Surface modifications of composite materials by atmospheric pressure plasma treatment

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(1)UNIVERSIDAD REY JUAN CARLOS ESCUELA SUPERIOR DE CIENCIAS EXPERIMENTALES Y TECNOLOGÍA DEPARTAMENTO DE CIENCIA E INGENIERÍA DE LOS MATERIALES. SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT Javier Sánchez Serrano. Submitted in total fulfillment of the requirements of the degree of Doctor of Philosophy. June, 2011. URJC coordinator name:. AIRBUS coordinator name:. Dr. Alejandro Ureña Fernández. Dr. Silvia Lazcano Ureña. Materials Science and Engineering.

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(3) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. D. ALEJANDRO UREÑA FERNÁNDEZ, Catedrático de Universidad y Director del Departamento de Ciencia e Ingeniería de Materiales de la Universidad Rey Juan Carlos Dña. SILVIA LAZCANO UREÑA, Directora del Departamento de Investigación y Tecnología de AIRBUS en España CERTIFICAN: Que el presente trabajo de investigación con el título “SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT” que constituye la Memoria presentada por JAVIER SÁNCHEZ SERRANO para optar al grado de Doctor por la Universidad Rey Juan Carlos con mención “Doctor Europeus”, ha sido realizado bajo su supervisión en el Departamento de Ciencia e Ingeniería de Materiales de la Universidad Rey Juan Carlos (Móstoles, España), en el Departamento de Materiales y Procesos de AIRBUS (Getafe, España), y como estancia de investigación en una institución europea, en el Departamento de Tecnologías Metálicas e Ingeniería de Superficies de EADS Innovation Works (Ottobrunn, Alemania), cumpliendo todos los requisitos necesarios. Y para que así conste a los efectos oportunos lo firman en Móstoles, a 21 de Junio de 2011.. Fdo.: D. Alejandro Ureña Fernández. Fdo.: Dña. Silvia Lazcano Ureña. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 3 of 302.

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(5) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. RESUMEN DEL PROYECTO Durante los últimos 40 años la industria aeronáutica ha mostrado una tendencia ascendente en la incorporación de materiales compuestos en estructuras primarias debido a las ventajas que esto supone en ahorro de peso y costes, asociados con la disminución en el consumo de combustible. En este sector, es capital por razones de seguridad asegurar la calidad, lo que lleva a la implementación de robustos procesos de fabricación que aseguran la calidad final de los componentes. Como resultado de estos procesos de producción, la superficie de los materiales compuestos se ve irremediablemente contaminada con agentes desmoldeantes (i.e., que previenen la adhesión de los materiales compuestos a los moldes en los que se curan), dando lugar a características superficiales perjudiciales para posteriores operaciones de encolado. De esta forma, la preparación superficial de substratos de material compuesto representa una de las fases del proceso de encolado que determina en gran medida la calidad final de la unión. Esta preparación no sólo sirve para eliminar la contaminación (i.e., agentes desmoldeantes base fluorocarbono o silicio), sino que también contribuye a un aumento en el área superficial a encolar, promueve interconexiones micromecánicas. (i.e.,. micromechanical. interlocking). o. modifica. químicamente. una. superficie.. Tradicionalmente, la preparación superficial previa al encolado de componentes aeronáuticos fabricados con materiales compuestos epoxi/carbono se ha llevado a cabo mediante combinación de los siguientes métodos: limpieza con disolventes, abrasión mecánica y utilización de tejidos pelables (i.e., peel-ply technique). La mayor desventaja de dichas técnicas reside en el hecho de que son procesos manuales, lo cual provoca su limitada repetitividad y su gran dependencia de la habilidad del operador. Además, requieren especial atención debido a que tienen que asegurar que sólo se modifica la química y la morfología de una fina capa superficial, evitando daños tanto en las fibras de refuerzo como en el material base, que debilitarían la posterior unión encolada. Es importante resaltar que los disolventes utilizados para la preparación superficial presentan riesgos de inflamabilidad así como problemas de seguridad e higiene para los operadores. La alternativa de retirar tejidos pelables con posterior limpieza mediante disolventes orgánicos supone que dicho proceso esté gobernado por una gran cantidad de parámetros que potencialmente pueden afectar la calidad de la unión, lo que requiere constantes controles de calidad. Por lo tanto, es de vital importancia determinar un método fiable, barato, continuo y reproducible capaz de sustituir a los mencionados anteriormente. Posibles alternativas como proyección de partículas abrasivas (i.e., grit blasting), láser, radiación ultravioleta y plasma han mostrado su potencial en varios estudios, pero ninguna de ellas se ha podido industrializar todavía, debido fundamentalmente a la falta de técnicas que evalúen la calidad superficial post-tratamiento. Se ha demostrado que bajo condiciones de proceso controladas, la tecnología de plasma atmosférico (i.e., Atmospheric Pressure Plasma, APP) aumenta de forma efectiva la resistencia de las uniones encoladas y la adhesión de pinturas en polímeros, debido a que es una herramienta que activa, limpia (i.e., eliminación de contaminantes), incrementa la energía superficial (i.e., cambiando la estructura de la superficie), y cuyas propiedades no se deterioran para tiempos de almacenamiento razonablemente prolongados en los casos de tratamiento previo al encolado o la aplicación de pinturas. Además esta tecnología no requiere operaciones auxiliares, y es susceptible de ser automatizada e instalada en sistemas de producción a gran escala.. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 5 of 302.

