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In order to improve the mechanical properties of PBO fiber wet-laid forming mesh, the hot pressing process was used to strengthen it, and the Box-Behnken response surface method was used to establish a response surface model by taking three factors of hot pressing temperature, hot pressing pressure and hot pressing time as independent variables, and taking the fracture strength of PBO fiber wet-laid nonwoven materials as the response value. The results show that the established response surface model is significant and has good fit. The Box-Behnken response surface method can predict the fracture strength of PBO fiber wet-laid nonwoven materials, and conclude that the factors affecting the fracture strength of PBO fiber wet-laid nonwoven materials are hot pressing pressure > hot pressing temperature > hot pressing time. The optimize process parameters of hot pressing are hot pressing temperature 245.6 ℃, hot pressing pressure 8.4 MPa, and hot pressing time 9.3 min. The average breaking strength of PBO fiber wet-laid nonwoven material obtained under this process parameter is 393.9 N.

Frequency domain method is a crucial technique for analyzing systems in classical control theory, relying primarily on logarithmic frequency characteristics. Characteristic curves generated in semi-logarithmic coordinate systems are typically displayed using a widely recognized chart known as a Bode diagram. However, creating a Bode diagram is an inconvenient process and results in abstract plots. Additionally, incomplete ranges of styles in basic links, along with varying expressions of open-loop frequency characteristics under different forms of feedback, create difficulties in understanding and challenges in application. This paper begins by classifying basic links in detail and constructing gain-phase frequency characteristics from logarithmic frequency characteristics. Then, a functional transformation is applied to plot characteristic curves in a Cartesian coordinate system of linear division, similar to those in a Bode diagram, by which gain-phase frequency characteristics are converted into elegant-frequency characteristics. This approach eliminates difficulties in plotting and understanding of a Bode diagram associated with using a semi-logarithmic coordinate system. On this basis, this paper proposes the concept of loop elegant-frequency characteristics, to solve the problems of misleading and inconvenient applications of open loop frequency characteristics. Elegant-frequency characteristics can facilitate efficient engineering applications, such as analysis, calculation and system correction, and enable the derivation of additional new features, such as wave-sign characteristics and stability criterion, which enhances the frequency domain method and advances the associated knowledge system.

In this paper, metal-organic framework material (Fe-PMOF) was prepared with biological phytic acid as ligand and ferric nitrate as metal ion donor. Fe-PMOF was amorphous and owned good thermal stability with thermal decomposition temperature of 390 °C. The flame retardant polyester composites (Fe-PMOF-PET) was prepared by melt blending. The SEM results show that Fe-PMOF distributes uniformly in PET matrix without obvious agglomeration. The melting temperature of PET remains at 226 °C with Fe-PMOF addition, indicating FE-PMOF has no significant effect on the processing performance of PET. Flame retardant test shows that the LOI value of Fe-PMOF-PET is 22%, and the UL-94 grade reaches V-2 rating. The combustion test shows that compared with neat PET, the peak heat release rate (PHRR), total heat release (THR) and total smoke release (TSP) decrease by 11%, 16% and 9.2% respectively, suggesting the smoke suppression and flame retardant properties of Fe-PMOF-PET. The residual carbon, XPS and TG-IR analysis reveal flame retardancy of Fe-PMOF in both condensed and gas phase. [ABSTRACT FROM AUTHOR]