Polyurethane Sustainability: Structure-Property Relationships

More and more, manufacturers are demanding bio-sourced raw materials to help their customers achieve their sustainability goals. In the service of these goals, manufacturers must focus on raw materials that are safer and derived from renewable resources.  Sustainability helps manufacturers and their customers achieve a triple bottom line based on profitability, greater social responsibility, and improved environmental conditions via a reduced CO₂ footprint.  

The world of polyurethanes has embraced sustainability

The world of polyurethanes has embraced sustainability. For many manufacturers and stakeholders in the industry, the concept of “green” polyurethanes is no longer a trend but a definitive path forward. As demand for green products continues to grow, raw material providers should offer a family of polyester polyols derived from bio-renewable, sourced raw materials for application in the performance segment of polyurethane elastomers.  We utilize raw materials from bio-renewable resources and also market polyols that produce durable and high strength polyurethane elastomers with superior performance attributes and good processing characteristics. We are steadfast in our belief that Gantrade customers should be able to achieve sustainability goals with polyurethanes without sacrificing their commitment to quality or performance. 

Polyurethane formulators can explore the advantages of using bio-based polyester polyols based on Gantrade’s portfolio as an example.  Our bio-based, linear, polyester polyols utilize bio-succinic acid and bio-sebacic acid as the aliphatic diacids and bio-1,3-propane diol and bio-1,4-butane diol to produce polyester polyols made with renewable content.  These polyols can be used to make sustainable polyurethane elastomers with a high level of renewable content, especially in conjunction with bio-1,4-butane diol and bio-1,3-propanediol as the chain extender.  Bio-PDO, bio-BDO, and succinic acid all derive from natural corn sugars via the process of fermentation.  Succinic acid’s counterpart, sebacic acid, is a natural C₁₀ linear fatty acid that’s directly produced by saponification of castor oil with caustic soda.

While bio-sourced adipic acid, the standard diacid used in performance polyester polyols, is currently unavailable, manufacturers are turning to bio-based succinic and sebacic acids, which are structurally similar and can produce polyols that afford high-performance polyurethanes.   

There are a variety of optimized applications for succinic and sebacic acids. Applications for these bio-based polyester polyols include cast and thermoplastic polyurethane elastomers, coating and adhesives, inks, artificial leather, footwear, and polyurethane foam products. 

Succinic Acid (SuA)Based Polyester Polyols 

100% bio-based polyester polyols can be produced from bio-succinic acid using bio-1,3-propane diol or bio-1,4-butane diol.  However, the rigid nature of the C₄ succinic acid and restricted degrees of rotational freedom, can lead to polyester polyol that have high melting points, high Tg’s and high degrees of crystallinity.  This is very much the case with BDO/SuA polyester polyols which shows dense crystal packing in models and exhibits a very high melting point of 110 °C.  This makes conversion of the BDO/SuA polyol into polyurethanes difficult, because of the high temperatures required to melt the  polyol.  

PURs based on BDO/SA at 1000 MW proved to have lower viscosities and lower crystallinity, which makes them useful in the preparation and processing of PURs.  A film study evaluated TDI polyurethanes based on sebacic acid-diol polyester in moisture-cured films.  Only the 1,4-BDO/SuA polyester polyol with a molecular weight of 1100 afforded a hard, semi-flexible film exhibiting a tensile strength of 540 psi and an elongation at break of 30 percent.  The film was opaque based on the crystallinity.  All of the other diol combinations with SuA gave brittle films.  Note that 1,3-PDO/AA was not evaluated in this study:  R.N Mukherjea and K.K. Saha, Chemical Engineering Department, Jadavpur University, Calcutta, India.                 

1,3-propanediol SuA polyester polyols do not exhibit the high crystallinity which is characteristic of the BDO/SuA polyester polyols.  This has explained by an odd-even carbon atom spatial effect of the 1.3-PDO copolymer with succinic acid.  The odd-even carbon sequences in the PDO/SuA copolyester leads to a reduction in the intermolecular bonding forces and chain packaging. This linear polyester polyol is a waxy solid at room temperature, exhibits a broad melting range of 36-56 °C, and can remain liquid at room temperature after melting-out.  Thus, the odd-even carbon atom effect observed in polyurethanes can be used to advantage in the design of polyols derived from succinic acid.  See the results in the table below.

Source: Duponttateandlyle.com 

Sebacic Acid (SA)-Based Polyester Polyols 

Now, let’s review succinic acid’s natural counterpart, sebacic acid, in the sustainable production of polyester polyols. The isocyanate is MDI, and the chain extender is 1,4-BDO.  Related studies on these systems showed the PDO sebacate exhibited better hydrolysis resistance.  As TPUs, the PDO sebacate-2000 required a lower processing temperature versus the other two adipates, as well as a shorter demold time. 

Better processing and better performance are possible with sebacic acid, and the performance doesn’t stop with hydrolysis resistance.  Polyols and PURs based on sebacic acid are more hydrophobic than their adipate counterparts.  For this reason, they exhibit better hydrolytic stability, as well as acid and alkali resistance.  See the table below.

Source: Duponttateandlyle.com

Gantrade Sales Specifications 

Gantrade’s line of 100 percent bio-based polyester polyols is outlined below.  These grades are based on the combination of succinic acid (SuA), sebacic acid (SA), bio-1,3-PDO, or bio-1,4-BDO.  The catalyst used in the production of these polyols is either a titanate catalyst or a tin catalyst.

Please keep in mind that there are also options where non-bio-based acids like adipic acid or other diols can be incorporated in the polyester polyol. 

Also, please note that there are three BDO sebacate polyester polyols at molecular weights of 1000 to 3000.  These are unusual polyols, in that they afford high-hardness polyurethane elastomers with Durometers up to 57 on the Shore D-scale, with excellent hydrolytic and chemical resistance, as well as high mechanical properties.  Due to the higher melting points and high viscosities of the BDO subacate polyols, PURs are best produced using a one-shot or a quasi-prepolymer process.

Contact Gantrade to Learn More about Polyester Polyols Derived from Raw Materials

We pride ourselves on the fact that our material production technologies are energy and environmentally efficient.  Thus, Gantrade itself  is merging superior polyurethane performance with a focus on sustainability.  

To explore how our bio-based polyester polyol can address your unique polyurethane elastomer application and achieve greater sustainability via succinic acid and other products from Gantrade, we welcome you to partner with us. Our team, armed with a wealth of technical knowledge and expertise, can guide you to the best solutions for your applications. We combine our expertise in product specification along with your aims for superior performance while aiming for better  environmental stewardship. We offer a wide portfolio of products to help you achieve all of these goals. Contact Gantrade today to get started