Dissolution and fibre spinning of cellulose from an ionic liquid

Abstract

Regenerated cellulose fibres can become a sustainable alternative to cotton and polyester in textile applications. One method of producing such is dissolution of cellulose in an ionic liquid (IL) and regeneration through air-gap spinning. In this master thesis, the dissolution state of cellulose in the ionic liquid 1-ethyl-3-methylimidazolium acetate (EmimAc) together with dimethyl sulfoxide (DMSO) has been studied through concentration series and diffusion nuclear magnetic resonance (NMR). It was shown that a stoichiometric relation of 3 or higher between the IL and anhydroglucose unit (AGU) is needed for complete dissolution and that one acetate ion bind to each AGU. In pure EmimAc, a structure of anions and cations is proposed to form around the polymer chain. The structure of the cellulose chains in solution was studied through small-angle x-ray scattering (SAXS) showing stiff cylinders with repulsive interactions. Rheological measurements were performed to evaluate spinnability of the solutions. Fibres were produced using air-gap spinning and the titer, tenacity, elongation at break and birefringence obtained at two different draw ratios (DR=4 and 6) and using two different coagulation mediums (water and isopropanol) were investigated. The level of crystallinity and internal fibre structure was evaluated using wide-angle x-ray scattering (WAXS) and SAXS. Fibres coagulated in water showed higher tenacity and a higher level of crystallinity but little dependence on the DR could be shown. An internal structure of 20 nm thick crystalline lamella in an amorphous matrix is proposed.

Popular Abstract

From tree to textile – cellulose dissolution and fibre spinning
I will make a guess: The clothes you are wearing are made of polyester or cotton, the two main textile fibres in use today. They are both related to several problems concerning sustainability but there are options on the way. This thesis investigates the dissolution of cellulose from wood and the spinning of textile fibres from this kind of liquid solution. It was shown to be a promising technique with many possibilities for future development.

The world’s population is increasing and with it the need for a sustainable and renewable society. Textile and clothing is an essential part of our everyday life and which materials we use can have a large effect on our environment. Polyester is produced from oil and is therefore an unsustainable alternative. Cotton is a natural fibre but the production consumes huge amounts of water and land and harmful pesticides are often used. Also, we seem to have reached the limit of how much cotton that can be produced per year and there is a need to develop alternative fibres with similar properties.

One such alternative is regenerated cellulose fibres. Two types are already produced on industrial scale: viscose and lyocell, but more environmentally friendly production methods using less dangerous chemicals are needed. Cellulose is the most abundant biopolymer on earth, but it does not melt as most polymers do and therefore has to be dissolved to be processed. Special solvents are needed for this and in this thesis dissolution in the ionic liquid EmimAc is investigated. Ionic liquids are salts that are in liquid form at temperatures below 100°C. In solution the cellulose was shown to take the form of a stiff cylinder, only bending in segments of around 20 glucose units. This is thought to be because of a structure created around the chain consisting of alternating positive and negative ions coming from the EmimAc.

Fibres could successfully be spun from the cellulose/EmimAc solutions using a technique called air-gap spinning where the solution is extruded and stretched in an air-gap before being coagulated in a suitable medium. The coagulation medium is thought to affect the crystallinity of the fibre and thereby the mechanical properties. Here, fibres coagulated in water showed higher crystallinity than fibres coagulated in the alcohol isopropanol. Evaluation of the mechanical properties showed that the water fibres had potential of reaching strength comparable to viscose, lyocell and cotton. The main problem is that they have to be made thinner and still maintain these properties.

A structure which differs from what is commonly assumed for regenerated cellulose fibres was proposed. This constitutes crystalline lamella with a thickness of 20 nm ordered along the length of the fibre and surrounded by an amorphous matrix, as opposed to the common model which instead contains different amounts of needle-shaped micro-voids.

The main characterisation technique used in this work was x-ray scattering. It involves exposing a sample to a narrow x-ray beam that will be scattered by the particles in the sample and create a pattern on a detector. From this pattern, properties such as size, shape and interactions of the particles in the sample can be determined.

• author: Andersson, Erika
• supervisor: Ulf Olsson
• organization: Centre for Analysis and Synthesis
• course: KASM10 20181
• year: 2018
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry; Technology and Engineering
• keywords: Cellulose, scattering, ionic liquid, dissolution, regenerated cellulose fibre, structure-property relationship, materials chemistry, materialkemi
• language: English
• id: 8951413
• date added to LUP: 2018-06-21 14:43:03
• date last changed: 2018-06-21 14:43:03