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Chemical Modification of Cellulose Fibres for Compatibilization in Bio-based Composites
KTH, School of Chemical Science and Engineering (CHE).
2014 (English)Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesisAlternative title
Kemisk modifiering av cellulosarika fibrer för kompatibilisering i biobaserade kompositer (Swedish)
Abstract [en]

One of the biggest industries today in Sweden is the forest industry. With products such as pulp, paper, packaging materials and sawn wood the industry is an important product supplier and a main contributor of export value for Sweden, with an annual export value of about 123 billion SEK. Despite this very successful business the industry faces some greater challenges, with decreasing demand in for example newspaper.

The interest to find new materials and applications of the fibres in wood is increasing, and the production of cellulose nanofibrils and oxidized fibres from pulp is an interesting development area. As for the composite materials with fibres, still many challenges exists in terms of blending the fibres with their hydrophilic character with hydrophobic matrixes such as thermoplastic poly(lactic acid) (PLA). A compatibilization of the fibres is needed to form better mechanical properties of these composites.

The purpose of this study was a chemical covalent modification and compatibilization of pulp fibres and cellulose nanofibrils for use in composites with biodegradable PLA. The focus was on Jeffamine block co-polymers, consisting of poly(ethylene glycol) and poly(propylene glycol), and to perform the compatibilization via indirect reductive amination of aldehyde groups in periodate-oxidized fibres.

The fibres were oxidized with sodium metaperiodate for 4 and 24 hours and the grafting-to reaction with Jeffamines were 24 hours with Jeffamine M-600, M-1000, M-2070 and M-2005. The most investigated parameters were the conditions during grafting reaction, a changed pH between 4.5 and 10, and the method for preparation of sheets. The reductive step was conducted by a sodium borohydride reaction of the grafted fibres for 1 to 3 hours.

Investigation of the reaction and the different pathways used were conducted with the aim of analysing the effect of the modification of the fibres in terms of mechanical properties of sheets and the chemical composition of the fibres/fibrils. This was performed by measuring the carbonyl content, tensile testing, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis and ANTEK (nitrogen) analysis. The most intriguing results were how the grafted Jeffamine M-600 and the oxidation treatment resulted in stiffer and more brittle fibre networks. The E-modulus of sheets from the reference fibres was 1.45 GPa whereas the modified fibres resulted in sheets with a maximum modulus of 2.27 GPa. The change of pH also showed trends for an increasing amount grafted Jeffamine M-600 at higher pH.

Other different and interesting results were the properties of the fibres grafted with Jeffamine M-2005 at the same conditions as the other Jeffamines. The so modified fibres were easily dispersed in organic solvents such as chloroform and acetone and could easily be used together with dissolved PLA to cast films. Mechanical testing of the casted films showed a significant improvement compared with neat PLA and sheets of fibres made from chloroform resulted in very flocky and weak sheets.

The effect of compatibilization of the modified fibres are still hard to quantify and further investigation on a micro- and nano-scale would be interesting, identifying  if the modification creates good adhesion and fibre/fibril distribution.

Place, publisher, year, edition, pages
2014.
Keyword [en]
Cellulose fibres, Jeffamine, Reductive amination, Composites, Poly(lactic acid)
National Category
Engineering and Technology
Identifiers
URN: urn:nbn:se:kth:diva-159086OAI: oai:DiVA.org:kth-159086DiVA: diva2:782402
Available from: 2015-01-22 Created: 2015-01-21 Last updated: 2017-08-31Bibliographically approved

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