Natural Polymer With Adhesive Properties Produced by Bacteria

Numerous studies have examined adhesives made by barnacles and mussels. Although the adhesive materials have amazing properties, large-scale production has been problematic and expensive.

Montana Biotech Corp. responded to a request by the Strategic Environmental Research and Development Program (Department of Defense, Department of Energy, Environmental Protection Agency), Arlington, Va., for development of an environmentally friendly adhesive. Rather than modifying a petrochemical-based adhesive or doing further work on mollusks, the biotech company proposed bacteria as the source for a natural adhesive.

Bio-process production plant.

To disbelievers, it should be pointed out that rocks in fast-flowing streams are always covered with slippery slime. It turns out that this material is an extracellular polymeric substance (EPS) naturally produced by bacteria. Bacteria make an EPS for several reasons, including sticking themselves in place in a favorable environment. Anyone who has ever tried to scrape the slime off rocks will recognize the strength of these adhesive bonds.

A stream is a typical location to find rocks covered with extracellular polymeric substances.

Many bacteria lose the ability to produce an EPS when grown under artificial conditions. After a long search, just the right organism was found that would not do this. The advantage of using bacteria rather than mollusks is that they can be produced by standard large-scale fermentation technology, facilitating recovery of a cost-effective product.

The EPS raw material is called C-902 Polymer. It is a high-molecular-weight polysaccharide made from a renewable resource. It is excreted from the bacterium, allowing it to be inexpensively separated from the biomass. Unlike highly branched polysaccharides such as xanthan gum, C-902 does not expand in water. The water-based polymer is non-cytotoxic and is biodegradable.

The “green” adhesive has good tensile strength and shear strength on aluminum, depending on the surface finish. (See table.) Bond shear strength is greater than the substrate for medium-density fiberboard, particleboard and fir. The material is very resistant to organic solvents such as d-limonene and jet fuel. The cured adhesive loses strength after a few hours under water but maintains full strength in an environmental chamber during an 85-percent humidity, one-week temperature-cycling program between 30 and 60 degrees C. After curing, the adhesive bond can be broken, moistened and rejoined.

Several successful runs to produce C-902 Polymer were made at Shanghai Cathay Biotechnology’s pilot plant in Jining, Shandong, China. The technology is now ready for full-scale production in its state-of-the-art facilities that opened last year.