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Approved for public release, distributionunlimited

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Distribution authorized to DoD only;Administrative/Operational Use; JUN 1967.Other requests shall be referred to U.S.Naval Ordnance Test Station, China Lake,CA.

AUTHORITYUSNWC ltr, 14 May 1975; USNWC ltr, 14 May1975

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Separate page printouts MUST be marked accordingly.

THIS DOCWNENT CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE OFTHE UNITED STATES WITHIN THE MEANING OF THE ESPIONAGE LAWS, TITLE 18,U.S.C., SECTIONS 793 AND 794. THE TRANSMISSION OR THE REVELATION OFITS CONTENTS IN ANY MANNER TO AN UNAUTHORIZED PERSON IS PROHIBITED BYLAW.

NOTICE: When government or other drawings, specifications or otherdata are used for any purpose other than in connection with a defi-nitely related government procurement operation, the U. S. Governmentthereby incurs no responsibility, nor any obligation whatsoever; andthe fact that the Government may have formulated, furnished, or in an9way supplied the'said drawingis, specifications, or other data is notto be regarded by implication or otherwise as in any manner licensingthe holder or any other-person or corporation, or conveying any rightsor permission to manufac•tlife' use or sell any patented invention that-may in any way be related thereto.

N'_

CONFIDENTIAL NOTS TP 4387

Downgraded at 3.year intuvals; Odeclassified after 12 years.

CASTABLE EXPLOSIVE COMPOSITIONS BASED ONDIN ITROPROPYLACRYLATE AND HMX

S~BY

Barbara A. Stott

Propulsion Development Departmert

U U S. NAVAL ORON ANCE TEST STATION

China Lake, California June 1967

CE I

DISTRIBUTION STATEMENT '

IN ADDITION TO SECURITY REQUIREMENTS WHICH APPLY TO THIS DOCUMENTf AND MUST BE MET, EACHTRANSMITTAL OUTSIDE THE DEPARTMENT OF DEFENSE MUST HAVE PRIOR APPROVAL OF THE U.S.NAVAL ORDNANCE TEST STATION.

CONFIDENTIAL* eas~uJ

CONFIDENTIAL

U. F. NAVAL O D I N O AN gA N TE ST STATiON )

AN ACTIVITY OF THE NAVAL MATERIAL COMMAND *s

G. H. LOWE, CAPT., USH Wm. B. MCLEAN, PAD.

Commander Technical Director

FOREWORD

The investigation of 2,2-dinitropropylacrylate as a castable,polymerizable binder for explosives was first undertaken at NOTS in1962. Need for a cast explosive with higher energy potential than thatof FBXN-101 and better heat resistance than that of relatively lowmelting TNT-based compositi.ons led to further development and subsequentimprovement of the HMX/DNPA system in 1965-1966. A report published inOctober 1966 describes the initial stages of this work. Additionalstudies to increase energy and improve processability have continuedduring the past year. Results are described in the present report.

This project was conducted under Task Assignment ORD-033-201/200-I/F009-08-05 and was reviewed for technical accuracy by Dr. H. J. Grytingand Dr. C. D. Lind.

Any reference to specific source or brand name does not necessarilyimply Government indorsement of any particular product.

Released by Under authority ofN. L. RUMPP, Head G. W. LEONARD, Head,Explosives and Pyrotechnics Div. Propulsion Development Dept.30 June 1967

NOTS Technical Publication 4387

Published by ............ Propulsion Development DepartmentCollation .... ........ Cover, 25 leaves, DD Form 1473, abstract cardsFirst printing ........ .................. .. 200 numbered copiesSecurity classification ......... ................ ... CONFIDENTIAL

Abstract alone ...... ............ ...... CONFIDENTIALTitle alone ........... .................... ... UNCLASSIFIED

SECURITY STATEMENTTHIS DOCUMENT CONTAINS INFORMATION AFFECTING THE NATIONAL DEFENSE OF THE UNITEDSTATES WITHIN THE MEANING OF THE ESPIONAGE LAWS, TITLE 19, U.S.C., SECTIONS 793 AND 794. THETRANSMISSION OR THE REVELATION OF ITS CONTENTS IN ANY MANNER TO AN UNAUTHORIZED PERSONIS PROHIBITED BY LAW.REPRODUCTION OF THIS DOCUMENT IN ANY FORM BY OTHER THAN NAVAL ACTIVITIES IS NOT AUTHOR-IZED EXCEPT BY SPECIAL APPROVAL OF THIS STATION.

ii CONFIDENTIAL


ABSTRACT

The castable explosive, HMX/dinitropropylacrylate, was improved byformulation modifications to obtain higher energy, better physicalproperties and stability, and greater efficiency in preparation. Use ofvolatile liquids in mixing operations, special casting techniques, andselection of optimum HMX particle size blends resulted in solids loadingsof 87% and higher with corresponding detonation velocities exceeding8600 meters per second. Optimization of monomer inhibitor concentrationmade it possible to eliminate pre-processing DNPA purification, yet atthe same time obtain adequate storage stability. Use of a new curative,cobalt acetyl acetonate, greatly facilitated curing by reducing timeand temperature and eliminating the necessity for oxygen exclusion.Resulting castings were harder, more uniform, and more stable, with150*C VTS values as low as 2.4 cc/g/48 hours.

Two new copolymers of DNPA were prepared and evaluated as energeticbinders, one with difluoraminopropylacrylate, the other with dodecafluoro-heptylacrylate. Detonation velocities, as predicted by computation, werecomparable to those for DNPA homopolymer at equivalent 11MN loadings.(Confidential)

CONFIDENTIAL iii

NOTS TP 4387 CONFIDENTIAL

LIST OF ABBREVIATIONS

HMX cyclotetramethylenetetranitran.inePBX plastic-bonded explosiveDNPA 2,2-dinitropropylacrylate

NFPA 2,3-bis(difluoramino)propylacrylateC5 A 1,1,5-trihydrooctafluoropentylacrylate

C7A 1,1,7-trihydrododecafluoroheptylac:, 2ateC9 A 1,1,9-trihydrohexadecaflucrononylacrylateCoAA cobalt acetyl acetonatetBPB t-butyl perbenzoatetBHP t-butyl hydroperoxide

DTA differential chermal rnalysisTGA thermal gravimetric analysisVTS vacuum thermal stabilityPBXN-10 HMX/polyester-styrene 82/18BDNPF-BDNPA bis-2,2-dinitropropyl formal-bis-2,2-dinitropropy!

[acetalFEFO bis-(2,2-dinitro-2-fluoroethyl)formaIHQ 'hydroquinoneMEHQ 1,ydroquinone methyl ether (p-methoxyphenol)

NDPA nitrodiphenylamineptBC paratertiary butyl catechol

ACKNOWLEDGEMENTS

The author acknowledges the assistance of the following:

Lily E. Koch for preparing and L-ting formulations.Otis K. Pennington and Mary Pakulak for analytical and thermal

studies.Jack Pakulak and Edward Kuletz for thermal evaluation.A. J. Dierolf and the Analysis Branch for performing theoretical

computations.Richard Eppinger for designing and fabricating equipment and

conducting detonation velocity mEasurements.Elsa A. Simmons for prepqring the report for publication.Aerojet-General Corporar-on, Hummel Chemical Company, Shepherd

Chemical, duPont, and Rohm ond Haas Company for samples, suggestions,and technical data.

iv CONFIDENTIAL


CONTENTS

Foreword ....................... .............................. iiAbstract ....................... .............................. iiiAbbreviations .................... .......................... ... ivAcknowledgements ................... .......................... ... ivIntroduction ................... ............................ . . .1

Background ..................... ........................... !Present Status ..................... ......................... 2

Curing of Dinitropropylacrylate Compositions ......... ............ 4Early Problems ..................... ......................... 4Cobalt Acetyl Acetonate .. .. .. .. .. .. .. .. .... 7Monomer Inhibition .. .. .. .. .. .. .. .. .. .. .. .i10

Attempts to Increase Energy through Higher Solids Loading .... ... 13

Prepacked Bed Method ............... ...................... ... 13Desensitization during Mixing .......... ................. ... 17HMX Particle Size Distribution ........... ................ ... 19

Modification of the DNPA Binder .......... .................. ... 22Copolymers with Fluoroalkyl Acrylate ....... .............. ... 22

Copolymers with Difluoroaminopropylacrylate ... .......... ... 25Other Binder Additives ............. ..................... ... 30

Allyl and Vinyl Trifluoroacetate ....... ............. ... 30FEFO ..................... ............................ ... 30BDNPF/BDNPA .................. ........................ .. 30Cross-Linking AGents ............. .................... ... 30

Stabilizers for HMX/DNPA Compositions ........ .............. ... 32

Coating HMX with Poly DNPA. .................... 33

Summary and Conclusions .............. ...................... ... 36Recommendations for Future Work .......... .................. ... 36Bibliogiaphy ..................... ............................ .. 43References ....................... ............................ .. 44Appendix:

