ipyChord: a package for evaluating small-angle X-ray scattering data of fiber symmetry

Investigating the Effect of Chain Extender on the Phase Separation and Mechanical Properties of Polybutadiene-Based Polyurethane

The thermodynamic incompatibility between the soft and hard segments of thermoplastic polyurethane (TPU) results in a microphase-separated behavior and excellent mechanical properties. However, the effect of the chain extender on the degree of microphase separation (DMS) and the resultant mechanical properties of TPU have not been well studied because of the complex interactions between the soft and hard segments. Herein, hydroxyl-terminated polybutadiene-based TPUs(HTPB-TPUs) without hydrogen bonding between the soft and hard segments are synthesized using hydroxyl-terminated polybutadiene, toluene diisocyanate, and four different chain extenders, and the effect of the chain extender structure on DMS is analyzed experimentally using a combination of analytical techniques. Furthermore, the solubility parameters of the soft and hard segments, glass transition temperatures, and hydrogen-bond density of the HTPB-TPUs, are computed using all-atom molecular dynamics simulations. The results clearly reveal that the chain extender significantly affects the DMS and thus the mechanical properties of HTPB-TPUs. This study paves the way for studying the relationship between the structure and properties of TPU.

A comparison of deep-learning-based inpainting techniques for experimental X-ray scattering

The implementation is proposed of image inpainting techniques for the reconstruction of gaps in experimental X-ray scattering data. The proposed methods use deep learning neural network architectures, such as convolutional autoencoders, tunable U-Nets, partial convolution neural networks and mixed-scale dense networks, to reconstruct the missing information in experimental scattering images. In particular, the recovered pixel intensities are evaluated against their corresponding ground-truth values using the mean absolute error and the correlation coefficient metrics. The results demonstrate that the proposed methods achieve better performance than traditional inpainting algorithms such as biharmonic functions. Overall, tunable U-Net and mixed-scale dense network architectures achieved the best reconstruction performance among all the tested algorithms, with correlation coefficient scores greater than 0.9980.

Structural Evolution of Polyglycolide and Poly(glycolide-co-lactide) Fibers during In Vitro Degradation with Different Heat-Setting Temperatures

The structural evolution of polyglycolide (PGA) and poly(glycolide-co-lactide) (P(GA-co-LA)) with 8% LA content fibers with different heat-setting temperatures was investigated during in vitro degradation using WAXD, SAXS, and mechanical property tests. It was found that the PGA fiber was more susceptible to the degradation process than the P(GA-co-LA) fiber and a higher heat-setting temperature reduced the degradation rate of the two samples. The weight and mechanical properties of the samples showed a gradual decrease during degradation. We proposed that the degradation of PGA and P(GA-co-LA) fibers proceeded in four stages. A continuous increase in crystallinity during the early stage of degradation and a gradual decline during the later period indicated that preferential hydrolytic degradation occurred in the amorphous regions, followed by a further degradation in the crystalline regions. The cleavage-induced crystallization occurred during the later stage of degradation, contributing to an appreciable decrease in the long period and lamellar thickness of both PGA and P(GA-co-LA) samples. The introduction of LA units into the PGA skeleton reduced the difference in the degradation rate between the crystalline and amorphous regions, and they were simultaneously degraded in the early stage of degradation, leading to a degradation mechanism different from that of the PGA fiber.

Polymorphic microstructure of MDI/BD-block polyurethane as determined by temperature-sensitive conformation variation

MDI/BD-block thermoplastic polyurethanes (TPUs) crystallized at different isothermal temperatures and different cooling rates were investigated using multiple techniques. The MDI/BD blocks crystallized in form II when the isothermal temperature was equal to or higher than 150 °C, and in form I at lower isothermal temperatures. Form II had a higher crystal elastic modulus of 6.75 GPa than form I of 1.31 GPa. Form I exhibited contracted conformation, while form II exhibited an extended conformation when viewed from the length of the c-axis in the crystalline state. Based on an analysis of the second derivative in FTIR spectroscopy and simple modeling, the conformation differences were considered to stem from the urethane group's internal bond rotation concerning the phenyl ring and the opening bond angle of phenyl-CH₂-phenyl. The generation of form II above 150 °C may be due to the activation of urethane and the flexible methylene elevated by the high temperature. Overall, it was seen that the crystallization of MDI/BD blocks involved a physicochemical change.

Structural Evolution of Polyglycolide and Poly(glycolide-co-lactide) Fibers during the Heat-Setting Process

PGA and P(GA-co-LA) fibers applied as surgical sutures strongly depend on their microstructure. The structural evolution in both the relaxed and tensioned states during heat-setting after hot stretching, which included heating and postannealing, was investigated using in situ WAXD/SAXS and DSC techniques. We found that the fibers of both PGA and P(GA-co-LA) with 8% LA content under the relaxed state were more advantageous than the fibers under the tensioned state indicated by the larger crystallite sizes and unit cell parameters and the higher crystallinity. The mechanical properties of the samples increased after heat-setting. Heat-setting at 120 °C was more suitable for promoting the fiber properties, which can be ascribed to crystal formation and perfection. During the heating, the thermal expansion increased the unit cell parameters and the long period of PGA linearly, whereas the unit cell parameters of P(GA-co-LA) had an obvious turning point at 60-80 °C, and the long period showed a sudden decline in the temperature range of 60-80 °C, which was mainly the result of the discharge of LA units. The unit cell parameters and the long period of both PGA and P(GA-co-LA) decreased during the isotherm process due to crystal perfection. However, the P(GA-co-LA) decrease was more prominent than PGA because of the inclusion of LA monomers in the crystal structure of GAs.