Nitrocellulose Samples Research Articles

Thermodynamic analysis of cellulose nitration

In this study, the standard formation enthalpies and entropies of cellulose and nitrocellulose samples were determined. These characteristics were used for thermodynamic analysis of bulk nitration of the entire cellulose sample and local nitration only of amorphous domains (ADs) of cellulose. It was found that the reaction of bulk nitration of cellulose up to a substitution degree (DS) of 1.5 is endothermic and determined primarily by the contribution of the temperature-entropy component to the negative Gibbs potential. However, if DS is higher than 1.5, the bulk nitration becomes exothermic and its feasibility is determined by the impact of enthalpy on the Gibbs potential. In the case of local nitration of cellulose ADs, the main contribution to the Gibbs potential is made by the reaction enthalpy that determines the feasibility of this process. It was shown that with the enhancement in DS of nitrocellulose, the negative value of the Gibbs potential of the reaction increases. Thus, the cellulose nitration to higher DS is thermodynamically favorable. Since the locally nitrated samples are copolymers of amorphous nitrocellulose and crystalline cellulose, they should be significantly less hydrophilic than cellulose. Therefore, it can be expected that the local nitration method will find a wide practical application for inexpensive hydrophobization of cellulose materials.

Thermal kinetics and flash DSC experimental validation of conventional nitrocellulose and ladder-structured nitrocellulose under non-isothermal condition

To better understand the thermal decomposition mechanism of conventional nitrocellulose (NC) and ladder-structured nitrocellulose (LNC), and effectively improve their safety performance during storage and service, the NC and LNC samples were subjected to non-isothermal DSC experiments to analyze their thermal kinetics. The model-free methods and model-fitting methods were used to analyze the thermal decomposition process of NC and LNC. The reaction autocatalytic behavior is confirmed in the thermal decomposition process of NC and LNC by Friedman analysis. Considering the fitting degree and the degree of freedom of the methods and models, the composite autocatalysis reaction model is the most suitable method to describe the thermal decomposition process of NC and LNC. Furthermore, the prediction accuracy of the composite autocatalysis reaction model is validated by the Flash DSC experimental data. The error between the actual and predicted peak temperatures is only approximately 1.5 %. Based on the composite autocatalysis reaction model of NC and LNC, the process of the thermal decomposition reaction of NC and LNC is obtained with high precision for their Flash DSC experimental data. This study can provide theoretical guidance for the process control of the thermal decomposition of NC and LNC. Novelty and Significance statementThe thermal decomposition mechanism of NC and LNC is studied. The kinetic model for the thermal decomposition of NC and LNC are deduced. The thermal decomposition kinetics equations for NC and LNC is obtained. The accuracy of the thermal decomposition kinetics equations of NC and LNC in predicting thermal decomposition behavior at extremely high heating rates is verified. This study can provide theoretical guidance for the process control of the thermal decomposition of NC and LNC.

Effect of aniline-fullerene-based stabilizer on thermal decomposition of nitrocellulose

<p indent="0mm">The influence of aniline-fullerene-based stabilizer on the thermal decomposition behavior of nitrocellulose was studied by thermal analysis, isotherm thermogravimetric test, methyl purple paper test, adiabatic accelerated calorimetry and differential scanning calorimetry. The results of the differential thermal analysis showed that the critical temperature of the thermal explosion of nitrocellulose increased <sc>0.36–7.62 °C</sc> with the addition of aniline-fullerene-based stabilizer. The results of the isothermal thermogravimetric analysis are in good agreement with the conclusions of the methyl violet test paper. The results show that an aniline-fullerene-based stabilizer can effectively prolong the discoloration time of methyl violet test paper and the time required to achieve the same weight loss rate of nitrocellulose samples. The results of adiabatic accelerated calorimetry showed that although aniline-fullerene-based stabilizer had little effect on the pressure and temperature at the initial stage of adiabatic decomposition of nitrocellulose, it could effectively reduce the maximum temperature rise rate. The effects of thermal history on the thermal decomposition of nitrocellulose samples are investigated by DSC interruption and re-scanning method. The results showed that the aniline-fullerene-based stabilizer had obvious thermal stability effect on nitrocellulose and inhibited the autocatalytic decomposition of nitrocellulose.