(6) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. En este trabajo, se han investigado los efectos de tratamientos superficiales mediante técnicas de plasma atmosférico en adherentes aeroespaciales de material compuesto epoxi/fibra de carbono HEXCEL Hexply 8552/AS4 y CYTEC Cycom 977-2/HTS, utilizando dos equipos generadores de plasma diferentes (i.e., APP-System 1 y 2) desarrollados por la empresa alemana Plasmatreat. Los laminados termoestables se pusieron en contacto con diversos materiales auxiliares industriales durante el proceso de fabricación (i.e., agentes desmoldeantes como RICHMOND Release film VAC–PAK A-6200.001 y HENKEL LOCTITE Frekote 700NC), y un tejido pelable (i.e., Tygavac Advanced 60-B/R), de modo que se examinaron residuos y morfologías específicas con el fin de evaluar la viabilidad de esta técnica como pre-tratamiento superficial. Las modificaciones derivadas del tratamiento mediante APP y el entendimiento de sus efectos en términos de limpieza y activación, tiempo de vida del tratamiento APP, durabilidad de la unión encolada y diferentes condiciones de operación se han demostrado mediante diversas técnicas tales como: medidas de ángulos de contacto (Contact Angle, CA), análisis de energía superficial (Surface Free Energy, SFE), espectroscopia de energía dispersiva de rayos X (Energy Dispersive X-ray spectroscopy, EDX), espectroscopia de fotoelectrones emitidos por rayos X (X-ray Photoelectron Spectroscopy, XPS), perfilometría, y análisis de micrografías obtenidas mediante microscopio electrónico de barrido (Scanning Electron Microscopy, SEM) y microscopio de fuerzas atómicas (Atomic Force Microscope, AFM). Asimismo, se han corroborado las características particulares del tratamiento superficial con plasma mediante ensayos mecánicos como Cross-Cut-Test (CCT) en una imprimación (i.e., AKZO Barrier Primer 37045), y cortadura simple (Single Lap Shear, SLS) y tenacidad de la línea de encolado (Fracture toughness energy of bonded joints, Mode I, GIC) en adhesivos tipo film (i.e., HENKEL LOCTITE HYSOL EA9695 K.05 y CYTEC FM-300 K.05) y pasta (i.e., HUNTSMAN Epibond 1590-A/B). Como resultado de estas investigaciones, se han observado incrementos muy prometedores en la resistencia de las uniones encoladas de material compuesto epoxi/fibra de carbono. Además, se ha demostrado que es posible automatizar esta tecnología al integrar con éxito el sistema de plasma en una máquina pórtico de 3 ejes. La evaluación de varios métodos de control del estado físico-químico de las superficies tratadas mediante APP (i.e., tintas para medir energía superficial, ángulos de contacto utilizando agua y técnica de mojado por aerosol) ha revelado que los ángulos de contacto con agua muestran gran potencial para su aplicación, mientras que asimismo, la técnica de mojado mediante aerosol representa una aproximación muy prometedora. Por lo tanto, se ha demostrado que la aplicación de la técnica APP en materiales compuestos epoxi/carbono es efectiva y robusta, presentando eficiencia y potencial de automatización en procesos industriales de fabricación en línea, garantizando la calidad superficial y repetitividad del proceso a relativo bajo coste y consumo de energía. APP presenta otras ventajas como bajos requerimientos en personal y ser segura desde el punto de vista medio ambiental.. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 6 of 302.

(7) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. PROJECT SUMMARY In the last 40 years, the aeronautical industry has shown an increasing tendency to incorporate composite materials in primary structures for cost and weight savings advantages, associated with fuel consumption decreases. In this industry, quality assurance is critical for obvious safety reasons, leading to the implementation of reliable manufacturing processes that ensure the final output of the components. As a result of these production processes, the surface of composite materials may be contaminated with release agents (i.e., to prevent adhesion of the composites to the moulds in which they are cured), exhibiting detrimental characteristics for subsequent bonding operations. Thus, surface preparation of the composite substrates is one of the phases of the bonding process that determines to a large extent the final bond quality. Surface preparation not only serves to remove contamination (i.e., fluorocarbon and silicon release agents), but may also increase the surface area for bonding, promote micromechanical interlocking and/or chemically modify a surface. The main methods of surface preparation prior to adhesive bonding of aeronautical components manufactured with CFRP has traditionally been carried out by means of solvent degreasing, mechanical abrasion and use of peel-ply technique. These methods are often used in combination. The major drawback is the fact that, it is usually carried out by hand, which causes its limited repetitiveness and its great dependence of the operator. Furthermore, care must be taken to ensure that only the chemistry and morphology of a thin surface layer is modified, avoiding breaking reinforcing fibers, affecting the bulk properties of the composite and, in short, weakening the adhesive bond. It should be also noted that the use of these solvents in cleaning and surface preparation processes present risks of inflammability as well as safety and hygiene problems for operators. The alternative of stripping off a peel-ply fabric with subsequent cleaning through organic solvents involves a huge amount of parameters intervening in the process and that may affect the efficiency of the adhesive bond, requiring constant quality controls. Therefore, it is of paramount importance to determine a reliable, cheap, continuous and reproducible method that may replace the aforementioned ones. Alternatives like grit blasting, laser, ultraviolet radiation and plasma have shown some potential in various screenings, but none has found entry into series production yet, mainly due to a lag of methods for adequate assessment of surface quality. Atmospheric Pressure Plasma (APP) technique under controlled process conditions has been demonstrated to be effective at improving adhesive bonding strength and paint adhesion on polymers, particularly as a tool for activation, cleaning (i.e., contaminants removal), increasing surface energy (i.e., by changing the surface structure) and, prior bonding or painting, it has not appreciably lost its properties for reasonable storage times. In addition, this technology does not require auxiliary operations, and is susceptible of being automated and set up in mass production systems. In this project, effects of Atmospheric Pressure Plasma (APP) surface treatment for HEXCEL Hexply 8552/AS4 and CYTEC Cycom 977-2/HTS aeronautical epoxy/carbon fiber composite adherends were investigated by two different APP systems (i.e., APP-System 1 and 2) developed by the German company Plasmatreat. The thermoset laminates were in contact with different industrial ancillary materials during the manufacturing process (i.e., RICHMOND Release film VAC–PAK A-6200.001 and HENKEL LOCTITE Frekote 700NC) and a peel ply (i.e., Tygavac Advanced 60-B/R), so that specific morphologies and surface residues were examined to assess the feasibility of this technique as a surface pre-treatment. APP surface. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 7 of 302.

(8) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. modifications and understanding of its effects in terms of cleaning and activation, APP working life, durability of the bond and different treatment conditions were demonstrated by different characterization techniques such as contact Angle (CA) measurements, Surface Free Energy (SFE) analysis, Energy Dispersive X-ray spectroscopy (EDX), X-ray Photoelectron Spectroscopy (XPS), image analysis of micrographs obtained by Scanning Electron Microscopy (SEM), profilometry, and Atomic Force Microscope (AFM). Furthermore, the particular features of APP treatment were assessed by mechanical tests such as Cross-Cut-Test (CCT) on a primer (i.e., AKZO Barrier Primer 37045), Single Lap Shear (SLS) and bond line toughness (Fracture toughness energy of bonded joints, Mode I, GIC), using film (i.e., HENKEL LOCTITE HYSOL EA9695 K.05 and CYTEC FM-300 K.05) and paste adhesives (i.e., HUNTSMAN Epibond 1590-A/B). As a result, promising increases in the strength of epoxy/carbon fiber composite adhesive joints were observed. Moreover, the automation potential of the APP technology was demonstrated integrating the plasma system in an automated 3-Axis gantry prototype. An assessment on several methods to control the status of the physico-chemical condition of APP-treated surfaces (i.e., test inks, water contact angle and aerosol wetting test) has revealed that water contact angle tests have shown potential for application, whereas aerosol wetting technique represents a promising approach. Therefore, APP treatment on epoxy/carbon composites has been demonstrated to be a reliable an effective technique for surface pre-treatment of composite materials, with high throughput and potential for automation in in-line industrial manufacturing processes, guaranteeing surface quality and repetitiveness at relatively low costs and power consumption. APP has the considerable advantages of having low requirements on personal and being environmentally safe.. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 8 of 302.

