The novel phosphorus/nitrogen-containing flame retardant hexa(phosphaphenanthrene aminophenoxyl)cyclotriphosphazene (HPAPC), which contains phosphaphenanthrene [9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)] and phosphazene (hexachlorocyclotriphosphazene) groups, was synthesized by the classic Atherton−Todd reaction, and its chemical structure was characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. Poly(lactic acid) (PLA) composites containing HPAPC were prepared by melt blending, and their fire performance and thermal behaviors were investigated in terms of limiting oxygen index (LOI), vertical burning (UL-94), cone calorimeter tests, and thermogravimetric analysis (TGA). The LOI value could reach up to 34.7%, and UL-94 could pass V-0 for the PLA composite containing only 5 wt % HPAPC. TGA results showed that the char formation of PLA could be significantly improved by the presence of HPAPC. The evolved gas of the composite was analyzed by FTIR-TGA and pyrolysis−gas chromatography/mass spectrometry (Py−GC/MS). The dispersion of fillers in PLA was observed by back-scattered electron (BSE). The char morphology was characterized by FTIR spectroscopy and scanning electronic microscopy (SEM). It was suggested that the presence of HPAPC could release ammonia gas during combustion, which was beneficial to the formation of an intumescent char structure.

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Four novel intumescent flame retardants containing phosphaphenanthrene and phosphazene groups were synthesized by using the classic Atherton-Todd reaction and Kabachnik-Fields reactions. 9, 10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO) was firstly reacted with hexa-aminophenoxy-cyclotriphosphazene (compound 2) in the presence of carbon tetrachloride and triethylamine (Atherton-Todd reaction) to obtain hexa-(phosphaphenanthrene-anmino-phenoxyl)-cyclotriphosphazene (compound 3). Moreover, the condensation of hexa-aminophenoxy-cyclotriphosphazene with formaldehyde, salicylaldehyde, 4-hydroxybenzaldehyde respectively, followed by the addition of DOPO of compounds 3-6 were determined by FTIR, NMR, and elemental analysis. A preliminary investigation on compound 5 as a flame retardant for PLA has been carried out, and the result shows that the limiting oxygen index (LOI) of the PLA sample can reach up to 30% at the presence of only 5% compound 5.

Vehicle to vulnerable road user (VRU) crashes occupy a large proportion of traffic crashes in China, and crash injury severity analysis can support traffic managers to understand the implicit rules behind the crashes. Therefore, 554 VRUs-involved crashes are collected from January, 2017, to February, 2021, in a city in northern China, including 322 vehicle-pedestrian crashes and 232 vehicle-bicycle crashes. First, a descriptive statistical analysis is conducted to investigate the characteristics of VRUs-involved crashes. Second, the extreme gradient boosting (XGBoost) model is introduced to identify the importance of risk factors (i.e., time of day, day of week, rushing hour, crash position, weather, and crash involvements) of VRUs-involved crashes. The statistical analysis demonstrates that the risk factors are closely related to VRUs-involved crash injury severity. Moreover, the results of XGBoost reveal that time of day has the greatest impact on VRUs-involved crashes, and crash position shows the minimum importance among these risk factors.

Early warning on the ship deficiency is crucial for enhancing maritime safety, improving maritime traffic efficiency, reducing ship fuel consumption, etc. Previous studies focused on the ship deficiency exploration by mining the relationships between the ship physical deficiencies and the port state control (PSC) inspection results with statistical models. Less attention was paid to discovering the correlation rules among various parent ship deficiencies and subcategories. To address the issue, we proposed an improved Apriori model to explore the intrinsic mutual correlations among the ship deficiencies from the PSC inspection dataset. Four typical ship property indicators (i.e., ship type, age, deadweight and gross tonnage) were introduced to analyze the correlations for the ship parent deficiency categories and subcategories. The findings of our research can provide basic guidelines for PSC inspections to improve the ship inspection efficiency and maritime safety.