Strain-induced structural evolution during drawing of poly(ethylene terephthalate) fiber at different temperatures by in situ synchrotron SAXS and WAXD

Effect of KI Concentration in Correcting Tank on Optical Properties of PVA Polarizing Film

Polarizer is a key component of the liquid crystal display panel, and the optical properties mainly include transmittance, degree of polarization and chromaticity. Polarizer is made of a multilayer optical film, in which the PVA polarizing film is the core structure for realizing the polarization of the whole polarizer. PVA polarizing film is commonly manufactured through a multi-step craft, including rinsing, dyeing, stretching and correcting. The correction process has a significant impact on the final apparent color and optical properties of the polarizer. In this study, the KI concentration in the correcting tank, ranging from 1% to 3%, was systematically investigated. With the increase in KI concentration, the Raman vibration peak at 160 cm⁻¹ representing I5− ions gradually weakened, while the Raman vibration peak at 110 cm⁻¹ representing I3− ions gradually increased, indicating that the KI in the correcting tank changed the chemical equilibrium of polyiodide ions in PVA. Then abundant chromophore I5− ions were consumed and I3− ions generated, so that the apparent color of PVA polarizing film gradually changed from dark blue to dark gray, and the chromaticity a-value and b-value gradually increased. The change in the concentration of dichroic species (I5− and I3−) in PVA polarizing film had directly affected its transmittance in the visible range. From the UV-Vis transmittance spectrum of PVA polarizing film, when the I5− ions were consumed and I3− ions generated, the transmittance of PVA polarizing film in the region of 675–525 nm wavelength increased gradually while the polarization degree also increased.

Understanding multiscale structure-property correlations in PVDF-HFP electrospun fiber membranes by SAXS and WAXS

Electrospinning is a versatile technique to produce nanofibrous membranes with applications in filtration, biosensing, biomedical and tissue engineering. The structural and therefore physical properties of electrospun fibers can be finely tuned by changing the electrospinning parameters. The large parameter window makes it challenging to optimize the properties of fibers for a specific application. Therefore, a fundamental understanding of the multiscale structure of fibers and its correlation with their macroscopic behaviors is required for the design and production of systems with dedicated applications. In this study, we demonstrate that the properties of poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) electrospun fibers can be tuned by changing the rotating drum speed used as a collector during electrospinning. Indeed, with the help of multiscale characterization techniques such as scanning electron microscopy (SEM), small-angle X-ray scattering (SAXS), and wide-angle X-ray scattering (WAXS), we observe that increasing the rotating drum speed not only aligns the fibers but also induces polymeric chain rearrangements at the molecular scale. Such changes result in enhanced mechanical properties and an increase of the piezoelectric β-phase of the PVDF-HFP fiber membranes. We detect nanostructural deformation behaviors when the aligned fibrous membrane is uniaxially stretched along the fiber alignment direction, while an increase in the alignment of the fibers is observed for randomly aligned samples. This was analyzed by performing in situ SAXS measurements coupled with uniaxial tensile loading of the fibrous membranes along the fiber alignment direction. The present study shows that fibrous membranes can be produced with varying degrees of fiber orientation, piezoelectric β-phase content, and mechanical properties by controlling the speed of the rotating drum collector during the fiber production. Such aligned fiber membranes have potential applications for neural or musculoskeletal tissue engineering.

Influence of polyethylene terephthalate/ polyamide (PET/PA) bilayer structure on physical and strength-related properties of superpressure angioplasty balloons

BACKGROUND

Percutaneous transluminal coronary angioplasty (PTCA), including balloon angioplasty, is a standard clinical invasive treatment for coronary artery disease. The coronary lesion with calcification is difficult to dilate and the prevention of balloon failure is especially important.

OBJECTIVE

A novel superpressure balloon was fabricated with bilayered structure of polyethylene terephthalate (PET) and PA12 (polyamide).

METHODS

The structures of bilayer balloon were adjusted to achieve overall excellent performance. Physicochemical, thermal and mechanical properties of bilayer balloons were characterized by X-ray diffraction, differential scanning calorimeter, hydraulic tester and theoretical simulation.

RESULTS

Compared with pure PA12 and PET balloons, PA12 outer layer: PET inner layer balloon with layer ratio of 3:7 shows the highest burst stress and relatively low compliance due to an increase in crystallinity and orientation.

CONCLUSIONS

The produced bilayer balloon proved to possess a small folding dimension thanks to its ultrathin bilayer structure, which is good for crossing cramped vessels. We believe these optimally fabricated bilayer balloons are proved to provide attractive opportunities for preparation, performance enhancement, and practical applications of super-pressure balloon catheters and cryoablation balloons, that will significantly promote the development of percutaneous transluminal coronary angioplasty for clinical applications.

Fabrication of piezoelectric poly(L-lactic acid)/BaTiO3 fibre by the melt-spinning process

Poly(l-lactic acid) (PLLA) based piezoelectric polymers are gradually becoming the substitute for the conventional piezoelectric ceramic and polymeric materials due to their low cost and biodegradable, non-toxic, piezoelectric and non-pyroelectric nature. To improve the piezoelectric properties of melt-spun poly(l-lactic acid) (PLLA)/BaTiO₃, we optimized the post-processing conditions to increase the proportion of the β crystalline phase. The α → β phase transition behaviour was determined by two-dimensional wide-angle x-ray diffraction and differential scanning calorimetry. The piezoelectric properties of PLLA/BaTiO₃ fibres were characterised in their yarn and textile form through a tapping method. From these results, we confirmed that the crystalline phase transition of PLLA/BaTiO₃ fibres was significantly enhanced under the optimised post-processing conditions at a draw ratio of 3 and temperature of 120 °C during the melt-spinning process. The results indicated that PLLA/BaTiO₃ fibres could be a one of the material for organic-based piezoelectric sensors for application in textile-based wearable piezoelectric devices.

Effect of the Trifunctional Chain Extender on Intrinsic Viscosity, Crystallization Behavior, and Mechanical Properties of Poly(Ethylene Terephthalate)

In this work, poly(ethylene terephthalate) (PET) chain-extending products with different molecular weights were prepared by reactive extrusion using isocyanate trimer (C-HK) as the trifunctional chain extender. The effect of the chain extender C-HK on the intrinsic viscosity, melt flow property, crystallization behavior, crystallization morphology, and mechanical property of PET was investigated. The results showed that when the content of the chain extender was increased from 0.6 to 1.4 wt%, the viscosity average molecular weight of PET was effectively increased from 2.36 × 10⁴ to 5.46 × 10⁴ g·mol^-1. After the chain extending, the crystallinity and the time of semicrystallization of PET were significantly decreased. After the isothermal crystallization at 220 °C for 5 min, the spherulites formed by pure PET became larger. With the increase in molecular weight of PET after chain extension, its spherulite size was significantly decreased without changing the crystalline structure. The chain-extended PET also exhibited more excellent bending-resistant and impact-resistant properties. While the tensile strength of PET after chain extension was slightly decreased, the bending strength was increased by a maximum value of 56.8%, and the impact strength was increased by a maximum value of five times.