A. Description of Materials Used ........ ............... ... 38B. Purification Procedures for DNPA Monomer .... .......... ... 39C. Preparation of Compositions ........ ................ ... 40

D. Slurry Procedures for Precoating IMX ..... ............ .. 41E. Test Procedures .............. ...................... ... 42

Tables:1. Properties and Processability of DNPA From Various Sources 52. The Effect of Various Accelerators in Curing DNPA ... ..... 83. The Effect of 90 Day 50*C Storage on DNPA Monomer ........ 124. Castings Prepared by the Prepacked Bed Method of Loading 185. Liquids to Desensitize HMX/DNPA During Initial Stages of

Mixing ................... ........................... ... 206. Properties of 150 g HNX/DNPA Batches Prepared with

Desensitizing Liquids ............ ................... ... 217. Correlation of HMX Bulk Density With Processability in

Castable DNPA Compositions ........... ................ ... 23

CONFIDENTIAL v

i


8. Properties of HMX/DNPA-Fluoroalkyl Acrylate Formulatiuns . 249. Properties of NFPA Monomer ...... ................. ... 26

10. Properties of HMX/DNPA-NFPA Compared with Those ofHMX/DNPA ........... ........... ......... ... ........ 29

11. Substitute Crosslinkers for ATAC in HMX/DNPA Formulations. 3112. The Effect of Additives on the Heat Stability of HMX/DNPA

Formulations . . .*.*.*.*.. . . . . . . . . . . . . 3413. Properties of HMX/poly DNPA Slurry Coated Compositions . . . 35

Figures:1. 150*C Vacuum Thermal Stability of HMX/DNPA Compositions

Containing DNPA from Various Sources ......... .......... 62. Vacuum Thermal Stability Curves for HMX/DNPA with and

without CoAA 9........................93. The Effect of Curing Temperature on the Vacuum Thermal

Stability of HMX/DNPA ....... .................... . i.114. The Effect of HMX Loading on Detonation Velocity .... ...... 155. Equipment Used for Prepacked Bed Method of Loading ... ..... 166. The Effect of Composition on Explosive Properties: hMX

with DNPA and NFPA Binders ...... ................. ... 277. Minimolds for Curing Castabla Compositions of Questionable

Hazard ............. ........................... ... 28

vi CONFIDENTIAL


[VASTABTV EXVPLTITV COMPOSTTTONS RASFD ON

DINITROPROPYL ACRYLATE AND HMX

INTRODUCTION

Back&ground

In the latter part of 1965 a program was undertaken at NOTS todevelop an improved castable plastic-bonded explosive. This product,to be of value in advanced weapons applications, was to have energeticpotential approximating th-it of PqX 94041 or of some of the best TNT-based formulations such as octol. However, unlike the latter, the newcomposition should be able to withstand temperatures up to 150*C withno sigrificant physical or chemical changes. Other desirable character-istics would include safety in formulating and handling, ease andconvenience in processing, and ready availability and low cost of in-gredients. Resistance to vibration and thermal shock might also becritical.

Initial survey of possible candidate components indicated that HMXcombined with the energetic monomer, 2,2-dinitropropyl acrylate mightbe a promising choice. Studies carried out to verify the feasibilityincluded investigations of stability, energetic potential, and process-ability. A report has been published which describes the results ofthis work (Ref. 2).

Preliminary findings indicated that HM-dinitropropyl acrylatecompositions might be capable of fulfilling many of the desiredobjectives. The low viscosity of DNPA monomer permitted HMX loadingsof 85%, which, together with the inherent energy of the binder materialitself, resulted in detonation velocities higher than 8500 meters persecond. In addition, the heat resistance of these compositionsappeared to be good, with autoignition points averaging 225*C, and 1500vacuum thermal stability values ranging from 3 to 6 cc for a forty-eight hour period. The DNPA itself, although an energetic material,was insensitive to initiation by impact or friction and it acted as adesensitizing agent for HMX, raising the impact value to approximatelythat of tetryl.

Physical properties of cured DNPA binder, with and without filler,appeared advantageous. With proper selection of curing agents andcuring conditions the polymerized product was a tough, resilient solid

1 Compressible PBX developed at Los Alamos, 94% HMX, 3% tris(ý-

chloroethyl)phosphate, 3% nitrocellulose; detonation velocity 8710 ra/secat 1.821 g/cm3 (1/2-in. diameter). (Ref. 1.)

2 75% HMX/25% TNT, detonation velocity 8643 m/sec at 1.81 g/cm3 .

CONFIDENTIAL 1


with little or no visible change occurring after brief exposure to 1500 Ctemperatures. The monomer appeared to copolymerize readily with otherunsaturated compounds, including polyesters, fluoroacrylates and nitroderivatives such as petrinacrylate. Furthermore, a survey of possiblesources for DNPA revealed at least three manufacturers capable ofsupplying the material in laboratory quantities and interested in meet-ing eventual produttion demands. All suppliers anticipated that costswould decrease substantially with increased production and experience.

While initial studies were encouraging, they also pointed out someshortcomings or areas requiring further improvemert. One of these wasprocessability. Curing, for example, was lengthy and exacting, andrequired at least 80 0 C temperatures and exclusion of atmospheric oxygen.Moreover, physical consistency of cured polymer varied somewhat frombatch to batch. Mixing in the initial stages could be hazardous beforethe HMX was thoroughly wetted by the binder. Also energy fell somewhatshort of the desired goal. Although detonation velocity measurementsshowed a significant advantage over PBXN-101 or Composition B, 3 values

were still inferior to those for octol or PBX 9404.

Since publiration of the first report additional experimental workhas effected a solution for many of these problems and has affordedbetter insight into others. It is the purpose of the present report tobring up to date the available information concerning the development ofthe HMX/DNPA system. Significant progress has been made in respect toenergy improvement, greater =ase and safety in processing, betterphysical characteristics and stability, and increased knowledge concern-

ing availability and variability of bacic constituents. Severalinteresting new DNPA copolymers have been prepared including one basedon a difluoramino derivative. Additional Ruby calculations have beencarried out to predict the performance of such binder systems. Resultsof these computations, it is found, correlate well with actual testdata.

Prosent Status

ENERGY. With improved solids loading and processing techniquesit has been possible to raise the detonation velocity of HNX/DNPAcompositions to mote than 8600 m/sec. By combining accumulated smallcontributing factors it may be possile to gain still another 100 m/sec.Beyond 8700, further advances are expected to become increasinglydifficult with this particular system.

3 8000 m/sec average. See Ref. 3.

2 CONFIDENTIAL

CONFIDENTIAL 'WOT, 'rP 4387

acetonate, has eliminated most of the previous curing diffict•:-Lu- aadhas reduced curing requirements. Cures which formerly u,2cessltated 80%Ctemperatures for several days with oxygen rigidly excluded now can be

successfully accomplished at 50-60 0 C overnight in air. The resultingproduct is not only harder and more solid than previously, It is alsomore resistant to thermal decomposition as evidenced by vacuum theimalstability tests. Furthermore, the process is more tolerant of contami-nants such as residual traces of inhibitor. Some samples of monomerwhich consistently failed to cure adequately in earlier work can now bepolymerized to yield excellent castings.

SAFETY. Two processing modifications to achieve higher solidsloading under safer operating conditions offer considerable promise.One involves the use of volatile desensitizing liquids during preliminarystages of mixing. Inexpensive, non-flammable compounds such as dii:hloro-methane added to HMX and DNPA components prior to mechanical mixingprovided sufficient fluidity to permit solids loadings higher than 87%with no sacrifice in the quality of the final casting. The liquid wasreadily removed by evaporation during latter stages of mixing. Subse-quent castability and curability were excellent, and the final curedmaterial was dense, solid, and visibly void-free with detonationvelocities exceeding 8600 meters per second.

A second approach involving more technical difficulties but possiblyoffering still greater advantages in respect to safety and loadabilityutilizes a prepacked bed of HMX infiltrated by the low viscosity liquidbinder and then cured under pressure. Additional work is needed to fullyinvestigate and substantiate the feasibiliry of employing the lattertechnique.

AVAILABILITY. r dNPA monomer obtained from three different manu-facturers was found to be consistent in respect to processability andproperties. Products from all three sources were compounded with HMXto yeild compositions of comparable sensitivity, thermal stability aiidphysical consistency.

STABILITY. A number of different additives in DNPA/HMX formulations

failed to improve thermal stability when evaluated by means of DTA, TGAand 150 0 VTS. However, as pointed out previously, use of cobalt acetyl

acetonate as a curative, besides greatiy facilitating polymerization,also improved vacuum thermal stability and weight loss at elevatedtemperatures. Prior to the use of CoAA, some of the volatile matterevolved during VTS tests was identified as free monomer. More effectivepolymerization methods reduced the amount of this product.

