Formulating for Tannin Stain Inhibition April 23, 2013 Nathan Kofira
Tannin staining is the discoloration of a painted surface due to the migration of water soluble Tannins (tannic acids) through the film May appear immediately or after prolonged exposure to humid conditions Tannins may be more concentrated around high pressure areas (i.e. nails, strapping marks, knot holes)
Tannin Staining An Introduction: Phenolic compounds found in many tree species used commercially. Two main categories, Hydrolyzable and Condensed Hydrolyzable (HT) i.e. Chestnut, Oak Glucose or Gallic acid core Hydrolyzed by mild acid or mild bases to yield carbohydrate & phenolic acids Condensed (CT) i.e. Pine, Cedar, Merbau Flavonoid or catechol core Not readily hydrolyzable to simpler molecules
Tannin Staining Extractables from Wood Products Extractables include tannins, oils, and rosin component Wood color is generally related to tannin content All staining is not caused by tannins Softwoods Hardwoods Species % Species % Ponderosa Pine 5.9 American Elm 2.1 White Pine 7.0 Northern Red Oak 4.4 Redwood 10.8 White Oak 5.4 Western Red Cedar 15.0 Southern Red Oak 9.6 Wood/Bark Extractives; 3434Wood; Virgina Tech Department of Chemistry (2000)
Tannin Staining Methods of Reducing Tannins: WOOD CONDITIONING Natural ageing and washing with oxidative solution (i.e. Oxalic acid bleaching) BARRIER PROPERTIES Resin structure New developments in modified acrylics mimic the natural binding properties of tannin-lignin and tannin-protein complexes Ionization and solubility of tannins reduced when using cationics which can also mimic tannin-protein binding complexes
Tannin Stain Inhibition Origin and Binding of Tannins: Tannins (tannic acids) are high molecular weight polyphenolic molecules found in wood Lignins, Cellulose, and Hemicellulose
Tannin Staining Methods of Reducing Tannins: CHELATION Multivalent ions combine multiple water soluble tannins of lower M w to create large complexes that are no longer water soluble Powder Liquid Cations Aluminum Barium Antimony Aluminum Zirconium Aluminum Zirconium Zinc ph 7.3 9.5 13.0 9.0 Oil Absorption 38.8 35.4 N/A N/A % Water Solubility 0.17 0.11 100 100 Density g/ml 2.77 3.10 1.23 1.30 Mean particle size µm 5.1 3.1 N/A N/A
Tannin Stain Inhibition Simplified Model of Chelation: The chelation process is essentially the reaction of slightly water soluble metal cations from inhibitive pigments with hydroxyl groups on the phenolic rings present in all Tannins. OH Zn Zn + ² OH OH OH Zr + 4 OH Zr Al + ³ OH Al IN SOLUBLE
Formulation & Reformulation Coalescing Agents Ester Alcohols (i.e. Texanol) and Propylene Glycol are preferred. Increased H bonding results in increased effective M w and decreased mobility Glycol Ethers (i.e. Propylene Glycol Monobutyl ether) reduce tannin stain inhibitor efficiency. Why? Lewis Base Complexed metal ion rendered unavailable
Formulation & Reformulation Tropical wood contains more Condensed Tannins Bleaching agents has minimal impact Require higher loading of Tannin Inhibitive Pigments Temperate wood contains more Hydrolyzable Tannins More likely to bleed after initial coating M w of the tannins can change over time increasing molibility Blends of multivalent ions shown to be more effective
Formulation & Reformulation ph control of the coating can significantly impact the ionization of hydrolyzable tannins Low ph powder Tannin Stain Inhibitors can be used in mildly basic coating formulations High ph liquid Tannin Stain Inhibitors can replace neutralizing agents and buffers in formulations to effectively limit tannin mobility Zinc containing Tannins Stain Inhibitors can reduce the dependency of Zinc oxide in wood coatings
Acknowledgements Dr. Tony Gichuhi Director, R&D and Technical Service Jessica Olmos Project Chemist NOTICE: Although the information and recommendations set forth herein (hereinafter information ) are presented in good faith and believed to be correct as of the date hereof, ICL Performance Products LP ( ICL ) makes no representations or warranties as to the completeness or accuracy thereof. Information is supplied upon the condition that the persons receiving same will make their own determination as to its suitability for their purposes prior to use. In no event will ICL be responsible for damages of any nature whatsoever resulting from the use or reliance upon information or the product to which information refers. Nothing contained herein is to be construed as a recommendation to use any product, process, equipment or formulation in conflict with any patent, and ICL makes no representation or warranty, express or implied, that the use thereof will not infringe any patent. NO REPRESENTATIONS OR WARRANTIES, EITHER EXPRESSED OR IMPLIED, OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR OF ANY OTHER NATURE ARE MADE HEREUNDER WITH RESPECT TO INFORMATION OR THE PRODUCT TO WHICH INFORMATION REFERS. 2013 ICL Performance Products LP. All rights reserved.