from cross-linking to plasticization – characterization of glycerin/htpb blends

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From Cross-linking to Plasticization – Characterization ofGlycerin/HTPB Blends

Makoto Kohga*

Department of Applied Chemistry, National Defense Academy, Hashirimizu 11020, Yokosuka, Kanagawa 239-8686(Japan)

Received: April 7, 2008; revised version: March 23, 2009

DOI: 10.1002/prep.200800023

Abstract

Usually, a plasticizer is a relatively low-viscosity liquid ingre-dient that is added to improve the mechanical properties and theprocessing properties of a propellant, such as a lower viscosity forcasting or a longer pot life of the mixed, but uncured propellant.The effects of many plasticizers on the performance of thecomposite propellant have been studied in detail. Glycerin is atriol, a low viscosity material, and inexpensive. It seems that theprocessing properties and the mechanical properties of the HTPBbinder would be improved by the addition of glycerin. The curingbehavior, the mechanical properties, and the thermal decompo-sition of a glycerin/HTPB blend have been investigated in thisstudy. The viscosity of the glycerin/HTPB blend and the increasingratio of the viscosity versus the elapsed time are lower than thoseof only HTPB. The mechanical properties are improved by theaddition of glycerin, even for a low quantity of glycerin. Thethermal decomposition behavior of the blend occurs at lowertemperatures when compared to that of HTPB.

Keywords: Glycerin, Hydroxyl-Terminated Polybutadiene,Plasticization, Propellant Binder

1 Introduction

A composite propellant consists of an oxidizer, binder,curing agent, metal fuel, burning catalyst, etc. During thepreparation of the composite propellant, these propellantingredients are sufficiently mixed and then the uncuredpropellant slurry is cast into a rocket motor case. It isrequired that during the mixing and casting, the uncuredpropellant has a viscosity suitable for these processes. Lowviscosity uncured propellant slurry is desirable for easiermixing and casting. A lower viscosity of the uncuredpropellant allows not only an improved processability ofthe composite propellant, but also extends the pot life. Theviscosity of the uncured propellant decreases with decreas-ing viscosity of liquid propellant ingredients at constantsolid loading. It is likely that the viscosity of the uncured

propellant is significantly dependent on that of the liquidbinder.

On the other hand, the propellant grain undergoes highstresses that are induced by a rapid acceleration, sharpturn, or rapid chamber pressure rise during launch andflying. It is necessary for a proper propellant that itsmechanical properties prevent these stresses. When thepropellant grain cannot resist such stresses, cracks anddefects are generated in the grains. The cracks and defectsexpose additional burning surfaces and thus cause anincrease in the combustion gas evolution. Finally, themotor would be destroyed by a sharp pressure increase inthe combustion chamber.

A plasticizer is a liquid organic compound, which may actas a fuel or an energetic liquid compound (containingoxygen, azide, or nitrate groups), which adds energy to thepropellant. The plasticizer is usually a relatively low-viscosity liquid ingredient that is added to improve themechanical properties of the propellant and to improve theprocessing properties such as a lower viscosity for mixingand casting or a longer pot life of the uncured propellants.The burning characteristics, the mechanical properties, andthe processability of composite propellants containingplasticizers have been investigated [1 – 12].

The hydroxyl-terminated polybutadiene (HTPB) is pres-ently the most widely used binder, and isophorone diiso-cyanate (IPDI) is generally used as the curing agent. TheOH group of the HTPB molecule reacts with the NCOgroup of IPDI. That is to say, the reaction of HTPB and IPDIis the urethane reaction. This system has a rubberyconsistency due to the formation of a dense network.Glycerin has three OH groups in its molecular structure andis inexpensive. If the OH groups of glycerin that is mixedwith HTPB react with the NCO groups of IPDI, themechanical properties of the propellant might be improved.Furthermore, the viscosity of the glycerin/HTPB blendwould be lower than that of only the HTPB because glycerinis a significantly low-viscosity liquid compared to HTPB. It* Corresponding author; e-mail: [email protected]

436 Propellants Explos. Pyrotech. 2009, 34, 436 – 443

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was expected that the processability of the propellant wouldbe improved with the addition of glycerin to HTPB.