Surveillance of DNPA monomer showed outstanding stability to bothpolymerization and degradation. Several months of storage at 500 C, forexample, failed to produce detectable polymerization, even in the case

CONFIDENTIAL 3


of essentially inhibitor-free monomer. Thus, it may be possible inYcUdUCLLUtii 42PPiicatLIULM WLIeLCIU1L Fiteiali uL Uii±zeU rtl~ler~ iap '*i) Lu sub-stantially reduce or even elimina-e t.e u-,. of inhibitors such sbhydroquinone, which presently are beiLLg removed by tedious and lengthywashing processes before the monomer is cured.

CURING OF DINITROPROPYLACRYLATE COMPOSITIONS

Dinitropropylacrylate monomer used in compounding HMX/DNPA explosivecompositions was obtained from three suppliers, Aerojet Central Corpora-tion, Hummel ChemicdJ Company, and Northrup-Carolina (Appendix A). Atotal of six different shipments was evaluated. All were essentiailyequivalent except for !nhibitor content. With proper selection ofprocessing conditions all produced castings of acceptable strength andcomparable stability. A brief description of the six monomer lots andtheir behavior is given in Table 1. Vacuum thermal stability curves aftercompounding and curing are shown in Fig. 1.

Early Problems

Initial work described in earlier reports was carried out solely with iAerojet material. Difficulty in obtainiing consistent and complete curingled to a study of various initiator systems including mixed or synergisticperoxides (Ref. 2). Best results were achieved under the following conditions:

Binder - 95% 2,2-dinitropropylacrylate, 5% acetyltriallyl citrate4Accelerator - 0.1% dimethylanilineCuratives - 0.5% each t-butyl perbenzoate and t-butyl hydroperoxideTemperatures - 60°C overnight followed by 80°C 24-48 hoursAtmosphere - nitrogenThe resulting polymer was amber in color, resilient, tough and

relatively free from tack provided adequate precautions were takeninitially to remove inhibitor either by distillation or by oashing withdilute caustic. Attempts to reduce curing time or temperature or to curein air xesulted in incomplete polymerization with very inferior physicalproperties.

When a new shipment of monomer was obtained from a different supplier,namely, Hummer DNPA inhibited with O.%.p-methoxyphenol., use of thedescribed curing procedure resulted in total failure. Extensive purifica-tion techniques were tried in an effort to remove the inhibitor sufficientlyto obtain gelation. These included double distillation at reduced pres-sure, multiple washes with caustic, extraction with MgO, and variouscombined procedures (described in Appendix B). In addition, severaldifferent curing systems were tried including omission of dimethylanilineand substitution of methyl-n-amyl-ketone peroxide for the tBPB-tBHPsystem. All failed to cure Hummel material satisfactorily and itk mostcases it was -ot even possible to obtain gelation.

4 Crosslinking additive to prevent plastic deformation at elevated '

temperatures.

S4 CONFIDENTIAl,

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The best procedure was a triple extraction with caustic. Monomerthus treated gelled; however, was very weak and tacky. With HMX fillercohesion and strength were unacceptable. Aerojet DNPA treated by thesame methods continued to cure adequately provided the specificconditions of time, temperature and ambient atmosphere prevailed. Sinceinfrared studies and other observations indicated no significant

differences between the two monomer lots, it was concluded the variationin polymerization behavior must be due to trace impurities or residualinhibitor not readily removable or detectable.

Two methods of approach were used to solve the problem: (1) es-tablish minimum inhibitor levels and types of inhibitor necessary for

adequate storage stability, (2) search for a better catalyst system.Both approaches proved successful. Hu~nmel DNPA with no inhibitor addedafter synthesis cured satisfactori.y, yet showed no evidence ofdeterioration after three months of storage at 50*C. In addition, avery effective curing agent was found: cobalt acetylacetonate.

COBALT ACETYLACETONATE. Cobalt II is frequently used in conjunctionwith peroxide curatives to initiate vinyl polymerization. The usualcompound, the naphthenate salt, which served effectively to promotecuring in earlier cast PBX compositions, could not be used with DNPAbecause of its insolubility. More recently a greater variety of heavymetal and transition metal derivatives have become available for use inother polymerization applications. Among these newer introductions arecobaltous propionate, octoate, and acetylacetonate. It was felt thatone of these might have solubility characteristics such that cobalt IIcould be successfully introduced into DNPA binder compositions.

The propionate appeared to be essentially insoluble in DNPA, whilethe octoate only dissolved to a slight extent. The acetylacetonate,however, when finely ground and well dispersed, could be readilydissolved at concentrations somewhat higher than 0.2 percent.

Cures resulting from the use of CoAA were most encouraging. Itseffectiveness when compared with other accelerators under minimumcuring conditions is shown in Table 2. Among the advantages were lowercuring temperatures, shorter curing times, and tolerance of oxygen duringcure. Furthermore, acceptable cures were obtainable with all sources ofDNPA, including MEHQ inhibited Hummel washed only once with caustic.Physical properties without and with HMX filler were very promising andthe filled compositions were hard, solid, and tough with no evidence ofinstability or incompatibility due to the new additive. Vacuum thermalstability appeared to improve with CoAA inclusion. Measurementsrepresenting a number of different samples and DNPA sources are plottedin Fig. 2. Without CoAA, greater volatility and weight loss wereobserved. Also more liquid condensate was noted in the VTS tubes.This product was indicated by IR to be free DNPA monomer. By effectingmore complete polymerization, therefore, CoAA may thus improve hightemperature stability as well as physical properties and processability.

CONFIDENTIAL 7

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To further evaluate the efficiency of CoAA accelerator, tests wereperformed to determine the minimum temperature at which DNPA bindercontaining 0.1% CoAA and 0.5% each tBPB and tBHP could be cured. Resultsindicated that overnight cures at 50°C were essentielly as good as thoseat 600C. At 40 0 C the resulting polymer was qualitatively weaker andsofter but nevertheless well gelled and rigid. At ambient temperaturegelation occurred within several days, but acceptable strength andhardness were not achieved within a reasonable length of time. Thesesamples, however, could be further cured at 60 0 C to obtain the usualstrength, rigidity and freedom from tack. Such step-curing techniques,gelation at ambient followed by post curing at a higher temperature,may prove advantageous in applications where polymerization exothermsmight constitute a processing hazard; for example, in larger warheadswhere heat cannot be readily dissipated.

The effect of low temperature curing on thermal stability isshown in Fig. 3 where VTS curves are plotted for samples cured at roomtemperature only, and at 40 and 50 0 C. The compositions were stored forapproximately one month under ambient conditions prior to testing.

MONOMER INHIBITION. Experience with the two Hummel samplesindicated the advisability of maintaining inhibitor levels at as low avalue as permissible, both to simplify purification procedures and producebetter castings. Therefore, accelerated aging tests were conducted todetermine the minimum concentration and the most efficient type ofinhibitor to protect against premature polymerization in storage. Elevenmonomer samples were stored in an oven at 500C. These included threebatches of inhibited DNPA as received from the various suppliers as wellas a special shipment from Hummel to which no inhibitor had been addedafter esterification. Additional samples were prepared by adding knownamounts of ptBC, hydroquinone, and MEHQ to the "uninhibited" 5 Hummelmaterial. Approximately 3-ml monomer samples were placed in glass cubes12.8 cm by 5 mm ID with about 1/4-inch of air space above each liquidsurface. Each tube was then stoppered, placed in the oven, and periodi-cally observed for possible polymerization by cooling to 250C, inverting,and measuring the rate of time for the air bubble to rise.

At the end of 90 days the bubble viscosity test failed to reveal anysignificant change or difference in any of the samples. The test wasthen discontinued and the samples were further evaluated by IR, DTA, andobserving ability to polymerize after extraction of the inhibitor.Results of these tests are summarized in Table 3. Both IR and DTA failedto reveal differences between samples or degradation when compared with

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10 CONFIDENTIAL

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S..... .. .... . Pol ymerization tesL uw u slightly increased curingrates as a result of aging the monomer. This effect can probably beattributed to partial decomposition of the inhibitor resulting in lowerconcentrations which are less difficult to remove.

Both the CoAA and the surveillance studies point to a conclusionwhich is very significant in respect to efficiency in compounding DNPAbased formulations. By using optimum inhibitor types and concentrationsit is possible to supply monomer which will undergo severe storageconditions, yet will polymerize readily to give an excellent end product.Moreover, this polymerization may be effected with no lengtny distillationor washing procedures requiring considerable labor and extensive equipment.

ATTEMPTS TO INCREASE ENERGY THROUGH HIGHER SOLIDS LOADING

Experimental evidence obtained from measurements with HMX/DNPAformulations indicates that increases in detonation velocity of more than100 meters per second may be realized with each additional 2% of HMX at80-90% solids loading (Fig. 4). While this source of energy per se maybe fairly limited, nevertheless when coupled with other contributingfactors such as binder modification or inclusion of dense or oxidizingconstituents, the additive effect may be sufficient to produce substantialgains. Therefore, attempts have continuied to obtain the maximum HMXloading consistent with processability.

Studies completed at an earlier date (Ref. 2) showed that with a lowviscosity binder such as DNPA, solids loadings of 85% were entirely feasible.Further work with inert simulant binders indicated that 2-3% higher loadingsmight be possible and processable provided HMX particle size distributionwas optimized and carefully controlled. These studies were all carriedout with conventional mixing and casting equipment.

