Experimental Study On The Thermal Decomposition And Combustion Characteristics Of Nitrocellulose With Different Alcohol Humectants

Nitrocellulose(NC),as an important ingredient in industry,has been comprehensively used in the production of smokeless powder,blasting gelatin,single-base,double-base propellants,lacquer,paint and etc.Given the high potential of spontaneous combustion of pure NC,some humectants such as water or alcohol are added to it to improve its stability in the process of production,storage and transportation.Although the thermal behaviors including thermal instability of nitrocellulose and its mixtures with some humectants have been comprehensively examined previously in the literature,their combustion characteristics have not been systematically studied.To address the issue,the combustion properties of NC with alcohol humectants are investigated by the means of the ISO 5660 cone calorimeter.Two kinds of NC-humectant mixtures with 30 wt.%isopropanol and 30 wt.%ethanol,respectively,were employed as samples.The tests were conducted under different external radiations,ranging from 0-15 kW/m2.The experimental results indicate that the external radiation positively influences the peak heat release rate(HRR)intensity and the maximum mass loss rate(MLR),while the total heat release(THR)decreases with the elevated external radiation.Comparatively,the sample with isopropanol exhibits a higher fire risk,characterized by the higher peak HRR,THR and maximum MLR.To have an insight into the fire properties of nitrocellulose-isopropanol and-ethanol mixtures,the experimental data are further extracted and analyzed carefully.Generally,the effective heats of combustion of the two samples characterized by both the peak and mean heat release rates decrease with the increasing external irradiance levels.The combustion efficiencies characterized by the ratio of carbon dioxide to carbon monoxide,regardless of the maximum and mean values,also show the similar decreasing tendency,exhibiting a lower combustion efficiency at elevated external radiation.Moreover,the X-ray photoelectron spectroscopy(XPS)method is employed to identify the combustion residuals of the two NC samples.With respect to the x-ray photoelectron spectroscopy results,the two nitrocellulose-alcohol mixtures appear to yield the similar species of combustion residuals,but slightly different in the atomic concentrations,which may be due to the differences in the alcohol humectant and nitrogen content in nitrocellulose substrate.Auxiliary investigating methods,including Scanning Electron Microscopy and Differential Scanning Calorimeter-Thermal Gravimetric Analysis,were applied toexamine the micro structure and thermal behavior of NC-humectant mixtures.SEM results show similar fibrous structures and porosity.Hence the two alcohols,namely isopropanol and ethanol,barely affect the micro structures of pure NC.Based on the DSC-TGA tests,the activation energies for NC-alcohol humectant mixtures were calculated by Ozawa and Kissinger models,respectively.Higher activation energy for NC-I implies that NC-I has a greater thermal stability.These findings are expected to provide further understanding of fire properties of nitrocellulose-alcohol mixtures and help with fire investigation of such type of fires.