose environmental or health risks (eg chloroform or acetone) to weaken the bond between the toner and paper, or high-intensity light to reduce the toner. Both steps can damage the paper and make it unsuitable for reprinting, the researchers said.
Aside from sunflower pollen, the NTU team found that camellia and lotus pollen grains could also be used. The study builds on the team’s previous research on pollen.