Acoustical properties of polymeric fibres and their characterisation

This thesis is concerned with manufacturing and acoustical characterisation of polymeric fibres. The fibres studied in this work were made from a range of polymers and their material properties varied considerably. This work enabled us to develop a better understanding of the applicability of various empirical and theoretical models for the prediction of acoustical and non-acoustical properties of polymeric fibres. It was shown that these materials can be tailored for various noise control solutions in vehicles whilst meeting a range of design criteria.

In an attempt to improve the acoustical performance of traditional acoustic absorbers thin fibrous membranes were electrospun, characterised and modelled. These membranes presented fibre diameters ranging from 70nm to 2μm and were 10-250μm thick. Acoustic testing revealed that when used in conjunction with relatively thin porous substrates they are able to boost the value of the absorption coefficient of the substrate by up to 100% over a broad frequency range. It was found that existing prediction models are not sufficiently accurate to explain the measured acoustical performance of nanofibrous membranes. There are intrinsic problems with the existing standards for acoustic material characterisation which make it difficult to apply them to nanofibrous membranes. Several approaches to improve prediction and measurement methods, and to minimise the observed errors were made and the results were quantified. It is believed that this is the first systematic attempt to produce a controlled range of nanofibrous membranes, measure their acoustical properties carefully and explain them with a range of existing prediction models.

This thesis reports also presents recommendations on the improvements to the existing material measurement and modelling methods, and points to a fundamental knowledge gap that exists in this area of research. Closing this gap is important for areas of noise control, material engineering and polymer chemistry.