Glycerin is not an energetic material, but it has threeoxygen atoms in its molecular structure. When these oxygenatoms contribute to the combustion of the propellant, theburning characteristics may be improved. The specificimpulse and adiabatic flame temperature of the ammoniumperchlorate (AP)/HTPB-based propellant containing glyc-erin was calculated using the NASA SP-273 program [13]with a combustion pressure of 7 MPa, an exit pressure of 0.1MPa, and an initial temperature of 298 K. The result forpropellants with 50 – 80% AP is shown in Figure 1. For thepropellants at 70 and 80% AP, the specific impulse andadiabatic flame temperature increases with increasingglycerin content. At a high flame temperature, glycerindissociates and the oxygen atom of glycerin contributes tothe combustion of the propellant. Therefore, the specificimpulse of the propellant above 70% AP increases withincreasing glycerin content. On the other hand, the specificimpulse of a propellant with less than 60% AP gentlydecreases with increase in the glycerin content since theflame temperature is low due to the low AP content. Theaddition of glycerin to the AP/HTPB propellant above 70%AP would effectively enhance the propellant performance.

In this study, the curing behavior, the mechanical proper-ties, and the thermal decomposition of the glycerin/HTPBblend were investigated in order to verify the effect ofglycerin on the HTPB binder. Details of these investigationsare reported in this paper.

2 Experimental

2.1 Sample Preparation

HTPB R-45 M was used as a major binding ingredient andglycerin as a modifier for the processing and mechanicalproperties. The molecular weight of HTPB is 3270. IPDI was

the curing agent. Glycerin was first added to HTPB, and thismixture was then sufficiently blended for approximately5 min. Glycerin is a hygroscopic material. The moisture inglycerin was removed with molecular sieves before beingadded to HTPB. Next, IPDI was added to this mixture and itwas mixed well for approximately 10 min. IPDI was addedat 8.14 wt.-% of HTPB, i.e., the ratio of NCO groups of IPDIto OH groups of the HTPB was 1.2. The glycerin/HTPBblends with IPDI were maintained in a thermostated oven tobe cured for a week. The temperature of the oven was 333 Kin this study because this temperature is apt for themanufacture of HTPB-based propellants [14].

2.2 Analytical Method

The apparent viscosity of the sample was measured usinga ˘ 0.5 mm � 1 mm die under a load of 0.98 MPa at 333 Kby a capillary-type flow tester. The FTIR spectra wererecorded in the range of 4000 450 cm1 using an FTIRspectrometer. The transmittance of the liquid sample andthe reflectance of the cured sample were measured.

The mechanical properties of the cured blends wereinvestigated using a tension test and a hardness test. Themechanical properties were averaged from four measure-ments. The tensile test was carried out using dumb-bellsconforming to JIS K 6301 at a cross-head speed of 500 mmmin1 at 293 K with an autograph. The values of the elasticitymodulus, ultimate tensile strength, and ultimate tensilestrain were obtained for each sample. The hardness testmeasurements were done on the basis of ASTM D2240. Thehardness was measured at 253, 279, 298, and 333 K using aDurometer Type OO rubber hardness tester. This durom-eter is used to measure the hardness of soft rubber,thermoplastic elastomers, and very soft plastics.

The viscoelastic properties of the cured samples weremeasured by a dynamic viscoelastic analyzer using theextension mode. The shape of the sample was cuboidal

Figure 1. Influence of glycerin content in binder on the theoretical performance of AP/HTPB-based propellant containing glycerin.

From Closslinking to Plasticization – Characterization of Glycerin/HTPB Blends 437

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(6 mm � 3 mm � 20 mm). The measurements were carriedout in the temperature range from 123 to 353 K at afrequency of 1 Hz, a gap of 5 mm, a heating rate of 5 K min1,and a displacement of 0.01 mm.

The thermochemical behavior of the cured sample wasinvestigated by differential thermal analysis (DTA) andthermogravimetry (TG). The instruments were operated ina nitrogen flow condition at atmospheric pressure in therange from 300 to 820 K. The sample weight was approx-imately 5 mg. The heating rate was 20 K min1.

3 Results and Discussion

3.1 Curing Test

A mixture of glycerin and IPDI separated into two layers,and the glycerin was a viscous liquid even after 1 week sinceit had been heated. This result suggests that the chemicalreactivity between the OH group of the glycerin moleculeand the NCO group of IPDI is poor.

The glycerin/HTPB blend was hard enough to be used as abinder for a composite propellant when the glycerin/HTPBmole ratio (x) was below 10. The cured blend was white andthe depth of the white increased as x increased. Above a x of10, the glycerin adhered to the surface of the cured blend.Above a x of 20, the HTPB solidified and glycerin remainedas a liquid layer under the cured blend layer. That is to say,the blend above a x of 20 completely separated into twolayers of the cured blend and liquid glycerin. It was foundthat glycerin was not soluble and dispersed in the HTPB, andthe chemical reactivity of HTPB and IPDI is superior to thatof glycerin and IPDI.