A serious disadvantage in formulaing highly filled, castable mixesof the type in question results from the sensitivity of the HMX beforeit is wet by the binder. Precoating the explosive with a desensitizingagent has been used in some explosive applications to overcome thisdifficulty (Ref. 3). However, at the binder levels involved in thepresent work (i.e., 12%) replacing part of the monomer with an inertdesensitizing agent will sacrifice the energy advantages gained by thehigher filler level.

Prepacked Bed Method

One possible approach to obtain higher loading unaccompanied byextreme mixing hazards is to combine ingredients after the filler hasbeen introduced and dried in the mold. This method was investigated atNOTS in 1959 by H. Stanton (Ref. 4) in a series of preparations in whichHMX prepacked into mold3 was vacuum dried and then wet by monomersintroduced by suction. The work was not continued beyond the laboratory

CONFIDENTIAL 13 I


stage because of design difficulties in adapting to actual weapons and

to a greater extent because development of the PBXN-101 castable systemsatisfied existing needs more readily and more economically.

High solids loading with TNT-based compositions in prepacked moldshas been obtained by a German process (Refs. 5,6). This method employsa perforated disk which is rammed into the top of the filled mold cavity.Excess molten TNT, the constituent of lower energy, is forced upwardthrough the perforations and is separated and removed from the maincharge.

For HMX/DNPA, a procedure was tried which includes variations ofboth the Stanton and German procedure. A sketch of the equipment used isstiown in Fig. 5.6 Solids loadings of over 90% were obtained. However,experimental difficulties and failure to obtain homogeneous castingsindicate the necessity for considerably more study before the procedurecan be adapted to production needs.

Basically, the process involves loading the mold from the top withwet HMX of optimum size distribution for maximum packing. Suction isthen applied from the bottom by means of an aspirator to pack the bed anddry the HMX. A filter pad and reinforcing screen prevent the explosivefrom being pulled through. The aspirator is then disconnected and re-placed by a delivery tube leading from a container of binder. Vacuum isapplied at the top of the mold until the liquid binder appears in theriser tube. As at the bottom, a filter pad and perforated plate retainthe HMX. Binder supply and vacuum source are then disconnected and themold assembly is next placed in a jig. Pressure applied in the longitudinalaxis by means of a screw forces excess binder from the top and bottomorific'ýs by depressing the piston-shaped top plug. The composition isthen cured in the jig without relieving pressure.

The procedure described is attractive for the following reasons:

1. Theoretically loadability should be limited only by packingfactors.

2. The method involves no actual handling of dry HMX. Explosivecan be introduced into the mold either wet with water, or to facilitatedrying, rinsed with a more volatile liquid such as methanol.

3. Hazards due to mechanical mixing are eliminated.4. Air may be readily excluded during cure if oxygen inhibition is

a problem.

6 The assistance of R. Eppinger and J. Eldridge is acknowledged in

suggesting improvements for the technique outlined.

14 CONFIDENTIAL


E)t

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SCONFIDENTIAL 15

-4.

cuo


VACUUM SUPPLY

CYLINDRICAL TEFLON PISTONBDRIS• BINDER

SUPPLY

OLD

MOLD CAVITY

REINFORCING SCREENS ,,. FILTERS

ASP!RATOR I PACKING AND FILLING

SCREW - r

BOTTOM PLUG TOP PLUG (TEFLON CYLINDER)

LOADED MOLD

Ul PRESSURING TO REMOVE EXCESS BINDER

FIG. 5. Equipment Used for Prepacked Bed Method of Loading.

16 CONFIDENTIAL


However, actual practice was not as straightforward as theory wouldseem to indicate. Removal of the desensitizing liquid (water or methanol)was difficult and time consuming. When H1X mixtures of optimum packingdensity were used, not only was drying prolonged, but also subsequentpenetration of the bed ly the binder was made very difficult. Use ofexcessive vacuum resulted in loss of volatile components such as styrenein Laminac binders, so that the residual resin failed to cure adequately.Even with low viscosity non-volatile monomers such as DNPA, bed penetrationwa'j so time consuming that a compromise was necessary in selecting HMXtLends. This, in turn, resilted in inferior packing and lower solidsloading.

A brief summary of the compositions prepared by the prep~aked bedloading procedure is shown in Table 4. Included are observations concern-ing flow rates for both actuai and simulant binders through beds of vary-ing density. It is obvious Lhat improvement is needed both to increaseefficiency and produce castings of better homogeneity. However, theeventual advantages of the described system if successful should warrantthe expenditure of additional effort to insure that no reasonablepossibility has been overlooked.

Desensitization During Mixing

Another approach to achieve high solids loading with reduced processinghazard was based on addition of a volatile fluid desensitizer prior tomixing. This nonreactivý liquid could then be removed readily by evapora-tion after the relatively non-volatile DNPA binder was dispersed sufficientlyto wet and desensitize the HMX filler. While no: offering the promise ofas high ultimate loadability perhaps as Lhe prepacked bed method, thelatter, however, appeared to be more readily adaptable for immediate usewith existing equipment on both a small and large scale.

A liquid, to be suitable for the intended application, should have thefollowing characteristics: It should thoroughly wet the IMX and provideadequate interparticle lubrication and cushioning to minimize internalfriction during the mixing process. It should have no solvent effect onHMX to alter particle size. It should be compatible and non-reactive withevery component in the formulation. Preferably, it should be non-flammableand have high heat capacity, and lastly, it should be cheap and readilyavailable. The latter two characteristics are of secondary importancesince recovery and reuse could be readily accomplished.

For initial evaluation a number of liquids were examined in thelaboratory by mixing with weighed quantities of HMX and subsequently add-ing DNPA binder. Vacuum and heat were then applied to remove the volatileliquid. When evaporation appeared to be essentially complete, time unddifficulty of removal was noted and the remaining HMX/DNPA mixture wascured by conventional procedures. The effect of the process and theadditive on the cured composition was then roughly assessed. The liquids

CONFIDENTIAL 17


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CONFIENTIA

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ItIwhich appeared the most promising were then further tested in 150 grambatches with production-type mixing and casting apparatus. Proceduresare summarized in Appendix C and preliminary observations in Table 5.

Two liquids, dichloromethane and low boiling petroleum ether (exceptfor its low flash point) were especially promising. Freon 113 alsoappeared feasible. However, larger scale tesLing of the latter additivewas postponed pending more complete evaluation of the first two. Both ofthese, on scale-up (Table 6), provided excellent fluidity (uring mixing,were readily removable, and did not visibly affect curability and physicalproperties. Resulting castings were solid, dense, and strong. Further-more, VTS at 150%C and detonation velocity tests failed to reveal anydegradatory effects. Additional work is in progress to more fLllyevaluate the sensitnvit- of the wet mixes at various stages dLuingprocessing.

Success with dichloromethane and ligroine points to the advisabilityof evaluating additional liquids which might offer further improvement.For example, one which was miscible with water would facilitate directuse of MX which is normally shipped water-wet. Also monomeric liquidswith the DNPA binder thus reducing the possibility of void formation

during cure or excessive and non-homogeneous plasticization after cure.*• Small residual traces of such comonomers should not be sufficient to

affect the explosive energy of the final composition.

HMX PARTICLE SIZE DISTRIBUTION. Optimization of HMX particle size* - to obtain maximum solids loading consistent with processability was

described in detail in an earlier report (Ref. 2). Additional work inthis field, although comparatively limited, has tended to confirm andsubstantiate the earlier findings. In recent preparations those particlesize distributions found most promising in the initial studies weregenerally used. Little or no difficulty was experienced in mixingcompositions containing up to 87.5% filler when size distribution wasoptimum and volatile liquids were employed.

As concluded previously, either a 35/10/55 or 25/10/65 20p-Class A-Class D blend respectively produced the best overall results with DNPAbinder and conventional mixing and casting techniques. RTising thepercentage of coarse material resulted in greater fluidity with, however,graininess and inferior flow characteristics. Increasing the ratio offines made the composition softer and more readily extrudable but alsolimited the solids loading by reducing fluidity. Recent formulationscontaining optimum distributions combined with DNPA-based binders havebeen described in Table 6. As predicted earlier, solids loadings of87% are processable when the distribution is carefully controlled.

CONFIDENTIAL 19

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CONFIDENTIAL 21

NOTS TP 4387 CONFiDENTIAL

Bulk density was found to correlate ree-unably well with process-ability in highly filled HMX/binder compositions, with the 35/10/55 and25/10/65 blends yielding the highest values. Several years ago (Ref. 3)attempts oere made to predict the processability of 20p HMX lots used inPBXN-)01 preparation by comparing their bulk densities. In this instancecorrelation was poor.7 However, in cases where size ranges are moreextreme, the relationship apparently becomes more evident and the testmay be useful in. providing a short-cut for optimization. Examples ofthe correlation are shown in Table 7. Additional studies along theselines may serve not only to further improve processing and loadabilitybut may also prove of advantage in quality control of HMX blends used toprepare highly filled production compositions.