(9) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. TABLE OF CONTENTS TABLE OF CONTENTS .................................................................................................................... 9 TABLE OF FIGURES ...................................................................................................................... 14 TABLE OF TABLES ........................................................................................................................ 24 1. SCIENTIFIC AND TECHNOLOGICAL OBJECTIVES OF THE PROJECT ...................... 27 1.1. Objectives ......................................................................................................................... 27. 1.2. Work planning................................................................................................................... 27. 1.2.1 1.2.1.1. WP1: Literature review.................................................................................... 27. 1.2.1.2. WP2: Equipment set up .................................................................................. 28. 1.2.1.3. WP3: Selection of Materials, Pre-treatment Techniques, Tests and Methods .......................................................................................................... 28. 1.2.1.4. WP4: APP-System 1 pre-treatment application to standard release agents and composite system 1 ..................................................................... 29. 1.2.1.5. WP5: Pre-study of industrial feasibility and potential for automation .............. 30. 1.2.1.6. WP6: APP-System 2 pre-treatment application to standard release agents, peel ply and composite system 2 ....................................................... 31. 1.2.1.7. WP7: Quality control of the physico-chemical estate of APP-treated surfaces .......................................................................................................... 31. 1.2.2 2. Description of single Work Packages (WP’s) and Tasks (T) ............................... 27. Graphical presentation of work packages (WP’s)................................................ 32. BASIC AND FUNDAMENTALS ........................................................................................ 33 2.1. Adhesion........................................................................................................................... 33. 2.2. Interfacial contact, surface tension and wetting equilibrium ............................................. 33. 2.3. Theories and mechanisms of adhesion ............................................................................ 36. 2.3.1. Mechanical coupling ............................................................................................ 36. 2.3.2. Molecular bonding ............................................................................................... 37. 2.3.3. Thermodynamic adsorption mechanism of adhesion .......................................... 37. 2.3.4. Other adhesion mechanisms ............................................................................... 39. 2.4. Adhesive vs. mechanically fastened joints ....................................................................... 40. 2.4.1. Adhesive bonding for structural aerospace applications ..................................... 41. 2.4.2. Adhesives used for joining composites ............................................................... 41. 2.5. 2.4.2.1. Film adhesives ................................................................................................ 41. 2.4.2.2. Paste adhesives.............................................................................................. 42. Surface Pre-Treatment ..................................................................................................... 42. 2.5.1. Contamination on composite surfaces ................................................................ 42. 2.5.2. Surface preparation ............................................................................................. 42. 2.5.2.1. Chemical methods .......................................................................................... 43. 2.5.2.2. Physical methods ............................................................................................ 43. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 9 of 302.

(10) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. 2.5.2.3. Physicochemical methods .............................................................................. 43. 2.5.2.4. Current trends in aerospace ........................................................................... 44. a). Mechanical abrasion (grinding) + cleaning with organic solvents (MEK or IPA) ........ 44. b). To strip off a peel-ply fabric + cleaning with organic solvents .................................... 44. 2.5.2.5. 2.6. Future options in surface pre-treatment .......................................................... 45. a). Grit-blasting .......................................................................................................... 45. b). Laser .................................................................................................................... 45. c). Ultraviolet radiation .............................................................................................. 45. d). Plasma .................................................................................................................. 45. Plasma.............................................................................................................................. 46. 2.6.1. Plasma generation............................................................................................... 46. 2.6.2. Basics of plasma material interaction .................................................................. 47. 2.6.3. Plasmas classification ......................................................................................... 48. 2.6.3.1. Thermal plasmas ............................................................................................ 48. 2.6.3.2. Non-thermal plasmas ...................................................................................... 48. 2.6.3.3. Overview of various atmospheric plasma sources.......................................... 49. 2.6.4. Atmospheric Pressure Plasma (APP) .................................................................. 50. 2.6.4.1. Potential benefits of APP ................................................................................ 50. 2.6.4.2. APP sources ................................................................................................... 51. a). DC plasma torch .................................................................................................... 51. b). Corona discharge .................................................................................................. 51. c). Dielectric Barrier discharge (DBD) ......................................................................... 52. d). Cold plasma jets .................................................................................................... 53. 2.6.4.3. Comparison of the APP sources ..................................................................... 54. 2.6.5. Air plasma chemistry ........................................................................................... 56. 2.6.6. APP effects on the substrate ............................................................................... 57. 2.6.6.1. Electrostatic and organic cleaning .................................................................. 57. 2.6.6.2. Physical treatment: ablation ............................................................................ 57. 2.6.6.3. Free radicals and crosslinking ........................................................................ 58. 2.6.6.4. Chemical modification ..................................................................................... 58. 2.7. Effects of APP on wettability............................................................................................. 59. 2.8. Literature review on surface modification by plasma treatment ....................................... 60. 3. EXPERIMENTAL PROCEDURE ...................................................................................... 67 3.1. Based materials ................................................................................................................ 67. 3.1.1. Prepregs .............................................................................................................. 68. 3.1.1.1. CYTEC–CYCOM 977-2 / 34% / 12KHTS / 196 .............................................. 68. 3.1.1.2. HEXCEL Hexply 8552/AS4 RC34 AW194 ...................................................... 69. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 10 of 302.

