Paper bags are a popular alternative to plastic bags to reduce the environmental impacts caused by using plastics. However, paper bags have short lifespans due to their low durability, particularly when wet. A paper bag must be used several times to reduce its global-warming potential to below that of the conventional high-density polyethylene bag.
Now, researchers at Penn State University have developed a novel process to make paper bags stronger, especially when they get wet, making them a more viable alternative.
Their study suggests a process for creating paper bags durable enough to be used multiple times and then broken down chemically by an alkaline treatment to be used as a source for biofuel production.
In this innovative process, cellulose in the paper is torrefied or roasted in an oxygen-deprived environment to greatly increase its tensile strength when wet.
“Reuse is mainly governed by bag strength, and it is unlikely that a typical paper bag can be reused the required number of times due to its low durability upon wetting,” lead researcher Jaya Tripathi said. “Using expensive chemical processes to enhance wet strength diminishes paper’s eco-friendly and cost-efficient features for commercial application, so there is a need to explore non-chemical techniques to increase the wet strength of paper bags. Torrefaction could be the answer.”
The researchers reported that the wet-tensile strength of the paper increased by 1,533%, 2,233%, 1,567%, and 557% after torrefaction for 40 minutes at 392 degrees Fahrenheit, 428 F, 464 F, and 500 F, respectively.
“I was looking into something else, studying how torrefaction impacts cellulose for glucose yield for use as a biofuel substrate,” she said. “But I noticed that the paper’s strength was increasing as we torrefied the cellulose. That made me think that it probably would be good for packaging, an entirely different application.”
However, the torrefaction lowered its usefulness as a biofuel product, decreasing the product’s glucose yield significantly. But glucose yield increased after treating torrefied paper samples with an alkaline sodium hydroxide solution. The glucose yield of raw filter paper increased from 690mg/g of biomass substrate to 933 mg/g with 10% alkaline treatment.
“By switching to stronger, reusable paper shopping bags, we could eliminate much of that waste,” Tripathi said. “The implications of a technology like the one we demonstrated in this research – if it can be perfected – including using the worn-out bags as a substrate for biofuel production, would be huge.”
Although this lab study showed promise with the filter paper model, it’s clearly a long way from practical application.
“When the primary use of these paper products ends, using them for secondary purposes makes them more sustainable,” he said. “Recycling and reducing paper waste also helps in reducing total solid waste destined for landfills. This is a concept we think society should consider.”
- Jaya Tripathi, Daniel Ciolkosz, 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, 2023; DOI: 10.1016/j.resconrec.2023.106882