Researchers transform textile waste into stronger recycled paper

Until now, old clothes have mainly been incinerated. Using adapted processes from paper production, it is possible to recover the cellulose fibers from used clothing and use them to produce cardboard and other packaging materials.

In Austria alone, about 220,000 tons of textile waste are produced every year, of which almost 80% is incinerated. As a result, valuable raw materials are irretrievably lost. A team led by Thomas Harter from the Institute of Bioproducts and Paper Technology has come up with a sustainable solution to this problem.

The researchers have developed a process to recover the fibers from cotton-based, used textiles and use them to produce paper for packaging materials. Compared to conventional recycled paper, the paper with textile fiber content proves to be significantly stronger.

“Strictly speaking, the conversion of textile fibers into paper is a downgrade,” says Harter. “However, it has a major advantage from an environmental point of view. The paper cycle is highly closed, with recycling rates of over 90% in the packaging sector. If we bring valuable textile fibers into this cycle, they remain usable for a long time.”

Recycled textiles can be an important source of raw materials for the production of packaging paper and help to reduce the amount of paper imports currently used for this purpose.

Very similar to normal papermaking suspension

To make paper from old items of clothing, the clothing is first cut into small shreds and soaked in an aqueous solution. This mixture of water and shreds is milled to separate the interwoven cotton fibers without knotting or clumping.

As part of his master’s thesis, Alexander Wagner determined the most suitable beating machine, the necessary processing time and the optimum ratio of water to textiles in order to extract the maximum amount of usable fibers from the textile waste.

“At the end of our tests, we obtained a suspension that is very similar to a normal papermaking suspension and that we can process into paper using established methods,” says Harter.

Significantly more tensile strength than conventional recycled paper

Visually, the paper with textile content hardly differs from ordinary recycled paper; it is slightly brownish with occasional colored speckles, which come from colored items of clothing. However, these splashes of color are irrelevant for cartonboard and other packaging materials.

Tensile tests have shown that the addition of textiles increases the strength of recycled paper: “Even with a textile-based proportion of 30%, the paper is significantly stronger, while the processability remains the same,” says Alexander Weissensteiner, who is also working on optimizing the recycling process as a master’s student.

This is due to the length of the fibers. “The fiber lengths of recycled waste paper are quite short. At 1.7 millimeters, our recycled textile fibers are significantly longer.”

The researchers’ next goal is to reduce the energy consumption of the beating process. In addition to additives such as light acids and alkalis, they also test enzymatic pre-treatments to support fiber disintegration in the beating unit. “We also want to take the next scaling step and implement the process on industrial devices,” says Harter.