In Situ Orientation Studies of a Poly(3-hydroxybutyrate)/Poly(ε-caprolactone) Blend by Rheo-Optical Fourier Transform Infrared Spectroscopy and Two-Dimensional Correlation Spectroscopic Analysis

Abstract

In the present study, the orientation of a poly(3-hydroxybutyrate) (PHB)/poly(epsilon-caprolactone) (PCL) blend was monitored during uniaxial elongation by rheo-optical Fourier transform infrared (FT-IR) spectroscopy and analyzed by generalized two-dimensional correlation spectroscopy (2D-COS). The dichroism of the delta(CH(2)) absorption bands of PHB and PCL was employed to determine the polymer chain orientation in the PHB/PCL blend during the elongation up to 267% strain. From the PHB and PCL specific orientation functions it was derived that the PCL chains orient into the drawing direction while the PHB chains orient predominantly perpendicular to the applied strain. To extract more detailed information about the polymer orientation during uniaxial elongation, 2D-COS analysis was employed for the dichroic difference of the polarization spectra recorded during the drawing process. In the corresponding synchronous and asynchronous 2D correlation plots, absorption bands characteristic of the crystalline and amorphous regions of PHB and PCL were separated. Furthermore, the 2D-COS analysis revealed that during the mechanical treatment the PCL domains orient before the PHB domains.

Molecular Order in Cold Drawn, Strain-Recrystallized Poly(ε-caprolactone)

“…These values are in consent with 2D order parameters, reported for pure PCL and in 80/20 wt % blends of PCL/poly(3-hydroxybutyrate). 54,58,59 In 70/30 blends of PCL/PVC crystallized under strain from the melt, the PCL chains crystallize oriented perpendicularly to the stretching direction. 85,86 This differs from our case, where an existing spherulitic structure is deformed.…”

“…19,49,67,73,76,84 Few orientational studies on the cold drawing of pure PCL exist. 30,45,54,58,59,67 In these, a weak increase of the lamellar long period in stretching direction due to strain is observed (less than 3 nm in step i), followed by a decrease by 1−5 nm during step ii. 19,41,54,67 Perpendicular to the stress tilted lamellae with expanding and broadening distance distributions evolve, simultaneously.…”

“…59 Blending of PCL may shift the stress−strain dependence upon cold drawing (due to a modified amorphous phase), but it does not change the resulting crystallite sizes and approximate orientation distributions. 41,45,58,67 Hence, the microscopic processes involved in steps i−iii appear to be the same. In contrast, crystallization of blended PCL from an oriented melt leads to differently oriented crystallites depending on strain rate and composition.…”

Polymer chain organization in tensile-stretched poly(ethylene oxide)-based polymer electrolytes

“…Unger and Siesler [23] used in situ rheo-optical FT-IR spectroscopy to investigate orientation effects for a blend of poly(3-hydroxybutyrate) and poly(ε-caprolactone). A combination of polarized FT-IR spectroscopy and 2D correlation spectroscopy was effectively used to determine that poly(ε-caprolactone) and poly(3-hydroxybutyrate) orient parallel and perpendicular to the stretching axis, respectively.…”

Temperature-Dependent Fourier Transform Infrared Spectroscopy and Raman Mapping Spectroscopy of Phase-Separation in a Poly(3-hydroxybutyrate)–Poly(l-Lactic Acid) Blend

“…On the other hand, the development of blends is a relatively fast and inexpensive option. The structure and the melting behavior of PHB 31,35 and its various blend systems such as PHB–poly(ε-caprolactone), 36,–38 PHB–poly( p -vinylphenol), 39 and pHB–cellulose acetate butyrate 23,40,41 were studied by various physicochemical methods such as FT-IR spectroscopy, X-ray crystallography, and differential scanning calorimetry. Poly(l-lactic acid) (PLA) 42,44 can be produced by polycondensation of lactic acid or by ring-opening polymerization of the cyclic lactide dimer.…”