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The Biomimicry Column

On the trail to safer plastics

When Leo Baekeland first combined phenol, formaldehyde and wood flour to make Bakelite in 1907, I am sure he had no idea of the future impact of the material he was introducing. Although he had said that the first thermosetting plastic ever made would have a thousand uses, little could he have imagined how short of the mark he was.

In a little more than 100 years, petroleum-based synthetic polymers have found their way into all aspects of our lives, from the toddler’s teething ring to the plastic-lined coffin. That reach even extends beyond the grave. Although our mortal flesh will decay, some of its plastic contents, accumulated over a lifetime, will tarry much longer. So it is with our oceans and land.  

It would be silly to suggest that we do away with plastics. They are too valuable, too ubiquitous and too useful. What we should do away with, however, is the way that they are made, some of the ways that we use them, and certainly what we do with them when they have done their job. New strategies should include the further development of bioplastics, some of which already are delivering promising results.

The age of plastics

We live in the age of plastics.

Although not as long as the Stone, Bronze or Iron Ages, the plastic age’s impact on the natural world has been greater in its short duration than all of these combined. The world produced about 299 million metric tons of plastics in 2013, most of which flowed from east to west. China is the biggest producer at 24.8 percent, followed by Europe at 20 percent, and North America at 19 percent.

Estimates of 2015 global consumption average 45 kilograms for every man, woman and child on the planet. As shocking as that is, this is about three times lower than what it could be because the average consumption in Europe and North America is more than 135 kilograms per capita. Only lack of development has kept the rest of the world from following suit, but many aspire to change that. The Indian plastics industry, for instance, projects its 2013 domestic consumption total to double within the next five years.

The good, the bad and the ugly

Plastic is wonderful stuff, of course: light, strong, waterproof, resistant to rot and decay, with high thermal and electrical insulation properties. It can be produced in any color you like or clear enough to see through, with no color at all. You can make it into sheets, rods or just about any shape you like.

It’s also cheap — at least when you omit the environmental and health costs, those troublesome externalities that most company accountants keep forgetting to enter in their books. Making something out of plastic, rather than glass or metal, often saves a lot of energy, material and subsequent greenhouse gas creation.

While nobody truly knows its environmental and health costs, some simple things are known. Most plastic lasts for a very long time without breaking down and 90 percent or more is never recycled. Much of it contains compounds that are toxic to animals and can leach out when it does break down.

Some plastics, including polycarbonate bottles and the resin lining of cans, contain plausible endocrine disrupters such as Bisphenol A (BPA) and phthalate that are absorbed while eating and drinking. Some 93 percent of people in the U.S. had detectable levels of BPA in their urine, according to the U.S. Center for Disease Control and Prevention. Nearly all adults also had measurable levels of phthalates in their bodies, along with eight out of 10 babies.

One third of the plastics produced are used in disposable packaging, most of it discarded within one year of manufacture. Used only once, these persistent and toxic compounds can be expected to hang around for decades. The energy cost, beyond the degradation of our health and environment: About 8 percent of petroleum production is used to make these plastics — half for feedstock and half to power the processing.

Getting the same performance without the costs

If we are to eliminate the most dangerous aspects of synthetic polymers, three things are needed: new formulas that allow sustainable sourcing and recycling; materials that break down in a benign way; and more sophisticated systems of collection, disposal and reuse.

Bioplastics will be part of this solution. They are comprised of two basic types of material: biodegradable material and substances that are bio-based but not biodegradable. The latter, made of such things as cellulose, represent the majority of the current production at 62.4 percent, with biodegradable material comprising the rest at 37.6 percent. Although 2013 worldwide production volume, at 1.6 million tons, is small relative to oil-based plastics, it is of an industrial scale and is expected to quadruple in the next five years.

While many of these plastics make use of natural materials, they must be categorized as examples of bio-utilization, not biomimetics. There are, however, materials being developed that attempt to mimic the form and process of nature to build in performance as well as use natural materials.

One of these is Shrilk, a conflation of the words “shrimp” and “silk,” the two sources of material for the plastic. The shrimp provides chitin, a sugar from which the more useful chitosan is made, and insect silk provides fibroin, a protein. These two substances are laid in a composite that takes advantage of the properties of each to make a product that is both strong and durable.

Chitin is the second most common organic material in the world after cellulose. It is a polysaccharide, or sugar, found in crustacean shells, insect cuticle, fungi walls and the nacre of mollusks. It is typically combined with other materials to make strong composites. The nacre of the abalone shell is a case in point. The chitin scaffolding holds protein gels that then are mineralized to make a composite material tougher than any ceramic.

Javier Fernandez, lead researcher and postdoctoral fellow, and Donald Ingber, director of the Wyss Institute for Biologically Inspired Engineering at Harvard, conceived and developed Shrilk two years ago and published their work in the journal Advanced Materials.

They had observed the cross-laid nature of some of these natural materials and mimicked it, plywood fashion, at the micro scale. The resultant material is not only bio-based, but also biodegradable and biocompatible. The U.S. Food and Drug Administration already had approved chitosan and fibroin, making them suitable for biomedical applications.

Reporting in March in Macromolecular Materials and Engineering, the pair revealed their latest results. Now working exclusively with chitosan, they have been able to demonstrate a scalable production process for a chitosan-based plastic that can be either injection molded or cast like any current plastic. Key to their innovation was a finely honed formula that retained the three-dimensional mechanical properties of the chitosan.

Chitin, which can be sourced by grinding up shrimp shells or growing fungi, does not affect land-based food production. Heretofore, ground shrimp shells have been used widely for fertilizer, cosmetics and food additives, but never in a structural way as nature does. The reconstituted chitosan is a first that uses structure, rather than material, to create strength, a basic principle of nature. Production costs are currently above that of petroleum-based plastics, but the adding of wood flour to the chitosan formula makes the cost comparable. Researchers believe that economies of scale will further reduce unit costs.

The material also gets high marks for recyclability and biodegradability, For one thing, dyes used within the polymer are recoverable, and therefore the plastic does not have to be sorted before being recycled. Additionally, the material not only will break down in a matter of weeks, but will add nitrogen to any soil that it is in, encouraging plant growth.

By a keen observation of nature and its principles, and a simplified translation to readily available methods and materials, these researchers have brought us much closer to a world where we can enjoy the benefits of plastics without the odious costs.

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