Functionalization of PP for the enhancement of adhesion between polypropylene and polyamide multilayers Von der Fakultät Energie-, Verfahrens- und Biotechnik der Universität Stuttgart zur Erlangung der Würde eines Doktor-Ingenieurs (Dr.-Ing.) genehmigte Abhandlung Vorgelegt von Claude Rustal aus Fort-de-France (Martinique) Hauptbericht: Prof. Dr.-Ing. H.-G. Fritz Mitberichter: Prof. Dr.rer.nat. C.D. Eisenbach Tag der mündlichen Prüfung: 14.10.2008 Institut für Kunststofftechnik der Universität Stuttgart 2009 ACKNOWLEDGEMENT Die vorliegende Arbeit entstand während meiner Tätigkeit als wissenschaftliche Mitarbeiterin am Institut für Kunststofftechnik der Universität Stuttgart. Herrn Prof. Dr.-Ing. H.-G. Fritz, der mir an seinem Institut die Möglichkeit gab, eine Vielfalt von wissenschaftlichen interessanten Aufgabenstellungen durchzuführen, danke ich herzlich für seine verständnisvolle Unterstützung und Betreuung der Arbeit. Mein Dank gilt den Herrn Prof. Dr.rer.nat. C.D. Eisenbach für die bereichernde Zusammenarbeit und die Übernahme des Mitberichts. Ich möchte mich bei allen Mitarbeitern und Studenten des Instituts für Kunststofftechnik bedanken, insbesondere denen, die zum Gelingen dieser Arbeit beigetragen haben. Ein besonderer Dank geht an den Mitarbeitern des Instituts für Angewandte Makromolekulare Chemie, Dr. I. Özen, Dr. Y. Zou and Dr. K. Dirnberger, für die gute Zusammenarbeit und Anregungen bei unserem gemeinsamen DFG-Projekt. Die Ergebnisse der Arbeit wurden im Rahmen von Forschungstätigkeiten, die dankenswerterweise von der Deutschen Forschungsgemeinschaft (DFG) finanziert wurden. Nicht zuletzt bedanke ich mich bei meiner Familie, meinem Lebensgefährten und meinen Freunden (insbesondere die 2C), die mich stetig und liebevoll unterstützt haben. Claude Rustal, Stuttgart, im Oktober 2008 CONTENT ACKNOWLEDGEMENT CONTENT I SYMBOLS III SUMMARY / KURZFASSUNG VII 1 INTRODUCTION 1 2 FUNCTIONALIZATION OF POLYPROPYLENE 4 2.1 Fundamentals of free-radical grafting of monomers onto polypropylene 4 2.1.1 General description of the grafting reaction 4 2.1.2 Organic peroxides 5 2.1.3 Maleic anhydride grafting onto PP 9 2.1.4 Glycidyl methacrylate grafting onto PP 13 2.2 Materials and process description 15 2.2.1 Polymers and chemical agents 15 2.2.2 Grafting formulations and process description 19 3 PROPERTIES OF THE FUNCTIONALIZED POLYPROPYLENE FILMS 26 3.1 Chemical analysis of the functionalized PP 26 3.1.1 Fourier Transform Infrared Spectroscopy 26 3.1.2 Analysis of the grafting reaction 33 3.2 Rheological characterization of the functionalized PP 43 3.2.1 Instrumentation 44 3.2.2 Influence of the formulations on the rheological properties of the grafted PP 49 3.2.3 Influence of the process parameters on the rheological properties of the grafted PP 62 3.3 Thermal properties of the functionalized PP 64 3.3.1 Differential scanning calorimetry 64 3.3.2 Influence of the formulations on the thermal behaviour of the functionalized PP 65 3.4 Mechanical properties of the functionalized PP 74 3.4.1 Sample preparation and measuring procedure 74 3.4.2 Tensile properties of the functionalized PP cast films 75 4 POLYPROPYLENE AND POLYAMIDE MULTILAYER FILMS 80 4.1 Basics of adhesion 80 4.1.1 Introduction 80 4.1.2 Theories of adhesion 81 4.2 Surface properties of the PP-g-MAH films 86 4.2.1 Contact angle measurement 86 4.2.2 Results of the contact angle measurements 87 4.3 Fusion bonding of functionalized PP and PA films 90 4.3.1 Materials and press procedure 90 4.3.2 Characterization of adhesion 91 I 4.4 Coextrusion of three-layer PP/PA/PP films 118 4.4.1 Process description 118 4.4.2 Materials used for the coextrusion trials 121 4.4.3 Tensile properties of the multilayer films 122 4.4.4 Characterization of adhesion 128 5 CONCLUSION 135 6 REFERENCES 140 7 APPENDICES 150 II SYMBOLS List of abbreviations AIBN Azobisisobutyronitrile ATR Attenuated Total Reflectance CTC Charge Transfer Complex CO Carbon dioxide 2 DHBP 2,5-dimethyl-2,5-di(tert.butylperoxy) hexane DSC Differential Scanning Calorimetry DSR Dynamic Stress Rheometer EPM Ethylene-Propylenen Monomer FTIR Fourier Transform Infrared Spectroscopy GMA Glycidyl metahcrylate HD Polypropylene grade HD601CF HB Polypropylene grade HB205TF IR Infrared radiation L/D Length