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In this study, aerial fireworks commonly used for celebrations in Taiwan were analyzed. These fireworks have propellant components, which are stored under varying humidity and temperature conditions. Differential scanning calorimetry (DSC) and the Vent Sizing Package 2 (VSP2) were used to assess the relationship between microscale heat transfer and temperature as well as thermal runaway in an adiabatic environment. Thermodynamic methods, namely the Friedman, Flynn–Wall–Ozawa, and ASTM E698, were used to analyze the safety and latent thermal hazards of aerial fireworks. DSC experiments confirmed the high solubility of potassium nitrate (KNO3), which enables it to readily dissolve in K+ and NO 3 - . Increasing the relative humidity and exposure time caused the surface of the oxidizer to dissolve, resulting in the reduction of the second exothermic peak and, in turn, incomplete combustion and launch failure. The results obtained using the ASTM E698 method revealed that when the samples were soaked in deionized (DI) water, their apparent activation energy increased considerably from 45.78 to 153.68 kJ mol−1, reflecting a decrease in the temperature sensitivity of the gunpowder in the fireworks. To reduce the reactivity of the gunpowder and minimize the thermal hazard associated with fireworks, a large amount of water must be added. However, the experiment performed using VSP2 showed that when the humidity increased, the adiabatic exothermic onset temperature was delayed. The maximum temperature of the original sample was the highest. The maximum reaction rate of the samples stored at a relative humidity of 40% was shorter than that of other samples, and that of the samples soaked in DI water was the longest. Regarding the relationship between pressure rise rate and temperature, (dP/dt)max can be used to determine whether the propulsion capacity of a firework during ignition is sufficient. When DI water was added, the propulsion capacity decreased, and fireworks could not be ignited. The samples stored at a relative humidity of 40% had higher pressure than did the original sample. The samples soaked in DI water had lower pressure than did the original sample. These results indicate that increasing humidity affects temperature and pressure. [ABSTRACT FROM AUTHOR]

In Taiwan, due to intensive religious ceremonial activities, the flying and pyrotechnic fireworks of firecrackers are commonly used. In the course of the activities, the use of water as a cooling measure has been pointed out in the past literature that it may cause pyrotechnic materials to deteriorate and reduce their thermal stability. To determine the possible influence of water addition on pyrotechnic deterioration, this study estimates the degree of thermal hazard of pyrotechnic based on the analysis of heat release, reaction kinetics, and the heat exchange model of pyrotechnic deterioration. The explosion sound (ES) firecracker was used to analyze the thermal hazard and mixed water (ES + W) to simulate the dampness condition using differential scanning calorimetry. Thermodynamic equations simulating thermal hazard safety parameters, combined with thermokinetic and thermal runaway data results, were used to discuss the safety and potential thermal hazard characteristics of ES, as the safety of fireworks in storage, transportation, process conditions, and operation assessment to curtail the probability of accidents. The results showed that if the initial exothermic temperature of ES + W is higher than ES, a thermal decomposition reaction will occur at a lower temperature, and the exothermic heat rises and the apparent activation energy decreases, indicating that the ES will increase its instability after being damp. The presence of water degenerated the ES and resulted in a violent reaction during the release process to explode the ES, which increased the chance of accidents among the onlookers. [ABSTRACT FROM AUTHOR]

The common biodegradable properties of polymer make them an excellent pair for blending, and the water solubility of polyvinyl alcohol (PVA) makes it easy to mix evenly with the starch. In this study, PVAs with different molecular weights were blended with various compositions of cross-linked starch (CLS) to explore the effects of molecular weight of PVA on the biodegradable characteristics of the PVA/starch blends. Comparing the biodegradability of all the various PVA/starch blends, a PVA was singled out from the PVA/starch blends of higher biodegradability. Further, the chosen PVA was then blended with the acid-modified starch (AMS) to systematically investigate the effects of the modified processing of starch on the biodegradable characteristics of the PVA/starch blends. Differential scanning calorimetry (DSC) analysis of PVA and PVA/starch specimens reveal that the T values of PVA/starch specimens reduce gradually as their CLS or AMS contents increase. After the CLS is blended in PVAs of different molecular weights, the tensile strength (σ) and elongation at break (ε) values of (PS)GM specimen increase and simultaneously reduce, respectively, as their molecular weights of PVA increase from about 80,000 (PVA) to 120,000 (PVA). The σ and ε values of the PVA/modified-starch blends decrease with an increase in the modified starch contents. The σ values of the PVA/AMS specimens decrease with an increase in the concentrations of hydrochloric acid. Comparing the σ values of the PVA/CLS specimens with those of the PVA/AMS specimens, the σ values of the PVA/CLS specimens are better than those of the PVA/AMS specimens. On the contrary, the ε values of the PVA/AMS specimens are better than those of the PVA/CLS specimens. According to the biodegradability of all the PVA/starch blends, PVA with higher molecular weights displays higher biodegradability. The biodegradability of the PVA/modified-starch blends increase as the modified starch contents of the PVA/modified-starch blends increase. As evidenced by the results of the biodegradability test, the biodegradability of the PVA/modified-starch blends, therein PVA is blended with 1N AMS, shows better biodegradability. The result of bio-reaction kinetics experiment can evaluate the decomposition tendency of the PVA/starch blends up to any biodegradable rate under ambient environment. Using the kinetic model of the first order reaction, it is estimated that 16.20 years and 12.47 years will be needed for the PVA/starch blends, containing 20 and 40% of CLS respectively, to be degraded up to 70% under ambient environment. In addition, it is 1.68 years for the PVA blends with the 40% 2N AMS under decomposition environment while it is 1.94 years for the 40% 1N AMS. Overall, the decomposition potential of PVA/AMS specimens is better than PVA/CLS specimens. Furthermore, the 1N(26PAS)GM specimen is coincidence the biodegradable material criteria of Environmental Protection Administration (EPA) of Taiwan. [ABSTRACT FROM AUTHOR]