Huntsman: Solvents as Solutions for Formulations

When a formulator begins a project on a new active ingredient, the appropriate solvent is one of the early considerations. Since many pesticide actives have aromatic characteristics, back in the 1960s, the formulator might use any number of aromatic hydrocarbons or halogenated solvents. As we began to understand the potential environmental and health impacts of various compounds, the field of choices naturally began to narrow. During the 1980s, N-methylpyrrolidone (NMP) became the choice for otherwise difficult formulations. Upon further study, however, it became clear that NMP was not the savior everyone had thought it would be.

The movement in the 1990s and 2000s to more environmentally responsible and, lately, to more sustainable ingredients, has changed the available choices. Paraffins are currently preferred if a hydrocarbon is needed, but they need help solubilizing aromatic actives. Aromatic hydrocarbons are still available, but with stricter regulations may not be a sustainable ingredient for the future, which leads them to be rarely, if ever, considered in a modern formulation. The future alternatives may very well be weaker solvents for the actives or not sustainable long-term.

The modern developer of a formulation to be used locally, regionally, or globally must consider an array of regulations that sometimes severely limit choices. The available choices are usually limited to a menu provided by regulatory authorities from which formulator must choose those solvents that may be compatible with the active. In addition, the other ingredients, such as wetting agents, compatibility agents and other ingredients, generally further narrows the available choices. Also, the company may have a particular solvent of choice for a particular class of ingredients.

The job of the solvent is to carry the active in liquid form in the container to primarily provide a stable environment for the rest of the ingredients. Solvents provide flowability and ease-of-delivery, two characteristics that make liquid formulations highly desirable.

The challenge is to choose the right solvent from the available menu. Modern solvents can include ingredients derived from both petroleum and biological sources. Biological sourcing is important for many companies, due to their environmentally responsible and sustainable credentials. Farmers, formulators and applicators around the world have understood, and integrated the need for environmental responsibility for many, many years, and so have naturally dialed into their thought and decision processes.

Since environmental factors are built into the choices by companies and governments, the primary key to making the right choice of solvent is driven by the core purpose of the solvent. The choice must be made from the available menu based on how well the solvent provides a stable liquid environment for the active and the other ingredients.

While solvents like paraffins and methylated vegetable oils (MSOs) are available, they tend not to solubilize the most difficult actives very well. In addition, MSOs can have temperature and other stability challenges. Other, more exotic choices may be available, but tend to be expensive.

“Simple” tends to be best. “Simple” small molecules tend to have very low freezing points. Small esters with small side chains or groups tend to dissolve many ingredients well. Aromatic solvents tend to dissolve aromatic actives.

JEFFSOL^® AG 1700 solvent and JEFFSOL^® AG 1705 solvent are two effective “simple” choices. Their aromatic character makes them compatible with various active ingredients. The simplicity of the molecules gives them a low freezing point with JEFFSOL^® AG 1705 being able to remain liquid by itself down to -50 C.

When aromatics are not the answer, but rather a more polar solvent is needed to bring in polar molecules, the formulators are recommended to look at carbonates as an alternative. They are available in a variety of forms, such as JEFFSOL^® AG 1555 solvent. JEFFSOL^® AG 1555 solvent is both polar and has a high degree of biodegradability. Used in non-aqueous systems, JEFFSOL^® AG 1555 solvent has been useful in a variety of formulations where NMP and other polar solvents may no longer be used.

Now, as ever, the choice of solvent is critical. However, with the environmental and toxicological limitations driven by today’s regulations, those choices are more and more limited. Choices of solvents may vary in the market, but “simple” solvents with low melting points can help with a diversity of performance needs, such as cold tolerance, viscosity and stability. Overcoming challenges such as these by using modern solvents, such as those mentioned above, will help bring success to your formulations.