| Abstract: | Physical aging was studied on particulate -filled glassy network polymers by means of mechanical -dilatational, differential scanning calorimetry (DSC) and density measurements on specimens that were aged at room temperature. The composites aged for 0.5 day fractured in a brittle manner at a constant ultimate stress, which is close to the tensile strength of the unfilled material, regardless of the filler content and the presence of a coupling agent. This type of mechanical behavior is caused by the compressive residual stresses that are present due to curing and differential thermal shrinkage. As aging takes place, the compressive residual stresses are relieved; as a result the ultimate tensile strengths of the composites decrease. The 120 -day -old untreated glass bead containing composites exhibited dilatation and yield in mechanical -dilatational testing. This type of behavior is described as “having no adhesion” between the filler and the matrix. The 120 -day -old composites with coupling agent -treated glass beads fractured at a tensile stress which is equal to 1/1.6 the tensile strength of the unfilled material. These materials did not exhibit dilatation and yield in mechanical -dilatational testing. Density and DSC data indicate densification and enthalpy relaxation upon again and support the hypothesis presented for the observed change in the mechanical -dilatational behavior. |
