Investigations on the Adhesion of Polyurethane Foams on Thermoplastic Material Systems Dissertation zur Erlangung des akademischen Grades Doktor-Ingenieur (Dr. -Ing.) genehmigt durch Mathematisch-Naturwissenschaftlich-Technische Fakult (cid:138)t (Ingenieurwissenschafticher Bereich) der Martin-Luther-Universit -Wittenberg (cid:138)t Halle von Herrn M.Phil. Nasir Mahmood geb. am 07.05.1974 in Bahawalpur (Pakistan) Gutachter: 1. Prof. Dr. J. Kressler 2. Prof. Dr. H. Roggendorf 3. Prof. Dr. G. Heinrich Merseburg, den 28-01-2005 urn:nbn:de:gbv:3-000007920 [http://nbn-resolving.de/urn/resolver.pl?urn=nbn%3Ade%3Agbv%3A3-000007920] Dedicated to My Wife and Daughter III List of publications 1 1DVLU 0DKPRRG .DUVWHQ %XVVH -RHUJ .UHVVOHU ³1HXWURQ UHIOHFWLRQ PHDVXUHPHQWVRQSRO\XUHWKDQHIRDPWKHUPRSODVWLFVLQWHUIDFHV´Polym. Mat. Sci. and Eng. 2004, 90, 831. 2 1DVLU 0DKPRRG -RHUJ .UHVVOHU .DUVWHQ %XVVH ³6WUXFWXUH $QDO\VLV LQ 3RO\XUHWKDQH)RDPVDW,QWHUIDFHV´in press). 3 Nasir Mahmood, Joerg Kressler, Karsten Busse, ³6XUIDFHDQGLQWHUIDFHVWXGLHVRQ SRO\XUHWKDQH IRDPWKHUPRSODVWLF V\VWHPV´ 3RVWHU DFFHSWHG LQ Polymeric Materials, Martin Luther University Halle-Wittenberg Halle (Saale) Germany Sep. 29-30th 2004. 4 .DUVWHQ %XVVH 1DVLU 0DKPRRG -RHUJ .UHVVOHU ³$GKHVLRQ EHKDYLRU RI SRO\XUHWKDQHIRDPRQWKHUPRSODVWLFV´3RVWHUSUHVHQWHGDWWKH)UKMDKUVWDJXQJ 2004 Fachverband Chemische Physik und Polymerphysik, Deutsche Physikalische Gesellschaft e. V., Regensburg, Germany, March. 8-12th, 2004. 5 1DVLU0DKPRRG.DUVWHQ%XVVH-RHUJ.UHVVOHU³1DQRVWUXFWXUHGSRO\XUHWKDQH IRDPV´3RVWHUSUHVHQWHGDWWKHInnovations forum Nano strukturierte Materialien Halle (Saale) Germany, Nov. 24-25th, 2003. 6 1DVLU0DKPRRG-UJHQ9RJHO$QGUH:XW]OHU-RHUJ.UHVVOHU³,QVLWX)7,5 $756WXGLHVRI6WUXFWXUH'HYHORSPHQWLQ3RO\XUHWKDQH)RDP6\VWHPV´3RVWHU presented at the Polymeric Materials, MLU Halle-Wittenberg Halle (Saale) Germany Sep. 25-27th, 2002. 7 1DVLU0DKPRRG.DUVWHQ%XVVH-RHUJ.UHVVOHU³Surface and Interface Studies on 3RO\XUHWKDQH)RDP7KHUPRSODVWLF6\VWHPV´WREHVXEPLWWHG 8 1DVLU 0DKPRRG .DUVWHQ %XVVH -RHUJ .UHVVOHU ³$GKHVLRQ EHKDYLRU RI 3RO\XUHWKDQH)RDPVZLWK7KHUPRSODVWLFV´WREHVXEPLWWHG Contents IV Contents List of publications III Abbreviations and symbols VII 1. Adhesion of polyurethane foams with thermoplastics 1 1.1. Introduction 1 1.1.1. Adhesive joint durability 2 1.1.2. Testing of adhesive joints 3 1.1.3. Adhesion theories 5 1.2. Polyurethane foams 9 1.2.1. Manufacturing of PU foams 9 1.2.2. Foam chemistry and morphology 12 1.3. Thermoplastic materials 15 1.4. Objectives and summary of this work 15 2. Experimental 18 2.1. Materials 18 2.2. Adhesion behavior of PU foams with thermoplastic material systems 18 2.2.1. Preparation of test samples 18 2.2.2. Aging of test samples 19 2.2.3. Peel test 21 2.3. Contact angle studies on thermoplastics and PU foam systems 22 2.3.1. Contact angle measurements 22 2.3.2. Tensiometry 23 2.4. Microscopic studies 24 2.4.1. Atomic force microscopy 24 2.4.2. Optical microscopy 24 Contents V 2.5. ToF-SIMS and XPS studies 25 2.5.1. Time of flight secondary ion mass spectrometry 25 2.5.2. X-ray photoelectron spectroscopy 25 2.6. Structure analysis in polyurethane foams at the interface 26 2.6.1. FTIR spectroscopy 26 2.6.2. Small angle X-ray scattering 26 2.6.3. Transmission electron microscopy 26 2.6.4. Neutron reflection 26 2.7. Diffusion coefficient studies of MDI in thermoplastics 27 2.7.1. Gravimetric analysis 27 2.7.2. FTIR microscopy 27 2.7.3. Optical microscopy 28 3. Results and discussion 29 3.1. Adhesion behavior of PU foams with thermoplastic material systems 29 3.1.1. Analysis of the peel test results 29 3.1.2. Adhesion performance before climate treatments 32 3.1.3. Adhesion performance after climate treatments 34 3.1.3.1. Testing of samples under modified climate cycles 35 3.1.4. Short summary of adhesion test results 39 3.2. Contact angle studies on thermoplastics and PU foam systems 40 3.2.1. Contact angle results of neat TP materials 41 3.2.2. Behavior of samples from PU foam/TP material interface 42 3.2.3. Contact angle results of PU foam samples 44 3.2.4. Contact angle hysteresis 44 3.2.5. Short summary of contact angle results 46 3.3. Microscopic studies 47 3.3.1. Atomic force microscopy 48 Contents VI 3.3.2. Optical microscopy 53 3.3.3. Short summary of microscopic results 54 3.4. ToF-SIMS and XPS studies 55 3.4.1. Time of flight secondary ion mass spectrometry 55 3.4.2. X-ray photoelectron spectroscopy 60 3.4.3. Short summary of ToF-SIMS and XPS results 62 3.5. Structure analysis in polyurethane foams at the interface 63 3.5.1. FTIR spectroscopy 