Investigation of the synergistic effect of red phosphorus and magnesium hydroxide on the thermal degradation behavior and flame resistance of the intumescent fire-retardant polypropylene system

High fire-resistance polypropylene (PP) composites were prepared by using environment-friendly flame retardants including expandable graphite (EG), red phosphorus (RP), and magnesium hydroxide (MH). Synergism between EG, RP, and MH on the thermo-oxidation behavior and flame resistance of PP was found. The incorporation of MH and RP formed highly thermally stable mixtures of magnesium phosphates consisting of Mg₃(PO₄)₂, Mg(PO₃)₂, and α-Mg₂P₂O₇ at both amorphous and crystalline phases in the burning process. The mixture not only covered the surface of burning materials but also could reinforce the char structure of the PP/EG composites, thereby significantly enhancing the condensed phase flame retardant mechanism of the composites. Mass ratios of the flame retardants were also optimized to obtain the composite with the highest flame retardant efficiency. The result revealed that the combination of EG, RP, and MH in PP at MH/RP mass ratio of 3/2 with only a total additive content of 18 wt.% could make its limiting oxygen index (LOI) increase from 16.8% to 27.2% and the UL-94 rating was improved from none to V-0. In addition, the mechanical properties of the composites were improved via the surface treatment of MH and RP with calcium stearate and silicone oil, respectively.     

High-Resolution 3D Deposition of Electrospun Fibers on Patterned Dielectric Elastomers

Electrostatic patterning has improved the performance of devices incorporating electrospun fibers in a wide variety of applications. However, the impact of process parameters on the final fiber pattern in these systems is rarely analyzed. Herein, a systematic analytical approach is developed to define quantitative metrics related to fiber patterning. Three-dimensional patterned dielectric elastomer collectors are fabricated via solution-casting polydimethylsiloxane with embedded carbon black or liquid metal droplets. Fiber patterning metrics are used to evaluate the effect of collector parameters such as insulating layer thickness, electrical ground surface area, and three-dimensional pattern geometry. Dielectric layer parameters such as conductive material concentration and particle diameter are also investigated. Using this framework, the best-performing collector is shown to improve selectivity 30-fold, uniformity ninefold, reproducibility eightfold, and increase fiber volume by one order of magnitude. Furthermore, eutectic gallium indium liquid metal and scaled-up pattern geometries demonstrate the tunability of this approach and broad applicability of systematic fiber pattern analysis. This rational approach to patterned fiber development can be applied to virtually any method or pattern to better understand the fiber patterning processes.     

The Trade-Off Between Performance and Security of Virtualized Trusted Execution Environment on Android

Nowadays, with the significant growth of the mobile market, security issues on the Android Operation System have also become an urgent matter. Trusted execution environment (TEE) technologies are considered an option for satisfying the inviolable property by taking advantage of hardware security. However, for Android, TEE technologies still contain restrictions and limitations. The first issue is that non-original equipment manufacturer developers have limited access to the functionality of hardware-based TEE. Another issue of hardware-based TEE is the cross-platform problem. Since every mobile device supports different TEE vendors, it becomes an obstacle for developers to migrate their trusted applications to other Android devices. A software-based TEE solution is a potential approach that allows developers to customize, package and deliver the product efficiently. Motivated by that idea, this paper introduces a VTEE model, a software-based TEE solution, on Android devices. This research contributes to the analysis of the feasibility of using a virtualized TEE on Android devices by considering two metrics: computing performance and security. The experiment shows that the VTEE model can host other software-based TEE services and deliver various cryptography TEE functions on the Android environment. The security evaluation shows that adding the VTEE model to the existing Android does not add more security issues to the traditional design. Overall, this paper shows applicable solutions to adjust the balance between computing performance and security.     

BAPRP: a machine learning approach to blackhole attacks prevention routing protocol in vehicular Ad Hoc networks

International Journal of Information Security - One of the network performance challenges of Vehicular Ad Hoc Networks (VANET) is the Black Hole attack. This destructive attack severely damages the...