(11) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. 3.1.2. Adhesives ............................................................................................................ 69. 3.1.2.1. Adhesive film: HENKEL LOCTITE HYSOL EA9695 K.05............................... 69. 3.1.2.2. Adhesive film: CYTEC FM-300 K.05............................................................... 70. 3.1.2.3. Adhesive paste: HUNTSMAN Epibond 1590-A/B ........................................... 70. 3.1.3. Release agents.................................................................................................... 71. 3.1.3.1. Release film: RICHMOND VAC–PAK A-6200.001 ......................................... 71. 3.1.3.2. Liquid release agent: HENKEL LOCTITE Frekote 700NC.............................. 72. 3.1.4. Peel plies ............................................................................................................. 73. 3.1.4.1 3.1.5 3.2. Nylon peel ply: Tygavac Advanced 60-B/R..................................................... 73 Paint .................................................................................................................... 73. Manufacturing techniques: laminates and surface treatment ........................................... 75. 3.2.1. Hand prepreg lay-up manufacturing technique and autoclave curing ................. 76. 3.2.2. Surface pre-treatment.......................................................................................... 77. 3.2.2.1. Grinding .......................................................................................................... 77. 3.2.2.2. Atmospheric Pressure Plasma (APP-System 1) ............................................. 78. a) 3.2.2.3 a) 3.3. Process parameters ................................................................................................ 81 Atmospheric Pressure Plasma (APP-System 2) ............................................. 82 Process parameters ................................................................................................ 84. Characterization techniques ............................................................................................. 84. 3.3.1. Contact Angle (CA) measurements ..................................................................... 85. 3.3.2. X-ray-Photoelectron Spectroscopy (XPS) ........................................................... 86. 3.3.3. Scanning Electron Microscopy (SEM)/ Energy Dispersive X-ray (EDX) ............. 88. 3.3.4. Atomic Force Microscope (AFM) ......................................................................... 90. 3.3.5. Profilometry ......................................................................................................... 92. 3.3.6. Roughness image analysis by Scanning Probe Image Processor (SPIP) .......... 92. 3.3.7. SFE according to Owens-Wendt-Rabel and Kaelble (OWRK) ............................ 93. 3.3.8. Test Inks (TI) ....................................................................................................... 95. 3.3.9. Cross-Cut-Test (CCT) ......................................................................................... 96. 3.3.10. Single Lap Shear Strength (SLS) ........................................................................ 98. 3.3.11. Fracture toughness energy of bonded joints (Mode I, GIC) .................................. 99. 4. RESULTS AND DISCUSSION ....................................................................................... 101 4.1. Characterization of the ancillary materials...................................................................... 101. 4.2. APP Pre-Treatment for CFRP Materials using APP-System 1 ....................................... 104. 4.2.1. Characterization of APP treated specimens ...................................................... 105. 4.2.1.1. Wettability and Surface Free Energy (SFE) .................................................. 105. 4.2.1.2. Chemical composition ................................................................................... 110. 4.2.1.3. Surface topography....................................................................................... 114. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 11 of 302.

(12) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. 4.2.1.4 4.2.2. Mechanical behavior and analysis of the fracture surface ............................ 115 APP Treatment lifetime...................................................................................... 120. 4.2.2.1. Wettability and Surface Free Energy (SFE) .................................................. 121. 4.2.2.2. Mechanical behavior and analysis of the fracture surface ............................ 125. 4.2.3. Durability of the bond-line .................................................................................. 129. 4.2.3.1 4.2.4. APP re-treatment possibility .............................................................................. 137. 4.2.4.1. Optical observation of APP-doubled phenomena ......................................... 137. 4.2.4.2. Wettability and Surface Free Energy (SFE) .................................................. 138. 4.2.4.3. Chemical composition ................................................................................... 139. 4.2.4.4. Mechanical behavior and analysis of the fracture surface ............................ 141. 4.2.5 4.3. Mechanical behavior and analysis of the fracture surface ............................ 129. Partial conclusions............................................................................................. 144. Pre-study of industrial feasibility and potential for automation ....................................... 145. 4.3.1. Industrial characteristics assessment for surface pretreatments ....................... 145. 4.3.2. Pre-treatment valorization for industrial application........................................... 147. 4.3.3. APP Automation possibility................................................................................ 148. 4.3.3.1. Preliminary study on APP-System 2 ............................................................. 149. a). Design of the 3 APP jets stepped adapter plate ....................................................... 149. b). Design of the exhaust system ................................................................................. 151. c). Validity of APP-System 1 parameters on APP-System 2 ........................................... 153. d). Definition of the operating parameters on APP-System 2 ......................................... 155 I.. Characterization of the free APP stream ............................................................ 155. II.. Characterization of the APP stream after impinging with the substrate................. 155 i.. Static APP treatment ................................................................................................. 156. ii. Dynamic APP treatment ........................................................................................... 157 e) 4.3.3.2. Homogeneity and width of the APP treatment .............................................. 163. a). Thermography ..................................................................................................... 164. b). Film radiography ................................................................................................. 164. c). Thermochromic paper .......................................................................................... 165. d). Test Inks (TI) ....................................................................................................... 166. 4.3.3.3. Pretreatment gaps and overlaps ................................................................... 168. 4.3.3.4. APP re-treatment possibility.......................................................................... 171. 4.3.3.5. Process Scale-Up ......................................................................................... 172. 4.3.3.6. Curved panels ............................................................................................... 174. 4.3.4 4.4. Wettability as a control property for selection of APP operating parameters ............. 161. Partial conclusions............................................................................................. 175. APP Pre-Treatment for CFRP Materials using APP-System 2 ....................................... 176. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 12 of 302.

(13) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. 4.4.1 4.4.1.1. Wettability and Surface Free Energy (SFE) .................................................. 177. 4.4.1.2. Chemical composition ................................................................................... 183. 4.4.1.3. Surface topography....................................................................................... 202. 4.4.1.4. Mechanical behavior and analysis of the fracture surface ............................ 230. 4.4.2. Effects of the operating parameters on APP-System 2 ..................................... 232. 4.4.2.1. Wettability and Surface Free Energy (SFE) .................................................. 232. 4.4.2.2. Chemical composition ................................................................................... 236. 4.4.2.3. Surface topography....................................................................................... 244. 4.4.2.4. Mechanical behavior and analysis of the fracture surface ............................ 257. 4.4.3. APP Treatment lifetime...................................................................................... 262. 4.4.3.1. Wettability and Surface Free Energy (SFE) .................................................. 262. 4.4.3.2. Chemical composition, mechanical behavior and analysis of the fracture surface .......................................................................................................... 268. 4.4.4. Durability of the bond-line .................................................................................. 277. 4.4.4.1. Mechanical behavior ..................................................................................... 277. 4.4.4.2. Analysis of the fracture surface..................................................................... 281. 4.4.5 4.5. Characterization of APP treated specimens ...................................................... 176. Partial conclusions............................................................................................. 284. Quality control of the physico-chemical state of APP-treated surfaces .......................... 285. 4.5.1. Test Inks (TI) ..................................................................................................... 286. 4.5.2. Contact Angle (CA) measurements ................................................................... 287. 4.5.3. Aerosol Wetting Technique (AWT) .................................................................... 288. 4.5.4. Partial conclusions............................................................................................. 289. 5. CONCLUSIONS ............................................................................................................. 290. 6. REFERENCES ............................................................................................................... 293. 7. ANEXO ................................................................................................................................ I Antecedentes....................................................................................................................... I Objetivos............................................................................................................................. II Metodología ....................................................................................................................... III Conclusiones .....................................................................................................................IV. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 13 of 302.

