Binding Interaction Between Dantocol and RDX Chris Williams Supervised by Dr Stephen Clarke Co-Supervised Dr Simon Mathew & Dr Ian Lochert (DST)
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
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
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 % 64.0 0.95 7.34 0.26 0.10 7.34 0.02 20.0
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
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
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
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
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
Scanning Electron Microscope Investigate the coating of bonding agent on RDX crystals XL30 Philips-XL30 FEGSEM w EDAX EDS Smooth crystalline surface
10% Dantocol Coating High level of RDX coverage Good adhesion to the surface
4% Dantocol Coating Less coverage observed Dantocol forms thick, malleable coating
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
DRIFT-IR Spectrum Vibrational Bands Vas ( 2 ) CH 2 Vs ( 2 ) + V (-) Ring Stretching ( 2 ) Peaks (cm -1 ) 1593, 1573, 1532 1459, 1434 1351, 1312, 1268, 1234, 1219 1039, 1019, 946, 924 784, 754 0.14 0.13 0.12 0.11 0.10 0.09 0.08 RDX 0.19 0.18 0.17 0.16 0.15 0.14 0.13 0.12 0.11 2 Asymmetrical stretching vibration 1590.15 1570.45 1537.70 KM 0.07 KM 0.10 0.06 0.09 0.05 0.04 0.08 0.07 0.06 0.03 0.05 0.02 0.01 0.04 0.03 0.02-0.00 3000 2500 2000 Wavenumbers (cm-1) 1500 1000 0.01 0.00 1660 1640 1620 1600 1580 1560 Wavenumbers (cm-1) 1540 1520 1500
Samples pre-ground with KBr Sample Grinding Excess grinding removed coating 0.2 RDX 1st Grinding KM 0.1 0.0 RDX 2nd Grinding KM 0.2 0.0 0.4 RDX 3rd Grinding KM 0.2 0.0 RDX 4th Grinding KM 0.1 KM 0.0 1 RDX 5th Grinding 0 3000 2500 2000 1500 1000 Wavenumbers (cm-1)
Peak Shifts Kubelka-Munk 0.50 0.45 0.40 0.35 0.30 0.25 0.20 0.15 0.10 RDX + 10% Dantocol RDX 1513.05 cm -1 1537.70 cm-1 0.05 0.00 3100 2600 2100 1600 1100 600 Wavenumber (cm -1 ) Sample V as ( 2 ) CH 3 Ring RDX 1590.15 1570.45 1537.70 1458.98 1433.52 1361.59 784.94 753.45 RDX + 10% Dantacol 1589.22 1568.23 1513.05 1460.12 1432.74 1360.07 788.04 753.42 V 0.93 2.22 24.65 1.14 0.78 1.52 3.10 0.03 Sample cm -1 V s 2 + V (-) Ring Stretching RDX 1318.77 1264.98 1234.40 1219.38 1038.17 1018.71 945.11 917.12 RDX + 10% Dantacol 1319.75 1258.90 1235.63 1221.25 1036.40 1018.54 945.54 911.76 V 0.98 6.08 1.23 1.87 1.77 0.17 0.43 5.36
Peak Shifts RDX & Dantocol 0.5% Dantocol V as 2 (cm -1 ) 1529.34 V as (cm -1 ) 8.36 1.0% Dantocol 2.0% Dantocol 1523.44 1526.40 14.26 11.3 0.24 0.22 RDX + 10% Dantocol 3.0% Dantocol 1522.51 15.19 0.20 4.0% Dantocol 1519.37 18.33 0.18 5.0% Dantocol 1517.91 19.79 0.16 6.0% Dantocol 1516.83 20.87 0.14 8.0% Dantocol 1513.23 24.47 0.12 10% Dantocol 1513.05 24.65 0.10 1596 1576 1556 1536 1516 1496 50% Dantocol - - Wavef unct ion ( cm -1 )
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
ATR-IR Spectra Sharp Peaks with low noise interference RDX peaks consistent with DRIFT-IR 100 95 RDX 90 85 80 %T 75 70 1537.70 cm-1 65 60 55 50 45 4000 3500 3000 2500 Wavenumbers (cm-1) 2000 1500 1000
RDX and Dantocol IR 80 RDX %T 60 40 1537.70 cm -1 20 Dantocol 80 %T 60 40 20 80 RDX + 50% Dantocol %T 60 40 1518.162 cm -1 20 3500 3000 2500 2000 Wavenumbers (cm-1) 1500 1000
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
Raman Peak Shifts Vibration Band RDX V(cm -1 ) RDX + 4% Dantocol V(cm -1 ) RDX + 3% Dantocol V(cm -1 ) V as 2 1592.1 0.2 0.2 CH Deformation 1428.0 0.3 1.6 V s 2 1383.5 5.3 3.8 1306.8 0.4 0.8 1270.6 0.6 0.5 1213.4 0.6 0.5 Ring Stretch 1028.3 2.3 1.7 940.0 1.4 1.6 879.6 0.4 0.6 844.5 1.8 0.1 V 2 664.0 0.2 0.2 599.6 14.0 14.3 Ring Deformation 456.8 0.9 2.0 409.6 8.2 5.3
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 2 2 2 CH 2 6.16ppm
MR Titration RDX : Dantocol RDX : Dantocol 1 : 0.5 1 : 1 6.17ppm 3.112ppm 2.843ppm 6.17ppm 3.127ppm 2.999ppm RDX : Dantocol RDX : Dantocol 1 : 2 1 : 3 6.19ppm 3.135ppm 2.999ppm 6.19ppm 3.190ppm 3.061ppm
MR Complexation 6.20 RDX CH 2 Peak Shift 6.19 6.19 Chemical Shift (ppm) 6.18 6.18 6.17 6.17 6.16 6.16 0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50 Dantocol Equivanents
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
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
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
Product Interaction SEM to determine adequate coating DRIFT spectroscopy and ATR consistent with peak change at 1537.7cm -1 100 99 98 RDX + 10% Bonding Agent %T 97 96 95 94 93 1529.4cm -1 92 91 90 89 88 87 86 85 84 4000 3500 3000 2500 Wavenumbers (cm-1) 2000 1500 1000
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
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 1.0 0.9 RDX + 10% Bonding Agent 0.8 0.7 0.6 KM 0.5 0.4 0.3 1533.85cm -1 0.2 0.1 4000 3500 3000 2500 2000 Wavenumbers (cm-1) 1500 1000
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
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
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