In recent years, there has been a growing interest in the use of bio-based resin building blocks in the synthesis of polymers for use in coatings. Bio-based products are derived from plants and other renewable agricultural, marine, and forestry materials and provide an alternative to conventional petroleum-derived products.
Driving forces include a growing public and private awareness and interest in the use of renewable raw materials that can meet sustainability expectations and certifications such as Green Seal and Green Guard as well as the USDA BioPreferred Program for product labeling. Green Seal and Green Guard are environmentally driven, whereas the USDA BioPreferred Program functions to encourage the use of renewable agricultural raw materials in products. ASTM d6866 was developed to standardize, certify and classify the bio-based content of materials. Minimum renewable carbon content categories (MRCC) have been established for purchasing by Federal agencies and their contractors.
Table I – BioPreferred Coatings Categories[1]
Bio-based resins for coatings are normally referred to as alkyds (EU). Alkyds are comprised of fatty acid modified polyester resins. These resins are sometimes modified to include a urethane (EU) linkage and thus called uralkyds or oil modified urethanes. The fatty acid portion is derived from naturally occurring or renewable oils derived from sunflower (EU), safflower, soybean (EU), castor (EU), tall (EU) and others. Polyesters (EU) are derived from the reaction product of a polyol (EU) and a di or multifunctional acid or carboxylic acid and anhydride (EU) to form multiple ester linkages in a polymer chain.
Solvent borne alkyds (EU) have been used in coatings for several decades. However, due to stricter air pollution regulations, lower VOC alternatives such as waterborne alkyds (EU) or polyurethane dispersions (PUD) (EU) have gained greater acceptance. PUDs can offer improved performance over waterborne alkyds by virtue of the urethane linkage. PUDs are mostly linear or lightly branched relatively high molecular weight polyurethane dispersions dispersed in water. One of the advantages is a lower film forming temperature at a higher Tg as urethanes hydrogen bond strongly to water, swell the latex particles and thus provide a plasticizing effect. PUD resins can thus provide lower VOC (little or no co-solvent necessary for coalescence), lower film formation temperatures and improved mechanical, chemical resistance and environmental resistance than waterborne alkyds or conventional acrylic latexes.
Newer bio-based resin technologies also feature low odor, low or no VOC, free of alkoxy phenolethoxylates (APE) with performance comparable to their solvent borne counterparts. The challenge is to formulate bio-based resins and paints that provide performance attributes equal or better than that derived from coatings formulated with higher levels of petroleum based materials.
Schematic I – Simplified reaction sequence to form an Alkyd Resin from penterthritol, a vegetable oil and phthalic anhydride[2]
Table II – Examples of Bio-based Building Blocks for Resin Synthesis[3] [4] [5]
Bio-based resins containing a high level of MRCC polymer building blocks currently on the market include PUDs based on polyols derived from castor oil. Renewable waterborne alkyd latexes are reported to have the flow leveling characteristics of their solvent borne counterpart. Soy oil and castor oil based polyols are also available. Caprolactone lactide copolymers also being optimized for use as polyols in coatings.
The use of bio-based raw materials in resins and coatings is a growing area of interest as many companies are adding such materials to their product portfolio. Properly formulated bio-based coatings can provide equivalent performance to their non bio-based counterparts providing low or no VOC, low odor, APE free and with MRCC content to be qualified as BioPreferred coatings. Manufacturers of bio-based raw materials and resins include Alberdingk Boley, Cargill, Purac, Perstorp and BYK USA (EU).
For additional information concerning bio-based resins and raw materials, please navigate to www.ulprospector.com.
[1] www.biopreferred.gov
[2] nzic.org.nz/ChemProcesses/polymers/10A.pdf
[3] http://www.pcimag.com/articles/98699-biobased-resin-technology-helping-define-high-performance
[4] http://www.icis.com/resources/news/2015/03/06/9866307/bio-based-chemicals
[5] https://www.wageningenur.nl/en/show/Biobased-resins.htm
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Hello
I am a researcher on uralkyd. Would you please help me about amount of production of this product and its price.
Thank you very much