64 3.5.2. Small angle X-ray scattering 69 3.5.3. Transmission electron microscopy 71 3.5.4. Neutron reflection 73 3.5.5. Short summary of structure analysis results 77 3.6. Diffusion coefficient studies of MDI in thermoplastics 78 3.6.1. MDI mass uptake by thermoplastics 79 3.6.2. Determination of type of diffusion 81 3.6.3. Optical microscopy 82 3.6.4. Determination of diffusion coefficient 84 3.6.5. FTIR microscopy 84 3.6.6. Short summary of diffusion coefficient results 88 4. Summary 89 5. Zusammenfassung 94 6. Future work 98 7. Literature 99 Appendixes 107 Acknowledgement 115 Resume 116 Abbreviations and symbols VII Abbreviations and symbols ABS acrlyonitrile-butdadiene-styrene polymer AFM atomic force microscopy ATR attenuated total reflectance ASTM American Society for Testing and Materials a.u. arbitrary unit a diffusion exponent BE binding energy CFCs chlorofluorocarbons CFHCs chlorofluorohydrocarbons CD compact disc D diffusion coefficient d diffusion length, interdomain spacing DMF dimethyl formamide DABCO diazabicyclooctane eV electron volt FTIR Fourier transform infra-red spectroscopy F force f work function g surface tension G adhesion energy or fracture energy GF glass fiber hn photon energy HDI hexamethylene diisocyanate IC isocyanates IMFP inelastic mean free path IPDI isophorone diisocyanate IRE internal reflection element l wavelength Abbreviations and symbols VIII lv liquid vapour M mass MA maleic anhydride MDI 4,4/-diphenylmethane diisocyanate mrad milliradian NDI naphthalene diisocyanate NR neutron reflection PB polybutadiene PC polycarbonate PEO polyethylene oxide PG propylene glycol pK negative logarithm of dissociation constant of acid a PU polyurethane PO polyol PPO polypropylene oxide PS polystyrene r density q scattering vector Ra and Rz surface roughness factors RH relative humidity RMM relative molecular mass RMS root mean square RPM revolution per minute RT room temperature RuO Ruthenium tetraoxide 4 SAR Silicone acrylate rubber SAN styrene-acrylonitrile SAXS Small angle X-ray scattering sl Solid liquid SMA poly (styrene-co-maleic anhydride) sv solid vapour Abbreviations and symbols IX t time TDI toluene diisocyanate TEA tertiary amine TMP trimethylolpropane ToF-SIMS time of flight secondary ion mass spectrometry TP thermoplastic TEM transmission electron microscopy qa advancing contact angle qr receding contact angle V volume W width WA work of adhesion wt weight XPS X-ray photoelectron spectroscopy Chapter 1 Adhesion RI« 1 Chapter 1 Adhesion of polyurethane foams with thermoplastics 1.1. Introduction The process that allows the adhesive to transfer a load from the adherend to the adhesive joint is known as the adhesion. In general the adhesive can be a complex polymer, which intimately interact, either through chemical/physical forces, to the adherend surface to which it is being applied. The chemical interactions result from atomic scale attractions between specific functional groups of the adhesive and the adherend surface. During the early phase of the curing process the viscous adhesive material will flow to enable contact with the adherend and penetration of the surface asperities. As curing proceeds, the viscous mixture becomes a rigid solid as the compounds react and cohesively link the adhesive, often referred to as crosslinking. This process enables strength to be established between the joined adherends. There are a large number of areas where adhesives are used to join materials. The wide range of industries using the technology indicates the diversity of application. In the automotive industry, examples of the use of adhesive bonding include the manufacture of doors, engines and car bodies. Other industrial examples include bridge construction and electronic component manufacture.1 Polyurethanes (PU) today account for the largest percentage (by weight or volume) of any plastic materials used in automotive industry and their growth rate is also faster than that of other plastics.2,3 PU have influenced automotive developments over the past two decades. Their modest beginning was in the late 1950s when cut slabstock foam was used to soften hard metal spring seats in combination or in competition with horse hair, cotton wadding, etc. Nowadays, an estimated 20 kg of various PU are used per automobile, ranging from all foam seat cushions and backs to crash pads, bumpers, fenders, etc.4 The developments in adhesives technology, particularly the discovery of PU adhesives,5 have lead to the recommendation to use adhesive bonding technology in many industrial applications.6