Eco-friendly transparent paperboard developed by JAMSTEC, University of Tokyo, and Tokyo University of Science

Paper cups and paper packaging containers are distributed as products made from environmentally friendly materials, but they have not yet replaced plastic as their contents cannot be seen. A research group led by Researcher Noriyuki Isobe at the Research Institute for Marine Resources Utilization of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Professor Tadahisa Iwata from the Graduate School of Agricultural and Life Sciences at the University of Tokyo, and Associate Professor Kojiro Uetani from the Department of Industrial Chemistry, Faculty of Engineering at Tokyo University of Science, has succeeded in making paperboard transparent. This material can also be made (upcycled) from cellulose sources such as wastepaper and clothing, and can be three-dimensionally molded into transparent cups and straws, with strong resistance to moisture.

Isobe explained, "Normal paper cellulose fibers are micrometer-sized, but transparent paper has a structure in which nano-sized cellulose fibers are densely packed, so light does not scatter, making it transparent. There are still many challenges to overcome for social implementation. We want to develop a prototype for a continuous production process."

Deep-sea floors are known to accumulate large amounts of plastic waste (mostly disposable packaging containers). Although recycling has progressed, it is difficult to completely stop the unintentional outflow of large amounts of plastic waste into the ocean due to typhoons and other severe storms. Therefore, there is a demand for materials that are derived from biomass without using petroleum, can be recycled, and are biodegradable if released into the ocean. Paper meets these conditions, but as a packaging container, it has the major problem that the contents cannot be seen.

The research group has successfully developed "transparent paperboard" using plant-derived cellulose, which is the same component used in normal paperboard. Transparent cellulose already exists as cellophane. However, cellophane is made by solidifying a cellulose solution using a coagulation bath, which limits its thickness to only very thin sheets of about 0.03 millimeters. Therefore, the group considered whether a coagulation bath might become unnecessary if cellulose were dissolved in a lithium bromide solution.

In the experiments, cellulose was placed in a 60% lithium bromide solution, heated to 115℃ to dissolve it, and then cooled to form a gel. The gel was washed to remove the lithium bromide and dried to create transparent paperboard. The waste solution from washing can be concentrated to recover the lithium bromide, and the remaining water can be reused for washing, thus achieving a closed recycling system that does not discharge waste solution externally.

This transparent paperboard maintains high transparency while having a thickness of 0.3 to 1.5 millimeters, which is equivalent to or more than five times thicker than normal paperboard. In particular, at thicknesses of 0.3 to 0.7 millimeters, which are typically used for packaging materials, it shows high transparency with a haze value of less than 30%, allowing clear visibility of objects up to 100 meters away through the transparent paperboard. Its hardness and strength exceed those of polycarbonate, a representative hard plastic, and it can be molded into three-dimensional shapes such as straws and cups. Because its wet strength is higher than that of normal paperboard, it can hold liquid as a cup even without any treatment, but it can also be made water-repellent while maintaining transparency by using naturally derived fatty acid salts.

The deep-sea floor, where waste ultimately accumulates, has low water temperature and few microorganisms. Therefore, paper cups, transparent paperboard cups, and plastic cups were submerged off Hatsushima Island in Atami City, Shizuoka Prefecture (depth 855 meters); off Misaki in Miura City, Kanagawa Prefecture (depth 757 meters); and off Minamitorishima, one of the Ogasawara Islands (depth 5,552 meters) to observe biodegradation over 4-9 months. It was confirmed that the transparent paperboard cups degraded at the same level as regular paper cups. In particular, they almost disappeared within 4 months in the relatively shallow waters off Misaki. Metatranscriptomic analysis showed that the accumulated microorganisms produced enzymes involved in cellulose degradation, such as cellulase and β-glucosidase.

According to Isobe, at the current laboratory level of manual work, a single transparent paper cup costs approximately 3,000 to 5,000 yen, but if a continuous manufacturing process including counterflow washing can be established, the cost of transparent paper could be reduced to about three times that of normal paperboard.

Journal Information
Publication: Science Advances
Title: Fully circular shapable transparent paperboard with closed-loop recyclability and marine biodegradability across shallow to deep sea
DOI: 10.1126/sciadv.ads2426