Biodegradable Plastics from New York State's Forest Industry Byproducts

Tom Keenan

The intention of my research in Dr. Nakas' laboratory is to channel two of New York State's forest-derived renewable byproducts into the production of biodegradable plastics that have the potential to replace conventional, environmentally recalcitrant, petroleum-based plastics. This new generation of biopolymer thermoplastics represents an attractive alternative to plastics derived from fossil fuel-based feedstocks during a time marked by increasing trends in crude oil prices, waste management problems, and continued global pollution. Polyhydroxyalkanoates (PHAs) represent a polymeric intracellular carbon and energy storage reserve synthesized by a variety of microorganisms when cultured under the appropriate conditions. Recently, PHAs have received increased attention because of their thermoplastic or elastomeric properties that resemble those of petroleum-based plastics, yet are completely biodegradable. Thus, in addition to being synthesized biologically, these alternative polymeric materials are capable of being converted to harmless degradation products of CO2 and H2O through natural microbiological mineralization. The research in our laboratory is focused on developing innovative ways to produce these PHA polymers and modify their composition in order to make them more amenable to commercial production. The promising benefit of research in this field is the possibility of replacing conventional, plastic-based products, ranging from plastic films and coatings to food packaging materials, with environmentally friendly PHA polymers.

For PHA bioplastics to be economically competitive, they must be produced on a large-scale and from inexpensive raw materials. Several factors influence the production cost of biodegradable plastics and each must be considered in order to minimize this expense, particularly when the fermentation process is to be upscaled to an industrial level. Substrate cost is one of the most important economic factors, which means that identifying the cheapest carbon sources is of upmost importance if large-scale production is to take place. The use of alternative, renewable substrate feedstocks is being investigated in our laboratory for its potential to lower the substrate costs associated with the use of relatively expensive carbon sources including glucose, sucrose, and starch.

The polymer production in our laboratory is generally carried out in two stages, the first designed to produce abundant microbial biomass and the second to trigger accumulation of intracellular PHA. The current bacterial fermentation processes utilized for commercial production of bioplastics are somewhat more expensive than plastic production from petrochemicals and unfortunately have resulted in a slow entry of this promising "green" generation of plastics into mainstream industry. Much of our research focuses on incorporating inexpensive, renewable carbon substrates in both fermentation stages in an attempt to reduce production cost. We have shown that several paper and pulp byproducts can actually be utilized as substrates by bacteria to produce PHA polymers. Thus, a dual benefit is possible, as the majority of these byproduct materials are generally combusted for heat within the pulping facility or simply enter the waste stream. Not only have we produced biodegradable plastics, but we have also identified a method to do so that actually funnels a very substantial forest industry byproduct into the production of these useful compounds.

Currently, the principal markets for biodegradable plastics are in Europe, particularly Germany, where environmental regulations favor degradable products. The PHA copolymer marketed there has been produced commercially under the brand name Biopol for almost 20 years, initially by Zeneca (a subsidiary of Imperial Chemical Industries) and now by Monsanto after its purchase of Zeneca Bioproducts. This PHA product is produced by a bacterium through a controlled fermentation, similar to the process used in our laboratory. The PHA can then be processed using conventional equipment by extrusion, injection molding, and fiber spinning. The first major product, a biodegradable shampoo bottle, has been marketed in Europe, although the plastics can be used for many applications including food packaging. However, because Biopol resin prices are ranging close to double the target cost, the current market for Biopol remains rather limited.

The research efforts in our laboratory focus on the development of higher yielding strains and more efficient fermentations that could channel two of New York State's major forest industry byproducts into the cost-efficient production of bioplastic polymers. We have identified a bacterium that can metabolize these substrates and incorporate the products into PHA polymer. Several experiments have been carried out that test the effects of varying the substrate recipe on the biomass and subsequent PHA yield. The inhibitory effects that relatively high concentrations of substrates can have on our microorganism's growth must be appropriately balanced with culture conditions that foster intracellular accumulation of PHA. We have identified the concentrations and ratios substrates to include in the fermentation that produce the highest yields of plastic.

These concentrations of substrates have been applied to larger scale fermenters, where appreciable yields of polymer have been obtained using the bacterium and culture conditions we have determined.

We have found that the duration of fermentation time plays a pivotal role in the polymer yield, for PHA will metabolized by the bacterium as a carbon and energy reserve when incubated long enough to deplete the nutrients available in the broth that it is grown in. For this reason, a compromise had to be determined between increasing the polymer-producing biomass with longer culture times and optimizing PHA yield, which decreases after broth nutrients are depleted. Varying the time of culture harvest has been shown to produce markedly different PHA yields.

Research in our laboratory has led to the identification of optimal harvest times, tailored to the particular fermentation recipe and schedule of substrate additions. Building on this information, we have determined the harvest times most appropriate for optimizing yields in different culture conditions. These results will play a very important role in designing an efficient fermentation protocol to be applied to industrial PHA polymer production, where decreased production durations will make the process more economically feasible.

Future research in our laboratory is aimed at optimizing PHA production for potential industrial applications. Different strains of microorganisms are to be screened for their potential to produce high yields of product over relatively short periods of fermentation. Modifications of the production recipe are being sought that may lead to more cost-effective bioplastic production. We also look forward to genetic engineering applied to the selected microorganism holding the greatest potential for high yields in order to create the most efficient production system.

If you have any questions, feel free to contact Dr. James Nakas or Tom Keenan (201/202 Illick Hall, jpnakas@syr.edu, tkeenan22@yahoo.com)

About the author:
B.S. Biology at SUNY Geneseo, currently Ph.D. student at SUNY-ESF. Research interests include the microbiological production of biodegradable plastics from renewable forest byproducts. Other interests include most any activity in the Great Outdoors. After finishing my Ph.D., I am planning on landing a research-oriented career in a laboratory as well as rainbow trout on my fly rod.