Damping properties of a mica-filled latex IPN structure and applications in constrained-layer damping

The influence of platelet mica fillers on the damping properties of a polym er specimen produced from a core-shell latex based on styrene, methyl metha crylate and ethylhexylacrylate was evaluated. This polymer is expected to e xhibit an interpenetrating network (IPN) structure, and in the unfilled sta te it exhibits a rather broad glass transition (T-g) region. The damping pe ak (tan delta), evaluated by dynamic mechanical analysis (DMA), became some what higher when mica filler was added to the polymer but the T-g-region be came somewhat narrower. The filler particle size had no appreciable influen ce on the damping properties of the filled polymer. Silane treatment of the mica resulted in a slight broadening of the glass transition (lower temper ature side of the peak) and a decrease in the magnitude of the damping peak compared to the result obtained with untreated mica of the same particle s ize. The results of the DMA measurements on the polymer samples were used t o calculate the composite loss factor (CLF) for a steel laminate consisting of two steel plates with a thin intermediate polymeric layer, using the th eory proposed by Ross, Ungar and Kerwin (RUK). The calculated results were compared with the measured composite loss factors at higher frequencies (20 0 Hz or more) determined in vibrating beam tests (VBT). The agreement betwe en the calculated and measured values with regard to the temperature locati on of the damping peak was reasonably good for the unfilled material, provi ded that the DMA values used for the calculations were recalculated using t he time-temperature superposition principle to the actual higher frequencie s used in the VET. For the filled systems, the RUK theory predicted the loc ation of the CLF-damping peak to be ca. 5 degrees C higher than was observe d experimentally. Possible reasons for this are discussed. Addition of the mica to the polymer affected the experimentally determined CLF values somew hat, but the changes were not very dramatic.