An experimental study on the effects of ethanol content on the decomposition and burning risks of nitrocellulose

Ethanol is often used as a humectant during the storage of nitrocellulose (NC). To mitigate the fire hazard of NC, which is a highly flammable compound, during storage, and to understand the fire hazards of NC–ethanol mixtures, it is imperative to study the thermal behavior of NC–ethanol mixtures and determine the optimal range of ethanol content in the mixture. In this study, the decomposition and burning behaviors of NC–ethanol mixtures with different ethanol contents (0–100%) were studied via thermogravimetric (TG) analysis and cone calorimetry (ISO 5660), respectively. The results of TG/differential TG analyses suggested that NC samples with a low ethanol content are more prone to thermal runaway such as burning or explosion during their decomposition under a constant temperature increase. Furthermore, ignition and burning characteristics of the mixtures, which were analyzed by cone calorimetry, revealed that the ignition of the sample is mainly caused by the volatilization of ethanol. According to the results, an ethanol content of ~ 30–50% helps reduce the thermal hazard of NC during fire. This study provides a perspective on ensuring the safe storage of NC, and elucidates effective fire suppression and rescue measures for fires caused by such materials.

Experimental study on the effect of storage conditions on thermal stability of nitrocellulose

Nitrocellulose (NC) is an energetic material that is widely used in the industrial and military fields. However, as a kind of hazardous chemical, it has potential thermal hazards during actual storage, especially when stored improperly. In order to study the effect of storage conditions on the thermal stability of NC, experimental analysis was carried out using the CALVET heat flux calorimeter and three representative conditions were considered in the experiments: (1) drying time, (2) moisture content, (3) cycles. The results show that with the increase of drying time, the onset temperature of NC samples changes little, while the peak heat flow increases obviously. Increased moisture content leads to an obvious increase both in the reaction onset temperature and in the maximum heat flow, which reveals a double action of evaporation cooling and hydrolysis. Compared with the original NC sample, the cycles can not only reduce the onset temperature of the reaction, but also change the peak shape obviously. A small “peak envelope” is formed before the main peak. Besides, relevant kinetic parameters such as heat of reaction, activation energy, and the self-accelerating decomposition temperature (SADT) under different conditions were obtained. Comprehensive analysis reveals that dry environment and multiple water addition cycles under damaged packing conditions are not conducive to safe storage, while the increase of moisture content lowers the thermal hazard of NC. The results have practical significance for revealing the effect of actual storage conditions on thermal stability of NC.

Thermal kinetics and reactive mechanism of cellulose nitrate decomposition by traditional multi kinetics and modeling calculation under isothermal and non-isothermal conditions

Cellulose nitrate, also known as nitrocellulose (NC), is a highly flammable energetic cellulose derivatives formed by exposing cellulose to nitric acid, whose producing procedure has been greatly employed in daily life and military area. In this study, to explore its pyrolysis and combustion kinetics, NC samples were subjected to isothermal and non-isothermal DSC experiments. The isothermal experiments were carried at 150, 155, 160, and 165 °C, while the non-isothermal experiments were taken at 2, 4, 8, and 10 °C min−1 for heating rates. By model fitting methods, several classical reaction models with high fitting degree were obtained. The model corresponding to isothermal conditions was f(α) = 4(1 − α)[−ln(1 − α)]3/4, while for non-isothermal conditions the model was identified as f(α) = (1 − α)3. The variation of activation energy with conversion was calculated by model free methods including FR, KAS, FWO, and advanced Vyazovkin methods. Finally, based on the results of kinetic analysis, the adjustment function was introduced and the accurate reaction mechanism functions of NC were identified for isothermal and non-isothermal conditions, respectively. This study has a high guiding significance for the thermal decomposition and combustion kinetics of NC under isothermal and non-isothermal heating conditions.

