Deformation Behavior of PET, PBT and PBT-based thermoplastic elastomers as revealed by SAXS from synchrotron

The present paper discloses the changes in the nanostructure as revealed by small-angle X-ray scattering (SAXS) of synchrotron radiation of anisotropic semi-crystalline samples-of polyester and poly(ether ester) type differing in their chemical composition, while subjected to controlled progressive elongation. From the group of polyesters poly(ethylene terephthalate) (PET), and poly(butylene terephthalate) (PBT) were selected. Two PBT-based commercial poly(ether ester)s were also studied differing in the molecular weight of their soft segments (poly(tetramethylene glycol), PTMG) being 1000 and 2000, respectively. A blend of PBT and EM550 (40/60 by wt.) was also characterized. All materials underwent the same sample preparation process resulting in highly oriented "bristles" of I mm diameter. It was found that epsilon(b), the elongation at break, strongly depends on the flexibility of the glycol residues of the materials studied - ranging from epsilon(b) = 8% for PET that contains ethylene glycol residues, through epsilon(b) = 18% for PBT including the more flexible tetramethylene glycol (TMG) UP to epsilon(b) = 510% for the PEE containing the longest PTMG moieties. During straining the relationship between the external elongation 8 and the changes in the long spacing L was determined. After relaxation from each deformation step the relationship between the tensile set epsilon(r) and the long period L was also followed and discussed. Such analysis led to a model describing the nanostructure evolution during the deformation-relaxation cycle that finally was verified and refined utilizing the multidimensional chord distribution function computed from the anisotropic SAXS patterns.