Binder dissolution also effects resin viscosity significantly. As the resin polymerizes, the viscosity of the resin increases. The gel time is the time at which there is a sharp rise in the viscosity of the resin as it starts to solidify into a cross-linked structure. Gelation sets the time available for filling large parts. The resin formulation may be changed to suit processing conditions.
Polymerization begins when reactive components first come in contact.
At this point in time, the viscosity of the mixture is a weighted mean of the component viscosities and it is denoted by u . The extent of reaction is zero at this time. It is plotted on the y-axis. In the beginning, the resin viscosity is very low, of the order of 0.1 Pa-s. This translates into low injection pressures which makes Resin Transfer Molding an attractive process.