Thermal Decomposition Of Azobisisobutyronitrile Research Articles

Photochemical Oxidation of NIR Photosensitizers in the Presence of Radical Initiators and Their Prospective Use in Dental Applications

AbstractPhotochemical oxidation of near infrared (NIR) photosensitizers in the presence of diaryl iodonium salts bearing either bis(trifluoromethylsulfonyl)imide or hexafluorophosphate was investigated by exposure with NIR LEDs emitting either at 790 nm, 830 nm, 850 nm or 870 nm. Four different cyanines with barbituryl group at the meso position exhibit similar absorption in the NIR. These photosensitizers initiate in combination with diaryliodonium salts radical photopolymerization of dental composites with the focus to cure large thicknesses. Furthermore, the mixture comprising the cyanine and the iodonium salt was used to generate brown color in dental composites on demand. This required to understand the mechanism of dye decomposition in more detail applying exposure kinetics and a coupling of Ultra Performance Liquid Chromatography (UPLC) with mass spectrometry (MS) to analyze the photoproducts formed. Data showed cleavage of the polymethine chain at typical positions in case of the oxidized species. These were formed as result of electron transfer between the excited state of the photosensitizer and the iodonium salt. UPLC‐MS experiments additionally indicated a certain sensitivity of the system upon adding of acids and radicals generated by thermal treatment of azobisisobutyronitrile (AIBN). Thus, treatment of the photoinitiator composition led almost to the same products no matter the system was either exposed with NIR light or treated with acids or radicals generated by thermal decomposition of AIBN. These findings helped to understand the large curing depth of 14 mm upon NIR exposure at 850 nm and the brown color formed.

Thermal decomposition of AIBN, Part B: Simulation of SADT value based on DSC results and large scale tests according to conventional and new kinetic merging approach

The paper presents the results of the common project performed with the Federal Institute for Materials Research and Testing, Berlin, Germany (BAM) concerning the comparison of the experimental results with simulations based on the application of the kinetic-based method and heat balance of the system for the determination of the self accelerating decomposition temperature (SADT). The substantial potential of the kinetic-based method is illustrated by the results of the simulation of SADT of azobisisobutyronitrile (AIBN). The influence of sample mass and overall heat transfer coefficient on the SADT values were simulated and discussed. Simulated SADT values were verified experimentally with a series of large-scale experiments (UN test H.1 [1]) performed with packaging of 5, 20 and 50kg of AIBN in an oven at constant temperatures. Additionally, the results of small-scale test H.4 for SADT determination based on the heat loss similarity as described in details in the UN Manual [1] were compared with the simulated data based on kinetic approach. The paper presents also the basic principles of a new kinetic analysis workflow in which the heat flow traces (e.g., DSC) are simultaneously considered with results of large-scale tests as e.g., H.1 or H.4. Application of the newly proposed kinetic workflow may increase accuracy of simulations of SADT based on results collected in the mg-scale and considerably decrease the amount of expensive and time consuming experiments in kg-scale tests.

Two decoupling methods for non-isothermal DSC results of AIBN decomposition

During thermal decomposition of azobisisobutyronitrile (AIBN), the endothermic process of phase transition disturbed exothermic decomposition, which brought deformation in its thermal graphs. Therefore, exact kinetic parameters of the decomposition could not be obtained by the existing kinetics analytic models, and the accurate enthalpy data of the decomposition and phase transition were not available. Two methods, i.e., a solvent method and a mathematical method, were introduced in this paper to resolve the coupling phenomenon. In the former method, AIBN was dissolved into aniline to eliminate the endothermic process and obtain curves of the liquid-state decomposition. In the latter method, MATLAB software was employed to get the “pure” exothermic decomposition curve without the influence of phase transition by fitting coupling curves within the section after the transition point and extrapolating to the initial stage of decomposition. Moreover, the kinetic parameters of the “pure” exothermic decomposition of AIBN obtained by the mathematical fitting agreed with the results from the solvent method, verifying the accuracy of the decoupling. The research is of great significance for comprehending the exact characteristics of thermal behaviors and safety parameters of AIBN. It also provides a great help to determine the safe operating temperature and alarm temperature for processes in industry.

Interrelation between the chemical structure and antioxidant properties of N-substituted amides of salicylic acid

The kinetics of the initiated oxidation of a model lipid (methyl oleate has been investigated in the presence of a group of new “hybrid” structures, namely, N-substituted amides of salicylic acid whose structure contains an amide residue conjugated with, or separated by a bridging fragment (three methylene groups) from, an N-phenolic substituent. The compounds also differ in the degree of screening of the OH groups. The process was initiated by thermal decomposition of azobisisobutyronitrile at 60°C (initiation rate of wi = 4.2 × 10−8 mol L−1 s−1) or by UV irradiation (γ = 313−365 nm, wi = 0.6 × 10−8 mol L−1 s−1). The compounds examined exhibit antiradical activity owing to the presence of the phenolic hydroxyl groups. N-substituted salicylamides efficiently inhibit the overall methyl oleate oxidation process and are comparable in activity with dibunolum and α-tocopherol or are superior to them. The structures in which the residues of salicylamide and sterically hindered phenol are separated by the bridging fragment are particularly efficient. The advantages of the salicylamides absorbing at 300–365 nm manifest themselves in UV-initiated oxidation. The peroxidase activity of the N-substituted salicyl acid derivatives is determined by the structure of the amide moiety. The compounds examined here are new, promising, effective antioxidants, whose particular structural fragments act via different mechanisms in oxidation.