MODIFICATION OF THE DNPA BINDER

Copolymers With Fluoroalkyl Acrylate

Preliminary small-scale experiments with DNPA and octafluoropentylacrylate (C5A) indicated that successful copolymers could be preparedand used as binders for HMX-filled compositions (Ref. 2). A formulationcontaining 80% HMX with DNPA/Cs, binder, respectively 3:1, cured to adense, void-free solid with good physical prop rties and good stability.

Since a higher F/C ratio might be advantageous from the standpointof density and energy, two longer chain fluorocarbon monomers were morerecently investigated, and their properties compared with those of thefive carbon chain derivative. Initial small scale results are s ,wn inTable 8.

Although the C9 monomer was superior in respect to fluorine content 8

and binder density, its poorer processing characteristics tended tonullify these advantages by reducing solids loading. Also phys'calproperties were inferior. Therefore, the C7 acrylate was selected as themost feasible compromise for scale-up evaluation. Properties of a 150gram formulation containing this monomer are also described in Table 8.Detonation velocity is essentially the same as that of DNPA homopolymerwith comparable HMX loading.

7 Twenty micron lots produced varying degrees of fluidity whencombined with 100pI H•MX and Laminac EPX 147-2 in PBXN-IO,. Several methodsof size determination as well as measurements of bulk density failed toreveal the reason for processing differences. Size as measured by Buckbee-Mpars screens was later found to correlate with performance (Ref. 7).

8 The fluorinated monomers used in these studies were all acrylateesters of a, a, w-trihydro alcohols. One means of introducing morefluorine into the binder might be to substitute perfluoro derivatives.

22 CONFIDENTTAL

CONFIENTIAL NOTS IP 4387

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CONFIDENTIAL

f 24


Further studies are planned based on fluorocarbon compositions, inparticular, -,,;tallized ones, and theoretical computations are presentlybeing conducted in an attempt to optimize compositions. The results ofthis work will be reported at a later date.

Copolymers With Difluoroaminopropyl Acrylate

Compounds containing the -NF2 group have come into increasing

prominence during the past few years in propellant applications (Ref. 8and 9). Although promising in respect to energetic properties, theirmain drawback has been extreme sensitivity to impact and friction. Oneexccption is 2,3-bis(difluoramino)propylacrylate (NFPA) which nas animpact value approaching that of TNT.

NFPA was developed by Rohm and Haas Company and is presently beingsynthesized by this organization in production quantities. Some of itsproperties are listed in Table 9. Its chemical structure as well as itsphysical characteristics immediately suggest its applicability as abinder in castable explosive formulations, since it is a low viscosityliquid curable to a relatively hard and strong solid, with high density,favorable potential energy, and heat stability similar to that of DNPA.One drawback might be a high polymerization exotherm; however, in highlyfilled cumpositions where the filler could act as a heat sink, thisproblem should be minimized, especially if curing is carried out slowlyat low temperatures.

Ruby calculations were performed to predict the potential enei gyobtainable from formulations based on NFPA and HMX. Figure 6 shows sixsimplots for a three-component system containing HMX filler and DNPA/NFPAin varying ratios. Detonation velocity, peak pressure, face-on platepush (FOPP) and side-on plate push (SOPP) are plotted as functions ofcomposition. Methods of computation and their theoretical bases havebeen described by Dierolf in relation to the present project as well asearlier work at NOTS (Ref. 11, 12).

Study of the simplotb shows that at the 85% HMX level there is littleoverall advantage in substituting NFPA for DNPA. Side-on and face-oaplate push relative to PBXII-101 show NFPA superior to DNPA by 1-2%; how-

ever, other detonation properties are essentially the same for the twobinders.

Experimental studies were undertaken to verify the Ruby calculations.For preliminary evaluation one gram binder formulations were preparedcontaining DNPA/NFPA 1:1, 1:3, 3:1 and 0:1 respectively. These weremixed with curative systems used for DNPA and for safety and convenience,were cast and cured in Teflon "mini-molds" (Fig. 7). All four binderconstituent ratios resulted in similar products, clear, solid, amber-colored polymers wiLh slight flexibility.

CONFIDENTIAL 25


'AT~ A nT Ve n n-- 1fA SMot-ouc

Formula 2,3-bis(difluoramino)propylacrylateCH2 (NF2 )CH(NF 2 )CH2 0 C 0 CH = CH2

Physical appearance Low viscosity liquid curing to toughsolid similar to DNPA

Molecular weight 216

Density, g/•ca 1.25, 25-C

Freezing point, -Ca 75

Vapor pressurea 1 mm, 20°C

Heat of Formation, Kcal/Molea -109.28

ND2 0a 1.4070

\DTA, peak exotherm, °C 2 2 7 a at 10°C/minute heat rise218b at 2-3°C minute heat rise

Impact sensitivity, 50% pt. 35 Kg-inches, Picatinny methoda40-60 cm, monomer, NOTS methodb

63 cm, polymer, NOTS method

Friction sensitivity, 10 ZILd 1,000 lbb

Eleccrostatic sensitivity, 10/10 no firesb

12.5 joules

a Reference 9.b Evaluated by NOTS.c Composition B 36 + 3 cm, TNT = 70 cm.d ABL sliding friction (Ref. 10).

Two of the binders, the 1/1 and 100% NFPA compositions,were thenformulated with HMX, 30/70 respectively to determine compatibility.Sensitivity tests and DTA indicated results similar to those for HMX/DNPAalone. Furthermore, an HMX/NFPA sample of larger dimensions (0.5"D x 3"H)cured in a 60 *C oven evidenced no detectable polymerization exotherm whenthermocouples were embedded in the casting.

2I

26 CONFIDENTIAL

I


I |

DNPA 30% ONPA 30%/o

B,200- 300

9,300310

76% HMX 6,400 0% NFPA 70/ HMX - 320 0% NFPA

8, 7 0 0 I X A t l V ' / / / J • 3 6 0

NFPA 0% ONPA HMX NFPA 0% ONPA HMX30% 0oo10% 30% o00%

DETONATION VELOCITY, M/SEC C-j PRESSURE, K BARS

ONPA 30% ONPA 30%

1 08 I110 \I.08

11270% HMX K 0%/a NFPA -416% HM 110 0%6 #FPA

/ 116

NFPA 0% DNPA HMX NFPA 0% UNPA HMX30% .00% 30% 100%

FOPP, V3L, RELfTIVE TO PBXN-01 FOPP, WT, RELATIVE TO PBXN-,0I

ONPA 30% DNPA 30%

03.1.1

700A HMX 0% NFPA 70% HMX 0% NFPA

- 114

NFPA 0% DNPA HMX NFPA 0% DNPA HMA30% 100% 30% goo%

SOPP, VOL, RELATIVE TO PBXN-IO SOPP, WT, RELATIVE tO PBXN-IOI

FIG. 6. The Effect of Composition on Explosive Properties.HMX with DNPA and NFPA Binders. Ruby Calculations, 98% TMD.

CONFIDENTI.AL 27


The 1:1 composition was scaled up to 150 grams to obtain samplesfor further characterization. The formulation was prepared withoutincident; processability was excellent, curing was effected withoutdifficulty, and :z•sulting castings were strong, dense, and free fromimperfections. T-ble 10 summarizes the properties of this compositionand compares theri with those of an analogous formulation containing DNPAas the primary binder constituent. Although experimental results forthe detonation velocity of these compositions range slightly higher thancomputed values, the comparative figures, as predicted, are essentiallythe same. The composition containing NFPA, however, is inferior inrespect to thermal stability.

4N

IN

FIG. 7. "Mini-Molds" for Curing Castable Compocitionsof Questionable Hazard Together With Ejected Castings.

28 CONFIDENTIAL

TAL 100. of HMX/DNPA-NFPA Compared w 437h

Those of HMX/DNPA

Composition HMX/DNPA-NFPA HMX/DNPA

Binder comp % 48 DNPA, 48 NFPA, 4 ATAC 95 DNPA, 5 ATAC

Curing agents 0. 1% CoAA, 0.5% ea tBPB- 0.2% DMA, 0.5 76tBHP ea tBPB-tBHP

Curing conditions 60°C overnight 60°C overnight+80°C 24 hr

HMX content, 7o 85.2 85.2

HMX distribution, % 35-20/1, 10-class A, 55-Cl D 29-204, 14-class A,57-Cl D

Processability Excellent, readily castable Wet but difficult toW!• cast

Appearance of Solid, tough, sl resilient Slightly porous due

castings to poor castability

Density, g/cm 3 .799 - 1.817 1.798 - 1.807

DTA exotherms, °C 143, 224 204, 256Peak 267 270

Autoignitionexotherms, °C 167-175, 185-187, 209 218

Ignition point 227 226

SVTS, 150°C 5.3 cc/g/24 hr 3.4 cc/g/4 8 hrar A2.2 cc/g/24 hr

SThermoplasticity, Approx 5% deformation None observable1506C ambient to 150'C to

ambient in 5 hr

Det vel m/sec0. 5 in. 1) 8512 8517

Plate dent, in.0.5in. D 0.11 0.11

Impact sens 50%.,pt cm 32 28

Friction sens 10/10 no fires, 1300 lb0 1/10 fires at440 lb

Electrostatic sens 10/10 no fires, 12.5 joules 10/10 no fires,12.5 joules

aMay be slightly high, C aAA not us ad.

bThis was measured on a separate sample, same binder but 80%HMX.

