ORIGIN OF THE INTERMEDIATE DAMPING PEAK IN MICROLAYER COMPOSITES

A comparison of glass transition temperatures measured by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (D MTA) was made using microlayer composites with many alternating layers of two polymers. What appeared to be a third transition at a temperat ure intermediate between the glass transitions of the two components w as observed in DMTA but not DSC. The mechanical origin of this interme diate damping peak in the layered composites was established. The visc oelastic properties of each polymer were modelled by a spring and dash pot in series, and the composite as a parallel arrangement of two Maxw ell elements. It was shown that an anomalous damping peak can appear b etween the glass transition temperatures when the modulus of the compo site can not drop below the modulus of the glassy layers, although the viscosity of the composite continues to be defined by the viscosity o f the rubbery layers in this temperature range. The intermediate dampi ng peak may be a general feature in the dynamic mechanical behavior of co-continuous multiphase systems including polymer blends and continu ous fiber composites.