| Abstract: | The effect of five fillers on the cross-linking macro-and microcharacteristics of simple unsaturated polyester resins was investigated by differential scanning calorimetry (DSC), reactivity tests, and gel time tests. Glass beads and silica flour appeared to have little influence on the cross-linking reaction of the resin itself, their effect being comparable to mere dilution of the resin. Kaolin presented some interaction with the resin due to its absorption characteristics and acid groups. Reground polyester/glass fiber powder and especially wood flour appeared to present clear chemical interactions with the curing behavior of the resin. Wood flour, in particular, was shown by DSC analysis to strongly co-react with the resin during cross-linking and altered markedly the resin enthalpy change and energy of activation during curing. The wood flour component causing the altered behavior of the resin appears to be lignin. DSC analysis of resins filled with three different types of isolated lignins indicated that this wood flour component reacts in a heterogeneous phase reaction with the resin during cross-linking. It appears that it is the lignin unsaturated carbon–carbon double bonds at the polyester/wood flour and at the polyester/lignin interphases that are likely to co-react by heterogeneous phase radical cross-linking with the polyester resin and styrene unsaturation, markedly changing the resin curing behavior. © 1993 John Wiley & Sons, Inc. |
