Natural oil polyols

Natural oil polyols, also known as NOPs or biopolyols, are polyols derived from vegetable oils by several different techniques. The primary use for these materials is in the production of polyurethanes. Most NOPs qualify as Biobased Products, as defined by the United States Secretary of Agriculture in the Farm Security and Rural Investment Act of 2002.

NOPs all have similar sources and applications, but the materials themselves can be quite different, depending on how they are made. All are clear liquids, ranging from colorless to medium yellow. Their viscosity is also variable and is usually a function of the molecular weight and the average number of hydroxyl groups per molecule (higher mw and higher hydroxyl content both giving higher viscosity.) Odor is a significant property which is different from NOP to NOP. Most NOPs are still quite similar chemically to their parent vegetable oils and as such are prone to becoming rancid. This involves autoxidation of fatty acid chains containing carbon-carbon double bonds and ultimately the formation of odoriferous, low molecular weight aldehydes, ketones and carboxylic acids. Odor is undesirable in the NOPs themselves, but more importantly, in the materials made from them.

There are a limited number of naturally occurring vegetable oils (triglycerides) which contain the unreacted hydroxyl groups that account for both the name and important reactivity of these polyols. Castor oil is the only commercially-available natural oil polyol that is produced directly from a plant source: all other NOPs require chemical modification of the oils directly available from plants.

The hope is that using renewable resources as feedstocks for chemical processes will reduce the environmental footprint^[1] by reducing the demand on non-renewable fossil fuels currently used in the chemical industry and reduce the overall production of carbon dioxide, the most notable greenhouse gas. One NOP producer, Cargill, estimates that its BiOH(TM)polyol manufacturing process produces 36% less global warming emissions (carbon dioxide), a 61% reduction in non-renewable energy use (burning fossil fuels), and a 23% reduction in the total energy demand, all relative to polyols produced from petrochemicals.^[2].

Sources of natural oil polyols

Ninety percent of the fatty acids that make up castor oil is ricinoleic acid, which has a hydroxyl group on C-12 and a carbon-carbon double bond. The structure below shows the major component of castor oil which is composed of the tri-ester of rincinoleic acid and glycerin:

Other vegetal oils - such as soy bean oil^[3], peanut oil, and canola oil - contain carbon-carbon double bonds, but no hydroxyl groups. There are several processes used to introduce hydroxyl groups onto the carbon chain of the fatty acids, and most of these involve oxidation of the C-C double bond. Treatment of the vegetal oils with ozone cleaves the double bond, and esters or alcohols can be made, depending on the conditions used to process the ozonolysis product.^[4] The example below shows the reaction of triolein with ozone and ethylene glycol.

Air oxidation, (autoxidation), the chemistry involved in the "drying" of drying oils, gives increased molecular weight and introduces hydroxyl groups. The radical reactions involved in autoxidation can produce a complex mixture of crosslinked and oxidized triglycerides. Treatment of vegetable oils with peroxy acids gives epoxides which can be reacted with nucleophiles to give hydroxyl groups. This can be done as a one-step process.^[5] Note that in the example shown below only one of the three fatty acid chains is drawn fully, the other part of the molecule is represented by "R₁" and the nucleophile is unspecified. Earlier examples also include acid catalyzed ring opening of epoxidized soybean oil to make oleochemical polyols for polyurethane foams ^[6] and acid catalyzed ring opening of soy fatty acid methyl esters with multifunctional polyols to form new polyols for casting resins ^[7].

Triglycerides of unsaturated (containing carbon-carbon double bonds) fatty acids or methyl esters of these acids, can be treated with carbon monoxide and hydrogen in the presence of a metal catalyst to add a -CHO (formyl) groups to the chain (hydroformylation reaction) followed by hydrogenation to give the needed hydroxyl groups.^[8] In this case R₁ can be the rest of the triglyceride, or a smaller group such as methyl (in which case the substrate would be similar to biodiesel). If R=Me then additional reactions like transesterification are needed to build up a polyol.

Uses

Castor oil has found numerous applications, many of them due to the presence of the hydroxyl group that allows chemical derivatization of the oil or modifies the properties of castor oil relative to vegetable oils which do not have the hydroxyl group. Castor oil undergoes most of the reactions that alcohols do, but the most industrially important one is reaction with diisocyanates to make polyurethanes.

Castor oil by itself has been used in making a variety of polyurethane products, ranging from coatings to foams, and the use of castor oil derivatives continues to be an area of active development. Castor oil derivatized with propylene oxide^[9] makes polyurethane foam for mattresses and yet another new derivative is used in coatings ^[10]

Apart from castor oil, which is a relatively expensive vegetable oil and is not produced domestically in many industrialized countries, the use of polyols derived from vegetable oils to make polyurethane products began attracting attention beginning around 2004. The rising costs of petrochemical feedstocks and an enhanced public desire for environmentally friendly green products have created a demand for these materials.^[11]. One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company, which first debuted polyurethane foam made using soy oil in the seats of its 2008 Ford Mustang.^[12][13]. Ford has since placed soy foam seating in all its North American vehicle platforms. The interest of automakers is responsible for much of the work being done on the use of NOPs in polyurethane products for use in cars, for example is seats^[14][15], and headrests, armrests, soundproofing, and even body panels.^[16].