Because the reactivity of glycerin and IPDI is poor, mostof the glycerin cannot react with the IPDI. When theglycerin/HTPB blend is cured with IPDI, the main curingreaction would be the urethane reaction between the OHgroups of HTPB and the NCO groups of IPDI. Therefore,this blend system had a rubbery consistency due toformation of a dense network of mainly HTPB and mostof the glycerin separated into the liquid phase. A smallamount of the glycerin would physically enter the voids inthe network of the cured HTPB. As mentioned above, theHTPB solidified and glycerin adhered to the surface of thecured HTPB above a x of 10, and the mixture above a x of 20

completely separated into two layers of the cured blend andliquid glycerin. These results suggested that for the blendabove a x of 10, the glycerin could not physically enter thematrix of the cured HTPB.

The glycerin, which did not occlude into the matrix of thecured HTPB, would settle to the bottom of the solid rocketmotor during storage. Therefore, the uniformity of theburning and mechanical properties would be significantlydegraded. For this reason, the curing behavior, the mechan-ical properties, and the thermal decomposition character-istics of the blends were investigated below a x of 10 in thefollowing experiments. Table 1 lists the formulations of theblends prepared below a x of 10 used in this study.

3.2 Curing Behavior

During the manufacture of the composite propellant, theuncured propellant is sufficiently mixed and then cast intothe motor case. A low viscosity uncured propellant isdesirable for easier mixing and casting. The pot life couldalso be extended by decreasing the curing rate of the binderand a sufficient time for mixing and casting can be attainedby extending the pot life. If there are no further bondingforces between the particles and binder ingredients, theviscosity of the uncured propellant is quite dependent onthat of the liquid propellant ingredients, and the viscosity ofthe uncured propellant decreases with decreasing viscosityof the binder and/or the plasticizer. As the viscosity of theglycerin is lower than that of HTPB, the viscosity of theglycerin/HTPB blend would decrease when compared onlyto HTPB.

Figure 2 shows the apparent viscosities of the HTPB andthe glycerin/HTPB blends versus time. These viscositiesincrease with increase in time because IPDI as a curingagent was added to HTPB and the blends. At the beginningof heating, the apparent viscosity of HTPB (x¼ 0) is 1.1 Pa s

Figure 2. Relationship between apparent viscosity and time at333 K.

Table 1. Formulations of the blends used in this study.

x Glycerin/HTPB Mass Fraction (%)

Mole Ratio Glycerin HTPB IPDI

0 0/1.0 0 92.47 7.530.1 0.1/1.0 0.26 92.23 7.510.5 0.5/1.0 1.28 91.29 7.431.0 1.0/1.0 2.53 90.13 7.342.5 2.5/1.0 6.11 86.82 7.075.0 5.0/1.0 11.51 81.83 6.66

10.0 10.0/1.0 20.65 73.38 5.97

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and that of the blend with a x of 10 is 0.9 Pa s. The initialviscosity slightly decreased with the addition of glycerin toHTPB. The increasing ratio of the apparent viscosity versustime for all the glycerin/HTPB blends is almost the same upto 100 min. Thereafter, the apparent viscosities of the blendsare lower than that of HTPB and the difference increaseswith increasing x. The viscosity of HTPB at 600 min afterheating is 23 Pa s and that of the blend with a x of 10 is9.4 Pa s. It was found that the increasing rate of the viscosityversus time decreased with the addition of glycerin, even fora small quantity of glycerin. Based on the experimentalresults described above, it was determined that the additionof glycerin would be effective not only to decrease theprocessing viscosity of the HTPB-based composite propel-lant, but also to extend the pot life. This is expected tofacilitate the manufacture of the HTPB-based propellant byusing glycerin as a modifier for processing.

3.3 FTIR Spectra

The FTIR spectra obtained for the liquid HTPB, IPDI,and glycerin are presented in Figure 3. For the HTPB, theband around 2920 cm1 belongs to alkanes. The bands around2260 cm1 for IPDI and 3400 cm1 for glycerin belong to theNCO group and the OH group, respectively.

