Biobased Polyols Improve the Sustainability in Polyurethane Applications
As companies aspire to develop sustainable products, demand for materials made from renewables-based polyurethanes also continues to grow. Biobased polyols are a crucial component in increasing the renewable content of these materials. High-performing, cost-competitive biobased polyols are commercially available for automotive applications, sporting goods, and many other flexible and rigid foam and thermoplastic applications.
Over the past twenty years, there have been many developments in biobased polyols. Before the 1990s, castor oil, with naturally occurring hydroxyl groups, was the predominant bio polyol. Castor oil polyols were used in various polyurethane products, including coatings, potting compounds, and flexible foam. Today, many other biobased polyols are available in the market ranging from 30% to 100% bio content.
Like petroleum-based polyols, bio-based polyols can have polyether and/or polyester hydroxyl groups. Below is a brief outline of commercially available bio polyol technologies.
Natural Oil Polyols
Some of the first bio-polyols developed after castor oil were based upon soybean oil. Initial polyols were essentially blown soybean oil. After that, several other polyol technologies were introduced that were more sophisticated. These technologies offer multiple functionalities (2 to 7), primary and secondary hydroxyl groups, and other functional groups than hydroxyl groups. More recently, several other manufacturers have brought additional soy and canola polyol technologies to the market. Each polyol has its benefits and advantages. While soy has been the raw material of choice (mainly due to financial considerations), most of these polyol technologies can be applied to other triglycerides – primarily vegetable oils, but also some animal fats. During the early development of flex foam systems using soy polyols, scientists proved that soy polyol impacts the glass transition temperature, imparting a silkier feel. These attributes make soy polyols ideal for their use in visco-elastic or memory foams. A major automotive interior supplier discovered that soy polyols increased energy dampening and sound absorption in automotive interiors. Soybean oil structure offers additional functional sites for crosslinking, which results in higher compressive strength for rigid foam applications.
Cashew nutshell liquid (CNSL) is another natural oil used to produce natural oil polyols. Arguably, the largest use of CNSL for polyurethanes applications is in the production of mannich amine polyols. CNSL can also be polymerized to produce a polyol with high aromatic content, which can offer good FR properties. There are spray foam systems produced using CNSL that exhibit fortified FR performance.
Most polyether polyols are produce using a starter and building molecular weight by the addition of propylene oxide and/or ethylene oxide. The starter determines the functionality of the polyol (e.g. Propylene glycol – two, glycerin – three, pentaerythritol – four, sucrose blends for higher functionalities). These starters may be biobased, which can offer a bio-content in the polyol. The resulting bio-content can be range from a few percent for the higher molecular weight polyols used in flexible foam and coatings applications, up to 40% for low molecular weight polyols, which are used in rigid foam applications. With the inception of bio ethylene oxide, these polyols may soon have much higher biobased content.
Several raw materials (diols and diacids), produced from biomass, have been introduced to the market, which creates many opportunities for polyester polyols with high bio-content. In 2004, the Department of Energy placed succinic acid and butanediol on its list of Top 12 chemical platforms from biomass, which encouraged their development.
Within the past decade, the development of polyester polyols based on bio-derived C4-C36 dicarboxylic acids combined with biobased diols, 1,3-propanediol (PDO), and 1,4-butanediol (BDO), have progressed rapidly, resulting in polyester polyols with up to 100% bio content. Applications for biobased polyester polyols include cast and thermoplastic polyurethane elastomers, coatings and adhesives, artificial leather, footwear, and polyurethane foam products
The bio polyol industry has come a long way since castor oil was first used in polyurethanes. Many more benefits of biobased polyols have been identified by coating, adhesive, elastomer, and foam formulators. Their use is rapidly growing as they perform like their petrochemical counterparts and enable manufacturers to increase the sustainability of end products and offer benefits not realized with petro-based polyo