Structural changes during deformation in carbon nanotube-reinforced polyacrylonitrile fibers

Influence of Carbon Nanotubes Concentration on Mechanical and Electrical Properties of Poly(styrene-co-acrylonitrile) Composite Yarns Electrospun

In this work, the influence of carbon nanotubes (CNTs) content on the mechanical and electrical properties of four series of polymeric matrix were made and their cytotoxicity on cells was evaluated to consider their use as a possible artificial muscle. For that, polymer composite yarns were electrospun using polymeric solutions at 10 wt.%. of poly(styrene-co-acrylonitrile) P(S:AN) and P(S:AN-acrylic acid) P(S:AN-AA) at several monomeric concentrations, namely 0:100, 20:80, 40:60, 50:50 (wt.%:wt.%), and 1 wt.% of AA. Carbon nanotubes (CNTs) were added to the polymeric solutions at two concentrations, 0.5 and 1.0 wt.%. PMCs yarns were collected using a blade collector. Mechanical and electrical properties of polymeric yarns indicated a dependence of CNTs content into yarns. Three areas could be found in fibers: CNTs bundles zones, distributed and aligned CNTs zones, and polymer-only zones. PMCs yarns with 0.5 wt.% CNTs concentration were found with a homogenous nanotube dispersion and axial alignment in polymeric yarn, ensuring load transfer on the polymeric matrix to CNTs, increasing the elastic modulus up to 27 MPa, and a maximum electrical current of 1.8 mA due to a good polymer–nanotube interaction.

Defect structure evolution of polyacrylonitrile and single wall carbon nanotube nanocomposites: a molecular dynamics simulation approach

In this study, molecular dynamics simulations were performed to understand the defect structure development of polyacrylonitrile-single wall carbon nanotube (PAN-SWNT) nanocomposites. Three different models (control PAN, PAN-SWNT(5,5), and PAN-SWNT(10,10)) with a SWNT concentration of 5 wt% for the nanocomposites were tested to study under large extensional deformation to the strain of 100% to study the corresponding mechanical properties. Upon deformation, the higher stress was observed in both nanocomposite systems as compared to the control PAN, indicating effective reinforcement. The higher Young’s (4.76 ± 0.24 GPa) and bulk (4.19 ± 0.25 GPa) moduli were observed when the smaller-diameter SWNT_(5,5) was used, suggesting that SWNT_(5,5) resists stress better. The void structure formation was clearly observed in PAN-SWNT_(10,10), while the nanocomposite with smaller diameter SWNT_(5,5) did not show the development of such a defect structure. In addition, the voids at the end of SWNT_(10,10) became larger in the drawing direction with increasing deformation.

Hierarchical radial structure of polyacrylonitrile precursor formed during the wet-spinning process

Electron probe micro-analysis (EPMA), micro-beam wide angle X-ray diffraction (Micro-beam WAXD), micro-Raman and nano-infrared (nano-IR) spectroscopy were performed to characterize the hierarchical radial structure within polyacrylonitrile (PAN) fibre which was obtained by the wet-spinning method, including morphology, aggregation structure and molecular chain conformation. The results indicated that along the radial direction of the PAN fibre, the skin layer reflects denser morphology compared to the core region. The crystallinity, d-spacing of the (100) Miller plane and crystalline orientation in PAN fibres were gradually decreased from the skin layer to the central part, while the crystalline size shows opposite distribution tendency which was affected by the diffusion depending on the coagulation environment. As to the molecular chain structure, PAN chains tend to keep the helical conformation rather than planar zigzag conformation and packed more orderly in the skin layer of fibres.

The study focused on the multiscale to clarify the radial structure in PAN precursors.

