It's in the cars we drive, the shoes on our feet, and the furnishings in our homes and businesses. It can be found in many forms such as a molded part, a foam cushion, a spray coating, or an adhesive. In other words, polyurethane is everywhere.
So where does polyurethane come from? Simply put, it is the result of a chemical reaction usually consisting of two components - isocyanate and polyol. What's exciting is the unlimited possibilities for creating new formulations - or "recipes" - that can manipulate the polyurethane to become hard or soft, flexible or rigid, light weight or gel-like.
For the non-technical person, it’s kind of like baking. With the two main ingredients – flour and sugar – you can make a huge variety of foods such as pie crusts, cookies, bread or angel food cake, by adjusting the quantities of flour and sugar and adding other ingredients such as baking soda and seasonings. Or, you can buy premade mixes that already have the right proportions of everything you need. Just mix in the liquids, pour the batter into a mold, or spoon it onto a cookie sheet, heat at a specific temperature for a certain amount of time, and you have a finished product.
Addition of a Catalyst
A catalyst is used to lower the activation energy required for a reaction to occur thus, increasing the speed of a chemical reaction. While air, water or heat may be enough to trigger the reaction, chemical catalysts may also be used – usually in small amounts.
When baking a cake, you could mix the ingredients and leave them on the counter, but you’ll probably never have a cake. The heat in the oven acts as the catalyst to turn the reactants (ingredients) into the desired product – your cake!
Polyurethane systems are like liquid cake mixes. In one-component systems, the ‘batter’ is a prepolymer that is already mixed. Once the container is opened, the mixture will start reacting with the moisture in the air and the pot life clock will start ticking. In a two-component system, the ISO and POLYOL components are kept separated so the chemical reaction will not start until the two components are mixed together in quantities defined by the mix ratio. For example, a mix ratio of 100:25 indicates 100 parts of POLY to 25 parts of ISO.
Caution – Handle polyurethane systems with care. They should never be ingested.The cake terminology is only a decorative way to explain how the ingredients combine and do not constitute the outcome as being edible.
When introduced to ISOs or prepolymers, even a tiny amount of water is enough to start the chemical reaction that can create enough pressure to deform a steel drum or turn it into a projectile. For this reason, it is extremely important to keep ISOs and prepolymers dry. Nitrogen is heavier than oxygen, so before sealing the drum, nitrogen gas is added – often called a nitrogen blanket – into the head space between the product and the top of the drum. This serves as an additional layer of protection against moisture.
Always be sure to consult Safety Data Sheets (SDS) and Technical Data Sheets (TDS) to learn about the precautions that must be taken when handling any chemicals.