Chemically modified alkyd resins

Modified alkyd resins In this group one finds styrenated alkyds, vinyl toluenated alkyds, oil-modified vinyl resins, acrylic alkyds, silicone alkyds and polyurethane alkyds. The modifying component usually has a number of effects. It always increases the molecular weight of the alkyd polymer, and may impart hardness, durability, or chemical resistance. It also affects the solubility of the polymer in solvents. 

Styrene-Modified Alkyd Resins. Styrene was first copolymerized with drying oils in the early 1940s. These binders had a substantially improved drying behavior and resistance to water and chemicals compared with untreated oils. The first patents for the production of styrenated alkyd resins were granted in the United Kingdom in 1942 [2.63]. Mixtures of styrene and a-methylstyrene are also used for a more reliable reaction vinyltoluene yields copolymers with improved thinnability in mineral spirit and pigment absorption. 

Styrene [100-42-5] is a colorless liquid that acts as a solvent for unsaturated polyester resins. Styrene is stabilized by the manufacturer to avoid polymerization on storage. Feedstock for chemical syntheses (polymers and copolymers, styrene-modified alkyd resins and oils). 

Arriving now at current practice, the oil is chemically incorporated as a component of a polyester resin, known as an alkyd resin or sometimes as an oil-modified alkyd resin. 

Alkyd resins are produced by reaction of a polybasic acid, such as phthaUc or maleic anhydride, with a polyhydric alcohol, such as glycerol, pentaerythritol, or glycol, in the presence of an oil or fatty acid. The resulting polymeric material can be further modified with other polymers and chemicals such as acryhcs, siUcones, and natural oils. On account of the broad selection of various polybasic acids, polyhydric alcohols, oils and fatty acids, and other modifying ingredients, many different types of alkyd resins can be produced that have a wide range of coating properties (see Alkyd resins). 

Although blending with other coating resins provides a variety of ways to improve the performance of alkyds, or of the other resins, chemically combining the desired modifier into the alkyd stmcture eliminates compatibiUty problems and gives a more uniform product. Several such chemical modifications of the alkyd resins have gained commercial importance. 

If the total alkyds consumed in recent years is classified by their dibasic acid component, about 50% belongs to the unmodified phthaHc type, about 28% modified phthaHc type, about 13% based on isophthaHc, and the balance based on polybasic acids other than phthaHc or isophthaHc. The top alkyd resin manufacturers in the U.S. are Cargill, Reichhold, a subsidiary of Dainippon Ink Chemicals, Inc., and Spencer KeUog, now a part of NL Industries, Inc. The median price (52,53), of general types of alkyd resin, soHds base, was 1.98/kg in Nov. 1990 compared to about 440 in 1955, about 660 in 1975, and about 1.54 in 1983, reflecting the increases in raw material cost. 

The phthalic alkyd class is broken down into resins which are unmodified, resins which are modified, except with rosin and rosin ester, and finally resins which are modified with rosin and rosin ester. Under each class various chemical compositions are broken out for purposes of analysis. The alkyd resins modified with rosin and rosin ester are going to be considered in the rosin ester class of materials rather than the phthalic alkyd class of materials. Figures on phthalic alkyds have been available since 1933 11), The Tariff Commission has used more than one type of breakdown over this period. In 1946 they broke down total alkyds into two classes oil-type alkyds as compared with other than oil-type alkyds. Before and after that year, this breakdown was not made. 

Urethane-modified alkyds are similar to simple alkyds except that dibasic acid is replaced with a difunctional isocyanate such as toluene diisocyanate or hexamethylene diisocyanate. The process is also similar to simple alkyds. Coatings made with urethane-modified alkyds dry faster and harder than alkyds, yet retain flexibility. These systems have better water-, chemical- and abrasion-resistance than alkyd resins, and cost is also relatively low (Wicks et al., 1998). These are used in clear finishes for wood floors, cabinets, OEM, maintenance, and architectural coatings. The aliphatic-based systems are excellent for exterior use, or where UV exposure is possible, while aromatic-based systems usually have better abrasion-resistance. Chemo-enzymatic synthesis of urethane-based systems produces better control of stereochemistry and can impart unique properties (Athawale Bhabhe, 1998 Athawale Gaonkar, 1999 Athawale Joshi, 2000, 2004 Bhabhe Athawale, 1998). 

The properties of bitumen paints (Section 2.14.2) can be favorably modified and adjusted to suit practical requirements by combination with other film-forming substances. For example, the thermoplasticity can be reduced and/or mechanical properties (e.g., hardness, extensibility) can be improved by adding polymers such as polyethylene, polypropylene, polyisobutene, and styrene-butadiene copolymers. The chemical resistance can also be improved high-quality corrosion protection coatings can be obtained by combination with alkyd resins. 

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