Application of Raman spectroscopy to determine the strain-level in polybutylene terephthalate (PBT)

A strain measurement technique for studying the strain distribution in polybutylene terephthalate (PBT) has been developed. In this study, strain level up to 11% was measured by monitoring the reversible conformational changes of the glycol residue in PBT as a function of applied strain. In the unstrained state, the glycol residue is close to gauche-trans-gauche sequence (phase I) and changes to the all-trans states (phase II) on straining. In both cases, intensities of Raman bands originating from different phases of the glycol residue were either increased or decreased. The intensity change of these strain-sensitive Raman bands varied linearly with the applied strain. Furthermore, this intensity change was recovered as the strain was released. Therefore, we have demonstrated that this technique will be useful in analyzing the strain level in PBT polymer and its composites.