Binding Interaction Between Dantocol and RDX. Chris Williams. Supervised by Dr Stephen Clarke Co-Supervised Dr Simon Mathew & Dr Ian Lochert (DSTO)

Transcription

1 Binding Interaction Between Dantocol and RDX Chris Williams Supervised by Dr Stephen Clarke Co-Supervised Dr Simon Mathew & Dr Ian Lochert (DST)

2 Introduction Components of polymer bonded explosives (PBX) Function of bonding agents Analysis of interaction between Dantocol and RDX Scanning electron microscope Raman spectroscopy Diffuse reflectance infrared spectroscopy Attenuated total reflectance infrared spectroscopy uclear magnetic resonance Conclusion Future work

3 Polymer Bonded Explosives itramine explosive material suspended in a polymer matrix Desire for increased safety in handling explosives Possess favourable mechanical properties Various constituents added to improve properties Decrease likelihood of detonation due to external stimuli Maintain a precise shape under severe stress High explosive energy Commonly used in military application

4 PBX-109 Investigating components of PBX-109 Forerunner in PBX formulation developed in 1980 s Provide maximum explosive force and minimal sensitivity PBX-109 Components RDX Isophorone diisocyanate Hydroxyl-terminated polybutadiene, -di(2-hydroxyethyl) dimethylhydantoin (Dantocol) 2,2 -methylenebis(6-tert-butyl)-4-methylphenol Dioctyl adiapate Triphenylbismuth Aluminium Function Energetic Filler Curing agent Binder Bonding agent Antioxidant Plasticiser Cure catalyst Metal fuel ominal Weight %

5 Bonding Agents Bonding agents utilised to overcome problem of dewetting Improve bonding through filler reinforcement Upon inclusion to a PBX formulation: Adsorbs onto RDX crystals Enables effective crosslinking reaction with binder Prevents formation of voids improved mechanical properties Dantocol example of a commercial bonding agent H 3 C CH 3 H H, -di(2-hydroxyethyl) dimethylhydantoin

6 Dewetting itramine-polymer composites suffer dewetting Caused by due to weak adhesion between nitramine crystals and binders surface of nitramine crystal Isocyanate side reaction with moisture: R C H 2 R H 2 C 2 R C R H 2 R H C H R Bonds fail under stress, allowing binder to break free or dewet nitramine Puts neighbouring particles under stress Void propagates until reaching the filler-binder interface

7 Problems Associated Filler-binder adhesion decreases overtime causing mechanical properties to deteriorate Increasing sensitivity of the PBX to that of a pure nitramine. Voids act as initiation sites for detonation Propellant Systems Causes an uneven burn Motor failure

8 Experimental Aim Analyse interaction between RDX and Dantocol Coating RDX crystals Reporting spectral shifts observed upon coating of Dantocol Determine functional groups responsible for spectral shifts Investigate the strength of the interaction Enabling synthesis of improved bonding agents

9 Coating Technique Heat RDX at 60 o C under vacuum to remove impurities Determine suitable solvent systems to dissolve Dantocol Weigh out samples of RDX and Dantocol 50%, 10%, 8%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5% (w/w) Tumble in centrifuge tube for 3hours Centrifuge at 3500rpm for 45mins Place sample under high vacuum

10 Scanning Electron Microscope Investigate the coating of bonding agent on RDX crystals XL30 Philips-XL30 FEGSEM w EDAX EDS Smooth crystalline surface

11 10% Dantocol Coating High level of RDX coverage Good adhesion to the surface

12 4% Dantocol Coating Less coverage observed Dantocol forms thick, malleable coating

13 Infrared Spectroscopy DRIFT-IR to examine interactions via bond shifts Advantageous for analysing solid samples Coated RDX samples mixed with KBr Ground and analysed in sample tray

14 DRIFT-IR Spectrum Vibrational Bands Vas ( 2 ) CH 2 Vs ( 2 ) + V (-) Ring Stretching ( 2 ) Peaks (cm -1 ) 1593, 1573, , , 1312, 1268, 1234, , 1019, 946, , RDX Asymmetrical stretching vibration KM 0.07 KM Wavenumbers (cm-1) Wavenumbers (cm-1)

15 Samples pre-ground with KBr Sample Grinding Excess grinding removed coating 0.2 RDX 1st Grinding KM RDX 2nd Grinding KM RDX 3rd Grinding KM RDX 4th Grinding KM 0.1 KM RDX 5th Grinding Wavenumbers (cm-1)

16 Peak Shifts Kubelka-Munk RDX + 10% Dantocol RDX cm cm Wavenumber (cm -1 ) Sample V as ( 2 ) CH 3 Ring RDX RDX + 10% Dantacol V Sample cm -1 V s 2 + V (-) Ring Stretching RDX RDX + 10% Dantacol V

17 Peak Shifts RDX & Dantocol 0.5% Dantocol V as 2 (cm -1 ) V as (cm -1 ) % Dantocol 2.0% Dantocol RDX + 10% Dantocol 3.0% Dantocol % Dantocol % Dantocol % Dantocol % Dantocol % Dantocol % Dantocol - - Wavef unct ion ( cm -1 )

