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.
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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.
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With a simple, inexpensive treatment, researchers have found a way to make paper bags strong enough to be reused multiple times, even when they get wet. The bags could be a true ecofriendly alternative to single-use plastic bags.
At the end of their lives, the durable paper bags can be broken down to be used as biofuel. &#;The implications of a technology like the one we demonstrated in this research&#; including using the worn-out bags as a substrate for biofuel production, would be huge,&#; said lead researcher Jaya Tripathi in a press release. Tripathi and her colleagues at Penn State University presented their work in the journal Resources, Conservation and Recycling.
The world makes five trillion plastic bags a year. Each bag takes over 1,000 years to decompose. A significant share of these wind up in waterways and oceans, littering the environment and harming wildlife. And even if they get to landfills, they can harm the environment because they eventually break down to produce harmful microplastics and toxic chemicals.
Paper bags are not only made from a renewable resource, they also decompose much faster than plastic bags, and present less danger to animals. But that does not necessarily give them an entirely clean environment bill.
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It takes a lot of energy to make paper bags, and because they are heavier than plastic, they take more energy to transport, translating to higher carbon emissions per bag. Some studies have shown that paper bags need to be reused anywhere from three to 43 times to make them more environmentally friendly than plastic bags.
Problem is, paper can be flimsy and doesn&#;t hold up well when soggy. So Tripathi and colleagues came up with a chemical process that makes them stronger. The technique, called torrefaction, involves heating the paper slowly in a low-oxygen environment. This makes the cellulose fibers in paper more water-repellant, makes it stronger even when wet.
In their study, the team found that the strength of filter paper increased by a high of 2,233% after 40 minutes of heating at 220°C. While the strength increases, however, torrefaction decreases the glucose content in the paper, which brings down its usefulness as a biofuel. The researchers&#; answer to this was to treat the paper with a sodium hydroxide solution, which boosted the glucose content.
The researchers will have to translate their laboratory work to practical paper bags of course. But the implications could be big. Americans throw away 100 billion bags annually. &#;By switching to stronger, reusable paper shopping bags, we could eliminate much of that waste,&#; Tripathi said.
Source: Jaya Tripathi, Daniel Ciolkosz, and Dan G. Sykes. Torrefied paper as a packaging material and subsequently as a bioethanol substrate: Synergy of torrefaction and alkaline treatment for increased utility. Resources, Conservation and Recycling, .
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