Rheological behaviour of polymer melts and its relationship with underlying structure and topology

Abstract

This thesis contains a detailed study of the relationship between the rheological properties of polymers and their underlying structure. Starting from model polymer systems, rheological complexity has been built up to enable predictions for industrially complex mixtures relevant to tyre processing and manufacture. Polymers which are representative of the tyre industry have been used (e.g. polyisoprene, polybutadiene, polystyrene).

Small amplitude oscillatory shear (SAOS) tests have been reported for a range of polymers of different molecular weight and architecture. Combining this with molecular modelling, in particular using branch-on-branch theory, is shown to allow predictions of polymer topology. Extensional rheometry is also reported using a variety of techniques (Sentmanat extensional rheometry, capillary breakup extensional rheometry, falling weight rheometry) and is shown to be sensitive to multiple branch points in the sample.

Complex flow has been examined using the multi-pass rheometer apparatus and the study of stress decays using a well-defined contraction-expansion geometry is reported, including a novel method of extracting of relaxation times. Cross-slot geometries are used to obtain steady state extensional measurements, not attainable using other techniques.

Large and medium amplitude oscillatory shear (LAOS and MAOS) have been explored with regards to elucidating polymer structure. Well-controlled amplitude sweeps are reported and analysed by Fourier transform and are shown to be sensitive to polymer structure. Frequency sweeps are also performed in the MAOS region, reporting phases and magnitudes, and results related to molecular models. By study of a range of linear polymers, stars and blends, the results are shown to relate to Rouse behaviour of the polymers.

The results detailed show that rheology is a multi-faceted technique that has great potential for identifying polymer structure. It is a key technique that should form part of the suite of analysis techniques available to the synthetic chemist in order to best characterise polymers produced.