Effects of nitrogen content on pyrolysis behavior of nitrocellulose

Although the thermal decomposition of nitrocellulose (NC) has been comprehensively examined, the effects of nitrogen content on the pyrolysis behavior of NC have not been clearly elucidated. In this work, the macro- and microstructures of NC samples with varying nitrogen contents were qualitatively and quantitatively analyzed. Higher nitrogen contents in NC samples were found to be associated with an increased number of nitro groups and cracks in the fiber surface. To elucidate the NC pyrolysis process and provide a theoretical basis for enhancing its stability, the pyrolytic behavior of NC was examined using thermogravimetric analysis-Fourier transform infrared spectrometry and pyrolysis-gas chromatography-mass spectrometry. The pyrolysis of NC primarily occurred within a temperature range of 180–240 °C; however, the peak temperature of the mass loss rate decreased with increasing nitrogen content. The initial nitrogen oxide produced by pyrolysis was nitrogen dioxide (NO2). During the main stage of pyrolysis, a wider variety of gases was produced by NC having a higher nitrogen content, with more cyclization recombination forms occurring in the post-reaction stage of pyrolysis. Based on the findings of this study, a detailed process of NC pyrolysis has been proposed.

Experimental and theoretical study on thermal kinetics and reactive mechanism of nitrocellulose pyrolysis by traditional multi kinetics and modeling reconstruction

Nitrocellulose (NC) has been applied in many fields of daily life and military industry, but its instability brings large danger during storage and usage, which greatly limits its application. In this study, decomposition behavior and reaction model of NC were explored. To obtain its kinetic triplets during decomposition, NC samples were heated in nitrogen atmosphere with different heating rates of 5, 10, 15, 20 °C min−1, respectively. A 3-th order reaction model was obtained by model fitting methods. Meanwhile, the relationship between activation energy and conversion was obtained by multi isoconversional methods, including KAS, FR, FWO, and Advanced Vyazovkin methods. Then the reaction model was reconstructed by introducing adjustment functions with result of an expression of f(α) = 19.38193α1.41177(1-α)4.60503.

A Promising Energetic Polymer from Posidonia oceanica Brown Algae: Synthesis, Characterization, and Kinetic Modeling

AbstractIn this study, microcrystalline cellulose nitrate (MCCN) as energetic polymer is successfully obtained from Posidonia oceanica brown algae (POBA). Fourier transform infrared spectroscopy (FTIR) results show alterations in the intensities of some absorption bands, suggesting a significant difference in the chemical structure between microcrystalline cellulose and the emergent MCCN samples. X‐ray diffraction (XRD) measurements indicate that MCCNs are more crystalline than conventional nitrocellulose (NC). According to scanning electron microscopy (SEM), both NC and MCCN reveal a compact structure and a rough surface. Differential scanning calorimetry (DSC) displays that the thermal degradation of MCCNs shifts to lower temperatures compared to the respective NCs. Furthermore, in comparison with NC samples, MCCN samples exhibit high density, high nitrogen content, low viscosity‐average molecular weight, and good thermal stability. On the other hand, kinetic modeling based on DSC data is carried out by isoconversional integral methods to determine Arrhenius parameters and the decomposition mechanisms. It is found that MCCNs present lower activation energies than conventional NCs with a decrease of ≈6%. Finally, this work opens a new pathway to prepare MCCN from POBA, and it is expected to have applications in several areas such as propellants, energetic binders, and gas generators.

Differentiation of stabilized nitrocellulose during artificial aging: Spectroscopy methods coupled with principal component analysis

AbstractIn this work, Fourier transform infrared spectroscopy (FTIR) and X‐ray powder diffraction (XRD) were selected as reliable, fast, and nondestructive techniques to assess their potentialities for characterization and discrimination of nitrocellulose (NC)‐based formulations containing different kinds of stabilizers and subjected to accelerated aging. Preliminary results based on visual comparison of the spectra point out that spectra obtained by both spectroscopic techniques were useful for a rapid detection of the aging process without additional sample preparation. Additionally, the existence of compatibility issues between NC and one of the stabilizers is easily recognized. The spectral data were subjected to principal component analysis (PCA) for visualization and to reveal differences between samples. The obtained results demonstrated that PCA plots were able to distinguish and classify the NC samples with respect to their respective stabilizers and aging.

