Advanced Vibrational Microspectroscopic Study of Conformational Changes within a Craze in Poly(ethylene terephthalate)

Abstract

Crazes constitute one of the most common failure mechanisms in polymers. They act as fracture precursors, severely degrading the mechanical properties of the material. Thus, a deep understanding of the chain rearrangement occurring inside crazes is of utmost fundamental and practical importance. We have employed synchrotron infrared microspectroscopy (SIRMS) and Raman microspectroscopy to investigate the conformational changes inside micron-sized crazes in poly(ethylene terephthalate), PET. A promotion of the full-extended chain conformational structure at the expense of mainly the trans amorphous mesomorphic phase along with an increase in crystallinity of around 4% has been found. These results differ from what we observed across the deformation neck during PET cold drawing, where no promotion of the all-trans crystalline conformation occurred for slow drawing speeds at temperatures well below the glass transition. Our results show the tremendous capabilities of advanced vibrational microspectroscopy techniques to investigate microscale phenomena in polymer science.

Optical Anisotropy of Polyethylene Terephthalate Films Characterized by Spectral Means

“…For the stretched PET, the enhanced dichroic character of the in-plane δ(C-H) ring at 1018 cm −1 was attributed by Mecozzi and Nisini [ 50 ] and Santoro et al [ 44 ] to a planarization of the benzene ring–ester frame. The ν(C=O) component, which in native PET appeared at 1707 cm −1 , downshifted to 1706 cm −1 after stretching the film and has a narrow shape due to the same phenomenon.…”

Vibrational Spectra of Poly(ethylene terephthalate) Chains in the Mesomorphic Form

“…[4][5][6][7][8] Of course, vibrational methods are particularly helpful when conformational disorder occurs in the mesomorphic phase, as for instance for mesomorphic forms of polytetrafluoroethylene [9][10][11] or of poly(ethylene terephthalate) (PET). [12][13][14][15][16] www.advancedsciencenews.com www.mcp-journal.de mesomorphic nature is clearly established by X-ray diffraction. Our main objective is a possible validation of the chain conformation of PET in the mesomorphic form, which was suggested by combination of X-ray diffraction data and conformational analysis.…”

“…Many papers have been devoted to the mesomorphic form of PET, mainly to the transition toward the usual triclinic crystalline form, [27][28][29][30][31][32] but also to the diffusion of organic vapors [33] and to the possible influence of π-π interactions between the main-chain phenylene groups on the mesomorphic order. [34] Few papers have also reported infrared [12][13][14][15][16] and Raman [13][14][15][16]31] spectra of mesomorphic PET samples.…”

“…In particular, the study of transitions between mesomorphic forms and crystalline forms, e.g., by thermal and vibrational methods, can be highly informative, as for instance observed for syndiotactic polystyrene . Of course, vibrational methods are particularly helpful when conformational disorder occurs in the mesomorphic phase, as for instance for mesomorphic forms of polytetrafluoroethylene or of poly(ethylene terephthalate) (PET) …”

Opportunities and challenges for polymer science using synchrotron-based infrared spectroscopy

“…Here the changes in dichroic ratios (D) and chain conformation through the necking zone of a drawn sample were followed. They further examined the orientation and conformational features inside micronsized micro-crazes that were generated perpendicular to the draw direction [ 35 ]. The crazing phenomenon is common in mechanically strained polymers and is a precursor for fracture and product failure.…”