基于AIBN材料的微流体驱动用微型正压源

In order to provide the driving force for the collection and transport of the micro liquid in a microfluidic chip developed by our research group in earlier research,this paper presents a micro positive pressure generator based on the released gas by thermal decomposition of azobisisobutyronitrile(AIBN).The AIBN is fixed to a micro-heater and heated to 70 ℃ to produce a certain amount of positive pressure.Experimental measurements show that this micro positive pressure generator can obtain 182 kPa pressure with heating 8.7 mg of AIBN by a heating current of 900 mA.The designed micro positive pressure generator is a smaller size,pressure controllable and easy to produce,and obtained pressure can satisfy the requirements of transdermal interstitial fluid(ISF) extraction.

Characterization and modification of commercial acrylic fibers grafted with acrylic acid

AbstractThe graft copolymerization of acrylic acid (AA) onto commercial acrylic fibers (PAN) has been studied using Azobis(isobutyro)nitrile (AIBN) as an initiator. AA grafting initiated by radicals formed from thermal decomposition of AIBN. In this study, the effects of monomer and initiator concentration, time and temperature reaction on the grafting yield have been investigated. The optimum conditions for this grafting reaction were obtained with an AA concentration of 1.67 M, an AIBN concentration of 0.0097 M, a reaction temperature of T=85 °C and with reaction time of 60 minutes.The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water absorption and also in this study has been investigated the mechanical property. The thermal analysis data showed that increasing in grafting yield, decreases the thermal stability of fiber. Grafting also affected slightly the fiber morphology. The experimental data of mechanical properties show clearly that by increasing of grafting yield, max extension will decrease. Grafting of poly AA improved water absorption.

Characterization and Studies on Grafting of Methyl Methacrylate onto PAN Fibers

The graft copolymerization of methyl methacrylate (MMA) onto commercial acrylic fibers (PAN) has been studied using Azobis(isobutyro)nitrile (AIBN) as an initiator. MMA grafting initiated by radicals formed from thermal decomposition of AIBN. In this study, the effects of monomer and initiator concentration, time and temperature reaction on the grafting yield have been investigated. The optimum conditions for this grafting reaction were obtained with an MMA concentration of 0.7 M, an AIBN concentration of 0.0073 M, a reaction temperature of T=85°C and with a 60 min reaction time. The fiber structure has been investigated by different experimental techniques of characterization such as Fourier transform infrared spectroscopy (FT‐IR), calorimetric analysis (DSC), thermogravimetric analysis (TGA), scanning electron microscopy (SEM), water absorption and the physical and mechanical properties has also been investigated in this study. The thermal analysis data showed that by increasing grafting yield, little changes have occurred in fibers samples up to 13.5% of grafting yield and the thermal transitions of grafted fibers have approximately the same behavior compared with the raw fibers sample. Grafting also slightly affected the fiber morphology. The experimental data of mechanical properties clearly show that by increasing grafting yield, max extension will decrease but this change up to 13.5% grafting yield is barely noticeable. Grafting of poly MMA improved water absorption.

Radical functionalization of single-walled carbon nanotubes with azo(bisisobutyronitrile)

The isobutyronitryl groups from thermal decomposition of azobisisobutyronitrile in a 1,2-dichlorobenzene solution were successfully attached to the sidewalls of single-walled carbon nanotubes; thermogravimetic analysis shows a weight loss of 20% (compared to raw SWNTs), which was calculated to be ca. 1 isobutyronitryl group in 23 carbon atoms.

Evaluation of Thermal Hazard of Azobisisobutyronitrile Using Accelerating Rate Calorimetry

The thermal decomposition of azobisisobutyronitrile (AIBN) has been studied under fully adiabatic conditions in a sealed bomb using an accelerating rate calorimetry technique (ARC). Data relating to temperature, pressure and time have been discussed. AIBN decomposes exothermally and the onset of decomposition occurs at 56.19°C. The reaction reaches its maximum at 112.28°C. During this temperature range, the self-heat rate, and the time to maximum rate of the reaction were evaluated. The experimental data have been also treated to evaluate the activation energy of the potential runaway reaction.

Fluorescence Detection of Free Radicals by Nitroxide Scavenging

The fluorescence quantum yield of 4-(1-napthoyloxy)-2,2,6,6-tetramethylpiperidine-1-oxyl (I) in acetonitrile and hexane is 55 and 30-fold lower, respectively, than those of diamagnetic analogs. Experiments described herein demonstrate that this property makes possible the fluorescence detection of radical scavenging reactions in which the paramagnetic nitroxide-substituted naphthalene is converted to a diamagnetic N-alkoxy derivative. 2-Cyanopropyl free radicals were generated by the thermal decomposition of azobisisobutyronitrile (AIBN) in cyclohexane or in acetonitrile containing I. The fluorescence intensity of the sample increased proportionally to the decrease in its ESR signal intensity, indicating the conversion of the paramagnetic nitroxide to the diamagnetic product. The linear relationship between the increase in fluorescence intensity and decrease in ESR signal intensity shows that the changes in the fluorescence intensity can serve as a sensitive means for optically detecting radicals.