Japanese washi paper has been a staple in traditional Japanese arts and construction for centuries. This paper is crafted from the fibers of the kozo plant, which provides exceptional strength. It’s also known for its durability and aesthetic appeal. However, like many craft materials, it’s been experiencing a decrease in popularity.

In a new study, researchers have found a new way to revive washi paper. By combining it with polymers, they created a version of the paper that is not only stronger, but also completely biodegradable, offering a sustainable alternative to synthetic materials that are challenging to dispose of.

“We created a green composite from washi, which itself stems from plant fibers, improving its properties further while still maintaining its classical beauty,” says Hiroki Kurita, co-author of the paper and associate professor at Tohoku University’s Graduate School of Environmental Studies.

A modern improvement for an ancient material

Washi paper was developed in Japan over 1,300 years ago, stemming from traditional Chinese papermaking techniques that were adapted to the unique resources and climate of Japan. Japanese craftsmen upgraded the paper by using fibers from native plants such as kozo (paper mulberry), gampi, and mitsumata, which are known for their long and strong fibers. The process involves steaming the plant fibers, beating them to create a pulp, and then spreading this pulp on a bamboo screen to form sheets. This labor-intensive process results in a paper that is not only durable and flexible but also has a distinct texture and translucence.

But Washi is more than just paper. It’s sometimes used as a tough paper in traditional crafts like origami and shodō. It’s also used to make various everyday goods like clothes, toys, and other household goods. Washi is also used to repair valuable things like paintings and books at museums and libraries around the world because of its thinness, pliability, and durability. But Kurita wanted to make it even better.

To produce the new material, the researchers took sheets of washi from an artisan maker and hot pressed them with polybutylene succinate (PBS). PBS is a biodegradable thermoplastic polymer resin of the polyester family. The resulting material was 60% stronger than the original washi and was also more biodegradable.

Although washi is much tougher than regular paper, it still has a lot of space between its entangled fibers. The PBS fills these spaces, locking them in place When combined with PBS, the plastic filled these spaces, thereby locking the fibers in place and preventing them from moving.

Sustainable, stronger washi

Another key property of the neo-washi is the biodegradability. In controlled compost environments, the material begins to degrade within weeks, with significant loss of mechanical integrity observed in just a few days under composting conditions. After six weeks, these composites are nearly indistinguishable from the compost itself, having degraded by up to 82%.

However, it’s not just a controlled lab setup — the material is biodegradable in many different environments.

“We utilized both standardized and non-standardized methods for measuring biodegradability. The differing methods used will help researchers compare biodegradability between different materials moving forward,” says Kurita.

This quick breakdown makes the material an ideal candidate for applications where temporary usage and swift disposal are required.

In packaging, they offer a sustainable alternative that reduces the environmental footprint of shipping materials. In agriculture, they could be used as biodegradable mulch films that enrich the soil after breaking down. Additionally, their use in disposable furniture or temporary installations could promote sustainability in industries traditionally reliant on more permanent, often non-recyclable materials.

Challenges with scale

Despite their promising attributes, the composite material also faces challenges, particularly when it comes to the scalability of washi production and the cost. Current production methods for washi are labor-intensive, and PBS, while biodegradable, is derived from petrochemical sources, although biobased alternatives are being developed.

The new material is promising, but it won’t be hitting the shelves just yet. Addressing these challenges will be crucial for the widespread adoption of washi-PBS composites.

Journal Reference: Lovisa Rova et al, Japanese washi-paper-based green composites: Fabrication, mechanical characterization, and evaluation of biodegradability, Composites Part A: Applied Science and Manufacturing (2024). DOI: 10.1016/j.compositesa.2024.108261