L SERDP TECHNICAL REPORT PRIMERLESS RTV SILICONE SEALANTS/ADHESIVES PP-1135 APRIL, 2003 U.S. Army Tank-automotive & Armaments Command (TACOM) Armament Research Development & Engineering Center (ARDEC) Armament Systems Processing Division Picatinny Arsenal, New Jersey 07806-5000 The views, opinions, and/or findings contained in this report are those of the authors and should not be construed as an official Department of Defense position, policy, or decision, unless so designated by other documentation. The citation in this report of the names of commercial firms or commercially available products or services does not constitute official endorsement by or approval of the U.S. Government. Destroy this report when no longer needed by any method that will prevent disclosure of its contents or reconstruction of the document. Do not return to the originator. TABLE OF CONTENTS LIST OF FIGURES iii LIST OF TABLES v LIST OF APPENDICES vi TEAM MEMBERS vii ABSTRACT viii INTRODUCTION 1 EXPERIMENTAL PROCEDURE 4 Formulations 4 Statistical Methods 4 Preparation of Lap Shear Samples 4 Preparation of Peel Adhesion Samples 5 Preparation of Wedge Adhesion Durability Samples 6 Aluminum Wedge – Surface Preparations 7 Abrade 7 Base Acid 8 P2 Etch 8 Coupling Agent 8 Plastic Surface Preparations 9 Cleaning 9 Surface Activation 9 Coupling Agent 9 Preparation of tensile Adhesion Samples 10 Spot Adhesion Tests 11 NMR Imaging 11 X-ray Photoelectron Spectroscopy 11 Second Ion Mass Spectrometry 11 RESULTS AND DISCUSSION 12 Elevated Temperature, Primerless Adhesion to Metal 13 House of Quality Analysis 14 Instron Sensitivity Analysis 16 Reformulation of RTV 630 Using First Generation Adhesion Promoter 17 Testing of Unamended and Amended RTV 630 Formulations 19 Aluminum Surface Analysis 20 Room Temperature, Primerless Adhesion to Metals and Thermoset Plastics 21 i TABLE OF CONTENTS (continued) Screening and Down Selection of Adhesion Promoters for RTV 866 21 P2 Framework Tool 23 Robust Optimization of Second-Generation Formulation 23 Process Capabilities for the Optimized Second-Generation Formulation 25 Testing of Optimized Second Generation Formulation 26 Durability Studies 27 Shelf Life Study of Second Generation Formulation 29 Room Temperature Adhesion to Thermoset Materials 30 Peel Evaluation for Second Generation Adhesion to Thermosets 30 Adhesion to Thermoplastic Materials 31 Primerless Adhesion to Thermoplastics at Ambient Temperature 32 Primerless Adhesion to Thermoplastics at Elevated Temperature 32 Lap Shear Specimen and Fixture Variation 33 Robust Optimization of Third Generation Formulation 36 Process Capability 38 Shelf Life Study of Third-Generation Formulation 41 General Electric Global Research Center 42 Alternative to RTV 866 42 Mechanism of Adhesion to Nylon 6,6 43 Chemical Structure Investigation 44 Effect of Cure Temperature and Interaction with Nylon 6,6 45 Virginia Polytechnic Institute 46 Surface Chemistry 46 Contact Angle Measurements 53 Durability Studies 54 Department of Energy 59 Air Force Materials Laboratory 60 Lap Shear Testing 60 NAVAIR Patuxent River 61 Lap Shear Testing 61 ARDEC 63 Spot Adhesion Testing 63 Lap Shear Testing 63 Technology Transition 65 CONCLUSIONS 66 REFERENCES 68 ii LIST OF FIGURES Figure 1. Lap Shear Sample Configuration 5 2. Peel Sample Configuration 6 3. Wedge Specimen Configuration 7 4. Tensile Adhesion Specimen Configuration 10 5. Process Capability of Baseline RTV 630 System With Primer 13 6. Process Capability of Primerless First Generation Formulation 14 7. House of Quality 15 8. Gage R&R for