DEVELOPING BIOCONVERSION PROCESSES FOR HIGH-VALUE CARBOHYDRATE PRODUCTS
Location: Renewable Product Technology Research Unit
Title: Anticorrosive Microbial Polysaccharides: Structure-Function Relationships
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: July 31, 2010
Publication Date: July 31, 2010
Citation: Finkenstadt, V.L., Bucur, C.B., Cote, G.L. 2010. Anticorrosive microbial polysaccharides: Structure-function relationships [abstract]. Plant Polymer and Applied Glycosciences Workshop. Abstract P-06.
Water-soluble microbial polysaccharides are often implicated in biofilm formation and are believed to mediate cell-cell aggregation and adhesion to surfaces. Generally, biofilm formation is considered harmful or undesirable, as it leads to increased drag, plugging of pores, dimished heat transfer, and sometimes to corrosion of metals. However, some microbial polysaccharides, when used as coatings for metal surfaces, can prevent corrosion of the metal. While corrosion resistance of some biopolymers has been suggested by anecdotal data and poorly refined electrochemical data, there has not been a comprehensive electrochemical analysis of corrosion behavior in metals coated with biopolymers.
A series of polysaccharides belonging to the dextran family were prepared either enzymatically or fermentatively from sucrose. They were partially purified by ethanol precipitation and dissolved in water, then either cast or sprayed as films onto steel surfaces. Polymeric films were evaluated for initial flash corrosion and corrosion inhibition. Inhibition of corrosion was measured electrochemically.
Charged polysaccharides such as xanthan gum performed poorly in such tests, whereas dextrans tended to perform the best out of those tested. Alternan was a poor film-former, yielding a brittle quasi-crystalline material. Levan formed good films, but was inferior to other neutral polysaccharides as an anticorrosive. Commercial dextran, made from Leuconostoc mesenteroides NRRL B-512F, was only moderately active. The best corrosion protection was observed with films made from dextran systems containing very low levels of branching in the main polymer chain. Dextran preparations from bacterial strains NRRL B-1498, B-1355, and B-1254 exhibited the highest anticorrosive activity. These are all characterized as having less than about 5% branching in the major polysaccharide present, and tend to be very viscous and difficult to dissolve relative to other dextrans. Interestingly, the presence of low levels of contaminating, more highly branched glucans in some of these preparations may have actually increased the anticorrosive activity. The presence of fructose, a reducing sugar, in the preparations was discounted, as activity was unchanged even after multiple ethanol precipitations and prolonged dialysis to remove low-molecular weight contaminants.
This research shows that specific exopolysaccharide coatings exhibit corrosion inhibition when applied to SAE 1010 steel and are bio-based, environmentally benign, and cost comparative to existing measures.