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Bagasse coffee cup

Another step to a better disposable coffee cup

The quest for a better single-serve beverage cup is ongoing – with US scientists reporting progress in developing a viable plastic replacement by combining bagasse and bamboo.

Sugar cane contains around 10% sugar, and that means there’s a huge amount of waste, bagasse, that remains once the cane has been pulverized. World production of cane sugar was 185m tonnes in 2017. That results in a lot of bagasse.

Currently, most of this is burned, often as fuel for local generators that power the mills, so it is not wasted. But Dr Zhu Hongli, a mechanical engineer at Northeastern University in Boston, thinks it can be put to better use.

As she and her colleagues describe in Matter, with a bit of tweaking bagasse makes an excellent — and biodegradable — replacement for plastic foodbev containers.

Dr Zhu is hardly the first person to have this idea. But previous attempts tended not to survive contact with liquids. She thought she could overcome that by spiking the sugar cane pulp with another biodegradable material.

She knew from previous research that the main reason past efforts fell to pieces when wet is that bagasse is composed of short fibres which are unable to overlap sufficiently to confer resilience on the finished product. She therefore sought to insert a suitably long-fibred substance.

Bamboo seemed to fit the bill. It grows quickly, degrades readily and has appropriately long fibres. And it worked. When the researchers blended a small amount of bamboo pulp into bagasse, they found that the result had a strong interweaving of short and long fibres.

“Making food containers is challenging. It needs more than being biodegradable,” said Zhu. “On one side, we need a material that is safe for food; on the other side, the container needs to have good wet mechanical strength and be very clean because the container will be used to take hot coffee, hot lunch.”

The researchers added alkyl ketene dimer (AKD), a widely used eco-friendly chemical in the food industry, to increase oil and water resistance of the molded tableware, ensuring the sturdiness of the product when wet.

With the addition of this ingredient, the new tableware outperformed commercial biodegradable food containers, such as other bagasse-based tableware and egg cartons, in mechanical strength, grease resistance, and non-toxicity.

As a bonus, they also discovered that the hot pressing used as part of the process had mobilised some of the lignin in the fibres, and that this stiff, water-repelling material was now acting as an adhesive that bound the fibres together.

They also found that when they made a cup out of the stuff and filled it with water heated almost to boiling point, the cup remained intact for more than two hours.

Though this is not as long as a plastic cup would last (it would survive indefinitely) it is long enough for all practical purposes. Moreover, the new material is twice as strong as the plastic used to make cups, and is definitely biodegradable.

When Dr Zhu buried a cup made out of it in the ground, half of it rotted away within two months, and she reckons six months would have seen it gone completely.

Another benefit is cost. She estimates that cups made from the new material would cost $2,333 a tonne. That is half the $4,750 a tonne cost of biodegradable cups made from polylactic acid (fermented plant starch), and only slightly more than the $2,177 a tonne that it takes to make plastic cups.

“It is difficult to forbid people to use one-time use containers because it’s cheap and convenient,” says Zhu. “But I believe one of the good solutions is to use more sustainable materials, to use biodegradable materials to make these one-time use containers.”

Source:, The Economist

Journal Reference:

  1. Chao Liu, Pengcheng Luan, Qiang Li, Zheng Cheng, Xiao Sun, Daxian Cao, Hongli Zhu. Biodegradable, Hygienic, and Compostable Tableware from Hybrid Sugarcane and Bamboo Fibers as Plastic Alternative. Matter, 2020; DOI: 10.1016/j.matt.2020.10.004