Self-emulsifiable soybean oil phosphate ester polyols for low-VOC corrosion resistant coatings

Abstract

A series of soybean oil phosphate ester polyols (SOPEP) was prepared by reaction of fully epoxidized soybean oil with phosphoric acid and simultaneous hydrolysis in the presence of a polar solvent. The polyols were characterized by determination of acid value, oxirane number, hydroxyl value, molecular weight (GPC), and FTIR spectra. These polyols with varying amounts of acid phosphate groups could be self-emulsified to form aqueous dispersions after neutralization with organic base. These aqueous dispersions showed varying degrees of stability and their appearance ranged from opaque dispersions to translucent to clear solutions. Waterborne coating compositions were prepared using these aqueous dispersions as principal components and their thermally cured film properties were studied. It was found that by careful selection and formulation, SOPEPs can be successfully used for low-VOC waterborne coating formulations. SOPEPs with 3.5% phosphate ester content showed visibly superior corrosion resistance properties. S oybean oil is the most readily available and one of the least expensive vegetable oils in the world. There is currently significant interest in the use of soybean oil as a component in printing inks, 1 as plasticizers, 2,3 and as stabilizers in the manufacture of plastic parts due to its environmentally friendly, biodegradable, and noncorrosive properties. Moreover, it is increasingly attractive to incorporate soybean oil into the making of water-dispersible polymers and resins for packaging films and curing agents used in surface coatings, 4 which are more energy conserving and environmentally desirable than solvent-based paints. 5 Epoxidized soybean oil (ESO, Figure 1), produced by reaction of soybean oil with peracetic acid, has been investigated as an epoxy resin in UV-cured coatings. 6,7 Thames and Yu have reported cationic UV-cured coatings of epoxide-containing soybean oils that provide corrosion resistance. 6 Recently, ESO has been an attractive option for use in high-solids, low-/zero-VOC thermal cure coatings, owing to its low viscosity, commercial availability, low cost, and numerous reactive oxirane groups.Our group has investigated direct incorporation of ESO into UV-cure systems as an additional epoxy component. 8 We also prepared soybean oil phosphate ester polyols (SOPEP, Figure 2) by careful hydrolysis of ESO with phosphoric acid as catalyst, and incorporated them into low VOC industrial bake coatings possessing improved adhesion properties due to the presence of the phosphate ester groups. 9,10 The authors investigated the effects of catalysts, solvents, and the amount of water on the hydrolysis of ESO. 11 Higher boiling hydroxylic solvents gave faster reactions and the water used in the hydrolysis of the phosphate triesters needs to be controlled to prevent hydrolyFigure 1-Epoxidized soybean oil. (15% saturates not shown.)

Soy-Based Polyols and Polyurethanes

“…Phosphoric acid plays an important role in the formation of phosphate esters. Phosphoric acid (o-H 3 PO 4 ) has been extensively used in the preparation of a series of soybean oil phosphate esters for rigid polyurethanes, coatings, surfactants and anti-wear additives (Dwan'Isa et al, 2003;Guo et al, 2007;Guo et al, 2006;Zhong et al, 2001). Soy-based polyols having tunable hydroxyl content and phosphate ester functionality are possible by controlling the type and amount of polar solvent and phosphoric acid content added to the reactants (Guo et al, 2007).…”

“…Much of the work done to produce soybean oil phosphate ester polyols used water and significant amount of polar solvents such as 2-propyl alcohol, methanol, to obtain high hydroxyl functionality while keeping the final acid values low (Guo et al, 2007;Guo et al, 2006;Mannari and Massingill, 2006;Lin et al, 2008 Another oxirane ring cleavage process that results to a higher molecular weight polyol and high hydroxyl functionality is the batch reaction of ESBO and ethylene glycol (EG) at temperatures greater than 200 °C and ethylene glycol concentration range of 2-9%. An optimal condition will obtain a product with complete incorporation of ethylene glycol in ESBO and decreased oxirane concentration in the final product which is characterized by homogeneity, high viscosity and low acid number (Lubguban et al, 2009).…”

“…The objective is to increase the average hydroxyl equivalent weight of the soybean oil to engage much of the mass of the crosslinked soy-based polyol complex while reacting its hydroxyl groups with the reactive -NCO groups of the isocyanates. Examples of high hydroxyl equivalent weight soy-based polyols are glycerolized bodied soybean oil, glycolysis oligomers, and soy phosphate esters (Lubguban, et al, 2009;Guo et al, 2006).…”

Soy-Based Building Blocks for Advanced Photocure Coating Systems

“…Our research group has focused on developing a platform of polymer building blocks derived from soybean oil for coatings and related applications (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19). Polymeric and oligomeric materials used for UV-cure systems must meet stringent requirements of functionality, reactivity, viscosity, thermo-mechanical properties of their films, and cost for their successful deployment as film formers (20).…”

Emulsion Copolymerization of Vegetable Oil Macromonomers Possessing both Acrylic and Allylic Functionalities

“…[7] Soybean oil phosphate ester polyols have been evaluated in low-VOC corrosion resistant coatings. [8] U.S. Pat. No.…”