Microfibrillated cellulose (MFC) is produced from naturally occurring, abundant and sustainable fibres of cellulose through mechanical treatments. It has been studied as a possible replacement for synthetic fibres in engineering composites, since it has many advantages that can enhance their mechanical properties.MFC and epoxy resin composites were prepared with varying weight fractions for three different sources of cellulose fibre (softwood Kraft pulp, hardwood Kraft pulp and recycled newsprint). The nature of the MFC fibres was altered by solvent exchange using acetone and re-dispersed in N,N-dimethylformamide to make them more compatible with the hydrophobic matrix, as well as to aid interfacial adhesion between the fibres and matrix. Their mechanical properties and fracture surfaces were characterised using tensile testing and scanning electron microscope, respectively. Dynamic mechanical thermal analysis (DMTA) was also conducted for the composites made using softwood Kraft pulp MFC only.The static tensile tests showed that significant enhancements were achieved by using MFC to reinforce epoxy resin. Improvements were found for tensile strength, Young's modulus, strain-at-failure and work of fracture for all weight fractions and sources studied. Mechanical properties improved until a reinforcement level of 2 to 3 wt. %, after which the mechanical properties plateaued and showed no further improvement. This was true for all sources and agreed with the calculated maximum critical volume concentration value. SEM images of the fracture surfaces showed that good interfacial adhesion between the MFC and matrix and toughening effect were achieved. Fibre fracture was determined to be the main failure mechanism from studying the SEM micrographs. The estimated modulus of a single fibril was 65 to 95 GPa, which is consistent with the modulus of cellulose II and MFC reported in the literature.Statistical analyses were carried out which showed that the results obtained from each source were comparable and repeatable. An assumption was made that as the static mechanical properties were similar, this would also be true for dynamic mechanical properties; and as such DMTA analysis was only carried out on the softwood MFC composites. A decrease in glass transition temperature was seen, whereas the storage modulus was found to increase. This confirmed that an observed toughening effect was achieved due to strong fibril-fibril interaction, despite the glass transition temperature being reduced. The storage modulus correlated well with the Young's modulus obtained from static mechanical properties.The results obtained indicated that MFC reinforcement could achieve a significant increase in mechanical properties of epoxy resin composites, regardless of the source of fibres. This effect was achieved by the good interfacial adhesion, which allowed for the efficient transfer of stress from the lower modulus matrix to the strong and stiff MFC.
|Date of Award||31 Dec 2015|
- The University of Manchester
|Supervisor||William Sampson (Supervisor) & Arthur Wilkinson (Supervisor)|