(14) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. TABLE OF FIGURES Figure 1: Graphical presentation of work packages. ...................................................................... 32 Figure 2: Surface tension results from an imbalance of molecular forces in a liquid. At the surface of the liquid, the liquid molecules are attracted to each other and exert a net force pulling them together [4]. ..................................................................................................................................... 34 Figure 3: Schematic of a liquid drop resting at equilibrium on a solid surface, indicating the contact angle and surface tensions for the three media as the derivation of Young’s equation, using a balance of horizontal forces at the three-phase interline................................................................. 35 Figure 4: (a) The mechanical interlocking mechanism of adhesion [5]. (b) Schematic representation of the effect of pore shape on the penetration of the adhesive. Arrows are related, respectively, to the wetting forces in the liquid and to the back pressure due to air entrapped in the cavity [2]. ......................................................................................................................................... 36 Figure 5: Schematic of the molecular bonding between substrates [1]. ......................................... 37 Figure 6: Contact angle analysis: hydrophobic and hydrophilic drops. .......................................... 38 Figure 7: Four major stresses possible in an adhesive bond. ........................................................ 41 Figure 8: Typical surface topography arising from woven peel-ply material [20]. ........................... 44 Figure 9: Relationship between temperature and energy [24]. ....................................................... 46 Figure 10: Overview of the atomistic processes occurred during plasma surface interactions relevant to particle recycling. The acronym RES represents radiation enhanced sublimation process [27]. .................................................................................................................................... 47 Figure 11: An illustration of several of the fundamental processes used in plasma processing of materials. In many cases, ions impart significant energy to a surface, helping to drive a chemical reaction, or bring about a purely physical reaction process. Combinations of both chemical and physical processes are common in many plasma process steps [28]. ............................................ 49 Figure 12: Electrons and ions frequencies in cold plasmas [1]. ..................................................... 49 Figure 13: Comparison of the process limits resulting from vapor pressure and economic constraints for both vacuum and APP processing. The rectangular blue box in the lower right corner represents the domain for vacuum processing. The larger yellow box represents the domain constraints for APP processing and it also contains much of the process domain represented for vacuum-based plasma processing [28]. .......................................................................................... 50 Figure 14: Four different kinds of APP sources: (a) DC Plasma torch (transferred arc); (b) Corona discharge; (c) Dielectric Barrier discharge; (d-e) Cold plasma jets: Atmospheric pressure plasma jet and Cold plasma torch [25, 28, 33]. ................................................................................................ 52 Figure 15: Comparison of the gas and electron temperatures for different atmospheric-pressure plasmas versus low-pressure plasmas [33]. ................................................................................... 55 Figure 16: Diagram of primary chemical reactions in air plasma induced by electron impact [27]. 56 Figure 17: Organic cleaning and activation [24]. ............................................................................ 57 Figure 18: Surface functionalization by APP [24]. .......................................................................... 58 Figure 19: Degree of wettability [24]. .............................................................................................. 59 Figure 20: APP makes materials wettable [24]............................................................................... 59 Figure 21: APP surface activation of incompatible materials for bonding [24]. .............................. 59 Figure 22: Cut-out of plies from unidirectional CYTEC–CYCOM 977-2 prepreg. .......................... 68 Figure 23: Cut-out of plies from unidirectional HEXCEL Hexply 8552/AS4 prepreg. ..................... 69 Figure 24: HENKEL LOCTITE HYSOL EA9695 K.05 epoxy film adhesive supported on a release paper. .............................................................................................................................................. 70 Figure 25: CYTEC FM-300K.05 epoxy film adhesive supported on a release paper. .................... 70 Figure 26: HUNTSMAN Epibond 1590-A/B epoxy adhesive considering different parameters of application. Courtesy of EADS-IW-Germany. ................................................................................. 71 Figure 27: The base plate and the upper face of the laminate are covered with ETFE release film to allow easy separation of the part from the base and from the breather fabric, respectively. ...... 72 Figure 28: Application of a thin wet film of F700NC release agent onto the base plate in order to form a barrier against adhesion of the laminate being cured. ......................................................... 72. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 14 of 302.

(15) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. Figure 29: Preparation of the T60-B/R peel ply layer prior to be incorporated in the surface of the composite laminate. ........................................................................................................................ 73 Figure 30: Application of ABP 37045 on epoxy-carbon fiber composite specimens (i.e., 150 mm x 75 mm x 2.2 mm): (a) Primer and hardener; (b) Mechanical shaking of the primer using S2200 Dual Head Vibrational Shaker; (c and d) Primer and hardener mixing according to the ratio 2:1; (e) Loading of the blend (including the thinner) into the empty cartridge; (f) Air-pressurized spray gun covering the CFRP surface with an even coating of ABP 37045. Painted samples have been stored for 168h at RT in order to reach full cure......................................................................................... 74 Figure 31: (a) Different manufacturing processes, namely secondary bonding, co-bonding, and cocuring. (b) Example of co-bonding: Eurofighter Typhoon wing spars co-bonded to the lower skin surface [76]...................................................................................................................................... 75 Figure 32: GIC laminates manufacturing (secondary bonding): (1-3) The advanced composites used in this project have required individual oriented plies to be cut to shape and sequentially stacked in precise locations in order to achieve the desired laminate thicknesses [17]; (4-9) Vacuum bag molding including: release agent application, GIC hand lay-up laminates, separator film, breather, bagging film, sealant tape, thermocouples and vacuum fittings; (10) Autoclave curing (2 hours at 180°C under the pressure of 0.7 MPa); (11-13) APP surface pre-treatment of the cured laminate before bonding operation and protection with aluminum foil; (14-15) Adhesive application to join together two GIC cured semi-panels and subsequent autoclave curing; (16) Cutting of the coupons according to the AIRBUS specification [77]. ..................................................................... 76 Figure 33: Desoutter random orbital surface grinding machine with Rhynogrip 180-grit sanding discs. ............................................................................................................................................... 78 Figure 34: Atmospheric pressure plasma APP-System 1 experimental set up. ............................. 78 Figure 35: Atmospheric pressure plasma system APP-System 1 [24]. .......................................... 79 Figure 36: (a) Scheme of the rotary plasma jet used to create the APP stream [81] and cross section of the nozzle head RD1004 [18]; (b) Detail of the nozzle and (c) rotary plasma beam. ..... 80 Figure 37: Width of the APP treatment using the rotary nozzle head RD1004. ............................. 81 Figure 38: Atmospheric pressure plasma APP-System 2 experimental set up. ............................. 82 Figure 39: (a) Scheme of the non-rotary PFW10 plasma jet used to create the plasma [84]; (b) Detail of the nozzle and (c) plasma discharge. ............................................................................... 83 Figure 40: A comparison of average sampling depths for several surface analysis techniques [85]. ........................................................................................................................................................ 85 Figure 41: Goniometer KSV CAM 101 ........................................................................................... 86 Figure 42: (a) Photoelectric effect [89] and (b) XPS survey spectrum of epoxy-carbon 8552/AS4 composite manufactured using ETFE release film (further discussed in Section 4.4). ................... 87 Figure 43: X-ray photoelectron spectroscopy (XPS) Quantum 2000-Scanning ESCA Microprobe. ........................................................................................................................................................ 88 Figure 44: Electron-specimen interaction and the regions from which the signals can be detected [89]. ................................................................................................................................................. 88 Figure 45: Different Scanning Electron Microscopes (SEM) used during the project: (a) Jeol JSM 6320F at the EADS Innovation Works facilities (Ottobrunn, Germany); (b) Philips XL30 ESEM at Centro de Apoyo Tecnológico (CAT) facilities, URJC (Móstoles, Spain); (c) Hitachi S-3400N at Materials Science and Engineering department, URJC (Móstoles, Spain) and (d) Hitachi S-4700 at AIRBUS Materials and Processes department (Getafe, Spain). ..................................................... 89 Figure 46: (a) Experimental set-up for AFM [91] and (b) AFM image of epoxy-carbon 8552/AS4ETFE composite, exhibiting features of different heights with a specialized color palette (further discussed in Section 4.4). ............................................................................................................... 90 Figure 47: Explorer SPM, Tip Scanning AFM ThermoMicroscopes SPMLab NT. V.5.01. ............. 91 Figure 48: HOMMEL TESTER T6000 roughness measurements system. .................................... 92 Figure 49: Disperse and polar fractions of the surface tension of a solid according to Rabel [10, 98]. .................................................................................................................................................. 95 Figure 50: Measurement of surface tension via TI solutions ranging from 28-72 mN/m. ............... 95. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 15 of 302.