Nondestructive Testing 16 9. Process Capability Calculation for Unmodified RTV 630 Without Primer 17 10. Process Capability of Unmodified RTV 630 Baseline System With Primer 17 11. Wire Frame Plot of the Model of the Optimized RTV 630 Formulation With First Generation Adhesion Promoter 18 12. Final Process Capability of First Generation Product 19 13. NMR Images of Curing Profile for Polydimethylsiloxane Network 22 14. Robust DoE Model Presented as a Wire Frame Plot 24 15. Process Capability of Primerless Second Generation Formulation 25 16. Ultimate Strength vs Temperature for Second Generation Formulation 27 17. Plot of Shelf Life Lap Shear Properties of PLS200-866 30 18. Plot of Adhesion Strength Versus Nylon 6,6 Thickness 34 19. Plot of Adhesion Strength Versus Change in Bond Thickness 35 20. Improved Nylon 6,6 Lap Shear Holding Fixture 36 21. Graphical Model Predicting the Impact of dBPA and Silicone Hydride on Adhesion of Primerless Third Generation RTV 866 to Nylon 6,6 37 22. Effect of the Levels of 2,2”-diallylbisphenol A on the Adhesion of Primerless Third Generation RTV 866 to Nylon 6,6 38 23. Effect of the Levels of 2,2”-diallylbisphenol A and Silicone Hydride on the Adhesion of Primerless Third Generation RTV 866 to Nylon 6,6 39 iii 24. Process Capability for Third Generation Primerless Formulation on 1/8” Nylon 6,6 Substrates. 41 25. Process Capability of RTV 630 With 1.25% diallyl bisphenol A (dBPA) 43 26. Wide Scan XPS Spectrum For As-Received Lexan 47 27. Wide Scan XPS Spectrum For Isopropanol Cleaned Lexan 47 28. Wide Scan XPS Spectrum For Isopropanol Cleaned Corona Treated Lexan 48 29. Wide Scan XPS Spectrum For Isopropanol Cleaned Plasma Treated Lexan 48 30. Wide Scan XPS Spectrum For Isopropanol Cleaned Silane Modified Lexan 49 31. Wide Scan XPS Spectrum For As-Received Nylon 6,6 50 32. Wide Scan XPS Spectrum For Isopropanol Cleaned Nylon 6,6 51 33. Wide Scan XPS Spectrum For Isopropanol Cleaned Corona Treated Nylon 6,6 51 34. Wide Scan XPS Spectrum For Isopropanol Cleaned Plasma Treated Nylon 6,6 52 35. Wide Scan XPS Spectrum For Isopropanol Cleaned Silane Modified Nylon 6,6 52 36. Crack Length Data for Three Nylon 6,6 Specimens Tested at 70oC/100%RH 55 37. Durability of IPA cleaned Lexan 55 38. Durability of IPA cleaned Nylon 6,6 56 39. Durability of Lexan Under Severe Environmental Conditions 56 40. Durability of Nylon 6,6 Under Severe Environmental Conditions 57 41. Durability of Silane Treated Lexan: Different Test Conditions 58 42. Durability of Silane Treated Nylon 6,6: Different Test Conditions 58 43. XM 984 120-Millimeter Extended Range Mortar 65 44. Bonding of Phenolic Insulator into Rocket motor Assembly 65 iv LIST OF TABLES Table 1. Physical Properties of Baseline Unamended RTV630 and Amended RTV630 19 2. Baseline and First Generation RTV 630 Formulation Durability Tests 20 3. P2 Evaluation for bis(trimethoxysilylpropyl)succinate 23 4. Lap Shear Performance for the Second-Generation formulation Tested on Selected Substrates 25 5. T-Hat Tensile Data for Optimized Second Generation Formulation 26 6. Durability Testing of Baseline and Second Generation RTV formulations 28 7. Shelf Life Lap Shear Properties of PLS200-866 29 8. Peel Strength Results for Second Generation Primerless Formulation Cured at Either Room Temperature or 7 Days or 100oC/1 Hour 31 9. Effect of the % of Glass Beads on Lap Shear Adhesion of RTV 300-866 33 10. Effect of Nylon 6,6 Thickness on Lap Shear Adhesion of RTV300-866 34 11. Properties of Baseline and Primerless Third Generation RTV 866 40 12. Shelf Life Lap Shear Properties