Figure 3 also shows the FTIR spectra obtained for thecured HTPB and the cured glycerin/HTPB blends. The bandaround 2260 cm1, which belongs to the NCO group of IPDIis hardly observed in these FTIR spectra. This indicates thatthe NCO group would react with the OH group and,

consequently, the urethane bond would be formed. Thehydroxide band peak around 3400 cm1 increases withincreasing x. This fact suggests that the quantity of glycerinthat does not react with IPDI increases with increasing x.

3.4 Dynamic Viscoelastic Properties

The dynamic mechanical properties of polymers arestrongly influenced by their internal structure. Figure 4shows the temperature dependencies of the modulus (E’)and the loss tangent for the cured HTPB and the curedblends with x values of 1 and 10, respectively. The E’ of thecured HTPB is almost constant below 200 K, but above that,it decreases as the temperature increases. This thermogramdecreases remarkably in the range from 205 to 225 K. Forthe cured blends, E’ is almost constant below 185 K, butabove that, it decreases with increasing temperature. Itdecreases significantly in the range from 195 to 215 K. TheE’ of the blends is lower than that of the HTPB aboveapproximately 195 K.

The loss tangent of the cured HTPB has a peak at 217 K.On the other hand, the thermograms of the loss tangent forthe blends have a peak around 207 K, and those for theblends have a broad peak around 290 K. The melting pointof glycerin is 291 K. As mentioned in Section 3.1, a smallquantity of glycerin would enter the voids in the network ofthe cured HTPB. The broad peak around 290 K would bedue to the melting of the glycerin.

The temperature of the maximum loss tangent on thethermogram is the glass transition point (Tg). Table 2 showsTg and the maximum loss tangent. Tg of the cured HTPB is217 K and those of the cured blends are almost constant, i.e.,208 K, and lower than that of HTPB. The maximum losstangent of HTPB is 1.00 and those of the blends are almostconstant in the range from 1.25 to 1.32. The maximum loss

Figure 3. FTIR spectra of liquid sample and cured blends. Figure 4. Temperature dependences of E’ and loss tangent.




tangents of the cured blends are larger than that of the curedHTPB.

The values of Tg and the maximum loss tangent changewith the addition of glycerin to HTPB. This fact suggests thatthe network structure of the sample matrix would be alteredby the addition of glycerin. Glycerin would physically enterthe network of the cured HTPB as described in Section 3.1.The amount of glycerin occluded in the network of the curedHTPB increased with increasing x. If the variations in themaximum loss tangent and Tg were caused by the presenceof glycerin that physically entered the matrix of the blend,these values should vary as x changes. The values of Tg andthe maximum loss tangent were almost independent of x

between 0.1� x� 10.0 as shown in Table 2, therefore, in thisconcentration range the changes in Tg and the maximum losstangent would not be due to the glycerin that entered thematrix of the blend.

During the curing test, a mixture of glycerin and IPDIseparated into two layers, and glycerin was a viscous liquidas mentioned in Section 3.1. Although the chemicalreactivity of glycerin and IPDI is poor, a very small quantityof glycerin would react with IPDI and be incorporated intothe network structure of the cured HTPB. It could beconsidered that Tg and the loss tangent of the cured blendsdid not agree with those of the cured HTPB because theglycerin would be incorporated into the matrix of the curedHTPB. Tg and the maximum loss tangents of the curedblends are constant because the chemical reactivity betweenglycerin and IPDI is poor and the amount of glycerin thatreacted with the IPDI did not increase even when x

increased.The dynamic mechanical properties are strongly influ-

enced by the internal structure of a polymer. The motions ofthe chain segments in the polymer structure have a profoundeffect on Tg and the loss tangent. The loss tangent is asensitive indicator of cross-linking. As the degree of cross-linking decreases, the motion of the chain segmentsincreases, and therefore, the loss tangent increases [15, 16].

As described above, the values of Tg of the cured blendswere lower than that of the cured HTPB and the maximumloss tangents of the cured blends were greater than that ofthe cured HTPB. These facts suggested that with theaddition of glycerin, the main chemical structure would bechanged and the motion of the chain segments of the blendpolymers would be slightly greater.

According to the temperature dependence of the blendpolymer of epoxy and methylene diamine, the Tg shifts to alower temperature as the amount of methylene diamineincreases, and the maximum loss tangent increased with anincrease in the amount of methylene diamine [17]. This is

because the ends of the epoxy segments react withmethylene diamine and dangling epoxy ends are formed;therefore, the dangling ends permit the greater mobility ofthe chain segments.