(16) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. Figure 51: Wetting tension test solutions [24]: (a) SFE of the sample is lower than the surface tension of test ink (broken droplets). (b) SFE of the sample is higher than the surface tension of test ink (homogeneous thin layer). .................................................................................................. 96 Figure 52: Positioning of adhesive tape; (a) Position of adhesive tape with respect to grid and (b) position immediately prior to removal from grid [88]. ....................................................................... 97 Figure 53: (a) SLS specimen and (b) Universal testing machine MTS 810 and test chamber. ...... 98 Figure 54: (a) Universal testing machine INSTRON 1185 and test chamber used for GIC tests; (b) Detail of the DCB specimen during crack propagation.................................................................... 99 Figure 55: Load–Cross head displacement diagram [77]. ............................................................ 100 Figure 56: Failure modes of the bonded joint according to [77, 101]. .......................................... 101 Figure 57: High-resolution spectra of the C1s peaks corresponding to C-C or C-H, C-O, and C-Fx’s bindings for the case of pure ETFE release film: (a) Side1 and (b) Side 2. .................................. 102 Figure 58: High-resolution spectra of the Fluorine F1s peak for the case of pure ETFE release film: (a) Side1 at 687.02 eV and (b) Side 2 at 687.04 eV. .................................................................... 102 Figure 59: XPS High Resolution Spectra of Carbon C1s (284.4 eV) and Silicon Si2p (102.2 eV) peaks for release agent F700NC. ................................................................................................. 103 Figure 60: High-resolution Si2p envelope resolved for independent peaks at 101.79 eV (Si 2p3/2) and at 102.5 eV (Si 2p1/2) according to literature reference [102] (a) and of release agent F700NC (b). ................................................................................................................................................. 103 Figure 61: High-resolution spectra of the C1s peaks corresponding to C-C or C-H and C-O bindings for the case of pure peel ply T60-B/R: (a) Side1 and (b) Side 2. .................................................. 104 Figure 62: High-resolution spectra of the silicon Si2p peak for the case of the pure peel ply T60B/R: (a) Side1 and (b) Side 2. ....................................................................................................... 104 Figure 63: CA on 977-2/HTS composites surfaces before and after APP treatment; (a) ETFE; (b) F700NC. ........................................................................................................................................ 106 Figure 64: Increase of wettability and relevant change of the CA on epoxy/carbon 9772/HTS/ETFE composites surfaces before (a-c) and after APP treatment (d-f) corresponding to water, ethylene glycol and diiodomethane droplets, respectively. ................................................ 107 Figure 65: Linear plot for SFE analysis from CA data according to OWRK on the laminate 9772/HTS/ETFE before (a) and after APP treatment (b), and on 977-2/HTS/F700NC before (c) and after APP treatment (d). ................................................................................................................ 108 Figure 66: Polar and disperse SFE according to OWRK (a) ETFE (b) F700NC. ......................... 108 Figure 67: SFE of 977-2/HTS/ETFE composite (mN/m) by means of TI before (a) and after APP (b). Note that before APP, only the test fluids of 28 and 34 mN/m remain as homogenous films after their application. Conversely, after APP, the complete set of TI has formed a continuous film and none of the liquids has pulled back into small droplets. ......................................................... 109 Figure 68: Trajectory of a jet from a rotary nozzle moving along a substrate at relatively slow linear and rotation speeds (i.e., 4.2 m/min and 60 rpm) [104]................................................................. 111 Figure 69: Calculated cycloids for a constant rotation of 1900 rpm and two linear speeds: (a) v=20m/min and (b) v=1m/min........................................................................................................ 112 Figure 70: Calculated cycloids for a constant rotation of 1900 rpm and two linear speeds: (a) v=20m/min and (b) v=1m/min. The white areas represent the untreated zones. .......................... 113 Figure 71: Idealized stylus profile showing the mean line; the evaluation length, L; the digitized points, yi; and a definition of the average absolute deviation of profile y(x) from the mean line (Ra) as the total shaded area divided by L [89]..................................................................................... 114 Figure 72: Evaluation of the APP effects on 977-2/HTS/ETFE surfaces using Cross-Cut Tests. 116 Figure 73: Failure surfaces of DCB and loading histories of GIC fracture tests: (a) ETFE (b) F700NC. Interestingly, each analysis has shown that GIC is higher at the start of the test. This is because a 0.02-0.03 mm thickness film of PolyTetraFluoroEthylene (i.e., PTFE) [77] placed at the loading end of the bondline to act as a starter crack, is relatively blunt and therefore more difficult to propagate. ................................................................................................................................. 117 Figure 74: Crack propagation behavior during GIC tests as a result of the plastic zone formed ahead of the “blunt” crack.............................................................................................................. 117. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 16 of 302.

