The Howdle group
Polymers & Supercritical Fluids
The group's interests lie in the use of supercritical carbon dioxide (scCO2) as a new solvent for polymer synthesis and materials processing.
This is an exciting area that has led to collaboration with many other disciplines, including chemical engineers, biotechnologists, physicists and clinicians. We also work closely with a wide range of colleagues from industry.
In all cases we explore areas where the use of supercritical fluids opens up new opportunities that would not be accessible using more conventional techniques.
Key aims and expertise
- Synthesis of new polymers
- Renewable polymers
- Supercritical CO2 (scCO2)
- Processing of polymers using CO2
- Exploring the properties of polymers in scCO2
Supercritical CO2 (scCO2) is a dense fluid which combines the properties of both a liquid and a gas. Supercritical conditions are achieved at a temperature above 31.1 oC and a pressure of 73.8 bar leading to a unique low viscosity environment for polymerisations and new processing opportunities.
Examples of current projects
The group is currently working on a joint project with the Stockman group synthesising and polymerising terpene monomers.
300 million tonnes of polymers are produced annually, mainly derived from fossil fuels, with <5% being sourced from renewable sources. The rapid depletion of these fossil fuels, along with their damaging contribution to the environment, means the need to source materials from renewable sources has greatly increased. Terpenes are abundant, inexpensive and are obtained from a renewable feedstock. Despite containing alkene moieties terpenes do not readily undergo radical polymerisation. Therefore the research carried out in our group focusses on the synthesis and polymerisation of new terpene derived monomers utilising radical polymerisation techniques, ring opening polymerisation and condensation polymerisation for a number of applications.
Structures of some common terpenes
Find out more about our work on terpenes with our review paper
Dispersion polymerisation is used by the group to produce particles with highly controlled morphologies.
Large molecules such as polymers are often insoluble in scCO2. Thus, the development of stabilisers to aid the dispersion of the growing polymer chain in the supercritical phase is a key area of research within the group.
The key advantage with this process is that high molecular weight polymers are obtained as clean, dry, solvent-free fine powders. Using RAFT control, we have recently created unusual nanostructured polymeric microparticles using dispersion polymerisation in CO2.
SEM image of polymer particles produced using a stabiliser
Internal morphology of block copolymer particles
This paper shows some of our recent work with dispersion polymerisation of methyl methacrylate
The group has recently purchased a rheometer with high pressure capabilities. This can be used to study the mechanical properties of polymers as they processed/synthesised in scCO2. As scCO2 is known to greatly decrease the viscoisty of some polymers, this is a valuable tool for material characterisation.