Plastics of the Future

Trained bacteria, potatoes and fruit juice are among the finalists

By Kevin O'Donnell

There are three basic markets for insulated packaging used in transportation: food, industrial and biopharmaceutical. The food market, which includes everything from the packaging and transport of perishables to foodservice items (i.e., coffee cups, dinnerware,  restaurant take-away, meat trays), is the largest one, consuming the most volume. Industrial applications include solvents, lacquers, solder pastes, paints, etc., and comprise only a fraction of the market. Somewhere in between lies the biopharmaceutical industry. Where food and industrial applications are generally commoditized markets, the biopharmaceutical industry uses highly specialized and often sophisticated designs to meet strict regulatory requirements and assure that rigid temperature specifications are maintained for certain products during transport.

But these markets represent only a small percentage of the overall consumption of foam insulation manufactured globally. Consumer use is the big player, where many of the same types of insulation materials used for insulated packaging in transportation are also applied to a wide range of products -- from protective packaging, to home insulation, from soundproofing our automobiles, to lining our picnic coolers.

Expanded Polystyrene (EPS) is the overwhelming foam insulation of choice for all these applications. There are a multitude of reasons for this. The raw material, polystyrene bead, is readily available, easily accessible and is comparatively inexpensive to other foams. It doesn't require a great deal of sophistication to mold, molding geometry is virtually limitless and, from a performance standpoint, it is lightweight, hydrophilic, has excellent cushioning properties, insulates reasonably well, and you can vary the density of the material to fit the application. A big problem for many, industry and consumers alike, is: what to do with it when you're done with it?

Worldwide, more than 14 million metric tons of polystyrene are produced annually, with 70% of it ending up in landfill within a year and 99% of all polystyrene ultimately ending up in dumps, according to the U.S. Environmental Protection Agency.   Polystyrene represents less than 0.6% of the overall 11% plastic solid waste generated in the U.S., but even at that volume that translates to 2.3 million metric tons dumped into U.S. landfills each year. Currently, only 1% of polystyrene is recycled.1

The world's insatiable appetite for this low-cost and versatile convenience has resulted in long-term problems, causing anxiety among local and national governments throughout the world and a global outcry from consumers for manufacturer's and providers of packaging to provide suitable alternatives that are more eco-friendly.

Most of us are familiar with kinder and gentler hydrocarbon plastics which incorporate cellulose and starch, and light-sensitive polymers that degrade under ultra-violet light, but these are not without their own drawbacks. Microbes are not the only ones who like to feast on starch and cellulose, bugs and rodents like them too. And light-sensitive polymers have a short shelf life and degradation can affect its ability to perform at a required level. So, what's being done to address these issues? Let's look at some of the more promising and intriguing research currently underway. It is important to note that even though all of the following examples have distinct advantages, all have limitations, not the least of which is that bio-based plastics simply cannot duplicate the insular properties of current fossil fuel-derived plastics.

The Goodness of Maize

The demand for ethanol fuels derived from corn has certainly increased over the past few years, and crept into the American consciousness -- completely overshadowing the growth of polylactic acid (PLA) plastic resin used primarily for food packaging. Total production of PLA resin off-sets about 1% of the total annual pounds of polystyrene currently produced in North America. Most PLA is made from genetically modified (GMO) corn. The concern over genetically modified crops has  been a source of concern among some environmentalists. (You can learn more from my article, Pharming, A Bountiful Harvest: The Promise of Edible, Temperature-Stable Vaccines, in the October, 2007 issue of Contract Pharma.)

Currently, there is a temperature limitation of 105° F for solid, non-film products made from PLA, making it unsuitable for hot foods or beverages. Used in warm climates, products made from this material may melt or distort during warehousing and shipping. PLA manufacturers are working to overcome this temperature limit.

While claims have been made that products produced from PLA resins are compostable in most commercial compost facilities, few such sites are available. Some newer facilities are reluctant to accept PLA packaging due to controversies over whether the inclusion of PLA makes the composted products too wet or too acidic and whether it degrades within the normal timeframe of other wastes with which it is typically processed.

Sweeten the Plastic

Chemists in India are lacing plastics with sugar to make them palatable to soil bacteria. The plastics which normally survive for decades in landfills begin to biodegrade within days.

According to the journal Chemical Communications, the tweaked plastics are polyethylene, polystyrene and polypropylene, which collectively make up about 20% of urban waste by volume. Bottles, bags and sacks are made of polyethylene; some food packaging, lotion bottles, shampoo bottles, etc., are made of polypropylene; and drinking cups, fast-food cartons, and casings for electronics are the types of items often fashioned from polystyrene.

Researchers at the National Chemical laboratory in Pune, India, discovered that combining the styrene subunits of polystyrene with small amounts of another, proprietary substance, provides a chemical hook for sucrose or glucose. The scientists add sugar to styrene chains like pendants on a necklace. By weight, less than 3% of the final polymer is sugar so the material is more or less the same, providing a smorgasbord for bacteria such as Pseudomonas and Bacillus, which break open the chains when they chomp, kicking-off the decay process.

