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Fracture of Polycarbonate/Abs Blends FRACTURE OF POLYCARBONATE/ABS BLENDS PROEFSCHRIFT ter verkrijging van de graad van doctor aan de Universiteit Twente, op gezag van de rector magnificus, prof. dr. F.A. van Vught, volgens besluit van het College voor Promoties in het openbaar te verdedigen op vrijdag 27 april 2001 om 13.15 uur door Judith Pouwlien Frederika Inberg geboren op 27 juli 1972 te Britswerd Dit proefschrift is goedgekeurd door de promotor: Prof. L.C.E. Struik en de assistent-promotor: Dr. R.J. Gaymans ".... Het voornaamste probleem met die Tijdbesparingsobsessie ligt heel eenvoudig: tijd kun je niet besparen. Je kunt hem alleen besteden." Benjamin Hoff, in Tao van Poeh Fracture of polycarbonate/ABS blends J.P.F. Inberg Thesis, University of Twente, Enschede, The Netherlands April 2001 ISBN 90 365 1553x Cover: TEM picture of deformation zone ahead of an arrested crack in a co-continuous polycarbonate/ABS blend Ó J.P.F. Inberg Printed by: Grafisch Centrum Twente, Enschede Voorwoord Met dit proefschrift sluit ik mijn tijd binnen de onderzoeksgroep 'Synthese en Technologie van Engineering Plastics' (STEP) af, en komt er tevens een einde aan mijn tijd in Enschede. Het schrijven van een proefschrift mag dan een wat eenzaam karwei zijn, velen hebben bijgedragen aan het tot stand komen van dit proefschrift, waarvoor allen dank. Een aantal van hen wil ik hier met name noemen. Mijn mentor Reinoud Gaymans, voor het bieden van de mogelijkheid te promoveren binnen een gezellige groep, en de begeleiding van de afgelopen 4 jaar. Mijn promotor Professor Struik, voor de kritische maar altijd bijzonder waardevolle opmerkingen en aanwijzingen. Ronald van Daele, werkzaam bij DOW in Terneuzen, voor het leveren van de nodige materialen en de bruikbare suggesties en informatie. Hiermee heb je een belangrijke inbreng in het project gehad. Ook de TEM foto's die opgenomen zijn in en om dit proefschrift zouden niet bestaan zonder jouw inspanningen. Professor van der Giessen, voor de enthousiaste ideeën en commentaren. De overige leden van de promotiecommissie en de FOM-gebruikerscommissie, voor alle suggesties en opmerkingen. Mark Smithers, voor de vele SEM foto's en de daarbij horende gezellige uren achter de elektronenmicroscoop. Annemiek Takens, voor je bijdrage aan het project, je was mijn beste student! Resultaten uit jouw afstudeerwerk zijn terug te vinden in hoofdstukken 3 en 5. Peter Reed, for going through my concept thesis with your 'little red pen' and commenting on the language as well as the science part. Alle collega's van de groepen RBT, PBM en MTP, voor alle gezelligheid en ongein tijdens koffie-, thee- en lunchpauzes, het handschoenschieten op de diverse labzalen, de verhitte discussies over de kwaliteiten van bepaalde F1-coureurs en hun prestaties tijdens de laatste race, maar vooral ook voor de vele uitstapjes: films, etentjes, laserquesten, karten, duiken, kortom teveel om allemaal op te noemen. Dit alles heeft bijzonder bijgedragen aan het plezier in mijn werk! Krachttrainmaatjes Louis en Dries bedankt voor de vele uren (?) trainen in het krachthonk en de bijbehorende magnetron-etentjes. Ook de naaste collega's van de STEP- groep, Peter, Pieter, Maarten, Krista, Meike, Wilco, Josien, Martijn en de vele studenten, dank voor de gezelligheid en de goede sfeer, vooral tijdens de vele uitjes zoals wandklimmen, schaatsen en memorabele uitstapjes naar de Efteling, het Vragender Veen en natuurlijk onze studiereis naar Rome. En dan werd er tussendoor, of juist daardoor, ook echt hard gewerkt! Karin 'Pam' Hendriks, voor het opknappen van allerlei administratieve klusjes. Ronald Popma en Louis Reuvekamp, voor het paranimfen en de rest. Mijn moeder, voor de onuitputtelijke steun. Judith Inberg maart 2001 Contents Chapter 1 General introduction 1 Chapter 2 Fracture of polymers and polycarbonate/ABS blends 3 Chapter 3 Influence of ABS type 23 Chapter 4 Co-continuous polycarbonate/ABS blends 39 Chapter 5 Strain rate effects in polycarbonate/ABS blends 59 Chapter 6 Co-continuous polycarbonate/ABS blends: Influence of specimen thickness 77 Chapter 7 Co-continuous polycarbonate/ABS blends: Influence of notch tip radius 101 List of main symbols and abbreviations 121 Summary 123 Samenvatting 127 Levensloop 131 Chapter 1 General introduction The toughness of a polymer is described as the ability to resist fracture by absorbing energy [1] and is therefore a very important material property. Much research in the polymer field aims at improving the toughness of a material and investigates the mechanisms by which such an improvement can be obtained. A polymer that is well known for its toughness is polycarbonate (PC). PC is an important engineering plastic that is widely used since its development in 1953 and first production in 1960 [2-3]. Polycarbonate-consumption was 1.1 million tons in 1997 and increasing [2]. Its main features are