Improved measurement and analysis techniques for melt extensional rheometry (ePub)

Research Paper (undergraduate) from the year 2006 in the subject Materials Science, grade: 1,8, Martin Luther University (Institut für Werkstoffwissenschaft), language: English, abstract: Characterising the deformation of a polymer melt is an important task to model its processing behaviour. Knowing only shear flow properties is not sufficient to explain processing behaviour of polymers in many processes such as blown film extrusion, thermoforming, fibre spinning or blow moulding that involve stretching. As Meissner (1979) realised on different LDPE resins using only shear data can not always sufficiently explain the deformation behaviour and therefore the processing behaviour of polymers. Since the 1980s the extensional or elongational viscosity has been recognised as a very important property for processes like blown film extrusion, thermoforming or fibre spinning (Baird 1999, Wagner et al. 2002, Bhattacharya 2004). Obtained results show that the elongational viscosity is also a very sensitive indicator for long-chain branching. Measuring the extensional viscosity means getting a value for the materials resistance to stretching flow or elongational deformation. Since the first theoretical works have been made on this topic by Trouton in 1906, different measuring methods have been developed. Apart from simple methods which are not well defined and perform only indirect measurements (like the melt strength test or capillary rheometry), some more complex and precise methods have been established. The widely accepted and commercial available and therefore the most important ones are the Munstedt-type and the Meissner-type, both introduced in the 1970's. The Munstedt-type rheometer operates via translating clamps suspended in an oil bath (Munstedt 1979) and the Meissner-type uses counter rotating belts (Meissner 1981). Both have been commercialised by Rheometrics, the Munstedt-type as the Rheometrics Extensional Rheometer (RER) in 1981 and a modified Meissner-type as the Rheometrics Melt Extensional Rheometer (RME) in 1994. The RME technique was used for various experiments such as Meissner et al. (1981, 1982), Meissner (1985), Meissner and Hostettler (1994), Levitt and Macosko (1997), Wagner et al. (1998, 2000, 2002), Schulze at al. (2001).
Nevertheless there are different problems occurring with the RME device discussed in various papers e.g. by Meissner (1994), Schweizer (2000), Schulze at al. (2001) and Barroso et al. (2002). [...]