It remains to be seen whether the polymer degrades into entirely non-toxic substances. Fully broken down, the end products are carbon dioxide and water. But along the way, all sorts of other compounds are produced including organic acids and aldehydes.

How quickly and to what extent the plastics will break down requires a significant and costly change in the way the plastics are manufactured. Other methods to initiate the decay process include the introduction of heat, ultraviolet light and exposure to oxygen. But to do this in the real world would be cumbersome and expensive.

Pass the Malt Vinegar

One innovative company in New Zealand whose "driving ambition is to reduce and replace toxic, undesirable, un-biodegradable polystyrene and other plastics from our global ecosystem," advocates a sustainable solution: 100% potato starch waste. The company utilizes the starch from the waste water of potato processing plants and converts it to solid, molded starch trays and other foodservice items. "It's 100% biodegradable and guaranteed not to last!" The company claims.

Just Add Water

Shanpu Ya and colleagues at the Polymer & Engineering College of Quingdao University of Science & Technology in China say that they have developed a method that involves embedding water-absorbing resin particles about 5 micrometers in diameter throughout a plastic like styrene before it is polymerized to form a polystyrene-like material. When the resulting solid comes in contact with water, the resin particles expand, reducing the polymer structure to a powder that then biodegrades. They state that the rate of disintegration can be controlled by altering the ratio of ingredients. The crucial factor, said the research team, is that the resulting foamed polystyrene is cheaper than conventional materials and can be readily adopted by cost-conscious companies that want to be environmentally responsible. Reviewing the patent, I noticed that the authors did not address the effects of humidity on the package and, as one colleague commented to me, "Who wants packaging that becomes worthless when it gets wet?"

Ph.D.'s on PHA

One new technology gaining widespread recognition and practice is a combination of chemistry and microbiology, and may help transform polystyrene into a useful biodegradable plastic. Kevin O'Connor, a lecturer at the School of Biomolecular & Biomedical Sciences Center for Synthesis and Chemical Biology at National University of Ireland, and Walter Kaminsky of the Institute for Technical & Macromolecular Chemistry, University of Hamburg, have applied a technique called Pyrolysis, which uses heat in a vacuum to break down the plastic into a crude Pyrolysis oil composed of 83% polystyrene. They feed the oil to a bacterium (Pseudomonas putida CA-3) and the tiny critters transform the oil into a biodegradable heat-resistant plastic that can be used in a variety of forms, ranging from plastic bottles to surgical devices. Originally, O'Connor and his team thought the thick, black oil would be too toxic for the bacteria but they grew quite well and formed tiny plastic granules called polyhydroxyalkanoate (PHA). They encouraged synthesis by starving the bacteria of nitrogen. Because nitrogen is needed, along with carbon and oxygen, to build the proteins and DNA, bacteria low on nitrogen need to store carbon until nitrogen becomes more readily available.  In these bacteria, carbon is stored as PHA. The process to extract the biodegradable PHA plastic from the organisms is as simple as washing with a mild detergent.

As with any recycling process, there is a concern about energy costs and byproducts. Pyrolysis is an energy-demanding fermentation process and can generate hazardous waste. To overcome this, Dr. Kaminsky has developed a fluidized-bed pyrolysis process in a totally closed system. By redistilling the crude pyrolysis oil the styrene becomes cleaner, which is then consumed by the bacteria while the remaining crud is burned, producing energy for the process. The burning of the oil residue after distillation produces only carbon dioxide and water. Calculations on energy consumption using various plastics are currently under investigation by Drs. Kaminsky and O'Connor and the results are encouraging.

Concentrating on increasing yield of the PHA is the current concern for the team and they eventually plan on evaluating total costs -- imagining a municipal recycling scheme where people are actually putting their polystyrene into the collection system to lower the costs. It remains undetermined whether the process can be done economically on a large scale.

Ultimately, the diversion of polystyrene from landfill and its subsequent conversion to a biodegradable plastic is doubly beneficial to the environment, as it reduces refuse and produces a plastic that can be composted, thereby assisting the carbon cycle.

As resin formulas, polymers and production techniques evolve, viable alternatives may appear. Currently, many within the industry are convinced that polystyrene foam foodservice products remain the soundest choice for environmentally conscious consumers. They state that there is no other large-scale, commercially viable product that can compete with polystyrene foam in terms of price and performance, while minimizing total environmental impact. They cite data of lifecycle inventories that repeatedly show that the production of poly-coated paper products consumes more energy and generates more waste than the production of an equal amount of foam.

Reference

1 The American Chemical Society Journal, Environmental Science and Technology, Microbes Convert Styrofoam into Biodegradable Plastic, April, 2006

Kevin O'Donnell is director and chief technical advisor to industry at Tegrant Corp., ThermoSafe Brands.