Natural Oils Get Rigid
March 1, 2011
In the past several years, designers have faced a whirlwind of changes when it comes to insulation options. From materials that have zero ozone depletion potential (ODP) to the push for materials with lower global warming potential (GWP), designers have had the challenge of adapting as material migrated from one environmentally acceptable product to the next.
Driven by economic and market forces, that evolution is not over. New and ever greener, insulation options are coming down the garden path. For instance, suppliers are incorporating vegetable oils into their insulation mix. Natural-oil polyols, or NOPs, are polyols derived from vegetable oils-particularly soybeans-by several different techniques. The primary use for these materials is in the production of polyurethanes, a product that traditionally used petroleum material in its polyols. In addition to the market demand for “green” products, the rise in petroleum prices has also given rise to the interest in natural-oil polyols.
For their part, NOPs are not new, nor are they are unknown. Today, natural-oil polyols are used in urethane coatings, elastomers and sealants. Commercial and residential insulation made with NOPs, whether spray-in, panel, or even insulation-in-a-can, are becoming readily available to contractors and consumers alike at the local hardware or do-it-yourself store.
Flexible foams made with NOPs are also become more en vogue. Companies such as BASF, Bayer MaterialScience, BioBased Technologies, Urethane Soy Systems, Cargill, Dow Polyurethanes and others, are producing flexible polyurethane foams for a range of industries including automotive and furniture.
Simmons, the bedding manufacturer, announced that it is using Renuva, a flexible foam made by Dow with a soy-based NOP as part of its Natural Care Collection. Seats, headrests, and armrests in the 2010 Hyundai Santa Fe, the Sonata Sedan and the 2009 Kia Amati Sedan are cushioned with NOP-based foam. One of the most vocal supporters of these polyurethanes made using natural oil polyols is the Ford Motor Company, which used polyurethane foam made using natural oil polyols in the seats of its 2008 Ford Mustang.
Insulating FoamsNatural-oil polyols used in rigid polyurethane foam, however, is a different matter. For this product, suppliers have found NOPs to be a challenge.
Polyurethane rigid foams are widely used as insulation materials for appliances such as refrigerators and freezers, and these foams account for almost one-third of the polyurethane market. Polyols are a key ingredient in the manufacture of these foams.
Out of the annual 2.8 billion lbs. of North American polyol market, approximately 1.3 billion lbs. of polyols are used for manufacturing polyurethane rigid foams. The lion’s share of this amount has been made with mineral oil derived from petroleum.
Cellular insulation materials are made by reacting polyols with polyisocyanates and other catalysts, additives, and blowing agents according to the white paper, Natural Oil Polyol of High Reactivity for Rigid Polyurethanes, by BioBased Technologies. As a cross-linked material, the rigidity of polyurethane foams is closely associated with the formation of cross-linked structures and urea linkages. A highly cross-linked polyurethane material requires a reactive polyol that has a relatively high hydroxyl number ranging from 200 to 800 mg KOH/g and high functionality, typically in the range of 3 to 5.
Traditionally, the problem with NOPs is that they had low hydroxyl functionalities and relatively high equivalent weight, which made them more suitable for solid urethanes and flexible foam, not rigid urethane foam. They lacked solubility for blowing agents, as most NOP technology is based on fatty-acid triglycerides, which have different solubility characteristics than polyether or polyester polyols.
That is changing, however, as suppliers such as Bayer MaterialScience, a German-based company with U.S. headquarters in Pittsburgh, and BioBased Technologies, Fayetteville, Ark., have developed ways to overcome NOPs challenges. Dr. Geza Avar, head of Innovation in the polyurethane business unit at Bayer MaterialScience, said that in the past, the relationship between solubility, reactivity and attainable density has been “less than satisfactory” for NOPs, and they could only be used to a limited extent as a replacement for conventional polyols.
Bayer’s method is a one-step process that incorporates fatty acid residues and glycerin into functional polyols giving them higher renewable content and a wide range of possible properties. The company’s process merges two different chemical reactions in a single step. They combine the process of alkoxylation, the reaction between a hydroxyl and a propylene- or ethylene-oxide, and transesterification, to provide polyols with a high content of vegetable oil components that can deliver the same properties. The polyols can be used with various popular blowing agents and are compatible with conventional polyols. They have a hydroxyl weight of up to 280.
BioBased Technologies has two products, Agrol and Agrol Diamond, which is its rigid foam product. The company’s tri-functional polyol derived from natural soy oil has a biobased content of up to 96%, and is compatible with both conventional and other natural oil polyols. It is completely miscible (mixable) with hydrocarbon blowing agents.
The Agrol product, which is used more in spray and flexible foam applications, did undergo an interesting study sponsored by the United Soybean Board. The study compared production data of Agrol polyol to five petroleum-based polyols.
According to Jennifer Wilson, brand manager for BioBased Technologies, the study documented that the production of Agrol has a lower GWP than petroleum-based polyols -310 gm C02 eq/kg compared to petroleum polyols resulting in 4100 gm C02 eq/kq.
She added that it also helps manufacturers reduce their carbon footprint. As much as 5.5 lbs. of carbon dioxide equivalents are removed or prevented from entering the atmosphere for every pound of Agrol that replaces petroleum-based polyether polyol, she says.
Improved Marketing CapabilityBoth Bayer MaterialScience’s polyols and BioBased Technologies’ polyols qualify as biobased products, as defined by the United States Secretary of Agriculture, meaning that they can qualify for the USDA’s procurement guidelines, which accord preferential treatment to products made from renewable materials.
However, most NOPs do meet this threshold. The trick is to meet the threshold after the NOP has been mixed with other ingredients to create the rigid polyurethane foam. In the past, materials such as sugar and glycerin were used in the production of polyols. In fact, polyether polyols based on sugar may contain up to 30% renewable raw materials, but may not meet the threshold. Compare this to Bayer’s NOP that can contain between 40 and 70% renewable material, and when rigid foam is made, it can still hit about 10 to 15% total biobased content, which is a candidate for a biopreferred stamp.
While NOPs use in appliances are still limited, at least one manufacturer has successfully used NOP-containing Baytherm rigid polyurethane foam from Bayer MaterialScience. Liebherr, German manufacturer of refrigerators and other appliances, used rigid foam made with natural-oil polyols as the insulation layer to insulate a refrigerator in Europe.
As new formulations for rigid natural-oil polyols come to market, it is likely that more companies will look to improve their green credentials by insulating their appliances with materials made from high content, biobased polyols.