A NOTE ON THE TAN DELTA(T) PEAK AS A GLASS-TRANSITION INDICATOR IN BIOSOLIDS

The plasticization of many biosolids can take place over a fairly broad temperature range. The resulting loss of stiffness is primarily expressed by a drastic drop of G' (T) whose magnitude is usually higher than G'' (T) by one or two orders of magnitude. Both G' (T) and G'' (T) have characteristic properties that can vary widely among biomaterials. Consequently, the tan delta (T) peak need not be a mark of the transition center and it can be observed at temperatures where different materials have undergone a very different degree of plasticization as judged by the magnitude of G' (T). This is demonstrated by computer simulations using typical functions that describe G' (T) and G'' (T) at the glass transition region and with published data on the dynamic mechanical behavior of a variety of biosolids.