Presentation on theme: "Thermal and Atmospheric Stability of Tungsten (VI) Chloride: Authors: Daniel Rey & Jason Kamphaus Applications to High-Temperature Self-Healing Polymer."— Presentation transcript:
Thermal and Atmospheric Stability of Tungsten (VI) Chloride: Authors: Daniel Rey & Jason Kamphaus Applications to High-Temperature Self-Healing Polymer Systems
Outline What is a self-healing polymer? Why use a tungsten (VI) chloride catalyst? Evaluate the thermal and atmospheric stability of the tungsten (VI) chloride catalyst Incorporate tungsten (VI) chloride into high- temperature self-healing polymers Problems, results, and conclusions Motivation for future work
How a self-healing polymer works
Why use tungsten (VI) chloride? Temperature Stability –Melting point of WCl 6 is 275 o C which is ~125 o C higher than 1 st Generation Grubbs’ Catalyst Cost –Approximately 1/40 th the cost per gram of 1 st generation Grubbs’ catalyst Drawbacks: –Tungsten (VI) chloride readily deactivated by water –High-density solid may cause dispersion problems in low-density polymers
Evaluate Atmospheric Stability Fill specimen vials in glove box with 100mg of RWCl 6 Fill specimen vials in glove box with 100mg of RWCl 6 Expose vials to atmosphere, place vials in vacuum oven Expose vials to atmosphere, place vials in vacuum oven Oven programmed to ramp from room temperature and hold at either 121 ⁰C or 177 ⁰C for 3 hours Oven programmed to ramp from room temperature and hold at either 121 ⁰C or 177 ⁰C for 3 hours Vials removed from oven, injected with 1mL healing solution and allowed to sit for 24 hours Vials removed from oven, injected with 1mL healing solution and allowed to sit for 24 hours Vials placed under vacuum to remove excess monomer Vials placed under vacuum to remove excess monomer Percent polymer yield calculated Percent polymer yield calculated Fig 1: Vials filled with RWCl 6 are placed in a jar and sealed.
Evaluate Thermal Stability Fig 2: Small specimen vials filled with 50mg RWCl 6. About 50 mg of RWCl 6 was sealed in vials, in a nitrogen environment and heatedAbout 50 mg of RWCl 6 was sealed in vials, in a nitrogen environment and heated Every half hour 3 vials were removedEvery half hour 3 vials were removed Injected with 0.5 mL of healing solutionInjected with 0.5 mL of healing solution Allowed to cure for 24 hoursAllowed to cure for 24 hours Vials were placed in a vacuum and the residual monomer was driven off for 24 hoursVials were placed in a vacuum and the residual monomer was driven off for 24 hours Polymer yield measurements were madePolymer yield measurements were made
TDCB Specimen Testing Create short pre crack with razor blade Test sample and record load-displacement Catalyst Embedded in Polymer Polymer
Self-Activated Results High -Temp Post-Cure Heal Ratio (Samples Healed/Total Samples) Average P H / P V None Hours 121 ° C Hours 177 ° C wt% RWCl 6 Samples Healed in Lab Atmosphere Inconsistent healing results –Polymer not fully cured after 48 hours –Results not improving after increasing catalyst concentration to 15 wt% Most likely due to high lab humidity Solution…?
Virgin Crack and Healing in N 2 Glove Box Consistent healing data –Exhibits high peak failure loads and non-linear healing Problem: –We no longer have virgin fracture data how do we analyze the data? Proposed Solution: –Compare healed data with a baseline of virgin data from similar samples (i.e. same catalyst weight% and post-cure).
Self-Activated Results, High-Temp Post Cure Weight % Catalyst Healing Conditions PVPV PHPH No Post Cure 12wt% Glove BoxNA… Lab114 ± 65 N32 ± 24 N 15wt% Glove BoxNA82 ± 22 N Lab180 ± 60 N4.31 N 4 121°C 12wt% Glove BoxNA51 ± 8 N Lab75 ± 19 N36 ± 15 N 15wt% Glove BoxNA68 ± 21 N Lab76 ± 8.8 N11 ± 3.8 N 4 177°C 12wt% Glove BoxNANo Healing Lab69 ± 13 NNo Healing 15wt% Glove BoxNANo Healing LabNo Healing
Results and Conclusions Under inert conditions RWCl 6 catalyst remains active even after 8 hours at 177 °C Consistent results: –Good non-linear healing up to at least 121 °C –No healing after 4 hours at 177 °C Conclusion: –Inconsistent results from healing in the lab atmosphere were caused by catalyst deactivation during the period between the virgin fracture and injection due to HIGH LAB HUMIDITY! A control sample injected in the glove box and placed on the lab bench to cure tested to a peak fracture load of 82.5 N –The diffusion of moisture into the polymer matrix is slow enough that the polymer remains protected while it heals
Future Work Determine why the catalyst deactivates in the polymer after a 4 hour post cure at 177 °C Test in-situ samples in glove box after high temperature cure cycle Determine the humidity level at which the catalyst deactivates Further investigate the potential of polymer- coating the catalyst as a means of protecting it against deactivation
Acknowledgements Jason Kamphaus Dr. Scott White NASA Illinois Space Grant Consortium
Experimental Calibration of 828/3046 Epoxy Calibration of new resin system performed for neat material and epoxy with 15 wt% capsules Compliance vs. crack length measurements were made using several specimens Modulus determined by DMA experiments (E neat =2.6 GPa and E 15%Caps =1.95 GPa) m values determined for each sample type (m neat =0.78 N -1 and m 15%Caps =0.80 N -1 ) α values varied by less than 1% (α neat =12.8 x 10 3 m -3/2, α 15%Caps =12.9 x 10 3 m -3/2 )
Tungsten catalyst initiates healing mechanism Exo-DCPD Tungsten (VI) Chloride Polymer ROMP polymerization of exo-DCPD with WCl 6 Phenyl acetylene reacts with tungsten to form an activated metal carbene Phenyl Acetylene