of PLS300-866 42 13. Physical Properties of RTV 630 & Amended RTV 630 Cured at 100oC/1 Hr 43 14. Structure of the Compounds Evaluated As Third-Generation Adhesion Promoters 44 15. Effect of Chemical Structure of the Adhesive Promoter on Failure Mode 44 16. Effect of Cure Conditions on the Failure Mode of Nylon 6,6 Lap Shear Samples 45 17. XPS Surface Analysis Results for Lexan Adherends (Atomic %) 49 18. XPS Surface Analysis Results for Nylon 6,6 Adherends (Atomic %) 53 19. Contact Angle and Adhesion Results for Lexan and Nylon 6,6 Adherends 54 v LIST OF APPENDICES A. Adhesion Promoter Synthesis 69 B. Primerless Silicone (PLS) Kit Formulations and Mixing Directions 70 C. Stein, J., Eichinger, B., and Early, T., “A New Class of Adhesion Promoters for Addition Curable Silicone Adhesives”. MST Conference Proceedings, Newark, NJ, May 2000. 74 D. Eichinger, B. E., Rigby, D., and Stein, J., “Simulating the cohesive properties of Ultem and related molecules”. Annu. Tech. Conf. Soc. Plast. Eng. 59th (Vol. 2), 1592 (2001). 85 E. Eichinger, B. E., and Stein, J., “The Mechanism of the Pt(0) Catalyzed Hydrosilylation Reaction”. Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 42 (1), 251 (2001). 90 F. Eichinger, B.E. and Stein J., “A Quantum Mechanical Study of the Bonding of a Silyl Ester to Hydrated Alumina”, Surface Science, 492, 75 (2001). 92 G. Eichinger, B.E., Rigby, D., and Stein, J., “Cohesive Properties of Ultem and Related Molecules from Simulations”, Polymer, 43, 599 (2002). 105 H. Virginia Polytechnic Institute (VPI) Wedge Test Data and Figures for RTV 630 Baseline and Primerless PLS100-630. 121 I. Adhesion Promoters Screened for the Second-Generation RTV 866 Formulation. 123 J. Virginia Polytechnic Institute (VPI) Wedge Test Data and Figures for RTV 866 Baseline and Primerless PLS200-866. 124 K. Adhesion Promoters Screened for the Third Generation Formulation. 126 L. Durability Curves for PLS300 630A and Lexan or Nylon 6,6 Samples. 129 M. Air Force Comparison of Lap Shear Properties of Baseline RTV 630 + Primer With First and Third Generation (PLS100-630 and PLS300-866) Primerless RTV 133 N. Navy Comparison of Lap Shear Properties of Baseline RTV 630 + Primer With First and Third Generation (PLS100-630 and PLS300A-630) Primerless RTV 134 O. Spot Adhesion Testing Results 135 P. Army Comparison of Lap Shear Properties of Baseline RTV 630 + Primer With First and Third Generation (PLS100-630 and PLS300A-630) Primerless RTV 136 vi TEAM MEMBERS Mr. Dean Martinelli Principal Investigator U. S. Army TACOM - ARDEC Mr. Joseph Brescia Team Leader U. S. Army TACOM - ARDEC Ms. Stacey Kerwien Team Leader U. S. Army TACOM - ARDEC Mr. Donald Rorabaugh U. S. Army TACOM - ARDEC Mr. John Osterndorf U. S. Army TACOM - ARDEC Mr. Francis Sullivan U. S. Army TACOM - ARDEC Mr. David Mao U. S. Army TACOM - ARDEC Dr. Brad Forch U.S. Army Research Laboratory Mr. Richard Beyer U.S. Army Research Laboratory Mr. James Tira Honeywell/DOE Kansas City Mr. Karl Davis Honeywell/DOE Kansas City Ms. Diane Kleinschmidt Naval Air Warfare Center Mr. Alan Fletcher U. S. Air Force Research Laboratory Mr. William Anspach U. S. Air Force Research Laboratory Dr. Judith Stein General Electric CRD Ms. Christina Darkangelo Wood General Electric CRD Dr. Rachid Kerboua General Electric CRD Ms. Gosia Rubinsztajn General Electric CRD Mrs. Eriny Youssef General Electric CRD Dr. James Cella General Electric CRD Dr. Richard Uriarte General Electric CRD Ms. Rebecca DiCola General Electric CRD Dr. Bruce Eichinger Molecular Simulations Inc. (Accelrys Inc.) Dr. Erich Wimmer