CONFIDENTIAL 29

%I


ULLLL D.LLUCK MUU1LJ.VeS

ALIVL TRIFLUOROACETATE. Ehis monomer contains less fluorine (37%)than the trihydrofluoroalkyl acrylates previously described. However, atpresent it is less costly and more readily available; thus it was examinedfor possible inclusion in DNPA systems. Four binder compositions weleprepared with DNPA, 1:1, 3:1, 1:3, and all fluoromonomer. Failure tocure resulted in all cases, even with 80°C temperature. 2-3 day exposures,and CoAA present. Vinyl trifluoroacetate, like the allyl derivative,failed to cure and also showed definite evidence of incompatibility.

FEFO. 2,2-bis(dinitrofluoroethyl)formal (FEFO), a non-reactiveplasticizzr. was evaluated with DNPA and NFPA monomers because of itspossible favorable contributions to energy, density, and low temperaturephysical properties (Ref. 13). However, like the vinyl and allyl tri-fluoroacetates, it inhibited curing. Even under fairly stringentconditions of time, temperature and atmosphere, mixtures of FEFO withDNPA, NFPA, or EPX 147-2 failed to cure to desirable consistency.

BDNPF/BDNPA, like FEFO, inhibited curing, and resulting physicalproperties were unacceptable. Compositionj with both DNPA and EPX 147-2failed to polymerize adequateJy.

Cross-Linking Agents

Poly-DNPA, when heated to 60-80°C, becomes soft and semifluid. Itis therefore necessary in formulating compositions for high temperatureuse to add a cross-linking agent to prevent plastic deformation. [nitialstudies (Ref. 2) showed that acetyl triallylcitrate in concentrations of3-5% was effective in maintaining dimensional stability under load up to150 0 C. Diallyl diglycolate, glycol bis-allyl carbonate, ethylene dimeth-acrylate, triethylene glycol dimethacrylate, an( triallyl cyanurate werealso examined and found inferior to ATAC.

Difficulty and expense in procuring ArAC led to investigation ofadditional possible substitutes. The ::esults of these studies aresummarized in Table 11.

Promising additives were evaluated at both 2 and 5% concentrationsin order to estimate minimum required levels. Autoignition tests andvacuum thermal stability measurements were carried out to verify compati-bility. Resistance to thermoplastic deformation was determined by the100 gram weighted piston test described in a previous report (Ref. 2).

Tetramethylene diacrylate appeared to be even more effective thanATAC, with hard and stable compositions obtained at both 2 and 5%concentration levels. Diallyl maleate was inferior to both ATAC and thediacrylate in that higher concentrations were required to be effective,a disadvantage energywise. Triallyl cyanurate, on reevaluation, showed

30 CONFIDENTIAL

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questionable compatibility at 1500C test temperatures. Diallyl etherfailed to provide the desired dimensional stability, and the remainingcomonomers, tetramethylene dimethacrylate, triallyl orthoformate, tri-crotyl orthoformato, and divinyl benzene inhibited cure.

STABILIZERS FOR HMX/DNPA COMPOSITIONS

One of the main requirements for a new high energy explosive is thatit be sufficiently heat stable to withstand aerodynamic friction generatedunder supersonic conditions of flight. A temperature of 1500C has beenspecified as an arbitrary minimum goal. To predict whether a givenweapon will withstand certain environmental conditions for a given lengthof time without undergoing deterioration which might impair efficiency orexpose personnel to hazards, basic data need to be known such as massand heat transfer characteristics of the weapon as well as decompositionconstants for the explosive itself. The latter can be determined bymeans of differential thermal analysis employing several rates of heatingand then evaluating the resultant thermograms. These techniques havebeen used to predict safe exposure conditions for both propellant andexplosive charges of a given composition (Ref. 14, 15).

Preliminary evaluation of HMX/DNPA because of the large number ofsamples and variations involved, was limited to relatively short testprocedures such as standard DTA, autoignition, VTS, and TGA. Thesemethods were useful in that they afforded a rapid and convenient meansof comparison for preliminary screening purposes. However, since result-ing values are dependent on environmental variables such as sample sizeand heating rate, more refined techniques will eventually be necessaryin order to predict safe conditions for a given charge in a given weapon.When selection of a definite composition and application warrants, morecomplete evaluation may be undertaken.

Preliminary small-scale testing of the HMX/DNPA system has indicatedthat stability at 150°C is good provided exposure times are not tooexcessive. For example, samples used in thermoplasticity tests showedonly slight darkening in color after exposure.9 DTA and autoignitiondata indicated decomposition exotherms started at about 1800C but werethen interrupted by the HMX endothermic crystalline transition so thatfinal ignition did not occur until the reference temperature reached 220-2250C. Gas evolution and weight loss at 1500C were affected to a largeextent by the degree of DNPA polymerization. Respective values averaged5-7 cc/gram and 3 to 6% over a 48 hour period in initial tests. WhenCoAA was used to facilitate cure, these values were reduced by nearly 50%.

In attempts to further improve the heat resistance of DNPA compo-sitions, a number of different stabilizing agents were added to thebinder at concentrations of 2 and 5%. These included: 2-nitrodiphenyl-

9 4-5 gram cylinderapprox. 30 min to reach 150*C, then cooled toambient over 2-3 hour period.

32 CONFIDENTIAL

CONFIDENTIAL NOTS TP 4387.

amine, ethyl centralite, Estynox 308, Plastolein 9232, graphite, sodium 5fluoride, sodium chloride, trlsodium phosphate, calcium fluoride,magnesium oxide, 4-dimethylamino-3,5-dinitroaniline, and a 50/50 mixtureof Estynox-Plastolein. Some of these materials have been found effectivein stabilizing propellant formulations containing either nitro or di-fluoroamino polymers (Ref. 16).

Detailed results of DTA, TGA, and VTS tests performed on compositionsformulated with the various additives are presented in Table 12. Sincethis work was conducted over a relatively long period of time, extracontrols containing no additive were included to afford a better compari-son. The main conclusion that can be drawn from studying the results is

that none of the additives were effective in improving stability. A few,namely: graphite, sodium chloride, possibly sodium and calcium fluorides,and magnesium oxide appeared to be compatible. The remainder eitherinhibited cure, accelerated gassing and weight loss, or produced DTAand autoignitiorn exotherms at relatively low temperatures. The mostsignificant stabilizing factor found thus far is, as was shown earlier,the curing agent CoAA.

COATING H!MX WITH POLY DNPA

Preliminary studies were carried out to determine the feasibility ofcoating IX with DNPA polymer. The objective was two-fold: First, toprovide a possible means of desensitizing HM prior to incorporation incastable mixes with DNPA monomer and, secondly, to prepare a compositionsuitable for processing as a high-energy extrudable explosive. Sincepoly-ONPA is soluble in the monomer, its use as a precoating agent should

S'offer some interesting possibilities for formulation without as great asacrifice in energetic potential as that introduced by comparable inertadditives.

Initial work was confincd mainly to preparative techniques andhazard evaluation of 85/15 HMX-DNPA mixtures for extrusion. Poly-DNPAdissolved in either ethyl acetate or acetone could be precipitated tocoat HMX by addition oi either water or aliphatic hydrocarbons. The twomajor difficalties were obtaining homogeneous coating and desirableagglomerate particle size. The most promising procedure involvedprecipitation of DNPA dissolved in ethyl acetate onto HMX in an aqueoussuspension. Descriptions of some typical products are summarized inTable 13. Sensitivity tests indicate that poly-DNPA applied as a pre-coat does afford some desensitization at the 15% level; however, itsefficiency at lower concentrations has not yet been established.Additional sensitivity studies, extrusion results, and use of DNPA coatedHMX in castable formulations will be described in a future report.

CONFIDENTIAL 33

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TABLE 13. Properties of HMXa/poly-DNPA Slurry-CoatedCompositions

p-DNPA in Ethyl Acetate p-DNPA in AcetoneObservations HMX in Water HMX in Petroleum ether

Precipitation Discrete granules becom- Immediate coagulationCharacteristics ing one soft tacky mass to form one soft tacky

after approx. 85/15 level massHMX-DNPA

Properties of dried Forms hard mass unless Forms hard, tough massproduct broken up mechanically unless broken up prior

prior to drying to drying

Analyzed % DNPA 14.49 15.66Spread (4 samples) 0.14 0.75

Impact Sensitivity, 31 2950% pt cm

Friction Sensitivity 1300 lb 1300 lb10 ZILb

Electrostatic Sensi-tivity, 12.5 joulescl0/l0 no fires 10/10 no fires

a 1:1:1 20P/lO0/Class D.b ABL method (Ref. 10). RDX = 300 lb.c Maximum limit of test instrument.

