Effect of chemical degradation and formulation stability on viscoelastic relaxation processes

Previous work at AWE has investigated stress relaxation and viscoelastic properties of polymer materials. However, the way in which different chemical processes effect the viscous relaxation process is not something that has been studied. This is particularly so with highly filled (e.g. boron) materials where changes (e.g. hydrolysis, physical rearrangement) at the boron/binder phase could alter load bearing properties. This area of investigation is novel particularly for highly filled Additively Manufactured (AM) materials. Improved understanding of formulation and the impact of processing variables on relaxation phenomenon will ultimately help the development of products with more controlled load bearing characterisations. These studies will provide processing-structure-property-performance relationships for soft materials.

Start date
1 October 2022
Duration
3.5 years
Application deadline
Funding source
University of Surrey and AWE
Funding information

Fully funded for UK fees. Stipend of £17,000 and University of Surrey fees met for duration of studentship.

About

Current accelerated stress relaxation tests indirectly show how a polymer network rearranges (viscoelastic considerations) to reduce the applied stress (thermodynamic considerations). During thermal acceleration however, many different processes occur in addition to the viscoelastic relaxation.

The rate of loss of formulation additives is often assumed to scale linearly with temperature (diffusion/out gassing/leaching), however, this has never been measured. A combination of experimentation and modelling are required to provide a modified age aware prediction.

Certain accelerated ageing test regimes study the chemical ageing of a network by thermo-oxidative degradation. It is known that a combination of polymer scission and / or cross-linking occurs to alter the state of the polymeric network (in addition to chemical modification). It is generally assumed that elastomeric materials stiffen (due to loss of viscous character) and thus the rate of stress relaxation diminishes however, this is not measured. It is therefore advantageous to understand how chemical degradation also directly affects the viscous relaxation process. This would require a combination of experimentation, modelling and also an understanding of formulation changes (i.e. leaching of additives, processing variables, additives, plasticisers) so that the complex behaviour exhibited by a dynamic system evolves due to the combination of physical, viscoelastic and chemical processes which occur through life. It is not fully understood how fillers (e.g. Silica, Boron, etc) alter these ageing processes. This is particularly so with highly filled soft AM materials where potential changes (e.g. hydrolysis, physical rearrangement) at the boron/binder phase could alter relaxation rates (and performance) in a complex way which is not fully understood.

Find out more about postgraduate research with the Centre for Engineering Materials.

Eligibility criteria

Candidates must have a First or Upper second in a physical sciences subject.

This studentship is for UK candidates only.

How to apply

If you are interested in this project, please contact Noelle Hartley in the first instance by emailing n.hartley@surrey.ac.uk. A formal application will also need to be submitted the Engineering Materials PhD programme page on the "Apply" tab. Please state clearly the studentship project that you would like to apply for and the name of your intended supervisor.


Application deadline

Contact details

Noelle Hartley
05 AB 03
Telephone: +44 (0)1483 683467
E-mail: N.Hartley@surrey.ac.uk
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