A 30% glass fiber-reinforced PBT (parallel and perpendicular to the fiber orientation) was measured in the 3-point bending mode at 1 Hz and 2 K/min. Considerably higher values for the stiffness and the onset of the E'-decrease (43°C) are obtained for the parallel-oriented type (solid line). The tanδ values are accordingly lower. The tanδ peaks are at the same temperature.
The polyester fiber tested in the tension mode shows relaxations in the low-temperature range, which can be evaluated at E' onset, E'' peak or tanδ peak. Glass transition starts at 75°C. The storage modulus decreased from approx. 4,200 MPa to 200 MPa. (measurement with DMA 242 E Artemis)