Xudong Fang

Rapid Vacuum Infusion and Curing of Epoxy Composites with a Rubber-Cushioned Mold Design

ABSTRACT Vacuum resin infusion has been developed as a low-cost process for manufacturing fiber-reinforced composites with high fiber loading. However, it is an extremely slow process due to the long time required to prepare a vacuum-tight mold and further to cure the resin at room temperature. In this work, a new mold with a rubber cushion suitable for rapid infusion and rapid curing under complete negative pressure was designed and fabricated. Experimental results demonstrated that the new mold is suitable for rapid heating and withstand dynamic loading under complete vacuum force. Composite plaques can be produced with a short cycle time of several minutes while desired mechanical properties are still achieved. Thermal analysis and rheological measurements were performed to study epoxy curing at elevated temperatures and define an optimal process window for rapid vacuum infusion. This study leads to the development of a completely vacuum-based liquid molding process that uses simple tooling, yet is suitable for rapid production. GRAPHICAL ABSTRACT

An effective and simple process for obtaining high strength silkworm (Bombyx mori) silk fiber

This article describes a new process for strengthening natural silk fibers. This process is simple yet effective for mass production of high strength silk fibers, enabled by drawing at a lower temperature and immediately heat setting at a higher temperature. The processing conditions were investigated and optimized to improve the strength. Silk fibers drawn to the maximum ratio at room temperature and then heat set at 200 °C show best tensile properties. Some salient features of the resulting fibers are tensile strength at break reaching 533±10.2 MPa and Young’s modulus attaining 12.9±0.57 GPa. These values are significantly higher than those of natural silk fibers (tensile strength increased by 44 % and Young’s modulus by 135 %). Wide-angle X-ray diffraction and FTIR confirm the transformation of silk I to silk II crystalline structure for the fiber obtained from this process. DSC and TGA data also provide support for the structural change of the silk fiber.

An Overview of Solid-Like Electrolytes for Supercapacitors

Supercapacitors with an electric double-layer design have attracted great attention in the recent years because they are promising energy storage devices for a number of applications, particularly for portable electronics and electric automobiles. They utilize the interface between the electrode and the electrolyte to store energy, resulting in energy storage devices with high power density but low energy density compared to batteries. To improve the performance and reduce the cost, researchers have made significant progress in increasing energy density, electrode voltage, and cycle life. The increase of the energy density is considered to be achieved mainly by increasing the effective specific interface between the electrodes and the electrolyte. Various electrodes with porous structure have been attempted to increase the specific surface area. The increase of electrode voltage is realized primarily via the change of liquid electrolytes to gel, solid and composite ones. In this overview, they are summarized as solid-like electrolytes. This paper reviews the materials adopted and the processing methods developed for solid-like electrolytes, as well as the general characteristics of supercapacitors employing such electrolytes.Copyright

Correction to: Fabrication of high-strength polyoxymethylene fibers by gel spinning

In the original article, the name of author Donggang Yao was misspelled. It is correct here.

Twist-film gel spinning of large-diameter high-performance ultra-high molecular weight polyethylene monofilaments

A twist-film gel spinning process was developed for large-diameter high-performance ultra-high molecular weight polyethylene (UHMWPE) monofilaments. By using polybutene as a spin-solvent, film twisting was demonstrated to be an effective method for solvent removal; approximately 70% of solvent contained in the gel film can be removed simply by film twisting. This mechanical solvent removal process also makes conventional solvent extraction proceed significantly faster. Besides improved solvent extraction efficiency, large-diameter high-strength UHMWPE monofilaments (with diameters of about 80 µm and strength exceeding 3.2 GPa) can be produced with this process, which is difficult to achieve using conventional processes. The capability of making large-diameter high-strength monofilaments may allow new products of UHMWPE to be developed in a number of high-performance applications.

Vacuum Infusion for Processing Thermosetting Composites Containing High Loading Solid Fillers

A new processing route for making thermosetting materials and products containing high loading solid fillers including waste solid scraps and natural mineral fillers was investigated. Traditionally, solid fillers are incorporated into thermosetting polymers by liquid-state mixing. However, due to the high viscosity in mixing, high loading above 50% by weight is difficult to achieve. The new process overcomes this hurdle by a two-step processing strategy. First, solid fillers are placed in the mold and compacted to conform to the mold shape. Next, with the mold closed, a thermosetting resin is infused by vacuum into the particulate preform and after curing to form the desired product. In the exploratory study, epoxy and mineral particles including sand were chosen as material systems for feasibility demonstration. Thermal analysis and rheology were performed to assist in understanding of the fluid flow in heated porous media to achieve an optimized process window for rapid infusion. The results indicated that epoxy matrix composites with extremely high solid filler loading exceeding 70% by weight, as well as with complex external geometry, can be successfully produced. The resulting material is structurally uniform and its mechanical properties can be adjusted by changing the composition and makeup of the filler materials.Copyright