The effect of curing light intensity and test temperature on the dynamic mechanical properties of two polymer composites.

The dynamic modulus of elasticity of two composite materials cured by three light intensities was investigated using a dynamic thermal and mechanical analyser at 37 degrees C and 60 degrees C. The lowest light intensity, 180 mW/cm2, was found to be unsatisfactory in that specimens were weak and mostly untestable. The higher intensities, 350 and 700 mW/cm2, cured the materials to slightly different extents with the elevated temperatures of testing leading to post-cure maturation of the materials. An interesting finding was that one material had a significantly higher modulus when tested at 37 degrees C in comparison with that found at 60 degrees C. In one material the higher light intensity resulted in significantly higher modulus values and these values were increased by post-curing. In the other material the higher light intensity did not result in higher modulus figures at either test temperature, and lower test temperature resulted in better post-cure maturation. These findings are most likely to be caused by differences in base monomer and activator/initiator concentrations. The results indicate that optimum polymerization may not be achieved in all materials by the same method, in particular, high curing light intensities may not achieve the most desirable results.