Shear induced irreversible gelation through physical network formation

A resin mixture of vinyl ester and carboxyl terminated butadiene diluted with styrene shows an increase of viscosity when shearing the sample. Unlike previous reports on rheopexy and shear induced gelation of unfilled systems, this behavior leads to permanently elevated levels of viscosity. FT-IR found no indication of a chemical reaction, and therefore, the changes must be physical in nature - believed to be an increase in the number of hydrogen bonds. On the basis of the results, it is concluded that a physical network based on supramolecular attractions between the -COOH groups of the carboxyl terminated butadiene is formed, which leads to a time-dependent behavior and increase in viscosity at certain shear rate, at longer shearing times. This is a new effect, which we call "irreversible shear induced gelation by supramolecular bonding".