Julia L F Goldstein

How Are You Changing the World?

Wash Before Wearing

You probably own clothing with a tag that reads, “wash before wearing.” There’s a good reason for this. In some cases, the dyes in clothing need to be washed away sufficiently that your jeans won’t stain your skin. In other cases, the fabric is coated with a finish that wicks moisture, repels water, or makes the clothing last longer. Unfortunately, many finishes cause irritation or allergic reactions or, even more worrisome, contain toxic chemicals linked to serious health problems. Some liquid fabric finishes, for example, contain carcinogenic compounds that can expose workers as the finishes evaporate during processing.

Even though solvents in fabric finishes evaporate before a garment leaves the factory, potentially irritating or toxic residues can remain in clothing. Machine washing removes some of these residual chemicals, but it doesn’t eliminate them, and washing also flushes them down the drain and into local waterways.

There is a safer, more environmentally-friendly solution on the horizon, thanks to science and silkworms. The silkworm is the larva (caterpillar) of the silk moth and is the source of natural silk fabrics. The life cycle of the silkworm is like that of other moths and butterflies: the caterpillar eats mulberry leaves, and when it’s grown to full size it spins a cocoon using secretions from its salivary glands. Inside the cocoon, the caterpillar develops into a pupa and then a moth. The moth eats a hole in the cocoon and emerges.

The silkworm cocoon is the source of silk fiber. But to be useful to the silk industry, the fiber needs to be extracted from the cocoon in a single long strand. Silkworm cocoons with holes, either because a moth ate its way out or the cocoon got damaged during processing, are useless to silk producers. The standard practice is to boil cocoons, which kills the silkworms but leaves the cocoon intact. The worms are a delicacy in many Asian countries, eaten boiled or roasted. I’ve never tried them, but insects can be a good source of protein that’s less resource-intensive than meat from large animals.

Silkworm cocoons contain two primary proteins—fibroin and sericin. The fibroin is in the form of filaments that give silk its characteristic strength and silky feel, while the sericin acts like a glue that holds the cocoon together.

Efforts to remove toxic chemicals from clothing or other products often involve natural alternatives, but these aren’t necessarily allergen-free. Some people are allergic to silk. It turns out that it’s the sericin in silk protein that causes allergic reactions. Fibroin is biocompatible.

A company in Boston, Evolved by Nature, has developed a process to isolate the fibroin protein and convert it into a liquid form. Processing starts by soaking silkworm cocoons in a hot salt water bath to dissolve the sericin, followed by a second treatment that liquifies the fibroin to produce what the company calls Activated Silk.

Fibroin is a complex molecule made up of segments with different properties. One primary component of fibroin is a large protein that is hydrophobic, meaning that it repels water. The other primary protein is hydrophilic and absorbs water. Fibroin in its natural state contains a random mix of these two components. But by exposing it to different temperatures, salt solutions, or acids, it is possible to engineer a specific arrangement of the components. The molecules self-assemble on a microscopic scale.

This liquid silk protein can act as a drop-in replacement for a variety of irritating or toxic liquid finishing chemicals applied to high-performance fabrics. Engineers take advantage of molecular self-assembly to tailor the liquid fibroin to make coatings that are water-repellent, or water absorbing, or possess other desirable properties. Fibroin coatings can even make fabrics less susceptible to shrinkage or pilling so that they last longer. It sounds like a great way to repurpose damaged cocoons that the textile industry discards.

Note: This blog post is related to a talk I gave on May 4 and 5, 2019 as part of Centrifuge, a theatre project that pairs five science writers with five playwrights to produce ten-minute science-inspired plays. A director and actors bring the script to life, and the performance includes an introduction by the science writer before each play to explain the science. My group’s play featured four characters: the down-to-earth CEO of a fictitious textile company, her anxious sister, a skeptical analyst, and a flamboyant fashion designer.