Formulating environmentally friendly barriers based on Micro Fibrillated Cellulose (MFC)

Lead Research Organisation: University of Birmingham
Department Name: Chemical Engineering

Abstract

Wood pulp is a fibrous material in which the fibres are made up of bundles of cellulose fibrils. In microfibrillated cellulose (MFC) the fibril bundles have been partially separated from each other, giving a high surface area product that is attracting great interest as a sustainable reinforcing material.
IMERYS has developed a novel way to produce MFC by grinding cellulose in water with calcium carbonate in a vertical stirred media mill; this product is known as FiberLean MFC. A mill comprises a motor, grinding chamber, impeller, and ceramic beads (media). The impeller fluidises the media which induce particle size reduction by shear and impact forces. In previous work, the specific energy input has been shown to have a logarithmic relationship to the reduction in size of the particles; milling is a high energy process (in the order of GJ per tonne). A particular product will have a particle size distribution associated with its highest quality. Final product quality and functionality can be improved through process optimisation.
The proposed EngD project will investigate the operation of a large pilot scale mill in continuous mode and relate the operating parameters to FiberLean MFC properties such as particle size distribution, rheology and application properties such as bursting and tensile strength.
Generally in milling processes, continuous production is preferred over batch production for several reasons: no start-up/shut-down, lower costs, and less equipment wear. However, product quality can decline when switching from a batch to a continuous process, which can be due to by-passing or hold-up. Residence time distributions (RTDs) help to identify these issues by measuring the deviation of the process from ideal conditions: backmixing and piston flow, also known as a continuous stirred tank reactor (CSTR) and plug flow reactor (PFR) respectively.
From the RTD the mean residence time (tbar) can be calculated and compared to the theoretical residence time. In addition the shape of the distribution is described by skewness and kurtosis. The dimensionless variance (DV) indicates how close the system is to a CSTR or PFR. The diffusivity coefficient is calculated from the DV, and the theoretical number of CSTRs can be calculated from both the DV and diffusivity. Other models combine different flows in the system, for example a PFR followed by a CSTR.
The operating variables to be investigated will include flowrate, volume of media, impeller speed and design and grinding vessel design. It is envisaged that the project will also develop techniques for the online physical measurement of FiberLean in an attempt to relate these to functionality in end use applications.

Publications

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Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/S023070/1 01/10/2019 31/03/2028
2296168 Studentship EP/S023070/1 01/10/2019 29/09/2023 Robyn Sarah Hill