Adhesives typically account for approximately 7% of a footwear’s composition, yet they play a significant role in determining its end-of-life recyclability.

To create biobased, recyclable adhesives in footwear and textile manufacturing, Tufts University’s Silklab researchers developed a silk-based bonding innovation and filed a patent on this silk-based adhesive.

Silk fibroin protein is a renewable biomaterial derived from silkworm cocoons. The adhesive is produced by dehydrating a solution of silk fibroin and chaotropic salts to create a non-sticky solid film that becomes adhesive only when rehydrated with water.

A controlled amount of water, around 10-100% of adhesive mass, is added prior to use. Within less than 1-5 minutes, the film rehydrates and forms a viscous adhesive. This allows the adhesive to be applied using existing industrial footwear processes, including brushing, spray guns, or roller systems.

The adhesive’s mechanical strength was tested using T-Peel tests, which evaluated silk-based adhesives on various footwear and textile materials under different rehydration (water/viscosity) conditions, including typical combinations such as leather, plant-based polyurethane, and synthetic outsole substrates.

Additionally, the tests demonstrate that the new silk-salt adhesive system bonds materials that pure silk adhesives previously failed to adhere to, particularly plastics and rubber substrates.

At large in the textile industry, mixed textile waste is becoming harder to recycle because garments often contain blended fibers, dyes, and finishing chemicals. The silk-salt bonding innovation signals a broader move toward bio-derived adhesives, that could pave the way for more recoverable multi-material footwear.

Our team analyzed five innovations changing how fabrics are designed and manufactured. They cover water repellency without fluorine chemicals, wireless charging printed onto fabric, and where the next phase of textile innovation is heading.

Read more about it here: https://greyb.com/blog/textile-innovations/