Processing, Forming and Modifying Cellulose to Produce Sustainable Materials and Composites

Abstract

The recent rise in public and governmental awareness of the negative effects of plastic waste has made sustainable biodegradable materials all the more sought after. This is evident in the recent ban on synthetic microbeads for use in personal care products in the UK, providing an even greater push in academia and industry for the production of non-persistent materials which can be manufactured at scale.

This thesis details a multidisciplinary approach to the continuous manufacturing of cellulose microbeads as a sustainable alternative to plastic microparticles. It consists of an Introduction (Chapter 1) describing the context and motivation for the project, a Literature Review (Chapter 2) detailing and interpreting the relevant research from the wider scientific and engineering community, Experimental Procedures (Chapter 3) describing the materials, experimentation and analysis conducted, Research Chapters (Chapter 4- 6) documenting the underpinning theory and research conducted for this thesis (described in greater detail below), Overall Conclusion (Chapter 7) providing an overview of the findings of this thesis as well as potential future considerations and an Appendix containing information that supports the research chapters.

The dissolution of cellulose in an organic electrolyte solution (OES, based on an ionic liquid coupled with a co-solvent) is a widely applied method for this polymer’s sustainable processing. This thesis details the use of such a route for the production of cellulose microbeads via coagulation, using an anti-solvent, from emulsions of cellulose-OES in sunflower oil (SFO)-Span 80. Membrane emulsification is utilised to generate these emulsions and, as far as the author is aware, is the first example of the generation of cellulose microbeads utilising membrane technology and was formally reported in a paper published from the work detailed in this thesis.

In Chapter 4, the use of ionic liquids, in conjunction with a co-solvent, is explored for the sustainable processing of cellulose. The solutions are characterised according to key parameters used for processing biphasic systems: rheology, interfacial tension and contact angle, when emulsified in a sunflower oil continuous phase using a membrane. With the aid of experimental design, it was concluded that a solvent system of [EMIm][OAc]:DMSO (30:70, w/w) was optimal for dissolution of cellulose with the formed solution showing Newtonian flow profiles and interfacial stability in a sunflower oil-Span 80 continuous phase.

These findings were used to design and construct a membrane emulsification rig suitable for continuous production of cellulose microbeads. In Chapter 5, a systematic analysis of process parameters is described. The dimensionless force ratios- capillary number (Ca) and Weber number (We)- were mapped and it was determined that, as with many examples in the literature, a low Weber number provided the optimal removal of droplets from the membrane surface producing cellulose beads in a controllable reproducible manner, after the addition of an anti-solvent. The cellulose-OES solutions were also applied to the production of larger cellulose beads via a scaled up dropping process. A techno-economic analysis highlighted the feasibility of this production process in terms of materials cost, aided by efficient recycling and separation streams.

Chapter 6 details the post processing of the formed cellulose beads to produce a range of materials of differing mechanical strength and surface functionality. Cross-linked cellulose beads with enhanced mechanical strength were prepared for potential use in abrasive applications. This was coupled with topographical alterations, via enzyme and acid etching, producing significantly rougher surfaces, useful for use as supports in extraction applications. Surface functionalisation to impart a hydrophobic surface functionality as well as coating with another biopolymer, chitosan, expanded the potential use of these materials further.

Finally, in Chapter 7 the overall findings of this thesis are detailed and potential extensions of this work, both with regards to production processes and materials, are discussed.

Date of Award	12 Jul 2018
Original language	English
Awarding Institution	University of Bath
Supervisor	Janet Scott (Supervisor), Davide Mattia (Supervisor), Laura Torrente Murciano (Supervisor) & Paul Murray (Supervisor)