transparency, toughness and high-temperature stability and it is applied in car-parts (e.g. headlights), glazing, lighting, housing for electrical equipment, packaging (e.g. milk bottles) or as data-carrier (CD). However, this material has several drawbacks, which sometimes limits its field of application. The material has a high melt viscosity, and this can be a problem in injection moulding of thin-walled products. In thick-walled applications PC loses its tough character and shows brittle fracture. One of the main problems, however, is that the material also becomes brittle when a small flaw or small scratch is present in the material. Such sharp hairline cracks can form when the material is exposed to the environment. This effect is known as ageing. To reduce the sensitivity to these conditions, PC is often blended with acrylonitrile-butadiene- styrene (ABS). This can, of course, only be done in applications where the transparent character of PC is not important. PC/ABS is one of the most successful commercial polymer blends. First patents date from 1964 [4]. This blend combines the good mechanical and thermal properties of PC and the ease of processability, notched impact resistance and the sometimes lower price of ABS [5-6]. PC/ABS actually is a ternary blend, since ABS itself usually consists of styrene-acrylonitrile (SAN) and a dispersion of polybutadiene (PB). The properties of such a ternary blend will depend on the structure properties of the components. The improvement of notched impact toughness through blending has been the subject of many studies. Two-phase systems such as SAN- [7-8], polypropylene- [9-10] and nylon-rubber blends [11-14] were used. The results from these studies and from other reports in open literature have led to the understanding that toughening of the matrix material by addition of a rubber phase is based on cavitation of the rubber particles, and the consequential initiation of plastic deformation at lower stresses and at many sites in the material. This results in plastic deformation and thus energy dissipation in a larger volume of material. PC/ABS is a ternary blend and is therefore more complex than the binary blends. Though the components of PC/ABS were studied separately in the past, the fracture behaviour of the ternary system has been rarely studied. This study therefore aims at gaining insight into the fracture behaviour of PC/ABS blends. The influence of several material and test parameters is investigated: ABS-structure, ABS-content, rubber content in ABS, strain rate, temperature and specimen geometry. The materials are tested in Single Edge Notch Tensile experiments under impact conditions. Energy absorption of the material can be monitored. Deformation 1 Chapter 1 General introduction mechanisms are investigated by studying the damage zone in the material using electron microscopy. Outline In Chapter 2 a concise overview of fracture mechanics is given as well as a short description of polycarbonate fracture behaviour. Literature on PC/ABS blends is also reviewed. Different ABS materials are dispersed into PC and compared, based on morphology and notched Izod test results in Chapter 3. Electron microscopy is used to investigate morphological aspects of the different materials. One of these 4 different types of ABS is used to produce a co- continuous PC/ABS blend. The processing, morphology and mechanical properties of this co- continuous material are described and discussed in Chapter 4. During fracture, temperature development in the material is measured using an infrared camera. The influence of rubber content in ABS is also investigated. In Chapter 5, the influence of strain rate on the fracture behaviour of the co-continuous PC/ABS blend is studied over a test range of 10-4 to 10 m/s, and compared to the effect of strain rate on fracture in a dispersed PC/ABS blend. Adiabatic effects are monitored using an infrared high-speed camera. Chapter 6 describes the influence of specimen thickness for co-continuous PC/ABS, and the results are compared to those on pure PC. Specimen thickness ranges from 8 mm to 0.1 mm. Finally, in Chapter 7 the influence of notch radius is studied. Co-continuous PC/ABS is tested in notched tensile tests, and notch radius is varied between 1 mm and very sharp notches with radii in order of several mm. The results are compared to neat PC. References 1. C.B.Bucknall, Polymer Blends Chapter 22, John Wiley and Sons, NY, 2000 2. J.R.Harder, H.-D.Reifenrath, Kunststoffe, 88 (1998) 1698 3. Kunststof en Rubber 11 (1997) 35-39 4. T. S. Grabowski, V. W. Va, United States Patent Office 3.130.177 5. B.S.Lombardo, H.Keskkula, D.R.Paul, J.Appl.Pol.Sc. 54 (1994) 1697-1720 6. R. Greco, A.Sorrentino, Adv. Pol.Tech. 13 (1994)4 249-258 7. A.C. Steenbrink, H.Janik, R.J.Gaymans, J. Mat. Sci. 32 (1997) 5505-5511 8. A.C.Steenbrink, E. van der Giessen, P.D.Wu, J.
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