to diameter ratio of the screw M Monomer MAH Maleic anhydride MMD Molar mass distribution N Nitrogen 2 O Oxygen 2 PA Polyamide PP Polypropylene PP-g-MAH PP grafted with MAH PP-g-GMA PP grafted with GMA P(St-alt-MAH) Equimolar copolymer of alternating styrene and MAH R Radical RD Polypropylene grade RD20CF RB Polypropylene grade RB501BF SEM Scanning Electron Microscope St Styrene TMCH 1,1-Bis(tert.butylperoxy)-3,3,5-trimethyl cyclohexane ZME Zahnmischelement ZSK Zweischneckenkneter, Twin-screw extruder III List of Latin symbols a [Pa.s] Zero shear viscosity A [-] Polymer constant 0 A [-] Surface or height of a specific absorption band of the monomer monomer A [-] Surface or height of the absorption band of the PP PP b [s] Material constant b [m] Peeled distance p b c [m2] Interfacial area p p c [-] Slope of the viscosity function at high shear rates c [m] Peeled distance p C [mol/l] Peroxide concentration C [phr] Quantity of MAH MAH C [phr] Quantity of GMA GMA D [mm] Diameter of the storage canal E [kJ/kmol] Activation energy A E [kJ/kmol] Flow activation energy 0 d [µm] Depth of penetration p F [N] Peel force F [N] Normal force Z G [J/m2] Fracture energy per unit interfacial area, joint strength or energy involved to separate materials G [J/m2] Energy required to propagate a crack through a unit 0 area of interface in the absence of viscoelastic energy losses G’ [Pa] Elastic modulus G’’ [Pa] Loss modulus H [mm] Slit height of die ∆H [J/mol] Enthalpy of crystallisation C ∆H [J/mol] Enthalpy of mixing m ∆H [J/mol] Experimental melting enthalpy m ∆H0 [J/mol] Equilibrium enthalpy of fusion determined for a 100% m crystalline polymer ∆G [J/mol] Gibbs energy of mixing m K [-] Intrinsic rate constant k [-] Maximal intrinsic rate constant max K [-] Polymer constant L [mm] Slit width of a die M [Nm] Torque amplitude MFR [g/10 min] Melt Flow Rate MVR [cm3/10 min] Melt Volume Rate M [g/mol] Molecular weight M [g/mol] Number average molecular weight n M [g/mol] Weight average molecular weight w N [-] Slope of the curve pressure drop against the flow rate N [-] Refractive index of the ATR crystal 1 N [-] Ratio of the refractive index of the sample to that of 21 IV the ATR crystal P [N/m] Peel force per unit width P [bar] Applied pressure ∆p [bar] Pressure drop R [kJ/kmol K] Gas constant R [m] Radius of the parallel plates in a rotational rheometer S [-] Spreading coefficient of the liquid on a surface S [J/m3] Deformation energy per unit volume of the adhesive a S [J/m3] Deformation energy per unit volume of the flexible adherend ∆S [J/I(mol.K] Entropy of mixing m T [K] Absolute temperature T [s] Healing time 0 T [s] Reaction time T [s] Half life time of the peroxide 1/2 & V [kg/h] Flow rate W [J/m2] Work of adhesion SL W [J] Work of peel V [J] Deformation energy for peeling an interfacial area V [m/s] Piston speed st List of Greek formulas β [-] Material constant given by − 3 ≤β≤ −1 2 2 δ, δ [J/m3]1/2 Parameter of solubility 1 2 δ [rad] Phase lag η(γ&) [Pa.s] Shear viscosity Η* [Pa.s] Complex viscosity η [Pa.s] Zero shear viscosity 0 ε [%] Deformation ε [%] Elongation at break B γ& [s-1] Shear rate at the wall w γ& [s-1] Corrected shear rate korr γ [N/m] Surface tension of the solid-vapour interfaces SV γ [N/m] Surface tension of the solid-vapour interfaces SV γ [N/m] Surface tension of the solid-liquid interfaces SL γ [N/m] Surface tension of the liquid-vapour interfaces LV γ [N/m] Surface free energy of the solid in vacuum S γ [N/m] Surface free energy after equilibrium adsorption of SV vapour from the liquid λ [-] Extension ratio λ [nm] Wave length of the radiation in the air 0 Ω [rad/s] Angular velocity ω [rad/s] Frequency θ [°] Angle of incidence θ [°] Peel angle θ [°] Apparent advancing contact angle of a liquid on a W rough surface θ [°] Contact angle of a liquid on a smooth surface S Φ [J] Energy irreversibly dissipated in viscoelastic and V plastic deformations φ [m2] Fractional interfacial contact area π [N/m] Spreading pressure σ [MPa] Tensile strength at break B Σ [-] Phase boundary τ [Pa] Critical stress C τ [Pa] Shear stress at the wall w V [m/s] Bond separation speed v [cm3/mol] Molar volume of a repeat unit r Γ [J] Energy expended in separating an interfacial area χ [-] Interaction parameter 12 VI