No abstract

In this article, the supercritical carbon dioxide (Sc-CO2) was used as a medium for hot-drawing of F-III fibers. The conditions of hot-drawing were selected to be the temperature of 250 °C, pressure of 14 MPa, time of 60 min, and different tensions, which were 0, 3, 4.5, 6, and 7.5 g·d-1, respectively. All samples including the untreated and treated F-III fibers were characterized by a mechanical tester and X-ray diffraction (XRD). Results showed that the Sc-CO2 and applied tension could both promote the crystallinity and degree of orientation of F-III fibers at a temperature below the Tg of F-III fibers in Sc-CO2. Moreover, compared with the untreated, the tensile strength and modulus of treated F-III fibers tended to increase with the increase of tension in the range of 0 ~ 6 g·d-1. In summary, this provided a new treatment mode for the hot-drawing of fibers.

Hot-drawing of polyacrylonitrile (PAN) fibers is an important step in the production of carbon fibers. In this article, we investigated the effect of strain on the crystallization behavior and mechanical properties of PAN fibers treated in supercritical carbon dioxide (Sc-CO2) fluid. We mainly used the methods of X-ray diffraction (XRD), monofilament strength analysis and differential scanning calorimeter (DSC) to study the crystallization behavior, mechanical properties and thermal behavior of PAN fibers during hot-drawing process. The experimental results showed that the crystallinity and mechanical properties of PAN fibers both increased a lot under the action of strain during hot-drawing in Sc-CO2 fluid. This provides an important method for preparation of higher performance PAN precursor for PAN-based carbon fibers.

In order to improve the uniformity of dispersion of aramid pulp (AP) in an epoxy resin (EP) system containing the EP and curing agent, a series of treatments including the surface cleaning, colloid mill grinding, freeze-drying of APs were carried out in this article. In addition, the composites were prepared by mixing the untreated and treated APs and EP system with the AP mass fractions of 0, 0.1, 0.3, 0.5 and 0.7%. The APs and their dispersion behaviors in EP system were characterized by scanning electron microscope (SEM), fiber quality analyzer, specific surface area tester and optical microscope, moreover, the impact strength and section morphology of composites after impact damage were tested and characterized by a universal material testing machine and SEM.