Evaluation of the critical safety temperature of nitrocellulose in different forms

Evaluating the critical safety temperature of nitrocellulose is necessary to reduce the possibility of nitrocellulose accidents (thermal explosion and fire) and to implement effective loss prevention. In the present study, isothermal and non-isothermal experiments were performed on different forms of nitrocellulose using a differential scanning calorimeter. A scanning electron microscope was utilized to detect the aging process of nitrocellulose under different constant temperatures. Thermodynamic parameters were simulated by thermal safety software, and the results indicated that autocatalytic simulation rather than nth order simulation was applicable to assess the apparent activation energy of nitrocellulose samples. Moreover, iso-conversional methods, including Kissiger–Akahira–Sunose, Ozawa–Flynn–Wall, Friedman, Tang et al. and distributed activation energy model methods, were employed to validate the simulated activation energy. The average activation energy calculated by the five iso-conversional methods was lower than that simulated by autocatalytic simulation. Moreover, critical storage temperatures, including the time to maximum rate and the time to conversion limit, were evaluated. It was found that the critical storage temperatures of nitrocellulose in white chip form were lower than that of nitrocellulose in white silky fibre form. Finally, the critical thermal explosion temperatures of two samples were calculated, and it was concluded the temperature of nitrocellulose in white silky fibre form was about 5.0 °C higher than that of nitrocellulose in white chip form.

Thermal behavior of nitrocellulose with different aging periods

To further understand the aging process of energetic materials such as nitrocellulose (NC), aging treatment of NC samples was performed by a constant temperature chamber and non-isothermal experiments were performed by a TG-DSC analyzer. Also, scanning electron microscope was utilized to detect the morphological changes of NC in different forms. The results revealed that, with the increasing aging time, the decomposition properties including mass loss, decomposition temperature, heat production rate and heat of decomposition exhibit significantly different trends for the two forms of NC. Furthermore, the thermal kinetic parameters of pure NC were calculated based on Kissinger method. It is found that pure NC has the highest thermal instability at the aging time of 24 days under the aging temperature of 90 °C, and the stability of NC will increase when the aging time exceeds 32 days.

Effect of plasticizer dibutyl phthalate on the thermal decomposition of nitrocellulose

This paper aims to investigate the effects of plasticizer dibutyl phthalate (DBP) on the thermal decomposition of nitrocellulose (NC) by using a series of analytical apparatuses. In the present study, the detailed structures of pure NC (NC-P) and NC with DBP (NC-D) were revealed by scanning electron microscope. It was found that the fibers in NC-D are more closely aligned than those in NC-P, which makes the thermal behaviors of NC-D different from NC-P. The thermal stability of both NC-P and NC-D was examined by means of simultaneous TG-DSC apparatus (STA). Three different kinetic methods (Kissinger–Akahira–Sunose method, Ozawa–Flynn–Wall method, and Friedman method) were applied for determining the activation energy E of these two NC samples. Moreover, the experimental data were compared with sigmoidal models and pre-exponential factor was calculated by compensation effect. Besides, in situ Fourier transform infrared (FTIR) and a TGA instrument coupled with Frontier FTIR spectrometer were employed to investigate the characteristic functional groups of decomposition residues and gaseous products at different temperatures, respectively. The results show that NC-P and NC-D have similar decomposition products and decomposition mechanisms.

