Online monitoring of birefringence development in heat-setting polymer films with a fast dual-wavelength optical technique. I. Uniaxially oriented poly(ethylene naphthalate)

A simple constrained uniaxial tensile apparatus for in situ investigation of film stretching processing

A simple constrained uniaxial tensile apparatus was designed and constructed to obtain stress-strain curve during stretching and subsequent structural evolution of polymeric films. Stretch is carried out through two motor driven clamps in the machine direction and scissor-like clamps in the transverse direction keeping the sample width constant. The force information during film stretching process is recorded by a tension sensor and structural evolution can be obtained by in situ X-ray scattering technique. All parameters related to film stretching manufacturing, such as temperature, draw ratio, and stretching speed can be set independently, making the apparatus an effective method to explore the relationship between processing parameters and structure.

Rapid integrated rheo-optical and polarized Fourier-transform infrared spectrometry measurement system for polymer films undergoing chemo-mechanical changes

The design and performance of a multisensory instrument to track physical and chemical changes of thin polymer films (typically 5 μm < thickness < 100 μm) subjected to thermal and mechanical treatments are described in this paper. For the first time, real-time measurements of spectral birefringence, true stress, true strain, and temperature are integrated together with ultra-rapid-scan polarized FT-IR spectrometer (URS-FT-IR) to investigate the relationships between true mechanical measures and structural features at different length scales. The rheo-optical properties (birefringence-true stress-true strain) are collected at a rate of 10 data points∕s and URS-FT-IR data are collected at a rate of 300 complete spectra∕s. The IR dichroism measurement is performed by exposing the sample to non-polarized IR beam in transmission mode with two mutually perpendicular polarizations, parallel and perpendicular to the stretching direction, received by detector unit. This design allows to analyze both polarizations simultaneously wavenumbers in the range of 500 cm(-1)-4000 cm(-1). Controlled processing parameters include air speed, air temperature, stretching rate, stretching ratio, stretch cycling, and holding times; while simultaneously measuring optical retardation, sample width, temperature, load cell, and both parallel and perpendicular IR spectra. Calibration and performance of this instrument is demonstrated with several film samples. These are: A polystyrene standard, an atactic polystyrene (homo-polymer), a polyurethane (consists of hard and soft segments) for physical changes during uniaxial deformation, and a polyamic acid during imidization reaction. This measurement system is particularly useful in unraveling molecular level details of complex physical and chemical events that take place during very fast deformation schemes (uniaxial stretching, retraction, relaxation, annealing, etc.) relevant to industrial processes. These include specific orientation behavior of each phase, block or filler, crystallization, relaxation and orientation state. It is also suited to track reaction rates and products in polymers undergoing thermal or photo curing.

On-line Measurement Studies on Orientation Development and Characteristic Short-Period Diameter Fluctuation in High Speed In-line Drawing of Poly(ethylene terephthalate) Fiber

To investigate the orientation development behavior in high-speed in-line drawing process of poly(ethylene terephthalate) filament, simultaneous on-line measurements of diameter and optical retardation were conducted under various spinning and drawing conditions. In the measurement of optical retardation, the order of interference could be determined successfully from the successive assembly of phase shift versus filament diameter correlations collected at different measuring positions along the spinning and drawing lines. Analyzed birefringence increased steeply in the vicinity of neck-like deformation in the high-speed spinning line or in the vicinity of necking deformations in the in-line drawing line. It was verified that the thinning in the in-line drawing line is more effective for the development of molecular orientation in comparison with that in the high speed spinning line. Analysis on the time-course variations of diameter and birefringence in the vicinity of neck-like deformation caused by the fluctuation of its position along the spinning line was conducted to obtain detailed orientation development behavior. This analysis confirmed that the local birefringence is governed solely by the local diameter (or velocity) in the high-speed spinning line. On the other hand, it was relatively difficult to analyze the time-course variation of birefringence near the necking deformation in the in-line drawing line because of an overlapping of unique short-period diameter fluctuation of around 125 Hz, which corresponds to several tens of centimeters along the filament, occurring during the necking deformation. Such diameter fluctuation moves toward downstream at the speed of running filament, and therefore was speculated to be originated from the intrinsic characteristics of fiber materials.

A new method for the time-resolved analysis of structure and orientation: polarization modulation infrared structural absorbance spectroscopy

Polarization modulation infrared linear dichroism (PM-IRLD) is often used for measurements of molecular orientation with high sensitivity and good time resolution. However, PM-IRLD is unable to provide the structural absorbance spectrum because it does not measure separately the parallel and perpendicular spectra. Here we propose a new method, named polarization modulation infrared structural absorbance spectroscopy (PM-IRSAS), to overcome this limitation of PM-IRLD. PM-IRSAS measures the dichroic difference and structural absorbance spectra simultaneously and, therefore, allows quantitative analysis of molecular orientation and conformation with 200 ms time resolution. The PM-IRSAS method was first validated through comparison with conventional polarized FT-IR spectroscopy using drawn polymer films. Second, it was demonstrated that the PM-IRSAS method can provide a quantitative analysis of dynamic orientation and conformation changes in PET films during deformation and crystallization processes.