Jessica Gwyther Characterisation of Plasticised Nitrocellulose using NMR and Rheology
2 Project Aims Prepare 5 inert PBX binder formulations using nitrocellulose polymer and a series of nitroaromatic plasticiser Characterisation of formulations that form gels Investigation of the molecular dynamics of the small plasticiser molecules in the NC matrix using NMR Characterisation of bulk physical properties of the binders using rheological measurements.
3 Binder Formulations NC + a) ethylbenzene (EB) Film b) mononitroethylbenzene (MNEB) Gel c) dinitroethylbenzene (DNEB) Gel d) trinitroethylbenzene (TNEB) Solid e) K10 (DNEB (65%) TNEB (35%)) Gel ONO 2 * O O 2 NO ONO 2 O 2 NO ONO 2 O O O * ONO 2 NC n EB MNEB DNEB TNEB 65% K10 35%
4 Binder Formulations EB + NC MNEB + NC K10 + NC TNEB + NC DNEB + NC
5 Rheology Amplitude Sweep Oscillation expt. Stress sweep at constant frequency to find linear viscoelastic region and good signal. 100000 K10 G' K10 G" MENB G' MNEB G" DNEB G' DNEB G" 10000 1000 100 0.01 0.1 1 10 100 Stress / Pa G greater than G for each gel more Elastic than viscous. Relative rigidity of gels: DNEB + NC < K10 + NC < MNEB + NC rigidity
6 Rheology Oscillation at Elevated Temperatures 1000000 100000 10000 G' 25oC G'' 25oC G' 80oC G" 80oC 10000 1000 G' 25oC G" 25oC G' 60oC G" 60oC 1000 100 0.001 0.01 0.1 1 10 100 Freq / Hz 100 0.001 0.01 0.1 1 10 100 Freq / Hz MNEB + NC binder DNEB + NC binder 100000 G' 25oC G'' 25oC G' 80oC G" 80oC 10000 1000 100 0.001 0.010 0.100 1.000 10.000 100.000 K10 + NC binder Freq / Hz
7 Rheology Oscillation at Sub-ambient Temperatures 1000000 100000 G' 25oC G'' 25oC G' -20oC G" -20oC 100000 G' 25oC G" 25oC G' -20oC G" -20oC 10000 10000 1000 1000 100 0.00 0.01 0.10 1.00 10.00 100.00 100 0.001 0.01 0.1 1 10 100 Freq / Hz Freq / Hz MNEB binder DNEB binder 1.00E+09 1.00E+08 1.00E+07 1.00E+06 1.00E+05 1.00E+04 1.00E+03 1.00E+02 0.001 0.010 0.100 1.000 10.000 100.000 Freq / Hz G' 25oC G'' 25oC G' -10oC G" -10oC G' -20oC G" -20oC Large G and G at -20 o C for K10 binder. Possible phase transition. K10 binder
8 Modulus versus Temperature Plot at 0.01 Hz 1.00E+08 1.00E+07 MNEB binder G' MNEB binder G" DNEB binder G' DNEB binder G" K10 Binder G' K10 Binder G" 1.00E+06 1.00E+05 1.00E+04 1.00E+03 1.00E+02-20 -10 0 10 20 30 40 50 60 70 80 T / o C
9 Time-temperature Superposition Log G' 5.0 4.5 4.0 3.5 3.0 2.5 2.0 80oC 60oC 40oC 25oC 10oC 0oC -10oC 1.5-4.0-2.0 0.0 2.0 4.0 6.0 Log reduced freq Good overlay of oscillation data for all gels Rheology dominated by NC not small molecule plasticiser M Doi and S. F. Edwards, The Theory of Polymer Dynamics Evidence of highly concentrated solution of entangled polymer, not cross linked gel
10 Creep Recovery Stress applied to sample and strain measured. Stress is removed after being applied for a time. If no flow has occurred = strain gradually recovers to zero. If some flow has occurred = strain does not recover to zero. / Pa -1 γ 8.0E-02 7.0E-02 6.0E-02 5.0E-02 4.0E-02 Minimum viscosity: σ η = γ / t 25oC 35oC 40oC 50oC 60oC 70oC 80oC T / o C 25 35 40 Min. η x 10 5 / Pas 13.1 9.57 7.37 3.0E-02 50 3.93 2.0E-02 60 1.63 1.0E-02 0.0E+00 0 100 200 300 400 500 600 700 70 80 0.78 0.25 Time / s Creep recovery plot for K10 binder
11 NMR T 2 of Gels T 2 is a time constant which is related to molecular dynamics by: 1 T τ c = A 2 2 2 1+ ω τ c + Bτ c τ c = Molecular Correlation Time ω is the Larmor frequency and A and B are constants. Liquids ω 2 τ c2 <<1 1 T 2 = ( A + B)τ c Aromatic protons Aliphatic and NC protons Solids ω 2 τ c2 >>1 1 T 2 = Bτ c K10 (DNEB + TNEB) < DNEB MNEB Spectrum K10 + NC gel Molecular Mobility
12 NMR Diffusion of Gels Pulse Field Gradient (PFG) NMR used to find translational diffusion co-efficient Larmor equation: ω = γb o B o spatially homogeneous, ω same throughout sample However, if in addition to B o magnetic field gradient applied Larmor frequency varies with position and becomes a spatial label.
13 NMR Diffusion Gels Whole molecule has same diffusion coefficient Relative ordering of gels according to D: K10 (DNEB + TNEB) < DNEB < MNEB (consistent with T 2 ) 14 12 10 8 6 4 2 0-2 -4 ppm Stack plot of K10 + NC binder ln D -21.00 2.80E-03 2.90E-03 3.00E-03 3.10E-03 3.20E-03 3.30E-03 3.40E-03-21.50-22.00 R 2 = 0.9987-22.50-23.00 R 2 = 0.9959-23.50 K10 + NC MNEB + NC DNEB + NC Diffusion expt s repeated between 25 o C 80 o C Arrhenius plots -24.00-24.50 R 2 = 0.9981-25.00 1/T / K -1
14 Conclusions Three formulations formed gels. Bulk Properties: - Rheological properties of the gels dominated by NC polymer Molecular Dynamics: -T 2 and diffusion coefficients of small molecules within gels. - Increasing molecular mobility with decreasing molecular size. - Molecular dynamics dominated by small molecule plasticisers. Evidence that gels are concentrated solutions of entangled polymer, not cross linked gels.
15 Acknowledgements AWE Dr. Paul Deacon Prof. Terence Cosgrove and Dr. Roy Hughes Polymers at Interfaces Group Dr. Youssef Espidel Bristol Colloid Centre Dr. Cheryl Flynn