Rheological Behavior of Amino-Functionalized Multi-Walled Carbon Nanotube/Polyacrylonitrile Concentrated Solutions and Crystal Structure of Composite Fibers

The rheological behavior of amino-functionalized multi-walled carbon nanotubes (amino-CNTs)/polyacrylonitrile (PAN) concentrated solutions in the dimethyl sulphoxide solvent and the effects of the amino-CNTs on the PAN precursor fibers by wet-spinning method were investigated. The amino-CNT/PAN concentrated solutions prepared by in situ solution polymerization with homogeneous dispersion of amino-CNTs have higher complex viscosity, storage modulus and loss modulus as compared to the control PAN concentrated solutions containing 22% PAN polymer by mass. The composite fibers with amino-CNTs of 1 wt % have lower degree of crystallization, crystal size and crystal region orientation compared to the control PAN precursor fibers. However, the amino-CNT/PAN composite fibers with diameter of about 10.5 μm exhibit higher mechanical properties than the control PAN precursor fibers with diameter of about 8.0 μm. Differential scanning calorimetry analysis demonstrated that the cyclization reaction in composite fibers have broad exothermic temperature range and low exothermic rate. These results indicate that the addition of amino-CNTs into PAN precursor fibers is beneficial to controlling the process of thermal stabilization and obtaining the higher performance of composite fibers.

Drawing dependent structures, mechanical properties and cyclization behaviors of polyacrylonitrile and polyacrylonitrile/carbon nanotube composite fibers prepared by plasticized spinning

Drawing to change the structural properties and cyclization behaviors of the polyacrylonitrile (PAN) chains in crystalline and amorphous regions is carried out on PAN and PAN/carbon nanotube (CNT) composite fibers. Various characterization methods including Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and thermal gravimetric analysis are used to monitor the structural evolution and cyclization behaviors of the fibers. With an increase of the draw ratio during the plasticized spinning process, the structural parameters of the fibers, i.e. crystallinity and planar zigzag conformation, are decreased at first, and then increased, which are associated with the heat exchange rate and the oriented-crystallization rate. A possible mechanism for plasticized spinning is proposed to explain the changing trends of crystallinity and planar zigzag conformation. PAN and PAN/CNT fibers exhibit various cyclization behaviors induced by drawing, e.g., the initiation temperature for the cyclization (Ti) of PAN fibers is increased with increasing draw ratio, while Ti of PAN/CNT fibers is decreased. Drawing also facilitates cyclization and lowers the percentage of β-amino nitrile for PAN/CNT fibers during the stabilization.

Structural evolution of OBC/carbon nanotube bundle nanocomposites under uniaxial deformation

A regulated morphology of multi-walled CNT bundles in an olefin block copolymer matrix is achieved via solution blending after sonication. We observed an unexpected inverse evolution trend of long period in nanocomposites compared to that in neat matrix.

Polyacrylonitrile fibers efficiently loaded with tamoxifen citrate using wet-spinning from co-dissolving solution

Tamoxifen citrate (TAM)-loaded polyacrylonitrile (PAN) fibers were prepared using an improved wet-spinning technique. TAM was used as a model drug to evaluate the potential application of the loaded fiber system for drug delivery. PAN was first homogeneously dissolved in the N,N-dimethylacetamide (DMAc) solution containing TAM and then the co-dissolving solution was solidified to prepare the fibers using a wet-spinning method. Chemical, morphological and mechanical property characterizations were carried out, as well as the studies of the drug release properties. TAM was successfully encapsulated into a monofilament fiber, and this system was stable in terms of high loading capacity and effectiveness in release. The diameter of drug-loaded fiber was in the range of 40-60 microm. The best values of the tensile strength at 2.968 cN/dtex and breaking elongation at 14.9% of drug-loaded fibers were obtained when the drug loading content was 23.1 wt.%. These characteristics were suitable for the weaving process. The in vitro release experiment indicated that constant drug release from the fiber was observed for a long duration of time. Kinetic studies demonstrated that the system followed the Higuchi kinetics. These findings demonstrate that controlled release of drugs from PAN fibers could be potentially useful in drug delivery systems.