NOTE: See Appendix D for formulation procedure. Test methods aredescribed in Appendix E.

CONFIDENTIAL 35

.m 4f "


SUD-*iAKi AND CONCLUSIONS

Significant advances in the development of HMX/DNPA compositionswere: higher energy obtained by better processing techniques and simplifi-cation of curing resulting from use of CoAA and monomers with low inhibitorcontent. Modifications in mixing methods not only resulted in greatersafety by insuring more complete wetting of 1MX but also permitted handlingmixes containing nearly 88% explosive filler. Cobalt acetyl acetonateproved to be a valuable additive in promoting more effective cures.Curing times, temperatures and conditions were greatly reduced and simpli-fied. Furthermore, tolerance for impurities such as residual inhibitorwas improved and monomer which was inhibited sufficiently to withstandthree months at 50%C could be adequately cured without prior washing ordistillation. CoAA-cured compositions not only were stronger and harder,they also evidence greater heat stability presumably through reductionin loss of free monomer.

Two new binders were formulated bascd on combination of DNPA with C7fluoroalkyl acrylate and difluoramino propylacrylate. Resulting polymerswere clear, solid, strong, and slightly flexible. When formulate l with85% HMX, these binders showed approximately the same explosive potentialas that of DNPA homopolymer. This experimental observation verifiedtheoretical computations which predicted negligible changes in energyresulting from inclusion of NFPA.

DNPA monomer obtained over a period of several years from varioussources was found to be consistent and curable in all cases to excellentend products of comparable strength and stability. Acceleratedsurveillance tests to determine minimum inhibitor levels as well asexperience with routine storage of purified monomer over a period ofseveral years indicated that excellent shelf life may be anticipated with-out excessive amounts of inhibitor requiring removal by laborious methodsprior to final processing.

RECOMMENDATIONS FOR FUTURE WORK

Planned work falls into two general categories: Further improve-ment of the present HMX/DNPA composition, and investigation of new butrelated systems.

In the first area, additional methods are being sought to evaluateexplosive effectiveness (Ref. 17). This approach should prove of interestnot only in better characterizing the DNPA formulation but also infurther correlating theory with actual performance.

Attempts should be continued to increase solids loading withoutsacrificing processability. Previous experience indicates that use ofdesensitizing liquids in mixing combined with optimizing HMX size andshape may permit up to 88-89% filling which is probably maximum for thisapproach. Increases of several percent, however, may be possible by

36 CONFIDENTIAL

I


the possibl contribution of new additive admifatosnbnder

may well result in raising detonation velocities to 8700 meters per

second or even slightly higher.

Poly-DNPA may be used to good advantage as a binder for extrudableexplosives and possibly propellants as well. Although this applicationis somewhat outside of the scope of the present project, the propertiesobserved for DNPA suggest its applicability. Its thermoplasticity wouldpermit processing at low temperatures. Its inherent energy would provideconsiderably better explosive potential than afforded by inert bindersnow in use. Furthermore, experiments have shown that it can be success-fully coated on HMX in both aqueous and non-aqueous slurries to producea molding powder with sensitivity similar to that of tetryl.

Calculations are presently being performed to predict the effect ofmetals such as aluminum in systems containing HMX or RDX with DNPA, NFPA,and C7 A. Solids loading in these cases should be excellent due to theshape and surface characteristics of the metal additive. Initial studiesthus far indicate no compatibility or processing problems.

Further studies should be carried out to better characterize thestability of HMX/DNPA formulations compounded under the most favorableconditions known at present. Such factors would inclode optimizationof both curing environment and composition, including choice of curative,crusslinker, and stabilizer. Sufficient basic data should be obtainedregarding decomposition rates and physical constants so that stabilitymay be calculated over a wide range of environmental conditions.

In the area of new binders, attempts are being made to optimize ahigh-energy structure by minimizing CH2 groups and raising the percentageof NO2 and F. This involves the synthesis of new unsaturated esters toreplace DNPA, serve as copolymers for DNPA, or precoat HNX. Examplesmight be dinitropropyl maleate or fluorodinitroethyl acrylate. New NF2derivatives might also be included in this study, sensitivity andstability permitting. Also solid oxidaijts and dense additives willcontinue to be investigated. Thus, by a combination of approaches--higher solids loading, more energetic binders, and better stabilization--it is anticipated that still further improvement of the existing HMX/DNPAsystem may result, leading to both a superior explosive end better under-standing of explosive phenomena.

CONFIDENTIAL 37


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38 CONFIDENTIAL


APPENDIX A

PURIFICATION PROCEDURES FOR DNPA MONOMER

1. Caustic Wash

100 ml of DNPA was placed in a 250 or 500 ml separatory funnel.10 ml of the following solution was added and the mixture shaken

well:

100 ml H2 020 g RaCl5 g NaOH

The top layer was discarded and the extraction repeated up tothree times.

The DNPA was then treated with six 53-ml distilled water washes,dried over anhydrous MgSO4 for two days, then tiltered and stored underrefrigeration.

2. MgO Extraction

100 ml DNPA and ) g MgO were agitated for three hours.The MgO was then filtered off and the DNPA stored under refrigeration.

3. Caustic Wash Plus MgO

DNPA washed twice with caustic solution and six times with waterfollowed by MgSO drying was stirred with MgO for 2-3 hours. The MgOwas then filter off.

4. Distillation

DNPA monomer was vacuum distilled twice at 1-2 mm pressure withsteam as heat source. Boi½i•g point: 62-78*C.

CONFIDENTIAL 39


APPENDIX C

PREPARATION OF COMPOSITIONS

Preliminary laboratory-scale formulations were hand-mixed in eitherone or ten-gram batches by combining premixed binder with HMX requiredto make a 20/80 composition respectively. The product wi. then loadedinto Teflon molds, vibrated, and cured either in closed nitrogen-filledvessels or directly in ovens.

Larger batches uri to 150-.200 grams were prepared remotely in aBakcr-Perkins model 2-PX one-pint mixer as described in Ref. 2. Slowmixing speeds were employed until the HMX was wetted by the binder

and/or the desensitizing liquid if the latter was included in theformuletion.

To remove volatile desensitizers 50*C heat and vacuum were appliedwith additional evacuation during final stages of mixing and casting.The composition was cured in 0.5-in. by 3.0-in. cylirderical Tpflonmolds with vibration during casting to facilitate compaction.

40 Co NFIDENTIAL

SCONFIDENTIAL NOTS TP 4387

APPENDIX D

SLURRY PROCEDURES FOR PRECOATING HMX WITH POLY-DNPA

Variations of the following basic procedure were used to prepareHMX coated with 5 and 15% poly-DNPA.

The DNPA was dissolved in solvent, either ethyl acetate or acetoneor a combination.

HMX and water were introduced into a three-necked flask fittedwith dropping funnel, "Tru-Bore" stirrer, and vacuum inlet.

The DNPA was added dropwise to the agitated HAx suspension.

A steam bath was then placed under the assembly and heat andvacuum were applied to remove most of the organic solvent.

The resulting coagulant was filtered off and dried in an airstream at ambient or slightly elevated temperatures.

T,

4

CONFIDENTIAL 41

34


APPENDIX E

TEST PROCEDURES

Autoignition

One gram samples heated in metal block at rate of 2*C per minute.Ignition temperature recorded as temperature of block when differentialthermocouple to sample indicates final exotherm.

Vacuum Thermal Stability

2.5 to 3.0 gram samples. Gas volume emitted during first hour wasrecorded and sample was then reevacuated. Zero time for given datastarts after reevacuation. Details are in Ref. 18.

Differential Thermal Analysis

14-53 mg samples heated at 2 to 3.5 0 C per minute.

Impact Sensitivity

35 mg samples, 2.5 Kg weight, with sandpaper and equipment describedin Ref. 18. Samples are pelletized where feasible. Composition B50% point by this method is 36 + 3 cm and FMX is 18-22 cm.

Friction Sensitivity

The ABL method for sliding friction was used. By this method 10 ZIL

(10/10 no fires, zero initiation level) for RDX is 300 lb, for 75/25

Octol 700 lb, for tetryl 700 lb, and for Composition B - 1000 lb. Detailsare described in Ref. 10.

Thermoplasticity

A cylindrical specimen 1/2-in. in diameter by 2-3-in. high is placedin a graduated cylinder with a 100 gram weighted piston resting on thesample (Ref. 2). The assembl; is immersed in an oil bath behind a shieldand the temperature is raised to 150*C within a 20-30 minute period.The temperature at which any deformation occurs is noted. The sample isthen cooled to ambient and any further deformation noted.

Electrostatic Sensitivity

50 mg samples, I pFd capacitor, variable voltage to 5000 maximum,(12.5 joules) 25 sbots per test.

