Dynamic viscoelastic properties of photo-activated composite resins containing short glass fibres

The dynamic shear modulus in torsion (G'), water absorption, thermal expansion and residual monomer of the reinforced materials produced by adding four short glass fibres (19 microm in mean diameter and 86.1--763 microm in mean length) and one spherical E glass (11.1 microm in mean diameter) were examined and discussed in comparison with those of the materials without filler. G' of short fibre reinforced composites increased with fibre length and reached a maximum value near 382 microm for a dry specimen and near 156 microm for a wet one. In addition, the coefficient of thermal expansion of the fibre reinforced composites and the amount of residual monomer decreased considerably compared with those of composites containing spherical glass. There was no significant difference in water absorption between the fibre reinforced composites and the composites containing spherical glass. Therefore, it was concluded that the reinforcement method of adding short glass fibres is favourable for improving the viscoelastic properties of the materials.