A team of Chinese scientists on a quest to develop bamboo into a biodegradable alternative to plastics say they have discovered a recipe to process the material into feasible products.
China – which has more bamboo forests than any other country – is in the midst of a long-term effort to reduce pollution and reach carbon neutrality and has been looking for ways to transform the tall, thick grass into a viable replacement for petroleum-based goods that can decompose quickly.
Plastic pollution has become a critical global concern, and the very slow biodegradation of traditional plastics has led to alarming accumulations of plastic waste in soil, waterways and even human bodies.
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“Bamboo, known for its rapid growth, renewability, biodegradability, and eco-friendliness, is regarded as a promising substitute for plastics,” the researchers wrote in a paper published in the American Chemical Society’s peer-reviewed journal ACS NANO on August 20th.
But significant technical challenges have prevented the widespread adoption of bamboo as a substitute for everyday plastics.
The natural structure of bamboo cells means its “plasticity” and self-adhesive properties are much lower than traditional plastics, making it necessary to combine it with other materials such as starch. However, bamboo-starch composites have potential drawbacks, such as poor mechanical strength, water sensitivity and processing costs.
To find a solution, the team developed a method to improve the plasticity of bamboo by altering its cellular structure before hot-pressing it into a water resistant and recyclable plastic.
To make bamboo-based thermosetting plastic on an industrial scale, the researchers ground bamboo into powder and used eco-friendly chemicals to remove part of the lignin – the organic substance binding the cell structures, giving the stalks their rigidity – and disturb the structure of another cellular component in the cells.
“This study presents a feasible approach to enhance the plasticity of bamboo by selectively removing part of its lignin and disrupting the crystalline structure of cellulose,” said the researchers, who are from the China National Bamboo Research Centre, Fujian Agriculture and Forestry University, and Chinese Academy of Forestry.
“This remodelling process not only significantly enhanced the reactivity of the bamboo cells, but also substantially improved their plasticity,” first author Guo Dengkang told Science and Technology Daily, the newspaper of the Ministry of Science and Technology.
The all-bamboo plastic showed “exceptional mechanical robustness”, meaning it could be classified as a hard plastic alongside traditional plastics like polystyrene and polyvinyl chloride (PVC), and could even be used as a substitute.
“The activated bamboo ... can be manufactured into a wide array of all-bamboo-based plastic products, including spoons, hats, phone cases, earphone cases, computer cases, and basins, offering a broad range of applications,” the team wrote in their paper.
Some lignin in the bamboo powder was removed using a sodium chlorite/acetic acid system to create the plastic.
This exposed cellulose and hemicellulose – structural components in plants – within the bamboo’s cell walls, was then oxidised using sodium periodate.
The process disrupted the crystalline structure of the cellulose and increased the reactivity of the bamboo, allowing it to form more bonds when hot-pressed at 95 degrees Celsius (203 Fahrenheit) to form the final plastic.
The colour of the resulting plastic, which the team pressed into utensils and bowls, ranged from pale yellow to reddish-brown based on the amount of lignin left in the bamboo.
“These products have the potential to replace petroleum-based plastics in various application scenarios,” the team said.
The all-bamboo plastic also had good tensile strength and maintained shape and rigidity when soaked in solvent and water, according to the researchers.
Because the material did not melt during the heating process, it is considered a thermosetting plastic rather than a thermoplastic, and could be recycled by being ground into a powder and mixed with water before hot-pressing again.
In soil burial tests, the scientists found that the bamboo plastic almost entirely degraded after 90 days. The team also showed that the plastic could be made using industrial bamboo pulp – which already has lignin removed – using fewer production steps.
“[All-bamboo based thermosetting plastic] offers promising solutions for replacing conventional plastics with sustainable alternatives and promoting the high-value utilisation of bamboo resources,” the team said in the paper.
More from South China Morning Post:
- Why Hong Kong uses bamboo scaffolding in construction and the potential risks
- China’s bamboo could replace high-emitting plastics, but tech bottlenecks are stunting growth
- For China, bamboo ‘is where the future lies’ in shift away from polluting plastics
- Climate change: German plastics firm works with Chinese carmakers to recycle parts
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