Selection of a Greener Set of Solvents Evenly Spread in the Hansen Space by Space-Filling Design

Abstract

New regulations call for the progressive substitution of harmful chemicals by sustainable alternatives with a good profile regarding environmental, health, and safety (EHS) hazards. In particular, the range of acceptable solvents for the coating and polymer industries has suffered a dramatic shrinkage over the past 10 years. The Hansen approach provides an empirical, yet effective, method for determining the solubility parameters of polymers and binders by exposing them to a predefined group of 88 solvents. As this original set of solvents is now unacceptable with regard to toxicological issues, a better set is defined in this work. This subset of greener solvents was selected from a database of 220 organic solvents using five main descriptors, namely, the dispersive (δd), polar (δp), and hydrogen (δh) Hansen solubility parameters and the toxicity indexes according to the CMR (carcinogenic, mutagenic, and reprotoxic) and Hodge and Sterner classifications, along with two secondary descriptors: the molecular volume and the boiling point. For this purpose, a special experimental design is introduced combining a space-filling design (SFD) based on the WSP algorithm with a desirability function to select greener solvents that span the Hansen space more evenly. By taking α-terpineol as a starting point, a new series of 40 solvents exhibiting satisfying EHS profiles and improved coverage of Hansen space was obtained. The relevancy of this new set was checked by determining the solubility parameters of cellulose acetate.