(17) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. Figure 75: Microscopic cohesive failure mode detected in 977-2/HTS/ETFE laminates tested at RT (a) low, (b) intermediate, and (c) high magnifications. .................................................................. 118 Figure 76: Microscopic cohesive failure mode detected in 977-2/HTS/F700NC laminates tested at RT (a) low, (b) intermediate, and (c) high magnifications.............................................................. 119 Figure 77: Results of 977-2/HTS composites treatment with APP and the ageing effect on (a) ETFE and (b) F700NC. ................................................................................................................. 122 Figure 78: Ageing effect after APP by SFE analysis according to OWRK on (a) ETFE, (b) F700NC ...................................................................................................................................................... 124 Figure 79: Durability of APP pre-treatment on 977-2/HTS laminates by means of SFE analysis according to OWRK and GIC tests using: (a) ETFE as released film and (b) F700NC as release agent. ............................................................................................................................................ 126 Figure 80: Example of a SEM micrograph depicting cohesive failure of the EA9695 K.05 adhesive co-bonded after 90 days to the 977-2/HTS/ETFE GIC specimens at different magnifications (a) low, (b) medium and (c) high. ............................................................................................................... 127 Figure 81: SEM micrographs showing typical microstructure of cohesive failure of the EA9695 K.05 adhesive co-bonded after 90 days to the 977-2/HTS/F700NC GIC specimens at different magnifications. .............................................................................................................................. 128 Figure 82: SEM micrograph showing an area of 100 µm where the adhesive layer has not completely covered the composite surface. Although cohesive failure is the main fracture mode in these samples (100% CF), negligible spots of adhesive failure mode has been also found at this magnification level. ........................................................................................................................ 129 Figure 83: Evaluation of the APP effects on 977-2/HTS/ETFE surfaces using Cross-Cut Tests after water immersion for 14 days (a-c)......................................................................................... 130 Figure 84: Comparison of APP treated single lap-shear adhesive joint strengths for 977-2/HTS epoxy/carbon specimens bonded with EA9695 K.05 epoxy adhesive considering different conditioning and test temperatures: a) Without conditioning and tested at -55°C, RT and 80°C; b) Hot-wet conditioning (i.e., 70ºC and 85%RH during 2000h) and tested at RT and 80°C; c) water immersion at 70ºC during 2000h and tested at RT and 80°C. ...................................................... 131 Figure 85: The dependence on contact angle of the magnitude and location of maximum stress concentration in a lap shear test [5]. ............................................................................................. 132 Figure 86: Failure surfaces of DCB and loading histories of GIC fracture tests after exposure to high humidity (85% RH) and elevated temperature (70ºC) during 2000 hours: (a) ETFE (b) F700NC. (c) Typical failure surface (Adhesive Failure, AF) and load-displacement history produced by insufficient surface preparation (e.g., soft plasma conditions leading to GIC values below 200 J/m2). As known, the lack of surface treatment leads to an almost continuous crack growth on GIC tests, and therefore, successions of rapid growth and arrest phases are not found. .................... 133 Figure 87: A schematic diagram of the strong interphase structure between the adhering layer and the composite base formed after APP treatment and the resulting cohesive failure. ............. 134 Figure 88: Cohesive fracture within adhesive bond in 977-2/HTS/ETFE laminates after APP treatment and conditioning at 2000h 70ºC and 85RH; (a) low, intermediate (b), and high magnifications (c). ......................................................................................................................... 135 Figure 89: SEM micrographs showing delamination failure (DF) within adhesive bond in 9772/HTS/ETFE laminates after APP treatment and conditioning at 70ºC and 85% relative humidity during 2000 hours; (a) low and (b) high magnifications. ............................................................... 136 Figure 90: Optical micrographs showing 2 consecutives APP treatment on epoxy/carbon 9772/HTS composites surfaces contaminated with ETFE (a and c) and F700NC (b and d). ............. 137 Figure 91: Contact angle measurements on epoxy/carbon 977-2/HTS composites surfaces before and after consecutive APP treatment; (a) ETFE; (b) F700NC. ..................................................... 138 Figure 92: SFE according to OWRK after consecutive APP treatments; (a) ETFE (b) F700NC. . 139 Figure 93: XPS elemental analysis on 977-2/HTS samples contaminated with ETFE (a) and F700NC (b) agents before and after consecutive APP treatments. .............................................. 140 Figure 94: SLS on 977-2/HTS samples contaminated with ETFE and F700NC agents before and after consecutive APP treatments. ................................................................................................ 142. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 17 of 302.

(18) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. Figure 95: SEM micrographs showing cohesive failure (CF) within adhesive bond in 9772/HTS/ETFE laminates after 2 APP treatments; (a) low and (b) high magnifications. .................. 143 Figure 96: In line APP process showing flexible nozzle systems with specially developed evaporation, in which the gap between the nozzles can be adjusted at will: (a) Nozzles for film activation (b) Surface treatment application developed by IFAM (c) [24]. ..................................... 148 Figure 97: Dimension of the robot flange and the designed adapter plate (including nozzle unit). APP jets on the mounting plate. .................................................................................................... 149 Figure 98: APP gun mount (a) and APP mounting plate (b) made of aluminum 6061-T6. .......... 150 Figure 99: S&P TD-250/100 exhaust system with a pump rate of 240 (m3/h) for a concentration goal below the threshold limit values (VLA-ED and VLA-EC). ...................................................... 152 Figure 100: Optical micrographs showing APP treatment on 8552-AS4/ETFE samples using the defined set parameters (i.e., distance 7.5 mm, speed 17mm/s) on (a) APP-System 1 and (b) APPSystem 2. ...................................................................................................................................... 153 Figure 101: APP free burning arc jet characterization: (a) digital camera, (b) temperature distribution thermographic image and (c) different distances nozzle-plasma stream and their correspondent diameters............................................................................................................... 155 Figure 102: Steady two-dimensional flow toward a “stagnation point” at a rigid boundary [118]. Due to this phenomenon the APP modifications using the non-rotating RD1004 nozzle have been supposed to be larger than 4 mm in width. ................................................................................... 156 Figure 103: IR-Thermographic photographs showing APP treatment on 8552-AS4/F700NC using a distance nozzle/substrate of 20 mm: (a) 1 second and (b) 10 seconds (overtreatment). .......... 156 Figure 104: Optical photographs showing APP treatment on 8552-AS4/F700NC after 10 seconds exposure; (a) low magnification (b) Detail of the central area showing surface damage. ............. 157 Figure 105: IR-Thermographic photographs showing automatic APP treatment on 8552AS4/F700NC using distance 30mm and 100mm/s: (a) 0 seconds and (b) 8 seconds. ................. 157 Figure 106: APP jet width measured with unaided eye in a dark room for 3 different operating parameters. ................................................................................................................................... 160 Figure 107: Effects of power density distribution of various heat sources on weld penetration and cross-sectional shape [120, 121]................................................................................................... 160 Figure 108: CA measurements have been used to evaluate APP effects in 8552-AS4/F700NC composites substrates, estimating the wettability of the surface by water droplets. Water CA measurements have been used as a discriminator for selection of APP operating parameters. .. 162 Figure 109: Selected sets of operating parameters according to water CA analysis. .................. 163 Figure 110: High (a) Medium (b) Low (c). The scratches have been copied from the tool side after curing............................................................................................................................................. 163 Figure 111: Thermography image showing 3 different zones determined by the heat distribution in the APP stream, following qualitative temperature versus color calibrations (i.e., Tred > Tyellow > Tgreen). ......................................................................................................................................... 164 Figure 112: APP effects on a sheet of film radiography: low (a) medium (b) and high (c) APP parameters. ................................................................................................................................... 164 Figure 113: APP effects on a sheet of thermal paper: low (a) medium (b) and high (c) APP parameters. ................................................................................................................................... 165 Figure 114: Cross-section of a typical thermal paper. Circles, color former; triangles, developer [123]. ............................................................................................................................................. 165 Figure 115: APP effects on 8552-AS4 epoxy/carbon composites manufactured using ancillary materials: high (a, d and g) medium (b, e, and h) and low (c, f and i) APP parameters. ............... 166 Figure 116: Width correlation between chemical-morphological variations on 8552-AS4 substrates contaminated with ETFE, F700NC and T60-B/R considering different APP operational scenarios. ...................................................................................................................................................... 167 Figure 117: Optical micrograph APP jets alignement (Configuration 2). ...................................... 168 Figure 118: Film radiography high APP. Configuration 1 (a) and 2 (b) Step-over 2 and 0 mm respectively. .................................................................................................................................. 168. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 18 of 302.

