Biobased Succinic Acid: The Flexible, Hard Renewable Acid
for Solvent-Based Liquid Polyester Resins for Protective Metal Coatings
Biobased succinic acid (SA) is a four-carbon diacid that is easily produced by direct glucose fermentation using a modified yeast or bacteria. Prior to the advances in yeast-catalyzed molecular engineering, succinic acid was typically obtained from petrochemical sources such as either a benzene oxidation/reduction process or more commonly from the partial oxidation of butane. Both of these processes involve the use of finite petrochemical feedstocks and multiple high-temperature and high-pressure conversion steps that produce significant amounts of CO2 emissions and thus add to greenhouse gas emissions, global warming and higher subsequent environmental costs. With the recent advances in biotechnology, biobased succinic acid has emerged as an extremely versatile and environmentally friendly chemical building block. BioAmber’s highly efficient yeast-based fermentation process produces a high-quality polymerization-grade succinic acid. The efficient process reduces CO2 emissions and saves energy compared to analogous petrochemical-based organic acids such as petroleum-based succinic acid, adipic acid and aromatic acids such as o-phthalic acid or isophthalic acid. Moreover, BioAmber completed its 30,000T capacity manufacturing facility in Sarnia, Ontario in August, 2015 – the largest manufacturing plant for biobased succinic acid. These technical and manufacturing advances enable the use of biobased succinic acid as a versatile new platform chemical in the development of biobased polyester thermoplastics, polyester polyols for urethanes, epoxies, acrylates, and saturated or unsaturated polyester resins for a variety of CASE applications. In addition to these high-performance polymers, the availability of high-quality biobased succinic acid enables a variety of other chemical intermediates derived from succinic acid such as ester-based solvents, lubricants, plasticizers and even agrichemicals.
BioAmber recently published several articles on the features and benefits of succinate polyols in polyurethanes, thermoplastics, coatings and adhesives.1a-c We have now extended our application knowledge to polyester resins, such as those used in solventborne metal coatings. In this article we will highlight and summarize the performance attributes of biobased LPE resins as protective coatings for metals.2 Several well-known technologies are available for metal coating applications. Typically, these resins are based on polyester, epoxy and acrylic chemistries. Within each of these technologies there are numerous formulation variables used to customize metal coatings to meet the application performance requirements. Regardless of the ultimate application, the coatings are primarily used to protect the metal from oxidation (corrosion). In order for the coating to accomplish this primary function, it must have excellent adhesion to the metal surface, be stable to UV and chemical attack and form a hard, scratch-resistance surface. However, just having the polyester form a “hard coating with excellent adhesion” is insufficient. The final coating also needs to be flexible in order to survive the metal fabrication processes for conversion into numerous shapes for applications such as metal siding, office furniture, automotive and industrial applications. It is this need to balance the hard, durable properties with flexible and impact-resistant properties that make the metal coating formulation such a challenge. For polyester-based resins, this balance of properties is achieved by the polymer design that balances harder, stiffer ester units based on aromatic acids, or cycloaliphatic acids and glycols with flexible segments based on aliphatic acids and aliphatic glycols. Typically ester repeat units of isophthalic acid (IPA) and neopentyl glycol/ethylene glycol (NPG/EG) would be considered the hard/stiff segments, whereas ester units based on adipic acid (AA) and NPG/EG would be considered soft and flexible. Moreover, the use of biobased SA enables the synthesis of “greener” formulations using less petrobased carbon.