Drawing and tensile properties of polyamide 6/calcium chloride composite fibers

Formation of Three-Dimensional Polysuccinimide Electrospun Fiber Meshes Induced by the Combination of CaCl2 and Humidity

Even though electrospinning is getting more and more attention, the preparation of 3D nanofibrous meshes is still a big challenge that limits the application of electrospun materials, especially in tissue engineering. To overcome this problem, several solutions are introduced but most of them focus on the postprocessing of the electrospun meshes. This paper presents a straightforward novel method that utilizes the joint effect of the addition of CaCl2 and the relative environmental humidity (RH), which can induce the random 3D formation of polysuccinimide (PSI) electrospun fibers with different such as wrinkled or ribbon-like structures. Although the effect of humidity and inorganic salt additives on the micro and macrostructure of electrospun fibers is known, the connection between the two in this manner has never been presented. To investigate the effect, fibers with different PSI and CaCl2 concentrations at different humidity RH levels are prepared, and their microstructure is visualized with high-resolution scanning electron microscopy (SEM). To reveal the nature of the interaction between the polymer and the CaCl2, Fourier-transformed infrared (FTIR), X-ray diffraction (XRD), and thermogravimetry (TGA) measurements are carried out and 3D nanofibrous structures are obtained.

Tentative Confinement of Ionic Liquids in Nylon 6 Fibers: A Bridge between Structural Developments and High-Performance Properties

A reversible confinement of ionic liquid (IL) among the amide segments has been carried out for the preparation of high-modulus and high-strength aliphatic semicrystalline nylon 6 fibers. In this research work, the suppression or the weakening of the hydrogen bonds during the conventional low-speed melt spinning process is followed by a hot-drawing stage and a subsequent IL extraction of the IL out of the 2% wt IL-confined fibers and an immediate thermal stabilization process for the improvement of the properties of the pristine nylon 6 fibers. The resulted crystal structural developments of the IL-confined fibers are attributed to ultimate molecular orientations, which have contributed to the developments of the overall fiber properties. Here, the influences of the IL on the γ and the α crystal phases, the γ-α transition, the morphological properties, and the tensile properties are investigated. The FTIR reported, experimentally, additional peaks at 1237 cm^-1 for the γ crystal phase and at 1417 and 1476 cm^-1 for the α crystal phase, in conformity with the theoretical computations. The XRD demonstrated that the conventional low-speed melt spinning can successfully be used to prepare as-spun IL-confined fibers having highly improved properties. The so prepared as-spun IL-confined fibers are found to have a γ phase structure that has a small crystal size and high crystal perfections. Fortunately, the γ-to-α crystal phase transition for the IL-confined nylon 6 fibers can be acquired during the hot-drawing stage (stress-induced phase transformation). Furthermore, the IL extraction process followed by a thermal stabilization process, interestingly, has led to significant increases in both of the tensile strengths and the tensile moduli of the reverted nylon 6 fibers. The values that are found are 8.46 cN/dtex for the tensile strength and 39.09 cN/dtex for the tensile modulus. The structure-property relationships between the IL-confined and the reverted nylon 6 fibers have also been discussed.

Multivalent Ions as Reactive Crosslinkers for Biopolymers-A Review

Many biopolymers exhibit a strong complexing ability for multivalent ions. Often such ions form ionic bridges between the polymer chains. This leads to the formation of ionic cross linked networks and supermolecular structures, thus promoting the modification of the behavior of solid and gel polymer networks. Sorption of biopolymers on fiber surfaces and interfaces increases substantially in the case of multivalent ions, e.g., calcium being available for ionic crosslinking. Through controlled adsorption and ionic crosslinking surface modification of textile fibers with biopolymers can be achieved, thus altering the characteristics at the interface between fiber and surrounding matrices. A brief introduction on the differences deriving from the biopolymers, as their interaction with other compounds, is given. Functional models are presented and specified by several examples from previous and recent studies. The relevance of ionic crosslinks in biopolymers is discussed by means of selected examples of wider use.

Spatial Structure Investigation of Porous Shell Layer Formed by Swelling of PA66 Fibers in CaCl2/H2O/EtOH Mixtures

This is a continuation of work on interactions between polyamide 66 (PA66) fibers and CaCl₂/H₂O/EtOH mixtures. It was observed that the mixtures dissolved the fibers, but with or without an intermediate stage of visibly evident swelling depending on the mixture composition. The interaction proceeds via Lewis acid-base complexation between the polymer carbonyl groups and Ca²⁺ ions and can be interrupted by rinsing the fibers with water. Swollen fibers retained their expanded diameters even after rinsing and exhibited a highly rough surface and increased water retention. The observed effects suggest that such mixtures may be used to increase the surface roughness of PA66 fibers for increasing the interfacial adhesion in composites applications. In this publication, we report the results of further investigations into the spatial structure of cross sections of swollen fibers. Using atomic force microscopy coupled with infrared spectroscopy on the length scale of 100 nm (nanoIR-AFM), we could show, for the first time, the PA66 core-shell structure, where the shell thickness increases with the treatment extent and exhibits a highly porous structure. Thus, the surface roughness observed previously is not limited only to the surface but extends toward the fiber core. The examination also showed no evidence of Ca²⁺ complexation in the fiber cores, which confirms a near-complete removal of the ions. Additional measurements of the crystallinity with differential scanning calorimetry and attenuated total reflectance Fourier transform infrared spectroscopy showed that the shell exhibits lower crystallinity than the core.