Paper usage in the US is decreasing, but wrapping, packaging, and board are increasing due to increased e-commerce. Paper bags are a popular alternative to plastic bags for reducing environmental impacts caused by plastic use. However, they have limited lifetimes due to their low durability.
Paper bags must be reused several times before their global warming potential is reduced to that of conventional high-density polyethylene bag (HDPE) bags.
Penn State researchers have developed a method to strengthen paper bags, especially when wet, making them a more viable alternative to plastic bags.
Daniel Ciolkosz, an associate research professor of agricultural and biological engineering, said, “When the primary use of these paper products ends, using them for secondary purposes makes them more sustainable. Recycling and reducing paper waste also helps reduce total solid waste destined for landfills. This is a concept we think society should consider.”
A new study suggests a process for creating paper bags that are durable enough to be used multiple times and then chemically broken down by an alkaline treatment to be used as a source for biofuel production.
Torrefying the cellulose in paper, or roasting it in an oxygen-deprived environment, increases its tensile strength when wet significantly.
After that, the paper is treated with a sodium hydroxide solution, also known as lye or caustic soda, to increase its glucose yield, making it a better source for biofuel production.
This method could reduce the use of single-use plastic bags, which have short lifespans due to their low durability. The researchers believe that by switching to stronger, reusable paper shopping bags, a significant amount of plastic waste could be avoided.
Jaya Tripathi said, “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. 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.”
She explained that Paper bags are a popular alternative to plastic bags for reducing the environmental impact of using plastics. However, they have short lifespans due to their low durability, especially when wet.
According to Tripathi, a paper bag must be reused several times before its global warming potential is reduced to that of a conventional high-density polyethylene bag.
Using filter paper as the medium, researchers reported that after 40 minutes of torrefaction at 392 degrees Fahrenheit, 428 degrees Fahrenheit, 464 degrees Fahrenheit, and 500 degrees Fahrenheit, the wet-tensile strength of the paper increased by 1,533%, 2,233%, 1,567%, and 557%, respectively.
Glucose yield decreased as torrefaction severity increased, but it improved after torrefied paper samples were treated with an alkaline sodium hydroxide solution. For example, the raw filter paper yielded 955 mg/g of substrate, whereas the same paper sample torrefied at 392 F yielded 690 mg/g of substrate. With 1% and 10% alkaline treatment, the glucose yield increased to 808 and 933 mg/g of substrate, respectively.
According to the United Nations Environment Programme, the need for a concept like this to replace plastic bags is evident, as 5 trillion plastic bags are produced each year globally. It can take up to 1,000 years for these bags to degrade completely. Every year, Americans throw away 100 billion bags, equivalent to dumping nearly 12 million barrels of crude oil.
She said, “By switching to stronger, reusable paper shopping bags, we could eliminate much of that waste. 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.”
The researcher discovered the synergy of torrefaction and alkaline treatment for increased paper capabilities by accident, as with many scientific discoveries.
She said, “I was looking into something else, studying how torrefaction impacts cellulose for glucose yield for use as a biofuel substrate. But I noticed that the paper’s strength was increasing as we torrefied the cellulose. That made me think it probably would be good for packaging, an entirely different application.”
The National Institute for Food and Agriculture of the United States Department of Agriculture funded this study.