42 CONFIDENTIAL


BIBLIOGRAPHY jAmerican Cyanamid Co., Research and Development on New High Energy

Explosive Compounds, Stamford, Conn., May-July, 1965.(Contract N60921-7186)

Hercules, Inc., Bacchus Works, Mixing of Highly Sensitive Solid Propel-lants (U), Magna, Utah. (Interim Report IR-8-246(l)), Oct. 1966.

Minnesota Mining and Manufacturing Company, Chemical Research as Relatedto Advanced Solid Propellants, St. Paul, Minn. Apr - June 1962,(3M Report No. 13, Contract NOrd 18688).

Rohm and IHaas Company. Properties of a New Acrylic Monomer, byK. E. Johnson, Huntsville, Ala., July 8, 1966, Report No. S-103.

--------- Quarterly Progress Report, Redstone Arsenal, Huntsville,Ala., July 15, 1962. Report No. P-62-12.

Sax, N. I., Dangerous Properties of Industrial Materials. Reinhold,New York. 1965.

U. S. Naval Ordnance Laboratory. Compounds Containing the TerminalFlu--odinitromethyl Group, by M. J. Kamlet, White Oak, Maryl'nd,2-14--59 (NavOrd Report 6207.)

U. S. Naval Ordnance Test Station. Tabulated Results of DetonationCalcalations for Novel Condensed Explosives (U), by A. J. Dierolfand D. M. Reuben, China Lake, Calif., Sept. 1966 (NavWeps 8625NOTS TP 3656).

--------- Bureau of Naval Weapons Purchase Description, Explosive,Plastic-Bonded, Cast; PBXN-101, China Lake, California, 2-24-64,(WS 3829).

CONFIDENTIAL 43

|I

4


REFERENCES

I. U. S. Naval Ordnance Test Station, China Lake, Calif. Correspondence,H. J. Gryting to University of California Lawrence Radiation Labora-tory, Ser. 0696, 4541/HJG:bw, 5-27-58.

2. -------. High Energy Castable PBX (U), by B. A. Stott, China Lake,Calif., NOTS, Oct. 1966 (NOTS TP 4106).

3. -------. PBXN-101, A Heat Resistant, Castabie Explosive for Fragmen-tatioti-Type Warheads (U), by B. A. Stott, E. F. Wiebke and H. D.Stanton, China Lake, Calif., NOTS, Nov. 1964 (NAVWEPS Report 8597,NOTS TP 3612).

4--------. Monthly and Quarterly Activity Reports, InternalCommunications, NOTS, 1960.

5. Boelkow-Entwicklungen, KG, Lie, Herstellung Von Springladungen nachVerschiedenen Giessverfahren, Bericht ueber das Projekt: 1.301,0-00-21.301.5-00, Schrobenhausen (Germany). 12-31-63. Restricted.

6. Ua S. Naval Ordnance Test Station, China Lake, Calif. Preparationof Explosive Charges by Use of Various Casting Processes (U), trans-lated by P.W.K. Dietrichson, China Lake, Calif., NOTS, Oct. 1966(1DP 2653). Restricted.

7. Holston Defense Corporation, Kingsport, Tenn. Private Communication,Test Results for Buckbee-Mears Determinations, Sep. 1965. UNCLASSIFIED.

8, Midwest Research Institute, Kansas City, Mo. A Critical Review ofthe Chemistry of Advanced Oxidizers (U), Vols. I and II. Dec. 1965.(Contract DA-31-124-ARO (D)-18 Mod No. 223)

9. Rohm and Haas Company, Reds:o:.e Research Laboratories, Huntsville,Ala. Production of NF Chemicals for Advanced Research ProjectsAgency (U), by J. W. Parrott (Report No. S-11).

A

10. Hercules Powder Co., Cumberland Maryland. Hazards Evaluation of theCast Double Base Manufacturinag Process. Dec. 1960. (ABL/X-47, U. S.Navy Bureau of Ordnance, Contract NOrd 16640). UNCLASSIFIED.

11. U. S. Naval Ordnance Test Station, China Lake, Calif. Ruby Calcula-tions for High-Energy Castable Plastic-Bonded Explosives (PBX) (U),by A. J. Dierolf. Nov. 1966, (NOTS TP 4105).

12. ------- FOPP and SOPP Velocity Predictions for the Cast PBX Systems,2-DNPA/NYPA/HMX Relative to PBXN-101, by A. J. Dierolf. InternalCommunication, Reg. 4541-j8-67, 3 Jan 1967.

44 CONFIDENTIAL

I


13. U. S. Naval Ordnance Laboratory, White Oak, Maryland. CompoundsContaining the Terminal Fluorodinitromethyl Groups, by M. K. Kamlet,White Oak Maryland, 3-26-62 (NOL-TR-62-43).

14. U. S. Naval Ordnance Test Station, China Lake, Calif. PredictingPropellant Safe Life, by J. M. Pakulak (NAVWEPS Report 7775).

15. ------. Investigation of the Thermodynamics and Reaction Kineticsof Large Propulsion Systems (U), by J. M. Pakulak, China Lake, Calif.April 1964 (NAVWEPS Report 8388).

16. Aerojet-General Corporation, Sacramento, Calif. Research in HighEnergy Propellant Ingredients, Jan. and April, 1966. (Report Nos,0950-81Q-3 and 0950-81Q-!.)

17. U. S. Naval Ordnance Test Station, China Lake, Calif. New ExplosiveEvaluation Techniques and inergy Release Studies (U), by C. D. Lind,J. C. Whitson, and C. T. Mitchell, China Lake, Calif. Nov. 1966.(NAVWEPS Report 9019, NOTS TP 4006, ATL-TR-65-71.)

18. ------- Standard Laboratory Procedures, Part I. Stability,Sensitivity, Physical Properties and Analyses for High Explosives,by 0. K. Pennington, China Lake, Calif., Aug. 1961 (NAVWEPS Report7764, NOTS TP 2746). UNCLASSIFIED.

CONFIDENTIAL 45

CnN1PTnRNTTAT.

Security Classification

fDCCUMENT CONTROL DATA- R&D[ Seour*ty classification of title, body of abstract and Indexing annotation must be entered when the overall report lassified)

I ORIGINATIN G ACTIVIIY (Corporate author) 20 REPORT SECURITY CLASSIFICATIONU. S. "Nava•.•l .=,•- .....nc Tc^^st Stto r.•.•••,ONFIDENTIAL

China Lake, California 2b GROUP4

3 REPORT TITLE

CASTABLP E2MLOSIVE COMPOSITIONS BASED ON DINITROPROPYLACRYLATE AND HMX (U)

4 DESCRIPTIVE NOTES (Type of report and Inclusive dates)

Technical Progress Report

5 AUTHOR(S) (Last na•n, first name, initial)

STOTT, Barbara A.

6. REPORT DATE 7s. TOTAL NO OF PAGE, 7b. NO. OF RE•S

June 1967 45 18

65 CONTRACT OR GRANT NO. 9a ORIGINATOR'S REPORT NUMBER(S)

bPROJECT NO ORD-033-201/200-I/ NOTS TP 4387

F009-08-05c9 .OTHER R IO T

hb. the repoPORT NO(S) (Any other numbers diat may be assigned

10 AVA ILABILITY/LIMITATION NOTICESIn addition to security requirements which apply to this document and must be met,each transmittal outside the Department of Defense must have prior approval of theU.S. Naval Ordnance Test Station.

11. SUPPLEMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY

Naval Ordnance Systems CommandNaval Material Command

Washington, D., C 2036013. ABSTRACT

ABSTRACT. The castable explosive, HMX/dinitropropylacrylate, was improved byformulation modifications tc obtain higher energy, better physical propertiesand stability, and greater efficiency in preparation. Use of volatile liquidsin mixing operations, special casting techniques, and selection of optimum HMXparticle size blends resulted in solids loadings of 87% and higher withcorrespnnding detonation velocities exceeding 8600 meters per second. Optimizatioof monomer inhibitor concentration made it possible to eliminate pre-processingDNPA purificatior., yet at the same time obtain adequate storage stability. Useof a new curative, cobalt acetyl acetonate, greatly facilitated curing by reducing

time and temperature and eliminating the necessity for oxygen exclusion. Result-ing castings were harder, more uniform, and more stable, with 1500 C VTS values aslow as 2.4 cc/g/48 hours. (C)

Two new copolymers of DNPA were prepared and evaluated as energetic binders, onewith difluoraminopropylacrylate, the other with dodecafluoroheptylacrylate.Detonation velocities, as predicted by computation, were comparable to those forDN-PA homopolymer at equivalent HMX loadings. (C)

DD,1 AN I 473 0101-807-6800 CONFIDENTIALSecurity Classification

I • m mN m • • mm mN m•m i •2

,*'T TDIVTITT A-Security Classification"' 14 ......... LINK A LINK 8 LINK C '

KEY WORDS .- Iw o. ,T .L ,

High energy explosive LHMXIDinitropropylacrylatePBX (Cast)Detonation VelocityPhysical propertiesPolymerCopolymer

INSTRUCTIONS

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