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Spotted: Paper bags are often seen as a sustainable alternative to the ubiquitous single-use plastic bag. But paper bags have a short lifespan as they are not very durable, particularly when they get wet, making them hard to reuse. However, a novel study by researchers at Penn State University, headed by lead researcher Jaya Tripathi, has demonstrated the viability of a process to make paper bags stronger and a practical alternative to plastic, even when they get wet. 

To increase their strength, the bags undergo a process called torrefaction, where the cellulose in paper is roasted in an environment without oxygen. This approach greatly enhances its tensile strength once it gets wet and is an improvement on other methods for strengthening paper, which tend to rely on costly chemical processes, meaning that even though the final product isn’t plastic, it still isn’t eco-friendly.  

When using filter paper as the medium, the researchers reported that the wet-tensile strength of the paper increased significantly after undergoing torrefaction for 40 minutes in high temperatures. The increased resilience of the paper varied depending on the temperature it was heated at, but results showed that the paper’s strength could be increased by over 2,200 per cent. The study suggests that it is possible to create paper bags that are stable enough to be used multiple times. 

When the bags reach the end of their life, the researchers report that they can then be turned into biofuel. Without intervention, torrefaction decreases the glucose yield in the paper, making it less suitable for biofuel production. But the researchers discovered that treating the paper with a sodium hydroxide solution – also known as lye or caustic soda – compensated for this, increasing the glucose yield sufficiently to make the paper an effective source of biofuel. 

This focus on the potential for the used paper bags to be converted to biofuel is unsurprising given that Tripathi was initially researching how torrefaction impacts the glucose yield of cellulose used as a biofuel substrate. It was while pursuing this line of inquiry that she noticed that torrefaction made paper stronger, and it was this that sparked the idea for its application in packaging.

While paper is a great alternative to plastic, it also has some disadvantages, which is why so many innovations are working to improve the material. Springwise has spotted a startup that transforms urban biowaste into paper and packaging to avoid deforestation, and a ceramic film that gives paper packaging a barrier to water vapour.

Written By: Anam Alam