IAWS PhD Prize
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- Barnett, J.R. Wood Sci Technol (2012) 46: 1017. doi:10.1007/s00226-012-0500-0
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The winners of this year’s prize were announced in the last issue of Wood Science and Technology. Gold medal winner, Houssine Sehaqui, will be presenting his work at the Academy meeting in Zvolen, where he will receive his award. The full abstract of the winner’s thesis is presented below, together with condensed abstracts of the theses of the second- and third-place winners.
Materials based on nano-fibrillated cellulose—Houssine Sehaqui
Nanofibrillated cellulose (NFC) from wood is an interesting material constituent of high strength and high aspect ratio, which easily forms networks through interfibril secondary bonding including hydrogen bonds. This has been exploited in preparation of new materials, which extend the range of properties for existing cellulosic materials. The objective is to explore processing–structure and structure–property relationships in NFC materials.
Dense networks of NFC referred to as “nanopaper” having a random-in-the-plane orientation of the fibrils have been successfully prepared by a papermaking-like process involving vacuum filtration and water evaporation using laboratory papermaking equipment. Large, flat and transparent nanopaper sheets have thus been prepared in a relatively short time. Using the same preparation route, NFC was used to reinforce pulped wood fibers in dense network structures. NFC networks formed in the pore space of the wood fiber network give an interesting hierarchical structure of reduced porosity. These NFC/wood fiber biocomposites have greater strength, greater stiffness and greater strain-to-failure than reference networks of wood fibers only. In particular, the work to fracture (area under the stress–strain curve) is doubled with an NFC content of only 2 %.
The papermaking preparation route was extended to prepare nanocomposites of high NFC content with a cellulose derivative matrix (hydroxyethyl cellulose, HEC) strongly associated with the NFC. Little HEC was lost during filtration. The NFC/HEC composites have high work to fracture, higher than that of any reported cellulose composite. This is related to NFC network characteristics, and HEC properties and its nanoscale distribution and association with NFC.
Higher porosity NFC nanopaper networks of high specific surface area were prepared by new routes including supercritical drying, tert-butanol freeze-drying and CO2 evaporation. Light-weight porous nanopaper materials resulted with mechanical properties similar to thermoplastics but with a much lower density and a specific surface area of up to 480 m2/g.
Freeze-drying of hydrocolloidal NFC dispersions was used to prepare ultra-high porosity foam structures. The NFC foams have a cellular foam structure of mixed open/closed cells and “nanopaper” cell wall. Control of density and mechanical properties was possible by variation of NFC concentration in the dispersion. A cellulose I foam of the highest porosity ever reported (99.5 %) was prepared. The NFC foams have high ductility and toughness and may be of interest for applications involving mechanical energy absorption. Freeze-drying of NFC suspended in tert-butanol gave highly porous NFC network aerogels with a large surface area. The mechanical behavior was significantly different from NFC foams of similar density due to differences in deformation mechanisms for NFC nanofiber networks.
Immunolocalization of hemicelluloses in differentiating xylem of Cryptomeria japonica—Jong Sik Kim
This project aimed to extend our knowledge of the spatial and temporal distributions of cell wall components in softwood by investigation of hemicellulose distribution in differentiating secondary xylem of Cryptomeria japonica. Immunocytochemical techniques, including immune fluorescence microscopy and immunogold electron microscopy, were applied in combination with immunocytochemical probes. The spatial and temporal distributions of glucomannans (O-acetyl-galactoglucomannans, GGMs), xylans (arabino-4-O-methylglucuronoxylans, AGXs) and β-(1-4)-galactans were investigated in differentiating secondary xylem of normal wood and compression wood. The thesis indicates that hemicellulose distribution in the cell wall varies depending on cell type, including in tracheids, ray cells and CW tracheids. Even in the same cell, the hemicellulose distribution differed not only in different cell wall layers, but also depending on the type of hemicellulose. The thesis also suggests that structurally different types of hemicelluloses may deposit in the cell wall depending on developmental stage of the cell wall.
Integrating genomics and quantitative genetics for discovery of genes that regulate bioenergy traits in wood species—Evandro Novaes
Wood can provide the so needed renewable source of energy to sustain our economic development. Eucalyptus and Populus are among the fastest growing woody species. To efficiently exploit them for bioenergy, it is important that genetics and genomics resources are accessible. With the genome sequenced and thousands of known genes, Populus had, at the time of this work, more developed resources than Eucalyptus. To start offsetting, this difference a next generation sequencing technology was utilized to generate 148 Mbp of gene sequences in Eucalyptus grandis. This work contributed to the annotation of the Eucalyptus genome sequence. Working with poplars, one genomic region was identified, in chromosome XIII, significantly associated with biomass growth and composition. By integrating the multiple genetic and genomic resources available for Populus, gene cpg13 (carbon partitioning and growth in LG13) was pinpointed as the likely regulator of these bioenergy traits.