(19) SURFACE MODIFICATIONS OF COMPOSITE MATERIALS BY ATMOSPHERIC PRESSURE PLASMA TREATMENT. Figure 119: Optical micrographs and loading histories showing APP jets alignment: (a) ETFE and configuration 1 (i.e., 30% AF), (b) ETFE and configuration 2 (i.e., 100% CF), (c) F700NC and configuration 1 (i.e., 100% AF) and (d) F700NC and configuration 2 (95% CF). .......................... 170 Figure 120: Optical micrographs showing 3 consecutive APP treatments on 8552-AS4 samples: (a) ETFE, (b) F700NC and (c) T60-B/R. ....................................................................................... 172 Figure 121: Schematic of the path followed by the APP jets scanning over the substrate. ......... 173 Figure 122: Robot assisted APP treatment on a single curved CFRP panel section (EADS-IW, Ottobrunn, Germany) [52]. ............................................................................................................ 174 Figure 123: Contact angle measurements on epoxy/carbon 8552/AS4 composites surfaces before and after high APP treatment; (a) ETFE, (b) F700NC and (c) T60-B/R. ....................................... 178 Figure 124: Linear plot for SFE analysis from CA data according to OWRK on the laminates 8552AS4 contaminated with ETFE, F700NC and T60-B/R before (a, c and e) and after APP treatment (b, d and f). .................................................................................................................................... 180 Figure 125: Polar and disperse SFE components by OWRK; (a) ETFE, (b) F700NC and (c) T60B/R. ............................................................................................................................................... 181 Figure 126: SEM image and the corresponding EDX spectra of the 8552/AS4 laminates; ETFE before (a-b) and after APP treatment (c-d), F700NC before (e-f) and after APP treatment (g-h), and T60-B/R before (i-j) and after APP treatment (k-l). ........................................................................ 188 Figure 127: XPS elemental composition of 8552/AS4-ETFE composites before and after high APP. .............................................................................................................................................. 190 Figure 128: (a) Depth profile from an ETFE surface without APP treatment. (b) Magnification of the 10% atomic concentration area. .................................................................................................... 191 Figure 129: XPS elemental composition of 8552/AS4-F700NC composites before and after high APP. .............................................................................................................................................. 192 Figure 130: XPS elemental composition of 8552/AS4-T60-B/R composites before and after high APP. .............................................................................................................................................. 193 Figure 131: XPS high resolution spectra of 8552/AS4-ETFE composites before and after high APP. .............................................................................................................................................. 195 Figure 132: High resolution C1s XPS spectra obtained from the untreated (a) and (b) APP treated composites contaminated with ETFE release film. ........................................................................ 196 Figure 133: XPS high resolution spectra of 8552/AS4-F700NC composites before and after high APP. .............................................................................................................................................. 197 Figure 134: High resolution C1s XPS spectra obtained from the untreated (a) and (b) APP treated composites contaminated with F700NC release agent. ................................................................ 198 Figure 135: High resolution Si2p XPS spectra obtained from the untreated (a) and (b) APP treated composites contaminated with F700NC release agent. ................................................................ 199 Figure 136: XPS high resolution spectra of 8552/AS4-T60-B/R composites before and after high APP. .............................................................................................................................................. 199 Figure 137: High resolution C1s XPS spectra obtained from the untreated (a) and (b) APP treated 8552/AS4-T60-B/R composites ..................................................................................................... 200 Figure 138: High resolution Si2p XPS spectra obtained from the untreated (a) and (b) APP treated 8552/AS4-T60-B/R composites. .................................................................................................... 201 Figure 139: Light microscope images showing 8552/AS4-ETFE laminates before (a and c) and after APP (b and d) at low and high magnifications, respectively. ................................................ 202 Figure 140: SEM micrographs showing 8552/AS4-ETFE laminates before (a) and after APP treatment (b). ................................................................................................................................. 203 Figure 141: SEM micrographs showing 8552/AS4-ETFE laminates before (a) and after APP treatment (b). ................................................................................................................................. 204 Figure 142: Digital photographs showing APP treatment on 8552/AS4-ETFE sample: (a) Plasma arcing due to heterogeneities in the surface (i.e., arcs between matrix and exposed fibres). (b) Detail of APP treatment. ................................................................................................................ 204 Figure 143: Detail of a selected AS4 carbon fibre and matrix (a), the fibre (b) and a highly magnified SEM view after APP treatment (c). ............................................................................... 205. © AIRBUS OPERATIONS S.L. 2011. ALL RIGHTS RESERVED. CONFIDENTIAL AND PROPRIETARY DOCUMENT.. Page 19 of 302.