Rheological Properties Of GAP/DGTN Composite Solid Propellant Slurries

GAP-based composite solid propellant with diglycerol tetranitrate（DGTN）as the energetic plasticizer possesses the advantages of high energy density,low mechanical sensitivity and excellent low-temperature mechanical properties,which are highly adaptable in the modern battlefield environment.The good process performance of propellant slurry is the foundation to develop energy performance and ensure safety during propellant storage and use.Regulating the rheological properties of solid propellant slurries is considered an important way to improve the process performance.In this paper,three composite solid propellant slurries（GAP/DGTN/AP,GAP/DGTN/AP/Al,GAP/DGTN/AP/CL-20）were prepared with GAP/DGTN as the binder system,and the steady rheological measurements and dynamic rheological measurements were employed to explore the rheological properties of GAP/DGTN composite solid propellants.The main research are as follows.（1）The rheological properties of GAP/DGTN/AP composite solid propellant slurries were studied.The effect of various factors（the content of AP,the molecular mass of GAP,particle gradation and temperature）on the rheological properties of slurries was investigated using steady rheological measurements,and the optimal formulation of GAP/DGTN/AP propellant was determined.The results reveal that the apparent viscosity of GAP/DGTN/AP slurries containing ultrafine AP is higher than that of GAP/DGTN/AP slurries containing micron-sized AP,with higher pseudoplasticity and higher sensitivity to temperature.The apparent viscosity of GAP/DGTN/AP slurries increases exponentially with the increase in ultrafine AP,accompanied by a gradual increase of shear thinning behavior.The reduced molecular weight of GAP and particle gradation of AP are beneficial for decreasing the apparent viscosity and weakening the pseudoplasticity of GAP/DGTN/AP slurries.The apparent viscosity of GAP/DGTN/AP slurries is minimum when the molecular weight of GAP is 2000 and the mass ratio of ultrafine AP to micron-sized AP is 1:1.（2）The rheological properties of GAP/DGTN/AP/Al composite solid propellant slurries were studied.Based on the formulation of GAP/DGTN/AP propellant with the best rheological properties,the GAP/DGTN/AP/Al propellant slurries were prepared.The linear viscoelastic regime and yielding behavior of slurries were investigated using strain sweep measurements,and the effect of particle gradation of micron-sized and nano-sized aluminum powders on the rheological properties of slurries was determined using frequency sweep measurements.On the basis of the time-temperature superposition principle,the master curve of storage modulus was also built.The results reveal that the yield strains of slurries with 10%nano-sized aluminum powders change from 0.0102%to 0.0147%and the flow strains decrease significantly with increasing frequency when the slurries were tested at 1 rad·s^-1,10rad·s^-1and 20 rad·s^-1,which suggests that the linear viscoelastic regime of the slurries is almost unchanged and the yield transition process is accelerated.The increased aluminum nano-powder content results in lower storage modulus and loss modulus.The K and|n-1|of the slurries are the smallest when the relative content of aluminum nano-powder is 0.7,which indicates that the apparent viscosity is the lowest and the pseudoplasticity is the weakest.In addition,the storage modulus of the slurries decreases with increasing temperature.The master curve of storage modulus broadens the frequency range to six orders of magnitude approximately,which is capable of predicting the rheological properties of the slurries within the range of 0.0073 rad·s^-1～7940 rad·s^-1.（3）The rheological properties of GAP/DGTN/AP/CL-20 composite solid propellant slurries were studied.Based on the formulation of GAP/DGTN/AP propellant with the best rheological properties,the GAP/DGTN/AP/CL-20 propellant slurries were prepared.The linear viscoelastic regime and yielding behavior of slurries were investigated using strain sweep measurements,and the effect of particle gradation of micron-sized and submicron-sized CL-20 powders on the rheological properties of slurries was determined using frequency sweep measurements.On the basis of the time-temperature superposition principle,the master curve of storage modulus was also built.The results reveal that the yield strains of slurries with 10%submicron-sized CL-20 powders change from 0.1543%to 0.1988%and the flow strains decrease significantly with increasing frequency when the slurries were tested at 1rad·s^-1,10 rad·s^-1and 20 rad·s^-1,which suggests that the angular frequency exerts little influence on the linear viscoelastic region and the yield transition process of the slurries.The increased submicron-sized CL-20 results in higher storage modulus and loss modulus.The K and|n-1|of the slurries are smaller when the relative content of submicron-sized CL-20powders is 0.5/1.0,which indicates that the apparent viscosity is lower and the pseudoplasticity is weaker.In addition,the storage modulus of the slurries decreases with increasing temperature.The master curve of storage modulus broadens the frequency range to six orders of magnitude approximately,which is capable of predicting the rheological properties of the slurries within the range of 0.0063 rad·s^-1～1254 rad·s^-1.