Preparation of Core-Shell-Structured RDX@PVDF Microspheres with Improved Thermal Stability and Decreased Mechanical Sensitivity.

Reducing the sensitivity of high-energy simple explosives is the key technology in improving the practical application of high-energy insensitive powder. As the most widely used high-energy explosive, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is limited in application due to its high sensitivity. In this work, polyvinylidene fluoride (PVDF) was used as an energetic binder. Core-shell-structured RDX@PVDF microspheres are produced using electrospray assembly technology and fully characterized by thermogravimetric analysis, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and mechanical sensitivity. Their thermal stability and mechanical sensitivity are directly related to the weight fraction of the added PVDF. Moreover, core-shell-structured RDX@PVDF microspheres with RDX and PVDF in the proportion three to one possess a spherical-like morphology, the lowest impact sensitivity, the lowest friction sensitivity, and the highest thermal stability. This work provides a facile method for the positive design energetic materials and the prediction of their environmental adaptability.

Thermal Decomposition Behavior of Polyimide Containing Flame Retardant SiO2 and Mg(OH)2.

The effects of flame retardant silica (SiO2) and magnesium hydroxide (Mg(OH)2) on the thermal decomposition process of polyimide (PI) are discussed in this paper. Firstly, the decomposition process of PI in a nitrogen and oxygen atmosphere was studied by thermogravimetric analysis and differential scanning calorimetry methods, and the kinetic parameters were calculated by the nonlinear fitting method. In an inert atmosphere, PI decomposition consists of a three-step endothermic reaction, whereas in an oxygen atmosphere, PI decomposition consists of two steps, in which the first step does not change, and the second step changes to a violent exothermic peak. The effects of 3 wt % SiO2 (SPI) and 3 wt % Mg(OH)2 (MPI) on the degradation kinetics of PI are discussed. The results show that under an oxygen atmosphere, SiO2 and Mg(OH)2 hydroxide mainly delayed the second-step oxidation exothermic peak temperature of PI by 5 °C. In summary, the first step of the PI degradation is not affected by oxygen, and the flame retardant mainly acts in the second step, which can delay the oxidation heat release. In addition, the addition of SiO2 could prevent PI from aging whereas Mg(OH)2 has barely effect on the aging of PI.

Intervention Effect of the Integration Model on Negative Emotions of Adolescents during the Outbreak of Corona Virus Disease 2019.

BACKGROUND: The World Health Organization has declared the Corona Virus Disease 2019 (COVID-19) epidemic as a public health emergency of international concern. Given the sudden infection from and extensive dispersion of COVID-19 and the absence of specific drugs, those infected are in danger if they are not treated in time. Consequently, COVID-19 has become an important factor influencing adolescents' mental health. The purpose of this study is to explore the intervention effect of the integration model on the negative emotions of adolescents during the COVID-19 epidemic. SUBJECTS AND METHODS: Adolescents were randomly selected from five middle schools in Zhejiang Province of China from May 2020 to July 2020. First, the Self-rating Anxiety Scale, Positive and Negative Affect Scale, and Psychological Well-Being Scale were used for measurement. Then, 72 patients with moderate and severe anxiety symptoms were chosen as the research objects, and the intervention and comparison time was determined to be eight weeks. The subjects were randomly divided into the experiment group (35 members) and the control group (34 members). The integration model was employed on the experiment group. RESULTS: Grade, physical condition, and sleep time are important factors influencing the anxiety level of adolescents during the COVID-19 period, and the anxiety risk of adolescents is higher during their third year of junior high school. After the intervention, the SAS score of the experiment group is lower than that of the control group, and the decrease in the SAS score is higher in the experiment group than in the control group (P<0.01). Moreover, the positive emotion score of the experiment group is higher than that of the control group, and the negative emotion score of the former is lower than that of the latter. The variances in the positive and negative emotion scores are higher in the experiment group than in the control group (P<0.01). The variance in the overall well-being index is also greater in the experiment group than in the control group (P<0.01). CONCLUSION: The intervention using the integrated model can significantly reduce negative emotions such as anxiety, increase positive emotions, and improve the overall well-being of adolescents during the epidemic period.