Search

4,4′-Azobis (4-cyanovaleric acid) (ACVA) is known as a kind of water-soluble azo initiator which was widely used in the radical polymerization process. As same as other azo compounds, ACVA may also trigger thermal runaway accidents at high temperatures due to its specific –N=N– structure. To qualify its pyrolysis characteristics, thermogravimetric analysis and differential scanning calorimetry were applied to this investigation, moreover, the TGA-FTIR combination technology was used in the product analysis part. The results showed that ACVA has a complex decomposition process, there are four mass loss stages during its pyrolysis, the heat release mainly occurred in the first and final decomposition stage and the heat flux in the middle stages was very disordered. Different decomposition stages were accompanied by different decomposition products, and some of them were considered toxic, such as HCN and CH4. Thermokinetic parameters such as apparent activation energy (Ea) were also calculated in this paper by using Kissinger–Akahira–Sunose (KAS) method. Surprisingly, ACVA has the lowest Ea (91 kJ mol−1) and the highest heat release (4706 J g−1) compared with some commonly used azos, which means it will more easily suffer a serious runaway accident. All these studies can give us a comprehensive understanding of the thermal decomposition of ACVA to prevent accidents. [ABSTRACT FROM AUTHOR]

Polystyrene is a multifunctional plastic used to manufacture consumables with a wide range of applications. Some azo compounds can produce free radicals when heated, which can be used as initiators for styrene polymerization. However, thermal runaway could occur during the styrene bulk polymerization initiated by azodiisobutyronitrile (AIBN) due to the release of a large amount of heat. To obtain thermal hazard properties, differential scanning calorimetry (DSC) and accelerating rate calorimetry (ARC) were applied to this investigation. The DSC experimental results showed that the extrapolated onset temperature and exothermic peak temperature decreased gradually after adding the initiator, which indicated initiator AIBN promoted the polymerization. ARC experiment decoded dynamic thermal parameters such as apparent activation energy, adiabatic temperature rise, initial runaway temperature, maximum temperature and polymerization heat of the hybrid system. Finally, the experimental and calculation results showed that the heat released by the polymerization reaction was basically unchanged at different heating rates; as the initiator concentration increases, the heat released by the polymerization reaction also increases, the polymerization temperature is controllable below 35.1 ℃. These results are critical for reducing the risk of loss of control and designing intrinsically safer styrene production, storage and transport processes. [ABSTRACT FROM AUTHOR]

Azo compounds are widely used in polymerization as an initiator for chain polymerization reactions. Although they have excellent initiating properties, the thermal instability and associated risk of ignition and explosion cannot be ignored. This paper aimed to decode the thermal behavior and evaluation thermal hazards of two water-soluble azo initiators 2,2′-azobis(2-methylpropionamidine) dihydrochloride (AIBA) and 2,2′-azobis(2-(2-imidazoline-2-yl) propane) dihydrochloride (AIBI). Thermogravimetric analysis and adiabatic experiments were used to investigate the decomposition process of these two azos under atmospheric and adiabatic conditions. The apparent activation energy (Ea) and time to maximum rate under adiabatic conditions (TMRad) were obtained based on above experiments. Decomposition products and mechanisms of AIBA and AIBI were preliminarily studied using a thermogravimetric analyzer coupled with Fourier transform infrared spectrometer system. Results showed that most decomposition products of AIBA and AIBI still existed in the form of organic compounds under nitrogen conditions. Furthermore, the leakage of pyrolysis gas (such as ammonia) should be prevented from causing environmental pollution. [ABSTRACT FROM AUTHOR]