Kinetics of curing of unsaturated polyesters in the presence of organic and inorganic fillers

The curing of unsaturated polyesters in the presence of organic and inorganic fillers was studied by rheology and differential scanning calorimetry (DSC). A commercial resin was used as unsaturated polyester and pressed olive stones, which are an agricultural by-product, talc and quartz in different concentrations were used as fillers. The viscosity versus time at different temperatures was recorded and the gel time (G) was determined by the sharp increase of viscosity, which involves the beginning of the crosslinking reaction. DSC records the exothermic peak due to the double bonds breaking to give crosslinked macromolecules. The results of both methods were treated kinetically. The activation energy Ev and the pre-exponential factor A′ from the rheological method remained almost constant in the case of talc and quartz compared with the neat unsaturated polyester. With pressed olive stones as filler, both parameters increased. On the other hand, the DSC results for the resins with inorganic and organic fillers showed a decreased activation energy Ea,D and frequency factor ko,D compared with the neat unsaturated polyester, whose activation energy Ea,D and frequency factor ko,D were calculated to be 23.5kcalmol-1 and 9.5 × 109s-1, respectively. The order of reaction was calculated to be close to 1. The olive stones influenced the curing reaction, acting as an auxiliary accelerator.