Experimental study on the fire characteristics of typical nitrocellulose mixtures using a cone calorimeter

To further understand the safety performance of energetic materials such as nitrocellulose (NC) mixtures, it is necessary to obtain the fire properties of commonly used NC mixtures. In the present study, an in situ calorimeter was employed to investigate the fire characteristics of pure NC, NC-plasticizer mixture and two NC-humectant mixtures, namely NC-isopropanol and NC-ethanol mixtures. The plasticizer (dibutyl phthalate) and humectants (ethanol or isopropanol) can effectively reduce the fire risk of NC. NC-plasticizer is more risky than NC-humectants in the burning process. Compared with the NC with isopropanol, the NC with ethanol exhibits higher fire risk. Also, the thermogravimetric (TG) curves of four NC samples were measured by a TG analyzer. The curves indicate that the decomposition of pure NC is more dramatic than NC mixtures, and the NC with plasticizer dibutyl phthalate can decompose in advance.

A Simplified Method to Predict the Heat Release Rate of Industrial Nitrocellulose Materials

To better understand the fire risk of nitrocellulose (NC) used for the civil industry, the combustion properties of NC-alcohol humectant (isopropanol and ethanol) and -plasticizer (dibutyl phthalate) mixtures were investigated experimentally in this work. Flames with considerable sparks were observed for nitrocellulose-humectant samples, while the nitrocellulose-plasticizer mixture exhibited extremely bright flames without obvious sparks. The flame heights for all the samples were determined from the video record. According to the fundamentals of fire phenomena, a simplified model to predict the heat release rates of current NC samples was developed based on the flame height data. By combining the experiment results by ISO 5660 and stoichiometric equations, the critical parameter H c / r is recalculated as 3251, 3228, and 3201 kJ/kg for NC-I, NC-E, and NC-D samples, respectively. Ultimately, the heat release rates predicted by the modified model coincided well with that measured by ISO 5660.

Correlating molar masses of nitrocelluloses with their intrinsic viscosities measured using capillary electrophoresis instrumentation

Specific viscosities for a set of six nitrocellulose (NC) standards comprising three different mass-average molar masses (between 20,000 and 300,000gmol−1) of two different nitrogen contents (11.2 and 12.1%) were measured at 20°C in tetrahydrofuran, using capillary electrophoresis instrumentation as a bench-top viscometer in frontal mode. Intrinsic viscosities were derived applying Huggins’ and Kraemer's models, showing excellent convergence of both models at infinitely diluted polymer concentration. Good overall consistency was shown between viscosity data experimentally acquired by this new protocol and the mass-average molar masses provided by the manufacturers. This simple protocol should be of interest for a better understanding of the solvent interaction given by this complex polymer, and beyond this, for tailoring NC solutions devoted to film deposition, and for the determination of mass-average molar masses of unknown NC samples.

Determination of nitrocellulose by capillary electrophoresis with laser-induced fluorescence detection

The industrial application of nitrocellulose depends on its nitrogen content. When nitrocellulose presents high nitrogen content is used in the manufacture of explosives whereas nitrocellulose with low nitrogen content is used to make a wide range of daily and non-explosive products (e.g. cigarettes, paints, lacquers). This fact makes really important to develop a method for the determination and discrimination of nitrocellulose samples. This work reports, for the first time, the qualitative determination of nitrocellulose previously derivatized with 8-aminopyrene-1,3,6-trisulfonic acid (APTS) by capillary electrophoresis (CE-LIF) with laser-induced fluorescence detection (CE-LIF). APTS-labeled nitrocellulose was determined in lowly and highly nitrated nitrocellulose samples present in collodions and smokeless gunpowders, respectively, after their pulverization in liquid nitrogen. The method described enables the visual discrimination of different nitrocelluloses on the basis of the different electrophoretic profiles obtained, and provides a useful tool to determine nitrocellulose. Additionally, the use of field-amplified sample injection (FASI) enabled enhanced sample detection, which made it possible to determine nitrocellulose contained in ∼15μg of gunpowder.