Isophorone diisocyanate has two isocyanate groups.Theoretically, the main curing reaction of HTPB is theurethane reaction between the OH groups of HTPB and theNCO groups of IPDI. This system has a rubbery consistencydue to the formation of a dense HTPB network. On theother hand, the glycerin/HTPB system also has a rubberyconsistency due to the formation of a dense HTPB network,mainly because the reactivity of glycerin and IPDI is poorand most of the glycerin could not react with IPDI.However, it could be considered that the very small quantityof glycerin that reacted with IPDI would be incorporatedinto the network structure of the cured HTPB and danglingends would be formed in the network. Therefore, themobility of the chain segments of the blends would beenhanced by the addition of glycerin; Tg was shifted to alower temperature and the maximum loss tangent in-creased. The increase in the mobility of the chain segmentswould enhance the chain extension of the cured binder andwould improve the mechanical properties of the binder.

3.5 Mechanical Properties

The stress – strain diagrams obtained by the tension testare shown in Figure 5. The tensile stress increases withincreasing tensile strain. The ultimate tensile strain is thesame as the elongation at break. There is an elastic regionbelow approximately 30% of strain for all the samples. Themechanical properties of the cured sample such as thetensile modulus, ultimate tensile strength, and ultimatetensile strain are listed in Table 3. Figure 6 shows theinfluence of x on the tensile modulus. The modulusdecreases below a x of 5, while above that, it is almostconstant.

Table 2. Tg and maximum loss tangent determined by tempera-ture dependence of cured blends.

x (�) 0 0.1 0.5 1.0 2.5 5.0 10.0

Tg (K) 217 207 208 207 207 207 207Maximum Loss Tangent (�) 1.00 1.26 1.26 1.25 1.26 1.29 1.32

Figure 5. Stress – stain diagram.

440 Makoto Kohga



Figure 7 shows the influence of x on the ultimate tensilestrength and ultimate tensile strain of the cured sample. Theultimate tensile strain sharply increases with a smallquantity of glycerin below a x of 0.5, while above this value,it gradually increases. The ultimate tensile strain of theblend at a x of 0.5 is approximately twice that of the curedHTPB (x¼ 0). The ultimate tensile strength also increasessignificantly with a small added amount of glycerin and themaximum value is obtained at a x of 0.5. Above 0.5, theultimate tensile strength decreases with increasing x. Themaximum value of the ultimate tensile strength is approx-imately 1.6 times that of the cured HTPB. It was found thatthe ultimate tensile strain and strength vary significantlywith the small quantity of glycerin below a x of 0.5.

Generally, the ultimate strength increases with decreasingelongation because a lower tensile strain indicates a higherdegree of cross-linking and the ultimate tensile strength isexpected to increase with the increase in the networkdensity [18]. As shown in Figure 7, below a x of 0.5, both theultimate tensile strength and the ultimate tensile strainincrease with increasing x. It was found that the cured blendshave a unique tension behavior below a x of 0.5. Asdescribed in Section 3.4, a small amount of the glycerin that

reacted with IPDI would be incorporated into the networkstructure of the cured HTPB and dangling ends would beformed in the network. Furthermore, the glycerin that wasnot incorporated into the network would be physicallyoccluded in the network of the cured HTPB and would act asa lubricant. The unique tension behavior would result fromthe chain extension due to the dangling ends and from thenonbonding parts of glycerin acting as a lubricant. In thisway, glycerin may be regarded as a pseudo plasticizer andlubricant.

The influence of x on the hardness is shown in Figure 8.The hardness decreases with increasing temperature, and itdecreases with increasing x at a constant temperature andsignificantly below a x of 0.5. Again, the reason might be thatthe chain extension of the binder was increased with theaddition of glycerin. It is expected that the hardness of thepropellant would be reduced by a decrease in the hardnessof the binder ingredient. The reduction in the hardnessindicates that the material becomes softer. A softer solidpropellant is convenient for resisting an explosion of therocket motor due to impact and friction; thus the vulner-ability of the propellant would be reduced. The addition ofglycerin to HTPB may be an effective way to obtain a lesssensitive HTPB-based propellant.

3.6 Thermal Decomposition

Figure 9 shows the DTA-TG thermograms of the curedHTPB and the cured blend with a x of 10. The DTA curve ofthe cured HTPB has an exothermic peak at 659 K, then anendothermic peak at 730 K, and a small exothermic peak at746 K. According to the TG curve, the consumption ofHTPB begins at 600 K with the total consumption around780 K.

