In resin transfer molding processes, the edge effect caused by the nonuniformity of permeability between fiber preform and edge channel may disrupt resin flow patterns and often results in the incomplete wetting of fiber preform, the formation of dry spots, and other defects in final composite materials. So a numerical simulation algorithm is developed to analyze the complex mold-filling process with edge effect. The newly modified governing equations involving the effect of mold cavity thickness on flow patterns and the volume-averaging momentum equations containing viscous and inertia terms are adopted to describe the fluid flow in the edge area and in the fiber preform, respectively. The volume of fluid (VOF) method is applied to tracking the free interface between the two types of fluids, namely the resin and the air. Under constant pressure injection conditions, the effects of transverse permeability, edge channel width, and mold cavity thickness on flow patterns are analyzed. The results demonstrate that the transverse flow is not only affected by the transverse permeability and the edge channel width but also by the mold cavity thickness. The simulated results are in agreement with the experimental results.

At the reactive mould‐filling stage in resin transfer moulding (RTM) processes, the correlation analysis of epoxy/amine resin cure, structure and chemorheological behavior plays a key role in the optimum control of RTM processes. A new methodology used to simulate the reactive resin flow in RTM processes with edge effect is presented in this article. The recursive approach and the branching theory are used to describe the evolution of molecular structure and resin viscosity, respectively. And then the resin flow process is simulated by means of a semi‐implicit iterative calculation method and the finite volume method. The results reveal the proposed resin cure‐structure‐viscosity model provides excellent agreement with the experimental viscosity data during the RTM filling process. It is also observed that the curing reaction causes the inhomogeneous distribution of resin conversion and resin molecular weight in the mould cavity, which will result in the spatially structural and performance inhomogeneities in the finished products. With the injection temperature or the edge width increasing, the discrepancy of resin conversion and resin molecular weight in the mould cavity is more evident. This study is helpful for understanding the complicated relationship among the processing variables, resin structures, and properties. POLYM. COMPOS., 2011. © 2011 Society of Plastics Engineers

Reactive mold filling is one of the important stages in resin transfer molding processes, in which resin curing and edge effects are important characteristics. On the basis of previous work, volume-averaging momentum equations involving viscous and inertia terms were adopted to describe the resin flow in fiber preform, and modified governing equations derived from the NavierStokes equations are introduced to describe the resin flow in the edge channel. A dual-Arrhenius viscosity model is newly introduced to describe the chemorheological behavior of a modified bismaleimide resin. The influence of the curing reaction and processing parameters on the resin flow patterns was investigated. The results indicate that, under constant-flow velocity conditions, the curing reaction caused an obvious increase in the injection pressure and its influencing degree was greater with increasing resin temperature or preform permeability. Both a small change in the resin viscosity and the alteration of the injection flow velocity hardly affected the resin flow front. However, the variation of the preform permeability caused an obvious shape change in the resin flow front. The simulated results were in agreement with the experimental results. This study was helpful for optimizing the reactive mold-filling conditions.

The surface property of a photocatalyst, including surface acid sites and oxygen vacancies, plays a pivotal role in photocatalytic organic synthesis reactions. Benzoin isopropyl ether (BIE) is usually produced via polycondensation of benzaldehyde and catalyzed with highly toxic cyanide . Here, we report a green photocatalytic approach for the selective synthesis of BIE over WO3 driven by a green-light-emitting diode. The improved photocatalytic activity can be attributed to the synergy of oxygen vacancies (V Os) and acid sites over N-doped WO3 nanobelts. The results revealed that reactant molecules were predominantly adsorbed and activated on surface oxygen vacancies (V OSs) and the Brønsted acid promoted the etherification reaction; the introduction of V Os and nitrogen altered the band structure and electronic properties, resulting in improved photocatalytic activity. Our work provides an efficient approach to the selective photocatalytic synthesis of organics over photocatalysts with finely tuned surface properties and band structures via defect and doping engineering.

Thermoplastic phenolphthalein poly(ether ether ketone) (PEK‐C) /epoxy composite foams were prepared by free foaming process (Fre‐foams) and limited foaming process (Lim‐foams), respectively, and the effects of PEK‐C content and foaming methods on the cell structures, phase morphologies, and impact strength of epoxy foams were investigated. The results showed that the gas pressure in the bubbles promoted the resin curing process and polymerization‐induced phase separation process (PIPS) during the free foaming process, while the resin curing process and PIPS were highly constrained in Lim‐foams. The incorporation of PEK‐C in the Fre‐foams showed superior improvement in impact strength compared with the PEK‐C/epoxy Lim‐foams. By adding 12 wt% PEK‐C, the specific impact strength of Fre‐foams could be enhanced by 72%, and the improved specific impact strength was because the phase‐inverted structures could prevent crack initiation and propagation, and moreover the presence of PEK‐C led to significantly refine cell structure and reduce foam density. Interestingly, the impact strength of Lim‐foams was nearly independent on the PEK‐C content, it was attributed to the obviously increased cell size with increasing PEK‐C content, and also that the phase separation process was not carried out.