Molecular Simulations Inc (Accelrys Inc.) Dr. John Dillard Virginia Polytechnic Institute David Xu Virginia Polytechnic Institute Eric Weber Virginia Polytechnic Institute vii ABSTRACT This is the final report for the Strategic Environmental Research and Development Program (SERDP) funded project PP1135, Primerless RTV Silicone Sealants/Adhesives. The objective of the project, the development of primerless addition curable silicone sealants/adhesives, was met for all three phases of the program. Detailed results for the first four years of effort also were reported in SERDP technical reports Primerless RTV Silicone Sealants/Adhesives - PP1135 issued in 1999, 2000, 2001, and 2002 (References 1-4). Three Six Sigma green belt projects were completed as part of this project. The research portion of the program was divided into three phases. In the first phase, primerless, elevated-temperature curing, RTV silicone formulations that adhere to metals and glass were developed, and in the second phase, primerless, room temperature curing, RTV silicone formulations that adhere to metals and glass were developed. In the third phase of the effort primerless RTV silicone formulations that provide adhesion to selected thermoplastic substrates were developed validated. Computational methods were used to guide the material formulation efforts, and calculations to determine the interaction between adhesion promoters and substrates resulted in the identification of promising adhesion promoter candidates. Lap shear screening tests of formulations modified with these adhesion promoters led to the development of optimized formulations, that provided adhesion to various substrates without the use of environmentally unfriendly silane primers. These formulations consisted of RTV 630 and RTV 866 base resins modified with combinations of adhesion promoters, cross-linking compounds, and inhibitors. The first-generation formulation, PLS100-630, consisting of RTV 630 modified with a bis(trimethoxysilylpropyl)fumarate adhesion promoter and a silicon hydride cross-linking compound, provided primerless adhesion to metals and glass under an elevated curing cycle. Similarly, the second- generation formulation PLS200-866, which consisted of RTV 866 modified with adhesion promoter bis(trimethoxysilylpropyl)succinate (US Patent 6,447,922) and a 2- methyl-3-butyn-2-ol inhibitor, provided primerless adhesion to metals, glass, and thermoset plastics under a room-temperature curing cycle. For the third phase, two primerless formulations, PLS-300-866 and PLS300A-630, that used a new adhesion promoter (dBPA) to provide excellent adhesion to Nylon 6,6 substrates, has been developed (Patent Application 20030049465). Lap shear properties with Nylon 6,6 substrates exhibited high strengths with cohesive failures. A technology assessment also was conducted for the XM 984 Extended Range Mortar. Simulations and actual flight tests were conducted successfully with the PLS200-866 primerless RTV formulation. The final phases of this effort were focused on additional technology assessment and transitioning of the optimized formulations into DoD and DOE applications. In support of this effort, the Polymer Production Facility (PPF) at the Department of Energy, Kansas City Plant, formulated the adhesion promoters and additives, and packaged and distributed complete primerless RTV kits, (PLS 100-630, PLS200-866, PLS300A-630 and PLS300-866) to the DoD and DOE team members for evaluation. Testing showed these kits to have properties equal to the laboratory-fabricated versions. viii