Figure 6. Influence of x on tensile modulus.

Table 3. Tensile modulus, ultimate tensile strength, and ultimatetensile strain of cured blends at 293 K.

x (�) TensileModulus

Ultimate TensileStrength

Ultimate TensileStrain

(MPa) (MPa) (%)

0 0.30 0.57 5000.1 0.27 0.74 9700.5 0.20 0.89 11901.0 0.19 0.85 12102.5 0.15 0.72 12205.0 0.11 0.62 1230

10.0 0.11 0.46 1250

Figure 7. Influence of x on ultimate tensile strength and ultimatetensile strain.




The DTA curve of the blend has exothermic peaks at 659and 740 K. Two endothermic peaks at 569 and 729 K are alsoobserved on the curve. The consumption of the blend isobserved from approximately 400 K and the blend iscompletely consumed around 780 K. Approximately 10%of the blend is consumed around 570 K. The endothermicpeak and the consumption around 570 K are attributed tothe principal evaporation of glycerin because the boilingpoint of glycerin is 564 K. The consumption around 730 K isdue to the principal decomposition of HTPB.

The beginning consumption temperature of the glycerin/HTPB blend is lower than that of HTPB. It is likely that the

burning rate would be increased by the combustion ofdecomposition gases generated at lower temperatures. Theendothermic peak at 569 K is small. This endothermic heatwould hardly influence the burning rate, whereas it ispossible to increase the burning rate by the combustion ofthe gases generated during the endothermic decomposition.

It was found that the thermal decomposition behavior ofthe blend is superior to that of HTPB. These results suggestthat the addition of glycerin to HTPB would allow anHTPB-based propellant to have an enhanced burning rate.

4 Conclusion

Glycerin is a triol and a low-viscosity material. Theprocessing properties and the mechanical properties of anHTPB-based propellant would be improved with theaddition of glycerin to HTPB. The curing behavior, me-chanical properties, and thermal decomposition of a glyc-erin/HTPB blend were investigated in this study.

The glycerin/HTPB blend was hard enough to act as abinder for the composite propellant when the glycerin/HTPB mole ratio x was less than 10. The viscosity of theblend was lower than that of only HTPB. The increase inviscosity versus time decreased with the addition of glycerin,even for a small quantity of glycerin. The addition ofglycerin would not only effectively decrease the processingviscosity of the HTPB-based composite propellant, but alsoprolong the pot life. Because the chemical reactivity ofglycerin and IPDI is poor, only a very small quantity ofglycerin would react with IPDI and then be incorporatedinto the network structure of the cured HTPB. Below a moleratio of 0.5, the cured blends have unique mechanicalproperties, which result from the glycerin being incorpo-rated into the network of the cured HTPB. The initialdecomposition temperature for the cured glycerin/HTPBblend is lower than that for the cured HTPB.

It was expected that glycerin would act conveniently as amodifier for improving the processing, mechanical proper-ties, and burning behavior of the HTPB-based propellant.

5 References

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[3] N. Wingborg, C. Eldsater, 2,2-Dinitro-1,3-bis-nitrooxy-pro-pane (NPN): A New Energetic Plasticizer, Propellants,Explos., Pyrotech. 2002, 27, 314.

[4] L. Gottlieb, S. Bar, Migration of Plasticizer Between BondedPropellant Interfaces, Propellants, Explos., Pyrotech. 2003, 28,12.

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Figure 8. Influence of x on hardness.

Figure 9. DTA-TG thermograms at 20 K min1.

442 Makoto Kohga



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[8] G. Doriath, Energetic Insensitive Propellants for Solid andDucted Rockets, J. Propul. Power 1995, 11, 870.

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[11] T. F. Nihal, U. B. Zuhtu, The Effect of Ammonium Nitrate,Coarse/Fine Ammonium Nitrate Ratio, Plasticizer, BondingAgent, and Fe2O3 Content on Ballistic and MechanicalProperties of Hydroxyl Terminated Polybutadiene BasedComposite Propellants Containing 20% AP, J. ASTM Int.2005, 2, 233.

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[13] S. Gordon, B. J. McBride, Computer Program for Calculationof Complex Chemical Equilibrium Compositions, RocketPerformance, Incident and Reflected Shocks, and Chapman-Jouguet Detonations, NASA SP-273, 1971, NASA LewisResearch Center, Wasington, D. C., USA.

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from cross-linking to plasticization – characterization of glycerin/htpb blends

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