18 ATR-IR Attenuated total reflection infrared spectroscopy Several advantages over DRIFT-IR vercomes problem of grinding Less preparation Fewer scans required (256scans 64scans) Reproducible spectra

19 ATR-IR Spectra Sharp Peaks with low noise interference RDX peaks consistent with DRIFT-IR RDX %T cm Wavenumbers (cm-1)

20 RDX and Dantocol IR 80 RDX %T cm Dantocol 80 %T RDX + 50% Dantocol %T cm Wavenumbers (cm-1)

21 Raman Spectroscopy Raman used to compare vibration spectra specifically nitro group Small spectral shifts observed Behaviour consistent with literature itro shifts coincide with FTIR data RDX

22 Raman Peak Shifts Vibration Band RDX V(cm -1 ) RDX + 4% Dantocol V(cm -1 ) RDX + 3% Dantocol V(cm -1 ) V as CH Deformation V s Ring Stretch V Ring Deformation

23 MR Complexation Investigate peak shifts upon increasing equivalency Dantocol Mole ratio RDX : Dantocol 1 : 0, 1 : 0.5, 1 : 2, 1 : 3 1 H MR, 300MHz, CD3C RDX CH ppm

24 MR Titration RDX : Dantocol RDX : Dantocol 1 : : ppm 3.112ppm 2.843ppm 6.17ppm 3.127ppm 2.999ppm RDX : Dantocol RDX : Dantocol 1 : 2 1 : ppm 3.135ppm 2.999ppm 6.19ppm 3.190ppm 3.061ppm

25 MR Complexation 6.20 RDX CH 2 Peak Shift Chemical Shift (ppm) Dantocol Equivanents

26 Hydrogen Bonding Data indicates hydrogen bonding responsible for bonding Between nitro of RDX and hydroxyl functional group of Dantocol H 3 C H 3 C H H RDX Dantocol

27 Synthesis of Bonding Agents Alternate bonding agents derived from Dantocol Used to determine if hydrogen bonding is responsible for interaction 1 st compound substituted hydroxyl group for strong proton donating carbamate 2 nd compound functioned to block the hydroxyl groups

28 Bond Promoting Carbamate Dantocol reacted with phenyl isocyanate under reflux conditions Product separated by column chromatography Characterised by MR and Mass Spectroscopy H 3 C H 3 C H H 2 C 10ml Toluene Heated 24hrs H 3 C H 3 C H C C H, -di(2-ethyl phenylcarbamate) dimethylhydantoin

29 Product Interaction SEM to determine adequate coating DRIFT spectroscopy and ATR consistent with peak change at cm RDX + 10% Bonding Agent %T cm Wavenumbers (cm-1)

30 Tert-butyldimethylsilyl Chloride Protection Dantocol reacted with tert-butyldimethylsilyl Chloride Product separated by column chromatography Characterised by MR and Mass Spectroscopy H 3 C H 3 C CH 3 CH 3 H H Cl Si CH 3 CH 3 CH 2 H 3 C Methlene chloride, Imidazole Heated 24hrs CH 3 CH 3 H 3 C CH 3 CH 3 H 3 C Si Si CH 3 CH 3 CH 3 CH 3 CH 3, -(tert-butyldimethylsilyl) dimethylhydantoin

31 Tert-butyldimethylsilyl Chloride Protection SEM to determine adequate coating DRIFT spectroscopy and ATR produce similar spectra to uncoated RDX Conclusive evidence of hydrogen bonding at the interface RDX + 10% Bonding Agent KM cm Wavenumbers (cm-1)

32 Conclusion RDX coated with Dantacol was analysed using ATR, DRIFTs, Raman, MR Peak shifts indicate the nitro group interacts with hydroxyl group to form a stable complex This was confirmed by synthesis of Dantocol derivatives Prevention of hydrogen bonding by reaction with hydroxyl group Promoted hydrogen bonding by formation of proton donating carbomate

33 Future Developments Further characterisation by analytical methods (MR, spectrophotometry, DSC, TGA) Informatively design and synthesise second generation bonding agents Exploit the understanding the molecular interactions to design highly sensitive explosive detection devices

34 Reference 1. Hamshere, B.L., Lochert, I.J., Dexter, R.M., Evaluation of PBX-109 : the explosive fill for the Penguin Anti-Ship Missile Warhead, W.S. Division, Editor. 2003, Defence Science & Technology rganisation: Edinburgh. p J. M. Bellerby, C.K., Explosive-Binder Adhesion and Dewetting in nitramine-filled energetic materials. Propellants, Explosives, Pyrotechnics, (2): p Bailey, A., et al., The identification of bonding agents for TATB HTPB polymer bonded explosives. Philosophical Transactions of the Royal Society of London Series a-mathematical Physical and Engineering Sciences, (1654): p C. Sue Kim, H.Y.P...A.G., Developement of neutral polymeric bonding agents for propellants with polar composites filled with organic nitramine crystals. Propellants, Explosives, Pyrotechnics, (1): p Guy Perrault, R.L., Jean-Francois Drolet, High-energy explosive or propellant composition. 1981, Her Majesty the Queen in right of Canada, as represented by the Minister of ational Defence: United States. p. 9.