NOPs are also finding use in polyurethane slab foam used to make conventional mattresses^[8] as well as memory foam mattresses^[17][18].

One of the first uses for NOPs (other than castor oil) was to make spray-on polyurethane foam insulation for buildings.^[19]

References

1. ^ J. Pollack. "Soy vs. Petro Polyols, A Life Cycle Comparison". http://www.sperecycling.org/GPEC/GPEC2004/pdffiles/papers/037.pdf. Retrieved 2008-12-16. 
2. ^ "Cargill’s BiOH polyols business opens manufacturing site Brazil". PU Magazine International. September 26, 2007. http://www.pu-magazine.com/index.php?id=177&tt_news=4157. Retrieved 2007-10-03. ^{[dead link]}
3. ^ Garrett, Thomas; Du, Xian Du. "Polyols for Diverse Applications". http://honeybee.cc/Garrett_Du_2.pdf. 
4. ^ Narayan, Ramani; Phuong Tran and Daniel Graiver (September 2005). "Ozone-mediated polyol synthesis from soybean oil". Journal of the American Oil Chemists' Society 82 (9): 653–659. doi:10.1007/s11746-005-1124-z. http://www.springerlink.com/content/q85p072054701280/. Retrieved 2007-10-01. 
5. ^ US 2006041156 
6. ^ US 4742087 
7. ^ US 6730768 
8. ^ ^{a b} Babb, D.; J. Phillips; C. Keillor (2006). "Soy-based Polyol for Flexible Slabstock Foam". Salt Lake City: Alliance for the Polyurethanes Industry. 
9. ^ Bauer, S.; R. Kuppel; J. Winkler; P. Coeckelberghs (2006). "Novel Polyols based on Renewable Resources". Maastricht: UTECH. 
10. ^ >Downey, William; Christofer Megson, Wayne Wright (2007). "New Castor oil-derived Polyols for Modified Performance Properties". Orlando: Center for the Polyurethanes Industry. 
11. ^ Niemeyer, Timothy; Patel, Munjal and Geiger, Eric (September, 2006). "A Further Examination of Soy-Based Polyols in Polyurethane Systems". Salt Lake City, UT: Alliance for the Polyurethane Industry Technical Conference. 
12. ^ "New Twist on Green: 2008 Ford Mustang Seats Will Be Soy-Based Foam". Edmunds inside line. July 12, 2007. http://www.edmunds.com/insideline/do/News/articleId=121682. Retrieved 2007-10-02. 
13. ^ "Bio-Composites Update: Bio-Based Resins Begin to Grow". Composites World (April). 2008. http://www.compositesworld.com/articles/bio-composites-update-bio-based-resins-begin-to-grow.aspx. Retrieved 2008-11-25. 
14. ^ Dawe, Bob; Francois Casati, Sabrina Fregni, Yoshiaki Miyazaki (September 2007). "Natural Oil Polyols: Applications in Molded Polyurethane Foams". Orlando: Center for the Polyurethane Industry Conference. 
15. ^ Stanciu, Romeo; Paul Farkas, Hamdy Khalil, Askar Karami, Liberato Mendoza, Yusuf Wazirzada (September 2007). "High Level Bio-inclusion Molded Flexible PU Foams". Orlando: Center for the Polyurethane Industry Conference. 
16. ^ James, Allan; Kenyatta Johnson, Clare Sutton, Mark Goldhawk, Helmut Stegt (September 2007). "Natural Oil Polyols as Co-polyols in Automotive Headrest, Armrest, RIM and NVH Applications". Orlando: Center for the Polyurethane Industry Conference. 
17. ^ Dai, Jack; Ricardo De Genova, David Simpson (September 2007). "Natural Recent Developments in Natural Oil Based Polyols for the Production of Viscoelastic Foams". Orlando: Center for the Polyurethane Industry Conference. 
18. ^ Obi, Bernard; Denise Butler, David Babb, Alfredo Larre (September 2007). "Recent Advances in TDI 80/20 with Stannous Octoate Catalyst Viscoelastic (VE) Foams Produced from both Hydrocarbon Based Polyols, as well as Natural Oil Derived Polyol (NOP)". Orlando: Center for the Polyurethane Industry Conference. 
19. ^ "BioBased Foam insulation homepage". http://www.biobased.net/index.php. Retrieved 2007-10-03.