Benchtop Energetics: Hyperthermal Species Detection

We propose a novel scheme for monitoring the transition between deflagration and “detonation-like” behavior of small-scale explosive samples-in-vacuum subjected to short duration shock stimuli. Our approach relies on measuring the chemical identities and velocity distributions of the gaseous species produced by such samples; e.g. the relatively low velocity expansion-quenched reaction intermediates produced by deflagration versus the hyperthermal thermodynamically stable molecules generated by the termination of a detonation wave at an explosive-vacuum interface. We demonstrate our ability to detect such species by time-of-flight mass spectrometry (TOFMS) using fast Al atoms produced by laser ablation of aluminum metal. Extensive SIMION simulations of ion trajectories in our mass spectrometer lead to a semi-quantitative model connecting the system operating parameters and the velocity-dependent neutral species detection efficiency. We present a method for correcting our data for these detection biases, and for transforming them into neutral species velocity and kinetic energy distributions. We also present preliminary TOFMS data of hyperthermal organic molecular species produced by direct laser ablation/ignition of thin-film nitrocellulose samples.

Comparisons of TGA and DSC approaches to evaluate nitrocellulose thermal degradation energy and stabilizer efficiencies

This study investigated the thermal degradation energy (activation energy, E a) for nitrocellulose (NC) with low nitrogen content of 11.71 mass%, so-called NC3, by using two different kinds of thermal analysis instruments: thermogravimetric analyzer (TGA) and differential scanning calorimetry (DSC). A comparison of E a for various nitrogen content NC samples at two scanning rates (5 and 10 °C min −1) tested by TGA and DSC is also discussed in this paper. Meanwhile, our aim was to analyze the anti-degradation of E a for NC with high nitrogen content, as so-called NC1. Thermal stability for NC1 with diphenylamine (DPA) was tested via DSC with 10 DPA concentrations in weights of 0, 0.25, 0.50, 0.75, 1.0, 1.25, 1.50, 1.75, 2.0, and 3.0 mass%. Experimental results indicated that E a of NC3s was 319.91 kJ mol −1. Moreover, that while dosing DPA into NC1 the best recipe could be employed to avoid any violent NC1 runaway and also can be used to distinguish the differences of thermal decomposition E a between NC with different nitrogen contents. This study established a fast and efficient procedure for thermal decomposition properties of NC, and could be applied as an intrinsically safer design during relevant operations.

New protocol for the isolation of nitrocellulose from gunpowders: Utility in their identification

In this work, a new approach for the isolation of nitrocellulose from smokeless gunpowders has been developed. A multistep solvent extraction method was needed to purify nitrocellulose contained in gunpowders. For single-base or double-base gunpowders six consecutive solvent extractions were selected: three extractions with methanol (to remove nitroglycerin, 2,4-dinitrotoluene, ethyl-centralite, diphenylamine, and diphenylamine derivatives); one extraction with dichloromethane (to remove colorants and plasticizers of organic nature); one extraction with methanol (to facilitate a final polar extraction); and one extraction with water (to remove ionic components) were necessary at 35 °C. For the triple-base gunpowder studied, eight solvent extractions were needed due to a high concentration of the water-soluble nitroguanidine was present. In addition to the same five initial phases used for the single-base and double-base gunpowders, three water extraction phases at a higher temperature (75 °C instead of 35 °C) were also needed. A final step to solubilize nitrocellulose in methyl ethyl ketone was used to remove inert components (mainly graphite). Nitrocellulose isolated from these propellants was characterized by Fourier-Transformed Infrared Spectroscopy (FTIR spectroscopy). The same FTIR spectra were observed for nitrocelluloses isolated from different types of gunpowders. A comparison of FTIR spectra of nitrocellulose samples of different nitration degree evidenced that the bands regions most affected by this factor were: 3600–3400 cm −1, corresponding to the stretching vibrations of residual hydroxyl groups; 1200–1000 cm −1, attributed to the valence vibrations νCO of the glucopyranose cycle; and 750–690 cm −1, assigned to vibrations of the nitrate group. In both cases, the bands appearing in these regions were more pronounced in the spectra of nitrocellulose samples of low nitration degree.